From 76541aea85aa3e655dae4d652703c577d5e48ecc Mon Sep 17 00:00:00 2001
From: Charlotte Som <charlotte@som.codes>
Date: Thu, 6 Mar 2025 09:42:49 +0000
Subject: [PATCH] add compaction for the wire protocol

this batches contiguous runs of characters from a host into a single
object
---
 compression.ts | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++
 deno.json      |  5 ++++
 2 files changed, 86 insertions(+)
 create mode 100644 compression.ts

diff --git a/compression.ts b/compression.ts
new file mode 100644
index 0000000..0643745
--- /dev/null
+++ b/compression.ts
@@ -0,0 +1,81 @@
+import { Timestamp } from "./sync/common.ts";
+import { CausalTree, CausalTreeOp, WeakCausalTreeOp } from "./sync/ordt/causal-tree.ts";
+import { PlainTextOperation } from "./sync/ordt/plain-text.ts";
+
+type VerbatimRun = WeakCausalTreeOp<PlainTextOperation>;
+type CompressedRun = { st: Timestamp; p: Timestamp | undefined; seq: string };
+type Run = VerbatimRun | CompressedRun;
+
+export function compressOps(ops: CausalTreeOp<PlainTextOperation>[]): Run[] {
+  if (ops.length === 0) throw new Error("can't create a compressed run!");
+
+  const runs: Run[] = [];
+  let seq = "";
+  let cnt = 0;
+  let start: Timestamp | undefined;
+  let firstParent: Timestamp | undefined;
+  for (let i = 0; i < ops.length; i++) {
+    const op = ops[i];
+    const lastOp = ops[i - 1];
+
+    if (!start) start = op.at;
+    if (!firstParent) firstParent = op.parent?.at;
+
+    if (
+      op.type === "insert" &&
+      op.sequence.length === 1 &&
+      (cnt === 0 ||
+        (op.parent?.at?.[0] === lastOp.at[0] &&
+          op.parent?.at?.[1] === lastOp.at[1] &&
+          op.at[0] === lastOp.at[0] &&
+          op.at[1] === lastOp.at[1] + 1))
+    ) {
+      seq += op.sequence;
+      cnt++;
+    } else {
+      if (cnt > 0) {
+        runs.push({ st: start!, p: firstParent, seq });
+        i--;
+      } else {
+        runs.push(CausalTree.toWeakOp(op));
+      }
+
+      start = undefined;
+      firstParent = undefined;
+      seq = "";
+      cnt = 0;
+    }
+  }
+
+  if (cnt > 1) {
+    runs.push({ st: start!, p: firstParent, seq });
+  }
+
+  return runs;
+}
+
+export function decompressOps(runs: Run[]): WeakCausalTreeOp<PlainTextOperation>[] {
+  const ops: WeakCausalTreeOp<PlainTextOperation>[] = [];
+
+  for (const run of runs) {
+    if ("st" in run) {
+      let i = 0;
+      let parent: Timestamp | undefined = run.p;
+      for (const c of run.seq) {
+        const op = {
+          at: [run.st[0], run.st[1] + i] as Timestamp,
+          parent,
+          type: "insert",
+          sequence: c,
+        } as const;
+        parent = op.at;
+        ops.push(op);
+        i++;
+      }
+    } else {
+      ops.push(run);
+    }
+  }
+
+  return ops;
+}
diff --git a/deno.json b/deno.json
index 8e26a11..e0f0251 100644
--- a/deno.json
+++ b/deno.json
@@ -1,5 +1,10 @@
 {
   "version": "0.1.0",
+  "tasks": {
+    "build": "deno run -A ./_build.ts",
+    "watch": "deno run -A ./_build.ts --watch",
+    "serve": "deno run -A ./server.ts"
+  },
   "imports": {
     "@char/aftercare": "jsr:@char/aftercare@^0.3.0",
     "@oak/oak": "jsr:@oak/oak@^17.1.4"