audio-ui/lib/history/history-manager.ts

/**
 * History Manager for Undo/Redo functionality
 */

import type { Command } from './command';

export interface HistoryState {
  canUndo: boolean;
  canRedo: boolean;
  undoDescription: string | null;
  redoDescription: string | null;
  historySize: number;
}

export class HistoryManager {
  private undoStack: Command[] = [];
  private redoStack: Command[] = [];
  private maxHistorySize: number;
  private listeners: Set<() => void> = new Set();

  constructor(maxHistorySize: number = 50) {
    this.maxHistorySize = maxHistorySize;
  }

  /**
   * Execute a command and add it to history
   */
  execute(command: Command): void {
    command.execute();
    this.undoStack.push(command);

    // Limit history size
    if (this.undoStack.length > this.maxHistorySize) {
      this.undoStack.shift();
    }

    // Clear redo stack when new command is executed
    this.redoStack = [];

    this.notifyListeners();
  }

  /**
   * Undo the last command
   */
  undo(): boolean {
    if (!this.canUndo()) return false;

    const command = this.undoStack.pop()!;
    command.undo();
    this.redoStack.push(command);

    this.notifyListeners();
    return true;
  }

  /**
   * Redo the last undone command
   */
  redo(): boolean {
    if (!this.canRedo()) return false;

    const command = this.redoStack.pop()!;
    command.redo();
    this.undoStack.push(command);

    this.notifyListeners();
    return true;
  }

  /**
   * Check if undo is available
   */
  canUndo(): boolean {
    return this.undoStack.length > 0;
  }

  /**
   * Check if redo is available
   */
  canRedo(): boolean {
    return this.redoStack.length > 0;
  }

  /**
   * Get current history state
   */
  getState(): HistoryState {
    return {
      canUndo: this.canUndo(),
      canRedo: this.canRedo(),
      undoDescription: this.getUndoDescription(),
      redoDescription: this.getRedoDescription(),
      historySize: this.undoStack.length,
    };
  }

  /**
   * Get description of next undo action
   */
  getUndoDescription(): string | null {
    if (!this.canUndo()) return null;
    return this.undoStack[this.undoStack.length - 1].getDescription();
  }

  /**
   * Get description of next redo action
   */
  getRedoDescription(): string | null {
    if (!this.canRedo()) return null;
    return this.redoStack[this.redoStack.length - 1].getDescription();
  }

  /**
   * Clear all history
   */
  clear(): void {
    this.undoStack = [];
    this.redoStack = [];
    this.notifyListeners();
  }

  /**
   * Subscribe to history changes
   */
  subscribe(listener: () => void): () => void {
    this.listeners.add(listener);
    return () => this.listeners.delete(listener);
  }

  /**
   * Notify all listeners of history changes
   */
  private notifyListeners(): void {
    this.listeners.forEach((listener) => listener());
  }

  /**
   * Get current history size
   */
  getHistorySize(): number {
    return this.undoStack.length;
  }

  /**
   * Set maximum history size
   */
  setMaxHistorySize(size: number): void {
    this.maxHistorySize = size;
    // Trim undo stack if needed
    while (this.undoStack.length > this.maxHistorySize) {
      this.undoStack.shift();
    }
    this.notifyListeners();
  }
}