import type { PromptBuffer } from "./buffer.js";

function sameSnapshot(left: PromptBuffer, right: PromptBuffer): boolean {
  return (
    left.cursor.line === right.cursor.line &&
    left.cursor.column === right.cursor.column &&
    left.lines.length === right.lines.length &&
    left.lines.every((line, index) => line === right.lines[index])
  );
}

function cloneSnapshot(buffer: PromptBuffer): PromptBuffer {
  return {
    lines: [...buffer.lines],
    cursor: { ...buffer.cursor },
    ...(buffer.pasteMarkerIds === undefined
      ? {}
      : { pasteMarkerIds: new Set(buffer.pasteMarkerIds) }),
  };
}

/** Private Readline undo history, independent of Pi's native editor stack. */
export class ReadlineUndoStack {
  readonly #snapshots: PromptBuffer[] = [];

  record(buffer: PromptBuffer, current?: PromptBuffer): void {
    const snapshot = cloneSnapshot(buffer);
    if (current !== undefined && sameSnapshot(snapshot, current)) return;
    if (
      this.#snapshots.some(
        (entry, index) =>
          index === this.#snapshots.length - 1 && sameSnapshot(entry, snapshot),
      )
    )
      return;
    this.#snapshots.push(snapshot);
  }

  undo(): PromptBuffer | undefined {
    return this.#snapshots.pop();
  }

  clear(): void {
    this.#snapshots.length = 0;
  }
}