gitmost/packages/prosemirror-markdown/src/lib/canonicalize.ts

/**
 * Semantic canonicalization of ProseMirror/TipTap documents for the round-trip
 * idempotency check (SPEC §11, "Task #0", option (b): compare a CANONICALIZED
 * form rather than raw bytes).
 *
 * `markdownToProseMirror` reconstructs schema DEFAULT attributes (e.g.
 * `indent: null` where the source omitted it) and regenerates per-block ids on
 * every import. A raw deep-equal of the source doc against the re-imported doc
 * therefore diverges even when the two are semantically identical. This module
 * normalizes a document so that two semantically-equal docs compare deep-equal
 * regardless of block ids and absent-vs-explicit-default-null attributes.
 *
 * It is a self-contained module with no external dependencies.
 */

/**
 * Known NON-NULL schema defaults that `markdownToProseMirror` materializes on
 * import, keyed by node/mark type → { attr: defaultValue }.
 *
 * Why this exists: `canonicalizeAttrs` already treats an absent attr as
 * equivalent to an explicit `null`/`undefined`. But several Docmost schema
 * attributes default to a NON-null value, so import fills them in even when the
 * source omitted them — making "attr absent" diverge from "attr at its default
 * value" under a raw deep-equal. To keep "absent ≡ explicit-default", we ALSO
 * drop any attr whose value equals its known schema default. A non-default
 * value (e.g. `orderedList.start: 5`) is NOT a default, so it is KEPT.
 *
 * Every entry below was read from `packages/docmost-client/src/lib/
 * docmost-schema.ts` (the line refs are the exact `default:` declarations) and
 * confirmed to be materialized by an export→import→export round-trip:
 *   - mark `link`    target / rel  — DocmostAttributes + StarterKit link.
 *       StarterKit's link extension defaults `target: "_blank"` and
 *       `rel: "noopener noreferrer nofollow"`; both materialize on import
 *       (empirically confirmed) even when the source had only `href`.
 *   - mark `comment` resolved      — docmost-schema.ts L213-214 (`default: false`).
 *   - node `orderedList` start     — provided by StarterKit's orderedList
 *       (`default: 1`); materializes on import (empirically confirmed).
 *   - node `drawio`/`excalidraw`/`video`/`youtube`/`embed` align — the diagram
 *       attribute set and the media nodes declare `align: { default: "center" }`
 *       (docmost-schema.ts L745-750 diagramAttributes; L564 video; L626 youtube;
 *       L667 embed). The diagram `align` is the one the round-trip materializes
 *       (docmost-schema.ts L745); the media/embed entries normalize the SAME
 *       `align` default for consistency. Note: this only normalizes `align` —
 *       full canonical stability of `embed` is separately limited by the
 *       converter coercing numeric `width`/`height` to strings, which is outside
 *       canonicalize's scope.
 *
 * NOTE: `image` align now defaults to `"center"` — unified with editor-ext
 * (#293 canon #4). It is listed below so a canonical image drops `align` when
 * it equals "center" (absent ≡ default), exactly like the diagram/media nodes.
 * A null align is likewise dropped by the null-drop rule and re-imports as the
 * "center" default, so bare `![](src)` images stay canonically clean.
 */
const KNOWN_DEFAULTS: Record<string, Record<string, unknown>> = {
  // mark types
  link: {
    target: "_blank",
    rel: "noopener noreferrer nofollow",
  },
  comment: {
    resolved: false,
  },
  // node types
  orderedList: {
    start: 1,
  },
  image: {
    align: "center",
  },
  drawio: {
    align: "center",
  },
  excalidraw: {
    align: "center",
  },
  video: {
    align: "center",
  },
  youtube: {
    align: "center",
  },
  embed: {
    align: "center",
  },
};

/**
 * Prune an `attrs` object in place on a fresh copy: drop keys whose value is
 * `null` or `undefined` (an absent attribute and an explicit default of `null`
 * are semantically equivalent here). Optionally also drop a node-level `id`
 * (block ids are regenerated on import, SPEC §11). ALSO drop any attr whose
 * value equals the node/mark `type`'s known NON-null schema default
 * (`KNOWN_DEFAULTS`), so "attr absent" ≡ "attr at its default value" — without
 * this, the import-materialized `link.target`/`comment.resolved`/
 * `orderedList.start`/diagram `align` defaults would be a phantom diff. Every
 * non-default attribute value is KEPT (level, language, src, href, commentId,
 * width, a non-default `start`/`align`, ...).
 *
 * Returns the pruned attrs object, or `undefined` if nothing meaningful is
 * left (so the caller can drop the `attrs` key entirely: `{attrs:{}}` ≡ no
 * attrs).
 */
function canonicalizeAttrs(
  attrs: Record<string, unknown>,
  dropId: boolean,
  type: string | undefined,
): Record<string, unknown> | undefined {
  const defaults = type ? KNOWN_DEFAULTS[type] : undefined;
  const out: Record<string, unknown> = {};
  // Stable key order so a JSON.stringify of the canonical form is comparable
  // regardless of the input's key order.
  for (const key of Object.keys(attrs).sort()) {
    // Block ids are regenerated on import; drop them on NODE attrs only.
    if (dropId && key === "id") continue;
    const value = attrs[key];
    // Absent ≡ explicit-default-null/undefined.
    if (value === null || value === undefined) continue;
    // Absent ≡ explicit known non-null default (e.g. link.target="_blank").
    // A non-default value (e.g. orderedList.start=5) does NOT match, so it is
    // kept. The `comment` mark's `commentId` is never a default, so it always
    // survives (SPEC §3); only its `resolved: false` default is normalized away.
    if (defaults && key in defaults && value === defaults[key]) continue;
    out[key] = value;
  }
  return Object.keys(out).length > 0 ? out : undefined;
}

/**
 * Return a DEEP COPY of a ProseMirror node tree, canonicalized so that two
 * semantically-equal documents compare deep-equal. Rules (applied recursively
 * to the node, its `content`, and its `marks`):
 *
 *  1. Remove node-level `attrs.id` (regenerated on import). Mark attrs are NOT
 *     touched for `id` (marks carry no block id; only their meaningful attrs).
 *  2. In any `attrs` object (node OR mark) drop keys whose value is `null`/
 *     `undefined` (absent ≡ explicit default null) OR equals that node/mark
 *     type's known non-null schema default (absent ≡ explicit default).
 *     Keep every non-default value. The type is passed into the attrs
 *     normalizer so it can look up `KNOWN_DEFAULTS`.
 *  3. If an `attrs` object becomes empty after pruning, drop the `attrs` key.
 *  4. Preserve `marks` (including the `comment` mark and its `commentId` — a
 *     meaningful anchor per SPEC §3; never strip it).
 *  5. Preserve `text`, `type`, and `content` order exactly.
 *  6. Never mutate the input.
 */
export function canonicalizeContent(node: any): any {
  if (Array.isArray(node)) {
    return node.map((child) => canonicalizeContent(child));
  }
  if (node === null || typeof node !== "object") {
    // Primitive leaf (string/number/boolean/null): returned as-is.
    return node;
  }

  // A node is a mark when it has a `type` but never carries block `content`
  // and lives inside a `marks` array. We cannot tell from the node alone, so
  // we distinguish at the recursion site: node `attrs` drop `id`, mark `attrs`
  // do not. This is handled by passing a `dropId` flag down for the `attrs`
  // key specifically (nodes) vs the `marks[].attrs` path (marks).
  const out: Record<string, unknown> = {};
  for (const key of Object.keys(node)) {
    if (key === "attrs" && node.attrs && typeof node.attrs === "object") {
      // Node-level attrs: drop the block id, null/undefined attrs, and any
      // attr at this node type's known non-null schema default.
      const canon = canonicalizeAttrs(
        node.attrs as Record<string, unknown>,
        true,
        typeof node.type === "string" ? node.type : undefined,
      );
      if (canon !== undefined) out.attrs = canon;
      // else: drop the `attrs` key entirely (rule 3).
    } else if (key === "marks" && Array.isArray(node.marks)) {
      // Marks: keep them all (incl. comment); canonicalize their attrs but do
      // NOT drop `id` (a mark's `id` would be a meaningful attr, not a block
      // id). An empty marks array is dropped so `marks:[]` ≡ no marks.
      const marks = (node.marks as any[]).map((mark) => canonicalizeMark(mark));
      if (marks.length > 0) out.marks = marks;
    } else {
      out[key] = canonicalizeContent(node[key]);
    }
  }
  return out;
}

/**
 * Canonicalize a single mark: keep `type`, prune its `attrs` (null/undefined
 * AND known non-null defaults dropped, empty attrs removed) but NEVER drop a
 * mark's attribute as a "block id" — marks have no block id, only meaningful
 * attrs (href, commentId, color, level, ...). Meaningful NON-default attrs
 * survive (the `comment` mark's `commentId` is never a default, so it always
 * survives — SPEC §3); only known defaults like `link.target="_blank"`,
 * `link.rel="noopener…"` and `comment.resolved=false` are normalized away.
 */
function canonicalizeMark(mark: any): any {
  if (mark === null || typeof mark !== "object") return mark;
  const out: Record<string, unknown> = {};
  for (const key of Object.keys(mark)) {
    if (key === "attrs" && mark.attrs && typeof mark.attrs === "object") {
      const canon = canonicalizeAttrs(
        mark.attrs as Record<string, unknown>,
        false,
        typeof mark.type === "string" ? mark.type : undefined,
      );
      if (canon !== undefined) out.attrs = canon;
    } else {
      out[key] = canonicalizeContent(mark[key]);
    }
  }
  return out;
}

/**
 * Deep structural equality of two values that is key-order-insensitive.
 * Used to compare canonical forms. (`canonicalizeContent` already emits
 * `attrs` in a stable key order, but the top-level node keys preserve input
 * order, so we compare structurally rather than by string.)
 */
function deepEqual(a: any, b: any): boolean {
  if (a === b) return true;
  if (typeof a !== typeof b) return false;
  if (a === null || b === null) return a === b;
  if (typeof a !== "object") return false;

  const aIsArr = Array.isArray(a);
  const bIsArr = Array.isArray(b);
  if (aIsArr !== bIsArr) return false;

  if (aIsArr) {
    if (a.length !== b.length) return false;
    for (let i = 0; i < a.length; i++) {
      if (!deepEqual(a[i], b[i])) return false;
    }
    return true;
  }

  const aKeys = Object.keys(a);
  const bKeys = Object.keys(b);
  if (aKeys.length !== bKeys.length) return false;
  for (const k of aKeys) {
    if (!Object.prototype.hasOwnProperty.call(b, k)) return false;
    if (!deepEqual(a[k], b[k])) return false;
  }
  return true;
}

/**
 * True when two ProseMirror documents are semantically equal: equal after
 * canonicalization (block ids stripped, absent-vs-default-null normalized).
 */
export function docsCanonicallyEqual(a: any, b: any): boolean {
  return deepEqual(canonicalizeContent(a), canonicalizeContent(b));
}