use crate::{database::Config, utils, ConduitResult, Error, Result};
use log::{error, info};
use ruma::{
    api::{
        client::r0::sync::sync_events,
        federation::discovery::{ServerSigningKeys, VerifyKey},
    },
    DeviceId, EventId, MilliSecondsSinceUnixEpoch, ServerName, ServerSigningKeyId, UserId,
};
use rustls::{ServerCertVerifier, WebPKIVerifier};
use std::{
    collections::{BTreeMap, HashMap},
    fs,
    future::Future,
    path::PathBuf,
    sync::{Arc, RwLock},
    time::{Duration, Instant},
};
use tokio::sync::{broadcast, Semaphore};
use trust_dns_resolver::TokioAsyncResolver;

use super::abstraction::Tree;

pub const COUNTER: &[u8] = b"c";

type WellKnownMap = HashMap<Box<ServerName>, (String, String)>;
type TlsNameMap = HashMap<String, webpki::DNSName>;
type RateLimitState = (Instant, u32); // Time if last failed try, number of failed tries
pub struct Globals {
    pub actual_destination_cache: Arc<RwLock<WellKnownMap>>, // actual_destination, host
    pub tls_name_override: Arc<RwLock<TlsNameMap>>,
    pub(super) globals: Arc<dyn Tree>,
    config: Config,
    keypair: Arc<ruma::signatures::Ed25519KeyPair>,
    reqwest_client: reqwest::Client,
    dns_resolver: TokioAsyncResolver,
    jwt_decoding_key: Option<jsonwebtoken::DecodingKey<'static>>,
    pub(super) server_signingkeys: Arc<dyn Tree>,
    pub bad_event_ratelimiter: Arc<RwLock<BTreeMap<EventId, RateLimitState>>>,
    pub bad_signature_ratelimiter: Arc<RwLock<BTreeMap<Vec<String>, RateLimitState>>>,
    pub servername_ratelimiter: Arc<RwLock<BTreeMap<Box<ServerName>, Arc<Semaphore>>>>,
    pub sync_receivers: RwLock<
        BTreeMap<
            (UserId, Box<DeviceId>),
            (
                Option<String>,
                tokio::sync::watch::Receiver<Option<ConduitResult<sync_events::Response>>>,
            ), // since, rx
        >,
    >,
    pub rotate: RotationHandler,
}

struct MatrixServerVerifier {
    inner: WebPKIVerifier,
    tls_name_override: Arc<RwLock<TlsNameMap>>,
}

impl ServerCertVerifier for MatrixServerVerifier {
    fn verify_server_cert(
        &self,
        roots: &rustls::RootCertStore,
        presented_certs: &[rustls::Certificate],
        dns_name: webpki::DNSNameRef<'_>,
        ocsp_response: &[u8],
    ) -> std::result::Result<rustls::ServerCertVerified, rustls::TLSError> {
        if let Some(override_name) = self.tls_name_override.read().unwrap().get(dns_name.into()) {
            let result = self.inner.verify_server_cert(
                roots,
                presented_certs,
                override_name.as_ref(),
                ocsp_response,
            );
            if result.is_ok() {
                return result;
            }
            info!(
                "Server {:?} is non-compliant, retrying TLS verification with original name",
                dns_name
            );
        }
        self.inner
            .verify_server_cert(roots, presented_certs, dns_name, ocsp_response)
    }
}

/// Handles "rotation" of long-polling requests. "Rotation" in this context is similar to "rotation" of log files and the like.
///
/// This is utilized to have sync workers return early and release read locks on the database.
pub struct RotationHandler(broadcast::Sender<()>, broadcast::Receiver<()>);

impl RotationHandler {
    pub fn new() -> Self {
        let (s, r) = broadcast::channel::<()>(1);

        Self(s, r)
    }

    pub fn watch(&self) -> impl Future<Output = ()> {
        let mut r = self.0.subscribe();

        async move {
            let _ = r.recv().await;
        }
    }

    pub fn fire(&self) {
        let _ = self.0.send(());
    }
}

impl Globals {
    pub fn load(
        globals: Arc<dyn Tree>,
        server_signingkeys: Arc<dyn Tree>,
        config: Config,
    ) -> Result<Self> {
        let keypair_bytes = globals.get(b"keypair")?.map_or_else(
            || {
                let keypair = utils::generate_keypair();
                globals.insert(b"keypair", &keypair)?;
                Ok::<_, Error>(keypair)
            },
            |s| Ok(s.to_vec()),
        )?;

        let mut parts = keypair_bytes.splitn(2, |&b| b == 0xff);

        let keypair = utils::string_from_bytes(
            // 1. version
            parts
                .next()
                .expect("splitn always returns at least one element"),
        )
        .map_err(|_| Error::bad_database("Invalid version bytes in keypair."))
        .and_then(|version| {
            // 2. key
            parts
                .next()
                .ok_or_else(|| Error::bad_database("Invalid keypair format in database."))
                .map(|key| (version, key))
        })
        .and_then(|(version, key)| {
            ruma::signatures::Ed25519KeyPair::from_der(&key, version)
                .map_err(|_| Error::bad_database("Private or public keys are invalid."))
        });

        let keypair = match keypair {
            Ok(k) => k,
            Err(e) => {
                error!("Keypair invalid. Deleting...");
                globals.remove(b"keypair")?;
                return Err(e);
            }
        };

        let tls_name_override = Arc::new(RwLock::new(TlsNameMap::new()));
        let verifier = Arc::new(MatrixServerVerifier {
            inner: WebPKIVerifier::new(),
            tls_name_override: tls_name_override.clone(),
        });
        let mut tlsconfig = rustls::ClientConfig::new();
        tlsconfig.dangerous().set_certificate_verifier(verifier);
        tlsconfig.root_store =
            rustls_native_certs::load_native_certs().expect("Error loading system certificates");

        let mut reqwest_client_builder = reqwest::Client::builder()
            .connect_timeout(Duration::from_secs(30))
            .timeout(Duration::from_secs(60 * 3))
            .pool_max_idle_per_host(1)
            .use_preconfigured_tls(tlsconfig);
        if let Some(proxy) = config.proxy.to_proxy()? {
            reqwest_client_builder = reqwest_client_builder.proxy(proxy);
        }
        let reqwest_client = reqwest_client_builder.build().unwrap();

        let jwt_decoding_key = config
            .jwt_secret
            .as_ref()
            .map(|secret| jsonwebtoken::DecodingKey::from_secret(secret.as_bytes()).into_static());

        let s = Self {
            globals,
            config,
            keypair: Arc::new(keypair),
            reqwest_client,
            dns_resolver: TokioAsyncResolver::tokio_from_system_conf().map_err(|_| {
                Error::bad_config("Failed to set up trust dns resolver with system config.")
            })?,
            actual_destination_cache: Arc::new(RwLock::new(WellKnownMap::new())),
            tls_name_override,
            server_signingkeys,
            jwt_decoding_key,
            bad_event_ratelimiter: Arc::new(RwLock::new(BTreeMap::new())),
            bad_signature_ratelimiter: Arc::new(RwLock::new(BTreeMap::new())),
            servername_ratelimiter: Arc::new(RwLock::new(BTreeMap::new())),
            sync_receivers: RwLock::new(BTreeMap::new()),
            rotate: RotationHandler::new(),
        };

        fs::create_dir_all(s.get_media_folder())?;

        Ok(s)
    }

    /// Returns this server's keypair.
    pub fn keypair(&self) -> &ruma::signatures::Ed25519KeyPair {
        &self.keypair
    }

    /// Returns a reqwest client which can be used to send requests.
    pub fn reqwest_client(&self) -> &reqwest::Client {
        &self.reqwest_client
    }

    pub fn next_count(&self) -> Result<u64> {
        utils::u64_from_bytes(&self.globals.increment(COUNTER)?)
            .map_err(|_| Error::bad_database("Count has invalid bytes."))
    }

    pub fn current_count(&self) -> Result<u64> {
        self.globals.get(COUNTER)?.map_or(Ok(0_u64), |bytes| {
            utils::u64_from_bytes(&bytes)
                .map_err(|_| Error::bad_database("Count has invalid bytes."))
        })
    }

    pub fn server_name(&self) -> &ServerName {
        self.config.server_name.as_ref()
    }

    pub fn max_request_size(&self) -> u32 {
        self.config.max_request_size
    }

    pub fn allow_registration(&self) -> bool {
        self.config.allow_registration
    }

    pub fn allow_encryption(&self) -> bool {
        self.config.allow_encryption
    }

    pub fn allow_federation(&self) -> bool {
        self.config.allow_federation
    }

    pub fn trusted_servers(&self) -> &[Box<ServerName>] {
        &self.config.trusted_servers
    }

    pub fn dns_resolver(&self) -> &TokioAsyncResolver {
        &self.dns_resolver
    }

    pub fn jwt_decoding_key(&self) -> Option<&jsonwebtoken::DecodingKey<'_>> {
        self.jwt_decoding_key.as_ref()
    }

    /// TODO: the key valid until timestamp is only honored in room version > 4
    /// Remove the outdated keys and insert the new ones.
    ///
    /// This doesn't actually check that the keys provided are newer than the old set.
    pub fn add_signing_key(&self, origin: &ServerName, new_keys: ServerSigningKeys) -> Result<()> {
        // Not atomic, but this is not critical
        let signingkeys = self.server_signingkeys.get(origin.as_bytes())?;

        let mut keys = signingkeys
            .and_then(|keys| serde_json::from_slice(&keys).ok())
            .unwrap_or_else(|| {
                // Just insert "now", it doesn't matter
                ServerSigningKeys::new(origin.to_owned(), MilliSecondsSinceUnixEpoch::now())
            });

        let ServerSigningKeys {
            verify_keys,
            old_verify_keys,
            ..
        } = new_keys;

        keys.verify_keys.extend(verify_keys.into_iter());
        keys.old_verify_keys.extend(old_verify_keys.into_iter());

        self.server_signingkeys.insert(
            origin.as_bytes(),
            &serde_json::to_vec(&keys).expect("serversigningkeys can be serialized"),
        )?;

        Ok(())
    }

    /// This returns an empty `Ok(BTreeMap<..>)` when there are no keys found for the server.
    pub fn signing_keys_for(
        &self,
        origin: &ServerName,
    ) -> Result<BTreeMap<ServerSigningKeyId, VerifyKey>> {
        let signingkeys = self
            .server_signingkeys
            .get(origin.as_bytes())?
            .and_then(|bytes| serde_json::from_slice::<ServerSigningKeys>(&bytes).ok())
            .map(|keys| {
                let mut tree = keys.verify_keys;
                tree.extend(
                    keys.old_verify_keys
                        .into_iter()
                        .map(|old| (old.0, VerifyKey::new(old.1.key))),
                );
                tree
            })
            .unwrap_or_else(BTreeMap::new);

        Ok(signingkeys)
    }

    pub fn database_version(&self) -> Result<u64> {
        self.globals.get(b"version")?.map_or(Ok(0), |version| {
            utils::u64_from_bytes(&version)
                .map_err(|_| Error::bad_database("Database version id is invalid."))
        })
    }

    pub fn bump_database_version(&self, new_version: u64) -> Result<()> {
        self.globals
            .insert(b"version", &new_version.to_be_bytes())?;
        Ok(())
    }

    pub fn get_media_folder(&self) -> PathBuf {
        let mut r = PathBuf::new();
        r.push(self.config.database_path.clone());
        r.push("media");
        r
    }

    pub fn get_media_file(&self, key: &[u8]) -> PathBuf {
        let mut r = PathBuf::new();
        r.push(self.config.database_path.clone());
        r.push("media");
        r.push(base64::encode_config(key, base64::URL_SAFE_NO_PAD));
        r
    }
}