@tldraw/state/dist-esm/lib/HistoryBuffer.mjs.map

tldraw infinite canvas SDK (state).

{
  "version": 3,
  "sources": ["../../src/lib/HistoryBuffer.ts"],
  "sourcesContent": ["import { RESET_VALUE } from './types'\n\n/**\n * A tuple representing a range of epochs and the associated diff.\n * Used internally by HistoryBuffer to store change information.\n *\n * @internal\n */\ntype RangeTuple<Diff> = [fromEpoch: number, toEpoch: number, diff: Diff]\n\n/**\n * A circular buffer that stores diffs between sequential values of an atom or computed signal.\n * This enables efficient change tracking and history retrieval for features like undo/redo.\n *\n * The buffer uses a wrap-around strategy to maintain a fixed-size history of the most recent\n * changes, automatically overwriting older entries when the capacity is exceeded.\n *\n * @example\n * ```ts\n * const buffer = new HistoryBuffer<string>(5)\n * buffer.pushEntry(0, 1, 'first change')\n * buffer.pushEntry(1, 2, 'second change')\n * const changes = buffer.getChangesSince(0) // ['first change', 'second change']\n * ```\n *\n * @internal\n */\nexport class HistoryBuffer<Diff> {\n\t/**\n\t * Current write position in the circular buffer.\n\t * @internal\n\t */\n\tprivate index = 0\n\n\t/**\n\t * Circular buffer storing range tuples. Uses undefined to represent empty slots.\n\t * @internal\n\t */\n\tbuffer: Array<RangeTuple<Diff> | undefined>\n\n\t/**\n\t * Creates a new HistoryBuffer with the specified capacity.\n\t *\n\t * capacity - Maximum number of diffs to store in the buffer\n\t * @example\n\t * ```ts\n\t * const buffer = new HistoryBuffer<number>(10) // Store up to 10 diffs\n\t * ```\n\t */\n\tconstructor(private readonly capacity: number) {\n\t\tthis.buffer = new Array(capacity)\n\t}\n\n\t/**\n\t * Adds a diff entry to the history buffer, representing a change between two epochs.\n\t *\n\t * If the diff is undefined, the operation is ignored. If the diff is RESET_VALUE,\n\t * the entire buffer is cleared to indicate that historical tracking should restart.\n\t *\n\t * @param lastComputedEpoch - The epoch when the previous value was computed\n\t * @param currentEpoch - The epoch when the current value was computed\n\t * @param diff - The diff representing the change, or RESET_VALUE to clear history\n\t * @example\n\t * ```ts\n\t * const buffer = new HistoryBuffer<string>(5)\n\t * buffer.pushEntry(0, 1, 'added text')\n\t * buffer.pushEntry(1, 2, RESET_VALUE) // Clears the buffer\n\t * ```\n\t */\n\tpushEntry(lastComputedEpoch: number, currentEpoch: number, diff: Diff | RESET_VALUE) {\n\t\tif (diff === undefined) {\n\t\t\treturn\n\t\t}\n\n\t\tif (diff === RESET_VALUE) {\n\t\t\tthis.clear()\n\t\t\treturn\n\t\t}\n\n\t\t// Add the diff to the buffer as a range tuple.\n\t\tthis.buffer[this.index] = [lastComputedEpoch, currentEpoch, diff]\n\n\t\t// Bump the index, wrapping around if necessary.\n\t\tthis.index = (this.index + 1) % this.capacity\n\t}\n\n\t/**\n\t * Clears all entries from the history buffer and resets the write position.\n\t * This is called when a RESET_VALUE diff is encountered.\n\t *\n\t * @example\n\t * ```ts\n\t * const buffer = new HistoryBuffer<string>(5)\n\t * buffer.pushEntry(0, 1, 'change')\n\t * buffer.clear()\n\t * console.log(buffer.getChangesSince(0)) // RESET_VALUE\n\t * ```\n\t */\n\tclear() {\n\t\tthis.index = 0\n\t\tthis.buffer.fill(undefined)\n\t}\n\n\t/**\n\t * Retrieves all diffs that occurred since the specified epoch.\n\t *\n\t * The method searches backwards through the circular buffer to find changes\n\t * that occurred after the given epoch. If insufficient history is available\n\t * or the requested epoch is too old, returns RESET_VALUE indicating that\n\t * a complete state rebuild is required.\n\t *\n\t * @param sinceEpoch - The epoch from which to retrieve changes\n\t * @returns Array of diffs since the epoch, or RESET_VALUE if history is insufficient\n\t * @example\n\t * ```ts\n\t * const buffer = new HistoryBuffer<string>(5)\n\t * buffer.pushEntry(0, 1, 'first')\n\t * buffer.pushEntry(1, 2, 'second')\n\t * const changes = buffer.getChangesSince(0) // ['first', 'second']\n\t * const recentChanges = buffer.getChangesSince(1) // ['second']\n\t * const tooOld = buffer.getChangesSince(-100) // RESET_VALUE\n\t * ```\n\t */\n\tgetChangesSince(sinceEpoch: number): RESET_VALUE | Diff[] {\n\t\tconst { index, capacity, buffer } = this\n\n\t\t// For each item in the buffer...\n\t\tfor (let i = 0; i < capacity; i++) {\n\t\t\tconst offset = (index - 1 + capacity - i) % capacity\n\n\t\t\tconst elem = buffer[offset]\n\n\t\t\t// If there's no element in the offset position, return the reset value\n\t\t\tif (!elem) {\n\t\t\t\treturn RESET_VALUE\n\t\t\t}\n\n\t\t\tconst [fromEpoch, toEpoch] = elem\n\n\t\t\t// If the first element is already too early, bail\n\t\t\tif (i === 0 && sinceEpoch >= toEpoch) {\n\t\t\t\treturn []\n\t\t\t}\n\n\t\t\t// If the element is since the given epoch, return an array with all diffs from this element and all following elements\n\t\t\tif (fromEpoch <= sinceEpoch && sinceEpoch < toEpoch) {\n\t\t\t\tconst len = i + 1\n\t\t\t\tconst result = new Array(len)\n\n\t\t\t\tfor (let j = 0; j < len; j++) {\n\t\t\t\t\tresult[j] = buffer[(offset + j) % capacity]![2]\n\t\t\t\t}\n\n\t\t\t\treturn result\n\t\t\t}\n\t\t}\n\n\t\t// If we haven't returned yet, return the reset value\n\t\treturn RESET_VALUE\n\t}\n}\n"],
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