import type { ProjectFile } from "./project";
/** Snapshot history for whole-project undo/redo. T-17. */
export class ProjectHistory {
  private items: ProjectFile[];
  private cursor = 0;
  private pending = false;
  constructor(
    initial: ProjectFile,
    private readonly limit = 100,
  ) {
    this.items = [structuredClone(initial)];
  }
  /** Adds one undoable snapshot unless a grouped edit is active. */
  push(value: ProjectFile): void {
    if (this.pending) {
      this.replaceTop(value);
      return;
    }
    this.add(value);
  }
  /** Starts grouping subsequent pushes into a single operation. T-17. */
  begin(): void {
    if (this.pending) throw new Error("History group already active");
    this.items = this.items.slice(0, this.cursor + 1);
    this.items.push(structuredClone(this.items[this.cursor]!));
    this.cursor = this.items.length - 1;
    if (this.items.length > this.limit) {
      this.items.shift();
      this.cursor--;
    }
    this.pending = true;
  }
  /** Commits the final grouped snapshot as one undo step. T-17. */
  commit(value?: ProjectFile): void {
    if (!this.pending) throw new Error("No history group active");
    if (value) this.items[this.cursor] = structuredClone(value);
    if (JSON.stringify(this.items[this.cursor]) === JSON.stringify(this.items[this.cursor - 1])) {
      this.items.pop();
      this.cursor--;
    }
    this.pending = false;
  }
  /** Replaces the current snapshot during a grouped drag. T-17. */
  replaceTop(value: ProjectFile): void {
    this.items[this.cursor] = structuredClone(value);
  }
  /** Moves to the previous snapshot. */
  undo(): ProjectFile {
    if (!this.canUndo) throw new Error("Nothing to undo");
    return structuredClone(this.items[--this.cursor]!);
  }
  /** Moves to the next snapshot. */
  redo(): ProjectFile {
    if (!this.canRedo) throw new Error("Nothing to redo");
    return structuredClone(this.items[++this.cursor]!);
  }
  get canUndo(): boolean {
    return this.cursor > 0;
  }
  get canRedo(): boolean {
    return this.cursor < this.items.length - 1;
  }
  /** Returns a copy of the current snapshot. */
  current(): ProjectFile {
    return structuredClone(this.items[this.cursor]!);
  }
  private add(value: ProjectFile) {
    this.items = this.items.slice(0, this.cursor + 1);
    this.items.push(structuredClone(value));
    this.cursor = this.items.length - 1;
    if (this.items.length > this.limit) {
      this.items.shift();
      this.cursor--;
    }
  }
}