-- ┌───┐                ┌───┐ --
-- │ ┌─┘ ┌─────┐┌─────┐ └─┐ │ --
-- │ │   │ ┌───┘│ ╶───┤   │ │ --
-- │ │   │ ├───┐└───┐ │   │ │ --
-- │ │   │ └─╴ │┌───┘ │   │ │ --
-- │ └─┐ └─────┘└─────┘ ┌─┘ │ --
-- └───┘                └───┘ --
---@module  "Animation Blend Library" <GSAnimBlend>
---@version v1.9.0
---@see     GrandpaScout @ https://github.com/GrandpaScout
-- Adds prewrite-like animation blending to the rewrite.
-- Also includes the ability to modify how the blending works per-animation with blending callbacks.
--
-- Simply `require`ing this library is enough to make it run. However, if you place this library in
-- a variable, you can get access to functions and tools that allow for generating pre-build blend
-- callbacks or creating your own blend callbacks.
--
-- This library is fully documented. If you use Sumneko's Lua Language server, you will get
-- descriptions of each function, method, and field in this library.

local ID = "GSAnimBlend"
local VER = "1.9.0"
local FIG = {"0.1.0-rc.14", "0.1.1"}

---@type boolean, Lib.GS.AnimBlend
local s, this = pcall(function()
  --|================================================================================================================|--
  --|=====|| SCRIPT ||===============================================================================================|--
  --||==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==||--

  -- Localize Lua basic
  local getmetatable = getmetatable
  local setmetatable = setmetatable
  local type = type
  local assert = assert
  local error = error
  local next = next
  local ipairs = ipairs
  local pairs = pairs
  local rawset = rawset
  local tostring = tostring
  -- Localize Lua math
  local m_abs = math.abs
  local m_cos = math.cos
  local m_lerp = math.lerp
  local m_map = math.map
  local m_max = math.max
  local m_sin = math.sin
  local m_sqrt = math.sqrt
  local m_huge = math.huge
  local m_pi = math.pi
  -- Localize Figura globals
  local animations = animations
  local figuraMetatables = figuraMetatables
  local vanilla_model = vanilla_model
  local events = events
  -- Localize current environment
  local _ENV = _ENV --[[@as _G]]

  ---@diagnostic disable: duplicate-set-field, duplicate-doc-field

  ---This library is used to allow prewrite-like animation blending with one new feature with infinite
  ---possibility added on top.  
  ---Any fields, functions, and methods injected by this library will be prefixed with
  ---**[GS&nbsp;AnimBlend&nbsp;Library]** in their description.
  ---
  ---If this library is required without being stored to a variable, it will automatically set up the
  ---blending features.  
  ---If this library is required *and* stored to a variable, it will also contain tools for generating
  ---pre-built blending callbacks and creating custom blending callbacks.
  ---```lua
  ---require "···"
  ---local anim_blend = require "···"
  ---```
  ---@class Lib.GS.AnimBlend
  ---This library's perferred ID.
  ---@field _ID string
  ---This library's version.
  ---@field _VERSION string
  local this = {
    ---Enables error checking in the library. `true` by default.
    ---
    ---Turning off error checking will greatly reduce the amount of instructions used by this library
    ---at the cost of not telling you when you put in a wrong value.
    ---
    ---If an error pops up while this is `false`, try setting it to `true` and see if a different
    ---error pops up.
    safe = true
  }
  local thismt = {
    __type = ID,
    __metatable = false,
    __index = {
      _ID = ID,
      _VERSION = VER
    }
  }

  -- Create private space for blending trigger.
  -- This is done non-destructively so other scripts may do this as well.
  if not getmetatable(_ENV) then setmetatable(_ENV, {}) end


  -----======================================= VARIABLES ========================================-----

  local _ENVMT = getmetatable(_ENV)

  ---Contains the data required to make animation blending for each animation.
  ---@type {[Animation]: Lib.GS.AnimBlend.AnimData}
  local animData = {}

  ---Contains the currently blending animations.
  ---@type {[Animation]?: true}
  local blending = {}

  this.animData = animData
  this.blending = blending


  -----=================================== UTILITY FUNCTIONS ====================================-----

  local chk = {}

  chk.types = {
    ["nil"] = "nil",
    boolean = "boolean",
    number = "number",
    string = "string",
    table = "table",
    ["function"] = "function"
  }

  function chk.badarg(i, name, got, exp, opt)
    if opt and got == nil then return true end
    local gotT = type(got)
    local gotType = chk.types[gotT] or "userdata"

    local expType = chk.types[exp] or "userdata"
    if gotType ~= expType then
      if expType == "function" and gotType == "table" then
        local mt = getmetatable(got)
        if mt and mt.__call then return true end
      end
      return false, ("bad argument #%s to '%s' (%s expected, got %s)")
        :format(i, name, expType, gotType)
    elseif expType ~= exp and gotT ~= exp then
      return false, ("bad argument #%s to '%s' (%s expected, got %s)")
        :format(i, name, exp, gotType)
    end

    return true
  end

  function chk.badnum(i, name, got, opt)
    if opt and got == nil then
      return true
    elseif type(got) ~= "number" then
      local gotType = chk.types[type(got)] or "userdata"
      return false, ("bad argument #%s to '%s' (number expected, got %s)"):format(i, name, gotType)
    elseif got ~= got or m_abs(got) == m_huge then
      return false, ("bad argument #%s to '%s' (value cannot be %s)"):format(i, name, got)
    end

    return true
  end

  local function makeSane(val, def)
    return (val == val and m_abs(val) ~= m_huge) and val or def
  end


  -----=================================== PREPARE ANIMATIONS ===================================-----

  -- This will at least catch players running at around 30 fps.
  -- Any lower and their computer is already having trouble, they don't need the blending.
  local tPass = 0.037504655

  local blendCommand = [[getmetatable(_ENV).GSLib_triggerBlend(%q)]]

  _ENVMT.GSLib_triggerBlend = setmetatable({}, {
    __call = function(self, id)
      if self[id] then self[id]() end
    end
  })

  local animNum = 0
  for _, anim in ipairs(animations:getAnimations()) do
    local blend = anim:getBlend()
    local len = anim:getLength()
    local lenSane = makeSane(len, false)
    lenSane = lenSane and (lenSane > tPass and lenSane) or false
    local tID = "blendAnim_" .. animNum

    animData[anim] = {
      blendTimeIn = 0,
      blendTimeOut = 0,
      blend = blend,
      blendSane = makeSane(blend, 0),
      length = lenSane,
      triggerId = tID,
      callback = nil
    }

    _ENVMT.GSLib_triggerBlend[tID] = function() if anim:getLoop() == "ONCE" then anim:stop() end end

    if lenSane then anim:newCode(m_max(lenSane - tPass, 0), blendCommand:format(tID)) end

    animNum = animNum + 1
  end


  -----============================ PREPARE METATABLE MODIFICATIONS =============================-----

  local animation_mt = figuraMetatables.Animation
  local animationapi_mt = figuraMetatables.AnimationAPI

  local ext_Animation = next(animData)
  if not ext_Animation then
    error(
      "No animations have been found!\n" ..
      "This library cannot build its functions without an animation to use.\n" ..
      "Create an animation or don't `require` this library to fix the error."
    )
  end


  -- Check for conflicts
  if ext_Animation.blendTime then
    local path = tostring(ext_Animation.blendTime):match("^function: (.-):%d+%-%d+$")
    error(
      "Conflicting script [" .. path .. "] found!\n" ..
      "Remove the other script or this script to fix the error."
    )
  end

  local _animationIndex = animation_mt.__index
  local _animationNewIndex = animation_mt.__newindex or rawset
  local _animationapiIndex = animationapi_mt.__index

  local animPlay = ext_Animation.play
  local animStop = ext_Animation.stop
  local animPause = ext_Animation.pause
  local animRestart = ext_Animation.restart
  local animBlend = ext_Animation.blend
  local animLength = ext_Animation.length
  local animGetPlayState = ext_Animation.getPlayState
  local animGetBlend = ext_Animation.getBlend
  ---@diagnostic disable-next-line: deprecated
  local animIsPlaying = ext_Animation.isPlaying
  ---@diagnostic disable-next-line: undefined-field
  local animIsPaused = ext_Animation.isPaused
  local animNewCode = ext_Animation.newCode
  local animapiGetPlaying = animations.getPlaying

  ---Contains the old functions, just in case you need direct access to them again.
  ---
  ---These are useful for creating your own blending callbacks.
  this.oldF = {
    play = animPlay,
    stop = animStop,
    pause = animPause,
    restart = animRestart,

    getBlend = animGetBlend,
    getPlayState = animGetPlayState,
    isPlaying = animIsPlaying,
    isPaused = animIsPaused,

    setBlend = ext_Animation.setBlend,
    setLength = ext_Animation.setLength,
    setPlaying = ext_Animation.setPlaying,

    blend = animBlend,
    length = animLength,
    playing = ext_Animation.playing,

    api_getPlaying = animapiGetPlaying
  }


  -----===================================== SET UP LIBRARY =====================================-----

  ---Causes a blending event to happen.
  ---
  ---If `time`, `from`, or `to` are `nil`, they will take from the animation's data to determine this
  ---value.
  ---
  ---One of `from` or `to` *must* be set.
  ---
  ---If `starting` is given, it will be used instead of the guessed value from the data given.
  ---@param anim Animation
  ---@param time? number
  ---@param from? number
  ---@param to? number
  ---@param starting? boolean
  ---@return Lib.GS.AnimBlend.BlendState
  function this.blend(anim, time, from, to, starting)
    if this.safe then
      assert(chk.badarg(1, "blend", anim, "Animation"))
      assert(chk.badarg(2, "blend", time, "number", true))
      assert(chk.badarg(3, "blend", from, "number", true))
      assert(chk.badarg(4, "blend", to, "number", true))
      if not from and not to then error("one of arguments #3 or #4 must be a number", 2) end
    end

    local data = animData[anim]

    if starting == nil then
      local _from, _to = from or data.blendSane, to or data.blendSane
      starting = _from < _to
    end

    ---@type Lib.GS.AnimBlend.BlendState
    local blendState = {
      time = 0,
      max = time or false,

      from = from or false,
      to = to or false,

      callback = data.callback or this.defaultCallback,

      paused = false,
      starting = starting
    }

    local blendSane = data.blendSane

    blendState.callbackState = {
      anim = anim,
      time = 0,
      max = time or (starting and data.blendTimeIn or data.blendTimeOut),
      progress = 0,
      from = from or blendSane,
      to = to or blendSane,
      starting = starting,
      done = false
    }

    data.state = blendState

    blending[anim] = true

    animBlend(anim, from or blendSane)
    animPlay(anim)
    animPause(anim)

    return blendState
  end


  -----==================================== PRESET CALLBACKS ====================================-----

  ---Contains blending callback generators.
  ---
  ---These are *not* callbacks themselves. They are meant to be called to generate a callback which
  ---can *then* be used.
  local callbackGenerators = {}

  ---Contains custom blending curves.
  ---
  ---These callbacks change the curve used when blending. These cannot be used to modify custom or
  ---generated callbacks (yet).
  local callbackCurves = {}


  ---===== CALLBACK GENERATORS =====---

  ---Given a list of parts, this will generate a blending callback that will blend between the vanilla
  ---parts' normal rotations and the rotations of the animation.
  ---
  ---The list of parts given is expected to the the list of parts that have a vanilla parent type in
  ---the chosen animation in no particular order.
  ---
  ---This callback *also* expects the animation to override vanilla rotations.
  ---
  ---Note: The resulting callback makes *heavy* use of `:offsetRot()` and will conflict with any other
  ---code that also uses that method!
  ---@param parts ModelPart[]
  ---@return Lib.GS.AnimBlend.blendCallback
  function callbackGenerators.blendVanilla(parts)
    -- Because some dumbass won't read the instructions...
    ---@diagnostic disable-next-line: undefined-field
    if parts.done ~= nil then
      error("attempt to use generator 'blendVanilla' as a blend callback.", 2)
    end

    ---@type {[string]: ModelPart[]}
    local partList = {}

    -- Gather the vanilla parent of each part.
    for _, part in ipairs(parts) do
      local vpart = part:getParentType():gsub("([a-z])([A-Z])", "%1_%2"):upper()
      if vanilla_model[vpart] then
        if not partList[vpart] then partList[vpart] = {} end
        local plvp = partList[vpart]
        plvp[#plvp+1] = part
      end
    end

    -- The actual callback is created here.
    return function(state, data)
      if state.done then
        (state.starting and animPlay or animStop)(state.anim)
        for _, v in pairs(partList) do
          for _, p in ipairs(v) do p:offsetRot() end
        end
        animBlend(state.anim, data.blend)
      else
        local pct = state.starting and 1 - state.progress or state.progress

        for n, v in pairs(partList) do
          ---@type Vector3
          local rot = vanilla_model[n]:getOriginRot()
          if n == "HEAD" then rot[2] = ((rot[2] + 180) % 360) - 180 end
          rot:scale(pct)
          for _, p in ipairs(v) do p:offsetRot(rot) end
        end

        animBlend(state.anim, m_lerp(state.from, state.to, state.progress))
      end
    end
  end

  ---Generates a callback that causes an animation to blend into another animation.
  ---@param anim Animation
  ---@return Lib.GS.AnimBlend.blendCallback
  function callbackGenerators.blendTo(anim)
    -- Because some dumbass won't read the instructions...
    ---@diagnostic disable-next-line: undefined-field
    if anim.done ~= nil then
      error("attempt to use generator 'blendTo' as a blend callback.", 2)
    end

    ---This is used to track when the next animation should start blending.
    local ready = true

    return function(state, data)
      if state.done then
        (state.starting and animPlay or animStop)(state.anim)
        animBlend(state.anim, data.blend)
        ready = true
      else
        if not state.starting and ready then
          ready = false
          anim:play()
        end
        animBlend(state.anim, m_lerp(state.from, state.to, state.progress))
      end
    end
  end

  ---Generates a callback that forces all given animations to blend out if they are playing.
  ---@param anims Animation[]
  ---@return Lib.GS.AnimBlend.blendCallback
  function callbackGenerators.blendOut(anims)
    -- Because some dumbass won't read the instructions...
    ---@diagnostic disable-next-line: undefined-field
    if anim.done ~= nil then
      error("attempt to use generator 'blendOut' as a blend callback.", 2)
    end

    local ready = true

    return function(state, data)
      if state.done then
        (state.starting and animPlay or animStop)(state.anim)
        animBlend(state.anim, data.blend)
        ready = true
      else
        if state.starting and ready then
          ready = false
          for _, anim in ipairs(anims) do anim:stop() end
        end
        animBlend(state.anim, m_lerp(state.from, state.to, state.progress))
      end
    end
  end

  ---Generates a makeshift blending callback by using the return value of the given function as the progress.
  ---
  ---The current progress is passed into the function.
  ---@param func fun(progress: number): number
  ---@return Lib.GS.AnimBlend.blendCallback
  function callbackGenerators.custom(func)
    -- Because some dumbass won't read the instructions...
    ---@diagnostic disable-next-line: undefined-field
    if type(func) == "table" and func.done ~= nil then
      error("attempt to use generator 'custom' as a blend callback.", 2)
    end

    return function(state, data)
      if state.done then
        (state.starting and animPlay or animStop)(state.anim)
        animBlend(state.anim, data.blend)
      else
        animBlend(state.anim, m_lerp(state.from, state.to, func(state.progress)))
      end
    end
  end

  ---Generates a callback that plays one callback while blending in and another callback while blending out.
  ---
  ---If a string is given instead of a callback, it is treated as the name of a curve found in
  ---`<GSAnimBlend>.callbackCurves`.  
  ---If `nil` is given, the default callback is used.
  ---@param blend_in? Lib.GS.AnimBlend.blendCallback | Lib.GS.AnimBlend.curve
  ---@param blend_out? Lib.GS.AnimBlend.blendCallback | Lib.GS.AnimBlend.curve
  ---@return Lib.GS.AnimBlend.blendCallback
  function callbackGenerators.dualBlend(blend_in, blend_out)
    -- The dumbass check is a bit further down.

    local tbin, tbout = type(blend_in), type(blend_out)
    local infunc, outfunc = blend_in, blend_out
    if tbin == "string" then
      infunc = callbackCurves[blend_in]
      if not infunc then error("bad argument #1 to 'dualBlend' ('" .. blend_in .. "' is not a valid curve)", 2) end
    elseif blend_in == nil then
      infunc = this.defaultCallback
    elseif tbin == "table" then
      -- Because some dumbass won't read the instructions...
      ---@diagnostic disable-next-line: undefined-field
      if blend_in.done ~= nil then
        error("attempt to use generator 'dualBlend' as a blend callback.", 2)
      end
      local mt = getmetatable(blend_in)
      if not (mt and mt.__call) then
        error("bad argument #1 to 'dualBlend' (function or string expected, got " .. tbin .. ")")
      end
    elseif tbin ~= "function" then
      error("bad argument #1 to 'dualBlend' (function or string expected, got " .. tbin .. ")")
    end

    if tbout == "string" then
      outfunc = callbackCurves[blend_out]
      if not outfunc then error("bad argument #2 to 'dualBlend' ('" .. blend_in .. "' is not a valid curve)", 2) end
    elseif blend_out == nil then
      outfunc = this.defaultCallback
    elseif tbout == "table" then
      local mt = getmetatable(blend_out)
      if not (mt and mt.__call) then
        error("bad argument #2 to 'dualBlend' (function or string expected, got " .. tbin .. ")")
      end
    elseif tbout ~= "function" then
      error("bad argument #2 to 'dualBlend' (function or string expected, got " .. tbout .. ")")
    end

    return function(state, data)
      if state.starting then
        infunc(state, data)
      else
        outfunc(state, data)
      end
    end
  end

  do ---@source https://github.com/gre/bezier-easing/blob/master/src/index.js

    -- Bezier curves are extremely expensive to use especially with higher settings.
    -- Every function has been in-lined to improve instruction counts as much as possible.
    --
    -- In-lined functions are labeled with a --[[funcName(param1, paramN, ...)]]
    -- If an in-lined function spans more than one line, it will contain a #marker# that will appear later to close the
    -- function.
    --
    -- All of the functions below in the block comment are in-lined somewhere else.

    local default_subdiv_iters = 10
    local default_subdiv_prec = 0.0000001
    local default_newton_minslope = 0.001
    local default_newton_iters = 4
    local default_sample_size = 11

    --[=[
    local function _A(A1, A2) return 1.0 - 3.0 * A2 + 3.0 * A1 end
    local function _B(A1, A2) return 3.0 * A2 - 6.0 * A1 end
    local function _C(A1) return 3.0 * A1 end

    -- Returns x(t) given t, x1, and x2, or y(t) given t, y1, and y2.
    local function calcBezier(T, A1, A2)
      --[[((_A(A1, A2) * T + _B(A1, A2)) * T + _C(A1)) * T]]
      return (((1.0 - 3.0 * A2 + 3.0 * A1) * T + (3.0 * A2 - 6.0 * A1)) * T + (3.0 * A1)) * T
    end

    -- Returns dx/dt given t, x1, and x2, or dy/dt given t, y1, and y2.
    local function getSlope(T, A1, A2)
      --[[3.0 * _A(A1, A2) * T ^ 2 + 2.0 * _B(A1, A2) * T + _C(A1)]]
      return 3.0 * (1.0 - 3.0 * A2 + 3.0 * A1) * T ^ 2 + 2.0 * (3.0 * A2 - 6.0 * A1) * T + (3.0 * A1)
    end

    local function binarySubdivide(X, A, B, X1, X2)
      local curX, curT
      local iter = 0
      while (m_abs(curX) > SUBDIVISION_PRECISION and iter < SUBDIVISION_MAX_ITERATIONS) do
        curT = A + (B - A) * 0.5
        --[[calcBezier(curT, X1, X2) - X]]
        curX = ((((1.0 - 3.0 * X2 + 3.0 * X1) * curT + (3.0 * X2 - 6.0 * X1)) * curT + (3.0 * X1)) * curT) - X
        if curX > 0.0 then B = curT else A = curT end
        iter = iter + 1
      end
      return curT or (A + (B - A) * 0.5)
    end

    local function newtonRaphsonIterate(X, Tguess, X1, X2)
      for _ = 1, NEWTON_ITERATIONS do
        --[[getSlope(Tguess, X1, X2)]]
        local curSlope = 3.0 * (1.0 - 3.0 * X2 + 3.0 * X1) * Tguess ^ 2 + 2.0 * (3.0 * X2 - 6.0 * X1) * Tguess + (3.0 * X1)
        if (curSlope == 0.0) then return Tguess end
        --[[calcBezier(Tguess, X1, X2) - X]]
        local curX = ((((1.0 - 3.0 * X2 + 3.0 * X1) * Tguess + (3.0 * X2 - 6.0 * X1)) * Tguess + (3.0 * X1)) * Tguess) - X
        Tguess = Tguess - (curX / curSlope)
      end
      return Tguess
    end

    local function getTForX(X)
      local intervalStart = 0.0
      local curSample = 1
      local lastSample = SAMPLE_SIZE - 1

      while curSample ~= lastSample and SAMPLES[curSample] <= X do
        intervalStart = intervalStart + STEP_SIZE
        curSample = curSample + 1
      end
      curSample = curSample - 1

      -- Interpolate to provide an initial guess for t
      local dist = (X - SAMPLES[curSample]) / (SAMPLES[curSample + 1] - SAMPLES[curSample])
      local Tguess = intervalStart + dist * STEP_SIZE

      local initSlope = getSlope(Tguess, X1, X2)
      if (initSlope >= NEWTON_MIN_SLOPE) then
        return newtonRaphsonIterate(X, Tguess, X1, X2)
      elseif (initSlope == 0) then
        return Tguess
      else
        return binarySubdivide(X, intervalStart, intervalStart + STEP_SIZE, X1, X2)
      end
    end
    ]=]

    local BezierMT = {
      ---@param self Lib.GS.AnimBlend.Bezier
      __call = function(self, state, data)
        if state.done then
          (state.starting and animPlay or animStop)(state.anim)
          animBlend(state.anim, data.blend)
        else
          local X1, X2 = self[1], self[3]
          local Y1, Y2 = self[2], self[4]
          local X = state.progress
          local T
          --[[getTForX(state.progress) #start getTForX#]]
          local intervalStart = 0
          local curSample = 1
          local lastSample = self.options.sample_size - 1
          local samples = self.samples
          local step_size = samples.step

          while curSample ~= lastSample and samples[curSample] <= X do
            intervalStart = intervalStart + step_size
            curSample = curSample + 1
          end
          curSample = curSample - 1

          -- Interpolate to provide an initial guess for T
          local dist = (X - samples[curSample]) / (samples[curSample + 1] - samples[curSample])
          local Tguess = intervalStart + dist * step_size

          local c1 = (1.0 - 3.0 * X2 + 3.0 * X1)
          local c2 = (3.0 * X2 - 6.0 * X1)
          local c3 = (3.0 * X1)
          --[[getSlope(Tguess, X1, X2)]]
          local initSlope = 3.0 * c1 * Tguess ^ 2 + 2.0 * c2 * Tguess + c3
          if (initSlope >= self.options.newton_minslope) then
            --[[newtonRaphsonIterate(X, Tguess, X1, X2)]]
            for _ = 1, self.options.newton_iters do
              --[[getSlope(Tguess, X1, X2)]]
              local curSlope = 3.0 * c1 * Tguess ^ 2 + 2.0 * c2 * Tguess + c3
              if (curSlope == 0.0) then break end
              --[[calcBezier(Tguess, X1, X2) - X]]
              local curX = (((c1 * Tguess + c2) * Tguess + c3) * Tguess) - X
              Tguess = Tguess - (curX / curSlope)
            end
            T = Tguess
          elseif (initSlope == 0) then
            T = Tguess
          else
            local A = intervalStart
            local B = intervalStart + step_size
            --[[binarySubdivide(X, A, B, X1, X2)]]
            local curX, curT
            local iter = 0
            while (m_abs(curX) > self.options.subdiv_prec and iter < self.options.subdiv_iters) do
              curT = A + (B - A) * 0.5
              --[[calcBezier(curT, X1, X2) - X]]
              curX = ((((1.0 - 3.0 * X2 + 3.0 * X1) * curT + (3.0 * X2 - 6.0 * X1)) * curT + (3.0 * X1)) * curT) - X
              if curX > 0.0 then B = curT else A = curT end
              iter = iter + 1
            end
            T = curT or (A + (B - A) * 0.5)
          end
          --#end getTForX#
          --[[calcBezier(T, Y1, Y2)]]
          local prog = (((1.0 - 3.0 * Y2 + 3.0 * Y1) * T + (3.0 * Y2 - 6.0 * Y1)) * T + (3.0 * Y1)) * T
          animBlend(state.anim, m_lerp(state.from, state.to, prog))
        end
      end,
      __index = {
        wrap = function(self) return function(state, data) self(state, data) end end
      },
      type = "Bezier"
    }


    ---Generates a callback that uses a custom bezier curve to blend.
    ---
    ---These are expensive to run so use them sparingly or use low settings.
    ---@param x1 number
    ---@param y1 number
    ---@param x2 number
    ---@param y2 number
    ---@param options? Lib.GS.AnimBlend.BezierOptions
    ---@return Lib.GS.AnimBlend.blendCallback
    function callbackGenerators.bezierEasing(x1, y1, x2, y2, options)
      -- Because some dumbass won't read the instructions...
      ---@diagnostic disable-next-line: undefined-field
      if type(x1) == "table" and x1.done ~= nil then
        error("attempt to use generator 'bezierEasing' as a blend callback.", 2)
      end

      -- Optimization. This may cause an issue if a Bezier object is expected.
      -- If you actually need a Bezier object then don't make a linear bezier lmao.
      if x1 == y1 and x2 == y2 then return callbackCurves.linear end

      ---===== Verify options =====---
      local to = type(options)
      if to == "nil" then
        options = {
          newton_iters = default_newton_iters,
          newton_minslope = default_newton_minslope,
          subdiv_prec = default_subdiv_prec,
          subdiv_iters = default_subdiv_iters,
          sample_size = default_sample_size
        }
      elseif to ~= "table" then
        error("bad argument #5 to 'bezierEasing' (table expected, got " .. to .. ")")
      else
        local safe = this.safe
        local oni = options.newton_iters
        if oni == nil then
          options.newton_iters = default_newton_iters
        elseif safe then
          assert(chk.badnum('5["newton_iters"]', "bezierEasing", oni))
        end

        local onm = options.newton_minslope
        if onm == nil then
          options.newton_minslope = default_newton_minslope
        elseif safe then
          assert(chk.badnum('5["newton_minslope"]', "bezierEasing", onm))
        end

        local osp = options.subdiv_prec
        if osp == nil then
          options.subdiv_prec = default_subdiv_prec
        elseif safe then
          assert(chk.badnum('5["subdiv_prec"]', "bezierEasing", osp))
        end

        local osi = options.subdiv_iters
        if osi == nil then
          options.subdiv_iters = default_subdiv_iters
        elseif safe then
          assert(chk.badnum('5["subdiv_iters"]', "bezierEasing", osi))
        end

        local oss = options.sample_size
        if oss == nil then
          options.sample_size = default_sample_size
        elseif safe then
          assert(chk.badnum('5["sample_size"]', "bezierEasing", oss))
        end
      end

      if this.safe then
        chk.badnum(1, "bezierEasing", x1)
        chk.badnum(2, "bezierEasing", y1)
        chk.badnum(3, "bezierEasing", x2)
        chk.badnum(4, "bezierEasing", y2)
      end

      if x1 > 1 or x1 < 0 then
        error("bad argument #1 to 'bezierEasing' (value out of [0, 1] range)", 2)
      end
      if x2 > 1 or x2 < 0 then
        error("bad argument #3 to 'bezierEasing' (value out of [0, 1] range)", 2)
      end

      local samples = {step = 1 / (options.sample_size - 1)}

      ---@type Lib.GS.AnimBlend.bezierCallback
      local obj = setmetatable({
        x1, y1, x2, y2,
        options = options,
        samples = samples
      }, BezierMT)

      local step = samples.step
      local c1 = (1.0 - 3.0 * x2 + 3.0 * x1)
      local c2 = (3.0 * x2 - 6.0 * x1)
      local c3 = (3.0 * x1)
      for i = 0, options.sample_size - 1 do
        local istep = i * step
        --[[calcBezier(istep, X1, X2)]]
        samples[i] = ((c1 * istep + c2) * istep + c3) * istep
      end

      return obj
    end
  end

  ---Generates a callback that plays other callbacks on a timeline.
  ---
  ---An example of a valid timeline:
  ---```lua
  ---...timeline({
  ---  {time = 0, min = 0, max = 1, func = <GSAnimBlend>.callbackCurve.easeInSine},
  ---  {time = 0.5, min = 1, max = 0.5, func = <GSAnimBlend>.callbackCurve.easeOutCubic},
  ---  {time = 0.5, min = 0.5, max = 1, func = <GSAnimBlend>.callbackCurve.easeInCubic}
  ---})
  ---```
  ---@param tl Lib.GS.AnimBlend.timeline
  ---@return Lib.GS.AnimBlend.blendCallback
  function callbackGenerators.timeline(tl)
    -- Because some dumbass won't read the instructions...
    ---@diagnostic disable-next-line: undefined-field
    if tl.done ~= nil then
      error("attempt to use generator 'timeline' as a blend callback.", 2)
    end

    if this.safe then
      assert(chk.badarg(1, "timeline", tl, "table"))
      for i, kf in ipairs(tl) do
        assert(chk.badarg("1[" .. i .. "]", "timeline", kf, "table"))
      end
      local time = 0
      local ftime = tl[1].time
      if ftime ~= 0 then error("error in keyframe #1: timeline does not start at 0 (got " .. ftime .. ")") end
      for i, kf in ipairs(tl) do
        assert(chk.badnum("1[" .. i .. ']["time"]', "timeline", kf.time))
        if kf.time <= time then
          error(
            "error in keyframe #" .. i ..
            ": timeline did not move forward (from " .. time .. " to " .. kf.time .. ")", 2
          )
        end

        if kf.min then assert(chk.badnum("1[" .. i .. ']["min"]', "timeline", kf.min)) end
        if kf.max then assert(chk.badnum("1[" .. i .. ']["max"]', "timeline", kf.max)) end

        assert(chk.badarg("1[" .. i .. ']["func"]', "timeline", kf.func, "function"), true)
      end
    end

    return function(state, data)
      if state.done then
        (state.starting and animPlay or animStop)(state.anim)
        animBlend(state.anim, data.blend)
      else
        ---@type Lib.GS.AnimBlend.tlKeyframe, Lib.GS.AnimBlend.tlKeyframe
        local kf, nextkf
        for _, _kf in ipairs(tl) do
          if _kf.time > state.progress then
            if _kf.time < 1 then nextkf = _kf end
            break
          end
          kf = _kf
        end

        local adj_prog = m_map(
          state.progress,
          kf.time, nextkf and nextkf.time or 1,
          kf.min or 0, kf.max or 1
        )

        local newstate = setmetatable(
          {time = state.max * adj_prog, progress = adj_prog},
          {__index = state}
        );
        (kf.func or this.defaultCallback)(newstate, data)
      end
    end
  end


  ---===== CALLBACK CURVES =====---

  ---A callback that uses the `linear` easing method to blend.
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.linear(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      animBlend(state.anim, m_lerp(state.from, state.to, state.progress))
    end
  end

  -- I planned to add easeOutIn curves but I'm lazy. I'll do it if people request it.

  ---A callback that uses the `easeInSine` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInSine)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInSine(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = (1 - m_cos(state.progress * m_pi * 0.5)) --
      animBlend(
        state.anim,
        from + (state.to - from) * (1 - m_cos(state.progress * m_pi * 0.5))
      )
    end
  end

  ---A callback that uses the `easeOutSine` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeOutSine)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeOutSine(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = (m_sin(state.progress * m_pi * 0.5)) --
      animBlend(
        state.anim,
        from + (state.to - from) * (m_sin(state.progress * m_pi * 0.5))
      )
    end
  end

  ---A callback that uses the `easeInOutSine` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInOutSine)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInOutSine(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = -(m_cos(state.progress * m_pi) - 1) * 0.5 --
      animBlend(
        state.anim,
        from + (state.to - from) * (-(m_cos(state.progress * m_pi) - 1) * 0.5)
      )
    end
  end

  ---A callback that uses the `easeInQuad` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInQuad)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInQuad(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = state.progress ^ 2 --
      animBlend(
        state.anim,
        from + (state.to - from) * (state.progress ^ 2)
      )
    end
  end

  ---A callback that uses the `easeOutQuad` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeOutQuad)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeOutQuad(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = 1 - (1 - state.progress) ^ 2 --
      animBlend(
        state.anim,
        from + (state.to - from) * (1 - (1 - state.progress) ^ 2)
      )
    end
  end

  ---A callback that uses the `easeInOutQuad` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInOutQuad)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInOutQuad(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- local prog =                    --
      --   x < 0.5                       --
      --   and 2 * x ^ 2                 --
      --   or 1 - (-2 * x + 2) ^ 2 * 0.5 --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          x < 0.5
          and 2 * x ^ 2
          or 1 - (-2 * x + 2) ^ 2 * 0.5
        )
      )
    end
  end

  ---A callback that uses the `easeInCubic` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInCubic)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInCubic(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = state.progress ^ 3 --
      animBlend(
        state.anim,
        from + (state.to - from) * (state.progress ^ 3)
      )
    end
  end

  ---A callback that uses the `easeOutCubic` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeOutCubic)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeOutCubic(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = 1 - (1 - state.progress) ^ 3 --
      animBlend(
        state.anim,
        from + (state.to - from) * (1 - (1 - state.progress) ^ 3)
      )
    end
  end

  ---A callback that uses the `easeInOutCubic` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInOutCubic)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInOutCubic(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- local prog =                    --
      --   x < 0.5                       --
      --   and 4 * x ^ 3                 --
      --   or 1 - (-2 * x + 2) ^ 3 * 0.5 --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          x < 0.5
          and 4 * x ^ 3
          or 1 - (-2 * x + 2) ^ 3 * 0.5
        )
      )
    end
  end

  ---A callback that uses the `easeInQuart` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInQuart)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInQuart(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = state.progress ^ 4 --
      animBlend(
        state.anim,
        from + (state.to - from) * (state.progress ^ 4)
      )
    end
  end

  ---A callback that uses the `easeOutQuart` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeOutQuart)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeOutQuart(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = 1 - (1 - state.progress) ^ 4 --
      animBlend(
        state.anim,
        from + (state.to - from) * (1 - (1 - state.progress) ^ 4)
      )
    end
  end

  ---A callback that uses the `easeInOutQuart` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInOutQuart)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInOutQuart(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      --local prog =                    --
      --  x < 0.5                       --
      --  and 8 * x ^ 4                 --
      --  or 1 - (-2 * x + 2) ^ 4 * 0.5 --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          x < 0.5
          and 8 * x ^ 4
          or 1 - (-2 * x + 2) ^ 4 * 0.5
        )
      )
    end
  end

  ---A callback that uses the `easeInQuint` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInQuint)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInQuint(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = state.progress ^ 5 --
      animBlend(
        state.anim,
        from + (state.to - from) * (state.progress ^ 5)
      )
    end
  end

  ---A callback that uses the `easeOutQuint` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeOutQuint)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeOutQuint(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = 1 - (1 - state.progress) ^ 5 --
      animBlend(
        state.anim,
        from + (state.to - from) * (1 - (1 - state.progress) ^ 5)
      )
    end
  end

  ---A callback that uses the `easeInOutQuint` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInOutQuint)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInOutQuint(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- local prog =                    --
      --   x < 0.5                       --
      --   and 16 * x ^ 5                --
      --   or 1 - (-2 * x + 2) ^ 5 * 0.5 --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          x < 0.5
          and 16 * x ^ 5
          or 1 - (-2 * x + 2) ^ 5 * 0.5
        )
      )
    end
  end

  ---A callback that uses the `easeInExpo` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInExpo)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInExpo(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- local prog =           --
      --   x == 0               --
      --   and 0                --
      --   or 2 ^ (10 * x - 10) --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          x == 0
          and 0
          or 2 ^ (10 * x - 10)
        )
      )
    end
  end

  ---A callback that uses the `easeOutExpo` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeOutExpo)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeOutExpo(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- local prog =           --
      --   x == 1               --
      --   and 1                --
      --   or 1 - 2 ^ (-10 * x) --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          x == 1
          and 1
          or 1 - 2 ^ (-10 * x)
        )
      )
    end
  end

  ---A callback that uses the `easeInOutExpo` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInOutExpo)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInOutExpo(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- local prog =                             --
      --   (x == 0 or x == 1) and x               --
      --   or x < 0.5 and 2 ^ (20 * x - 10) * 0.5 --
      --   or (2 - 2 ^ (-20 * x + 10)) * 0.5      --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          (x == 0 or x == 1) and x
          or x < 0.5 and 2 ^ (20 * x - 10) * 0.5
          or (2 - 2 ^ (-20 * x + 10)) * 0.5
        )
      )
    end
  end

  ---A callback that uses the `easeInCirc` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInCirc)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInCirc(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = 1 - m_sqrt(1 - state.progress ^ 2) --
      animBlend(
        state.anim,
        from + (state.to - from) * (1 - m_sqrt(1 - state.progress ^ 2))
      )
    end
  end

  ---A callback that uses the `easeOutCirc` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeOutCirc)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeOutCirc(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      -- local prog = m_sqrt(1 - (state.progress - 1) ^ 2) --
      animBlend(
        state.anim,
        from + (state.to - from) * m_sqrt(1 - (state.progress - 1) ^ 2)
      )
    end
  end

  ---A callback that uses the `easeInOutCirc` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInOutCirc)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInOutCirc(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- local prog =                                  --
      --   x < 0.5                                     --
      --   and (1 - m_sqrt(1 - (2 * x) ^ 2)) * 0.5     --
      --   or (m_sqrt(1 - (-2 * x + 2) ^ 2) + 1) * 0.5 --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          x < 0.5
          and (1 - m_sqrt(1 - (2 * x) ^ 2)) * 0.5
          or (m_sqrt(1 - (-2 * x + 2) ^ 2) + 1) * 0.5
        )
      )
    end
  end

  ---A callback that uses the `easeInBack` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInBack)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInBack(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- magic c1 <1.70158> = 1.70158                   --
      -- magic c2 <2.70158> = c1 + 1                    --
      -- local prog = 2.70158 * x ^ 3 - 1.70158 * x ^ 2 --
      animBlend(
        state.anim,
        from + (state.to - from) * (2.70158 * x ^ 3 - 1.70158 * x ^ 2)
      )
    end
  end

  ---A callback that uses the `easeOutBack` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeOutBack)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeOutBack(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress - 1
      -- magic c1 <1.70158> = 1.70158                       --
      -- magic c2 <2.70158> = c1 + 1                        --
      -- local prog = 1 + 2.70158 * x ^ 3 + 1.70158 * x ^ 2 --
      animBlend(
        state.anim,
        from + (state.to - from) * (1 + 2.70158 * x ^ 3 + 1.70158 * x ^ 2)
      )
    end
  end

  ---A callback that uses the `easeInOutBack` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInOutBack)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInOutBack(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      local x2 = x * 2
      -- magic c1 <1.70158>   = 1.70158                                     --
      -- magic c2 <2.5949095> = c1 * 1.525                                  --
      -- magic c3 <3.5949095> = c2 + 1                                      --
      -- local prog =                                                       --
      --   x < 0.5                                                          --
      --   and (x2 ^ 2 * (3.5949095 * x2 - 2.5949095)) * 0.5                --
      --   or ((x2 - 2) ^ 2 * (3.5949095 * (x2 - 2) + 2.5949095) + 2) * 0.5 --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          x < 0.5
          and (x2 ^ 2 * (3.5949095 * x2 - 2.5949095)) * 0.5
          or ((x2 - 2) ^ 2 * (3.5949095 * (x2 - 2) + 2.5949095) + 2) * 0.5
        )
      )
    end
  end

  ---A callback that uses the `easeInElastic` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInElastic)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInElastic(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- local prog =                                                     --
      --   (x == 0 or x == 1) and x                                       --
      --   or -(2 ^ (10 * x - 10)) * m_sin((x * 10 - 10.75) * m_pi / 1.5) --
      animBlend(
        state.anim, 
        from + (state.to - from) * (
          (x == 0 or x == 1) and x
          or -(2 ^ (10 * x - 10)) * m_sin((x * 10 - 10.75) * m_pi / 1.5)
        )
      )
    end
  end

  ---A callback that uses the `easeOutElastic` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeOutElastic)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeOutElastic(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- local prog =                                                 --
      --   (x == 0 or x == 1) and x                                   --
      --   or 2 ^ (-10 * x) * m_sin((x * 10 - 0.75) * m_pi / 1.5) + 1 --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          (x == 0 or x == 1) and x
          or 2 ^ (-10 * x) * m_sin((x * 10 - 0.75) * m_pi / 1.5) + 1
        )
      )
    end
  end

  ---A callback that uses the `easeInOutElastic` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInOutElastic)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInOutElastic(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- local prog =                                                                   --
      --   (x == 0 or x == 1) and x                                                     --
      --   or x < 0.5 and -(2 ^ (x * 20 - 10) * m_sin((x * 20 - 11.125) * m_pi / 2.25)) * 0.5 --
      --   or (2 ^ (-x * 20 + 10) * m_sin((x * 20 - 11.125) * m_pi / 2.25)) * 0.5 + 1         --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          (x == 0 or x == 1) and x
          or x < 0.5 and -(2 ^ (x * 20 - 10) * m_sin((x * 20 - 11.125) * m_pi / 2.25)) * 0.5
          or (2 ^ (-x * 20 + 10) * m_sin((x * 20 - 11.125) * m_pi / 2.25)) * 0.5 + 1
        )
      )
    end
  end

  ---A callback that uses the `easeInBounce` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInBounce)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInBounce(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = 1 - state.progress
      -- magic c1 <7.5625> = 7.5625                                        --
      -- magic c2 <2.75>   = 2.75                                          --
      -- local prog =                                                      --
      --   1 - (                                                           --
      --     x < 1 / 2.75 and 7.5625 * x ^ 2                               --
      --     or x < 2 / 2.75 and 7.5625 * (x - 1.5 / 2.75) ^ 2 + 0.75      --
      --     or x < 2.5 / 2.75 and 7.5625 * (x - 2.25 / 2.75) ^ 2 + 0.9375 --
      --     or 7.5625 * (x - 2.625 / 2.75) ^ 2 + 0.984375                 --
      --   )                                                               --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          1 - (
            x < 1 / 2.75 and 7.5625 * x ^ 2
            or x < 2 / 2.75 and 7.5625 * (x - 1.5 / 2.75) ^ 2 + 0.75
            or x < 2.5 / 2.75 and 7.5625 * (x - 2.25 / 2.75) ^ 2 + 0.9375
            or 7.5625 * (x - 2.625 / 2.75) ^ 2 + 0.984375
          )
        )
      )
    end
  end

  ---A callback that uses the `easeOutBounce` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeOutBounce)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeOutBounce(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      -- magic c1 <7.5625> = 7.5625                                      --
      -- magic c2 <2.75>   = 2.75                                        --
      -- local prog =                                                    --
      --   x < 1 / 2.75 and 7.5625 * x ^ 2                               --
      --   or x < 2 / 2.75 and 7.5625 * (x - 1.5 / 2.75) ^ 2 + 0.75      --
      --   or x < 2.5 / 2.75 and 7.5625 * (x - 2.25 / 2.75) ^ 2 + 0.9375 --
      --   or 7.5625 * (x - 2.625 / 2.75) ^ 2 + 0.984375                 --
      animBlend(
        state.anim,
        from + (state.to - from) * (
          x < 1 / 2.75 and 7.5625 * x ^ 2
          or x < 2 / 2.75 and 7.5625 * (x - 1.5 / 2.75) ^ 2 + 0.75
          or x < 2.5 / 2.75 and 7.5625 * (x - 2.25 / 2.75) ^ 2 + 0.9375
          or 7.5625 * (x - 2.625 / 2.75) ^ 2 + 0.984375
        )
      )
    end
  end

  ---A callback that uses the `easeInOutBounce` easing method to blend.
  ---
  ---[Learn More...](https://easings.net/#easeInOutBounce)
  ---@param state Lib.GS.AnimBlend.CallbackState
  ---@param data Lib.GS.AnimBlend.AnimData
  function callbackCurves.easeInOutBounce(state, data)
    if state.done then
      (state.starting and animPlay or animStop)(state.anim)
      animBlend(state.anim, data.blend)
    else
      local from = state.from
      local x = state.progress
      local s = x < 0.5 and -1 or 1
      x = x < 0.5 and 1 - 2 * x or 2 * x - 1
      -- magic c1 <7.5625> = 7.5625
      -- magic c2 <2.75>   = 2.75
      -- local prog =
      --   (1 + s * (
      --     x < 1 / 2.75 and 7.5625 * x ^ 2
      --     or x < 2 / 2.75 and 7.5625 * (x - 1.5 / 2.75) ^ 2 + 0.75
      --     or x < 2.5 / 2.75 and 7.5625 * (x - 2.25 / 2.75) ^ 2 + 0.9375
      --     or 7.5625 * (x - 2.625 / 2.75) ^ 2 + 0.984375
      --   )) * 0.5
      animBlend(
        state.anim,
        -- What the fuck.
        from + (state.to - from) * (
          (1 + s * (
            x < 1 / 2.75 and 7.5625 * x ^ 2
            or x < 2 / 2.75 and 7.5625 * (x - 1.5 / 2.75) ^ 2 + 0.75
            or x < 2.5 / 2.75 and 7.5625 * (x - 2.25 / 2.75) ^ 2 + 0.9375
            or 7.5625 * (x - 2.625 / 2.75) ^ 2 + 0.984375
          )) * 0.5
        )
      )
    end
  end


  ---The default callback used by this library. This is used when no other callback is being used.
  this.defaultCallback = callbackCurves["lin" .. "ear"] --Yes, I did this to trick the LuaLS
  this.callbackGen = callbackGenerators
  this.callbackCurve = callbackCurves


  -----===================================== BLENDING LOGIC =====================================-----

  local ticker = 0
  local last_delta = 0
  local allowed_contexts = {
    RENDER = true,
    FIRST_PERSON = true,
    OTHER = true
  }

  events.TICK:register(function()
    ticker = ticker + 1
  end, "GSAnimBlend:Tick_TimeTicker")

  events.RENDER:register(function(delta, ctx)
    if not allowed_contexts[ctx] or (delta == last_delta and ticker == 0) then return end
    local elapsed_time = ticker + (delta - last_delta)
    ticker = 0
    for anim in pairs(blending) do
      -- Every frame, update time and progress, then call the callback.
      local data = animData[anim]
      local state = data.state
      if not state.paused then
        local cbs = state.callbackState
        state.time = state.time + elapsed_time
        if not state.max then cbs.max = state.starting and data.blendTimeIn or data.blendTimeOut end
        if not state.from then
          cbs.from = data.blendSane
        elseif not state.to then
          cbs.to = data.blendSane
        end

        -- When a blend stops, update all info to signal it has stopped.
        if (state.time >= cbs.max) or (animGetPlayState(anim) == "STOPPED") then
          cbs.time = cbs.max
          cbs.progress = 1
          cbs.done = true

          -- Do final callback.
          state.callback(cbs, animData[anim])
          blending[anim] = nil
        else
          cbs.time = state.time
          cbs.progress = cbs.time / cbs.max
          state.callback(cbs, animData[anim])
        end
      end
    end
    last_delta = delta
  end, "GSAnimBlend:Render_UpdateBlendStates")


  -----================================ METATABLE MODIFICATIONS =================================-----

  ---===== FIELDS =====---

  local animationGetters = {}
  local animationSetters = {}

  function animationGetters:blendCallback()
    if this.safe then assert(chk.badarg(1, "__index", self, "Animation")) end
    return animData[self].callback
  end
  function animationSetters:blendCallback(value)
    if this.safe then
      assert(chk.badarg(1, "__newindex", self, "Animation"))
      if type(value) ~= "string" then
        assert(chk.badarg(3, "__newindex", value, "function", true))
      end
    end

    if type(func) == "string" then
      value = callbackCurves[value]
      if not value then error("bad argument #3 of '__newindex' ('" .. func .. "' is not a valid curve)") end
    end
    animData[self].callback = value
  end


  ---===== METHODS =====---

  local animationMethods = {}

  function animationMethods:play()
    if this.safe then assert(chk.badarg(1, "play", self, "Animation")) end

    if blending[self] then
      local state = animData[self].state
      if state.paused then
        state.paused = false
        return
      elseif state.starting then
        return
      end

      animStop(self)
      local cbs = state.callbackState
      local time = cbs.max * cbs.progress
      this.blend(self, time, animGetBlend(self), nil, true)
      return
    elseif animData[self].blendTimeIn == 0 or animGetPlayState(self) ~= "STOPPED" then
      return animPlay(self)
    end

    this.blend(self, nil, 0, nil, true)
  end

  function animationMethods:stop()
    if this.safe then assert(chk.badarg(1, "stop", self, "Animation")) end

    if blending[self] then
      local state = animData[self].state
      if not state.starting then return end

      local cbs = state.callbackState
      local time = cbs.max * cbs.progress
      this.blend(self, time, animGetBlend(self), 0, false)
      return
    elseif animData[self].blendTimeOut == 0 or animGetPlayState(self) == "STOPPED" then
      return animStop(self)
    end

    this.blend(self, nil, nil, 0, false)
  end

  function animationMethods:pause()
    if this.safe then assert(chk.badarg(1, "pause", self, "Animation")) end

    if blending[self] then
      animData[self].state.paused = true
      return
    end

    animPause(self)
  end

  function animationMethods:restart(blend)
    if this.safe then assert(chk.badarg(1, "restart", self, "Animation")) end

    if blend then
      animStop(self)
      this.blend(self, nil, 0, nil, true)
    elseif blending[self] then
      animBlend(self, animData[self].blend)
      blending[self] = nil
    else
      animRestart(self)
    end
  end


  ---===== GETTERS =====---

  function animationMethods:getBlendTime()
    if this.safe then assert(chk.badarg(1, "getBlendTime", self, "Animation")) end
    local data = animData[self]
    return data.blendTimeIn, data.blendTimeOut
  end

  function animationMethods:isBlending()
    if this.safe then assert(chk.badarg(1, "isBlending", self, "Animation")) end
    return blending[self]
  end

  function animationMethods:getBlend()
    if this.safe then assert(chk.badarg(1, "getBlend", self, "Animation")) end
    return animData[self].blend
  end

  function animationMethods:getPlayState()
    if this.safe then assert(chk.badarg(1, "getPlayState", self, "Animation")) end
    return blending[self]
      and (animData[self].state.paused
        and "PAUSED"
        or "PLAYING")
      or animGetPlayState(self)
  end

  function animationMethods:isPlaying()
    if this.safe then assert(chk.badarg(1, "isPlaying", self, "Animation")) end
    return blending[self] or animIsPlaying(self)
  end

  function animationMethods:isPaused()
    if this.safe then assert(chk.badarg(1, "isPaused", self, "Animation")) end
    return not blending[self] and animIsPaused(self)
  end


  ---===== SETTERS =====---

  function animationMethods:setBlendTime(time_in, time_out)
    if time_in == nil then time_in = 0 end
    if this.safe then
      assert(chk.badarg(1, "setBlendTime", self, "Animation"))
      assert(chk.badnum(2, "setBlendTime", time_in))
      assert(chk.badnum(3, "setBlendTime", time_out, true))
    end

    animData[self].blendTimeIn = m_max(time_in, 0)
    animData[self].blendTimeOut = m_max(time_out or time_in, 0)
    return self
  end

  function animationMethods:setOnBlend(func)
    if this.safe then
      assert(chk.badarg(1, "setOnBlend", self, "Animation"))
      if type(func) ~= "string" then
        assert(chk.badarg(2, "setOnBlend", func, "function", true))
      end
    end

    if type(func) == "string" then
      func = callbackCurves[func]
      if not func then error("bad argument #2 of 'setOnBlend' ('" .. func .. "' is not a valid curve)") end
    end
    animData[self].callback = func
    return self
  end

  function animationMethods:setBlend(weight)
    if weight == nil then weight = 0 end
    if this.safe then
      assert(chk.badarg(1, "setBlend", self, "Animation"))
      assert(chk.badarg(2, "setBlend", weight, "number"))
    end

    local data = animData[self]
    data.blend = weight
    data.blendSane = makeSane(weight, 0)
    return blending[self] and self or animBlend(self, weight)
  end

  function animationMethods:setLength(len)
    if len == nil then len = 0 end
    if this.safe then
      assert(chk.badarg(1, "setLength", self, "Animation"))
      assert(chk.badarg(2, "setLength", len, "number"))
    end

    local data = animData[self]
    if data.length then animNewCode(self, data.length, "") end

    local lenSane = makeSane(m_max(len - tPass, 0), false)
    data.length = lenSane and (lenSane > tPass and lenSane) or false

    if data.length then
      animNewCode(self, m_max(data.length - tPass, 0), blendCommand:format(data.triggerId))
    end
    return animLength(self, len)
  end

  function animationMethods:setPlaying(state)
    if this.safe then assert(chk.badarg(1, "setPlaying", self, "Animation")) end
    if state then self:play() else self:stop() end
    return self
  end


  ---===== CHAINED =====---

  animationMethods.blendTime = animationMethods.setBlendTime
  animationMethods.onBlend = animationMethods.setOnBlend
  animationMethods.blend = animationMethods.setBlend
  animationMethods.length = animationMethods.setLength
  animationMethods.playing = animationMethods.setPlaying


  ---===== METAMETHODS =====---

  function animation_mt:__index(key)
    if animationGetters[key] then
      return animationGetters[key](self)
    elseif animationMethods[key] then
      return animationMethods[key]
    else
      return _animationIndex(self, key)
    end
  end

  function animation_mt:__newindex(key, value)
    if animationSetters[key] then
      animationSetters[key](self, value)
      return
    else
      _animationNewIndex(self, key, value)
    end
  end


  -----============================== ANIMATION API MODIFICATIONS ===============================-----

  if animationapi_mt then
    local apiMethods = {}

    function apiMethods:getPlaying(ignore_blending)
      if this.safe then assert(chk.badarg(1, "getPlaying", self, "AnimationAPI")) end
      ---@cast animapiGetPlaying function
      if ignore_blending then return animapiGetPlaying(animations) end
      local anims = {}
      for _, anim in ipairs(animations:getAnimations()) do
        ---@diagnostic disable-next-line: deprecated
        if anim:isPlaying() then anims[#anims+1] = anim end
      end

      return anims
    end

    function animationapi_mt:__index(key)
      return apiMethods[key] or _animationapiIndex(self, key)
    end
  end


  return setmetatable(this, thismt)
end)

if s then
  return this
else -- This is *all* error handling.
  ---@cast this string
  local e_msg, e_stack = this:match("^(.-)\nstack traceback:\n(.*)$")

  -- Modify Stack
  local stack_lines = {}
  local skip_next
  for line in e_stack:gmatch("[ \t]*([^\n]+)") do
    -- If the level is not a Java level, keep it.
    if not line:match("^%[Java]:") then
      if not skip_next then
        stack_lines[#stack_lines+1] = ("    §4" .. line)
      else
        skip_next = false
      end
    elseif line:match("in function 'pcall'") then
      -- If the level *is* a Java level and it contains the pcall, remove both it and the level above.
      stack_lines[#stack_lines] = stack_lines[#stack_lines]:gsub("in function %b<>", "in protected chunk")
      skip_next = true
    end
  end

  e_stack = table.concat(stack_lines, "\n")

  local cmp, ver = client.compareVersions, client.getFiguraVersion():match("^([^%+]*)")
  local extra_reason = ""

  if FIG[1] and cmp(ver, FIG[1]) == -1 then
    extra_reason = ("\n§oYour Figura version (%s) is below the recommended minimum of %s§r"):format(ver, FIG[1])
  elseif FIG[2] and cmp(ver, FIG[2]) == 1 then
    extra_reason = ("\n§oYour Figura version (%s) is above the recommended maximum of %s§r"):format(ver, FIG[2])
  end

  error(
    (
      "'%s' failed to load\z
       \n§7INFO: %s v%s | %s§r%s\z
       \ncaused by:\z
       \n  §4%s\z
       \n  §4stack traceback:\z
       \n%s§r"
    ):format(
      ID,
      ID, VER, ver,
      extra_reason,
      e_msg, e_stack
    ),
    2
  )
end

--|==================================================================================================================|--
--|=====|| DOCUMENTATION ||==========================================================================================|--
--||=:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:=:==:=:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:==:=||--

---@diagnostic disable: duplicate-set-field, duplicate-doc-field, duplicate-doc-alias
---@diagnostic disable: missing-return, unused-local, lowercase-global, unreachable-code

---@class Lib.GS.AnimBlend.AnimData
---The blending-in time of this animation in ticks.
---@field blendTimeIn number
---The blending-out time of this animation in ticks.
---@field blendTimeOut number
---The faked blend weight value of this animation.
---@field blend number
---The preferred blend weight that blending will use.
---@field blendSane number
---Where in the timeline the stop instruction is placed.  
---If this is `false`, there is no stop instruction due to length limits.
---@field length number|false
---The id for this animation's blend trigger
---@field triggerId string
---The callback function this animation will call every frame while it is blending and one final
---time when blending finishes.
---@field callback? Lib.GS.AnimBlend.blendCallback
---The active blend state.
---@field state? Lib.GS.AnimBlend.BlendState

---@class Lib.GS.AnimBlend.BlendState
---The amount of time this blend has been running for in ticks.
---@field time number
---The maximum time this blend will run in ticks.
---@field max number|false
---The starting blend weight.
---@field from number|false
---The ending blend weight.
---@field to number|false
---The callback to call each blending frame.
---@field callback? function
---The state proxy used in the blend callback function.
---@field callbackState Lib.GS.AnimBlend.CallbackState
---Determines if this blend is paused.
---@field paused boolean
---Determines if this blend is starting or ending an animation.
---@field starting boolean

---@class Lib.GS.AnimBlend.CallbackState
---The animation this callback is acting on.
---@field anim Animation
---The amount of time this blend has been running for in ticks.
---@field time number
---The maximum time this blend will run in ticks.
---@field max number
---The progress as a percentage.
---@field progress number
---The starting blend weight.
---@field from number
---The ending blend weight.
---@field to number
---Determines if this blend is starting or ending an animation.
---@field starting boolean
---Determines if this blend is finishing up.
---@field done boolean

---@class Lib.GS.AnimBlend.BezierOptions
---How many time to use the Newton-Raphson method to approximate.  
---Higher numbers create more accurate approximations at the cost of instructions.
---
---The default value is `4`.
---@field newton_iters? integer
---The minimum slope required to attempt to use the Newton-Raphson method.  
---Lower numbers cause smaller slopes to be approximated at the cost of instructions.
---
---The default value is `0.001`.
---@field newton_minslope? number
---The most precision that subdivision will allow before stopping early.  
---Lower numbers cause subdivision to allow more precision at the cost of instructions.
---
---The default value is `0.0000001`.
---@field subdiv_prec? number
---The maximum amount of times that subdivision will be performed.  
---Higher numbers cause more subdivision to happen at the cost of instructions.
---
---The default value is `10`.
---@field subdiv_iters? integer
---The amount of samples to gather from the bezier curve.  
---Higher numbers gather more samples at the cost of more instructions when creating the curve.  
---Lower numbers gather less samples at the cost of more instructions when blending with the curve.
---
---The default value is `11`.
---@field sample_size? integer

---@class Lib.GS.AnimBlend.Bezier: function
---@overload fun(state: Lib.GS.AnimBlend.CallbackState, data: Lib.GS.AnimBlend.AnimData)
---The X1 value.
---@field [1] number
---The Y1 value.
---@field [2] number
---The X2 value.
---@field [3] number
---The Y2 value.
---@field [4] number
---The options used to make this bezier.
---@field options Lib.GS.AnimBlend.BezierOptions
---The samples gathered from this bezier.
---@field samples {step: number, [integer]: number}

---@class Lib.GS.AnimBlend.tlKeyframe
---The progress this keyframe starts at in the range [0, 1).
---
---If the first keyframe does not start at `0`, an error will be thrown.  
---A keyframe at or after time `1` will never run as completing the blend will be preferred.
---@field time number
---The starting adjusted-progress of this keyframe.  
---Despite the name of this option, it does not need to be smaller than `max`.
---
---All keyframes get an adjusted-progress which starts when the keyframe starts and ends when the next keyframe (or the
---end of the timeline) is hit.
---
---The default value is `0`.
---@field min? number
---The ending adjusted-progress of this keyframe.  
---Despite the name of this option, it does not need to be bigger than `min`.
---
---All keyframes get an adjusted-progress which starts when the keyframe starts and ends when the next keyframe (or the
---end of the timeline) is hit.
---
---The default value is `1`.
---@field max? number
---The blending callback to use for this entire frame.  
---The adjusted-progress is given to this callback as it runs.
---
---If a string is given instead of a callback, it is treated as the name of a curve found in
---`<GSAnimBlend>.callbackCurves`.  
---If `nil` is given, the default callback is used.
---
---Note: Blending callbacks called by this function will **never** call cleanup code. Care should be taken to make sure
---this does not break anything.
---@field func? Lib.GS.AnimBlend.blendCallback | Lib.GS.AnimBlend.curve

---@alias Lib.GS.AnimBlend.blendCallback
---| fun(state: Lib.GS.AnimBlend.CallbackState, data: Lib.GS.AnimBlend.AnimData)

---@alias Lib.GS.AnimBlend.bezierCallback
---| Lib.GS.AnimBlend.Bezier
---| Lib.GS.AnimBlend.blendCallback

---@alias Lib.GS.AnimBlend.timeline Lib.GS.AnimBlend.tlKeyframe[]

---@alias Lib.GS.AnimBlend.curve string
---| "linear"           # The default blending curve. Goes from 0 to 1 without any fancy stuff.
---| "easeInSine"       # [Learn More...](https://easings.net/#easeInSine)
---| "easeOutSine"      # [Learn More...](https://easings.net/#easeOutSine)
---| "easeInOutSine"    # [Learn More...](https://easings.net/#easeInOutSine)
---| "easeInQuad"       # [Learn More...](https://easings.net/#easeInQuad)
---| "easeOutQuad"      # [Learn More...](https://easings.net/#easeOutQuad)
---| "easeInOutQuad"    # [Learn More...](https://easings.net/#easeInOutQuad)
---| "easeInCubic"      # [Learn More...](https://easings.net/#easeInCubic)
---| "easeOutCubic"     # [Learn More...](https://easings.net/#easeOutCubic)
---| "easeInOutCubic"   # [Learn More...](https://easings.net/#easeInOutCubic)
---| "easeInQuart"      # [Learn More...](https://easings.net/#easeInQuart)
---| "easeOutQuart"     # [Learn More...](https://easings.net/#easeOutQuart)
---| "easeInOutQuart"   # [Learn More...](https://easings.net/#easeInOutQuart)
---| "easeInQuint"      # [Learn More...](https://easings.net/#easeInQuint)
---| "easeOutQuint"     # [Learn More...](https://easings.net/#easeOutQuint)
---| "easeInOutQuint"   # [Learn More...](https://easings.net/#easeInOutQuint)
---| "easeInExpo"       # [Learn More...](https://easings.net/#easeInExpo)
---| "easeOutExpo"      # [Learn More...](https://easings.net/#easeOutExpo)
---| "easeInOutExpo"    # [Learn More...](https://easings.net/#easeInOutExpo)
---| "easeInCirc"       # [Learn More...](https://easings.net/#easeInCirc)
---| "easeOutCirc"      # [Learn More...](https://easings.net/#easeOutCirc)
---| "easeInOutCirc"    # [Learn More...](https://easings.net/#easeInOutCirc)
---| "easeInBack"       # [Learn More...](https://easings.net/#easeInBack)
---| "easeOutBack"      # [Learn More...](https://easings.net/#easeOutBack)
---| "easeInOutBack"    # [Learn More...](https://easings.net/#easeInOutBack)
---| "easeInElastic"    # [Learn More...](https://easings.net/#easeInElastic)
---| "easeOutElastic"   # [Learn More...](https://easings.net/#easeOutElastic)
---| "easeInOutElastic" # [Learn More...](https://easings.net/#easeInOutElastic)
---| "easeInBounce"     # [Learn More...](https://easings.net/#easeInBounce)
---| "easeOutBounce"    # [Learn More...](https://easings.net/#easeOutBounce)
---| "easeInOutBounce"  # [Learn More...](https://easings.net/#easeInOutBounce)


---@class Animation
---#### [GS AnimBlend Library]
---The callback that should be called every frame while the animation is blending.
---
---This allows adding custom behavior to the blending feature.
---
---If this is `nil`, it will default to the library's basic callback.
---@field blendCallback? Lib.GS.AnimBlend.blendCallback
local Animation


---===== METHODS =====---

---#### [GS AnimBlend Library]
---Starts this animation from the beginning, even if it is currently paused or playing.
---
---If `blend` is set, it will also restart with a blend.
function Animation:restart(blend) end


---===== GETTERS =====---

---#### [GS AnimBlend Library]
---Gets the blending times of this animation in ticks.
---@return number, number
function Animation:getBlendTime() end

---#### [GS AnimBlend Library]
---Gets if this animation is currently blending.
---@return boolean
function Animation:isBlending() end


---===== SETTERS =====---

---#### [GS AnimBlend Library]
---Sets the blending time of this animation in ticks.
---
---If two values are given, the blending in and out times are set respectively.
---@generic self
---@param self self
---@param time_in? number
---@param time_out? number
---@return self
function Animation:setBlendTime(time_in, time_out) end

---#### [GS AnimBlend Library]
---Sets the blending callback of this animation.
---@generic self
---@param self self
---@param func? Lib.GS.AnimBlend.blendCallback
---@return self
function Animation:setOnBlend(func) end


---===== CHAINED =====---

---#### [GS AnimBlend Library]
---Sets the blending time of this animation in ticks.
---
---If two values are given, the blending in and out times are set respectively.
---@generic self
---@param self self
---@param time_in? number
---@param time_out? number
---@return self
function Animation:blendTime(time_in, time_out) end

---#### [GS AnimBlend Library]
---Sets the blending callback of this animation.
---@generic self
---@param self self
---@param func? Lib.GS.AnimBlend.blendCallback
---@return self
function Animation:onBlend(func) end


---@class AnimationAPI
local AnimationAPI

---#### [GS AnimBlend Library]
---Gets an array of every playing animation.
---
---Set `ignore_blending` to ignore animations that are currently blending.
---@param ignore_blending? boolean
---@return Animation[]
function AnimationAPI:getPlaying(ignore_blending) end