feat: implement Phase 5 - undo/redo system with command pattern

Added comprehensive undo/redo functionality:
- Command pattern interface and base classes
- HistoryManager with 50-operation stack
- EditCommand for all edit operations (cut, delete, paste, trim)
- Full keyboard shortcuts (Ctrl+Z undo, Ctrl+Y/Ctrl+Shift+Z redo)
- HistoryControls UI component with visual feedback
- Integrated history system with all edit operations
- Toast notifications for undo/redo actions
- History state tracking and display

New files:
- lib/history/command.ts - Command interface and BaseCommand
- lib/history/history-manager.ts - HistoryManager class
- lib/history/commands/edit-command.ts - EditCommand and factory functions
- lib/hooks/useHistory.ts - React hook for history management
- components/editor/HistoryControls.tsx - History UI component

Modified files:
- components/editor/AudioEditor.tsx - Integrated history system
- components/editor/EditControls.tsx - Updated keyboard shortcuts display

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/history/command.ts

@@ -0,0 +1,38 @@
+/**
+ * Command Pattern for Undo/Redo System
+ */
+
+export interface Command {
+  /**
+   * Execute the command
+   */
+  execute(): void;
+
+  /**
+   * Undo the command
+   */
+  undo(): void;
+
+  /**
+   * Redo the command (default: call execute again)
+   */
+  redo(): void;
+
+  /**
+   * Get a description of the command for UI display
+   */
+  getDescription(): string;
+}
+
+/**
+ * Base command class with default redo implementation
+ */
+export abstract class BaseCommand implements Command {
+  abstract execute(): void;
+  abstract undo(): void;
+  abstract getDescription(): string;
+
+  redo(): void {
+    this.execute();
+  }
+}

lib/history/commands/edit-command.ts

@@ -0,0 +1,155 @@
+/**
+ * Edit commands for audio buffer operations
+ */
+
+import { BaseCommand } from '../command';
+import type { Selection } from '@/types/selection';
+import {
+  extractBufferSegment,
+  deleteBufferSegment,
+  insertBufferSegment,
+  trimBuffer,
+} from '@/lib/audio/buffer-utils';
+
+export type EditCommandType = 'cut' | 'delete' | 'paste' | 'trim';
+
+export interface EditCommandParams {
+  type: EditCommandType;
+  beforeBuffer: AudioBuffer;
+  afterBuffer: AudioBuffer;
+  selection?: Selection;
+  clipboardData?: AudioBuffer;
+  pastePosition?: number;
+  onApply: (buffer: AudioBuffer) => void;
+}
+
+/**
+ * Command for edit operations (cut, delete, paste, trim)
+ */
+export class EditCommand extends BaseCommand {
+  private type: EditCommandType;
+  private beforeBuffer: AudioBuffer;
+  private afterBuffer: AudioBuffer;
+  private selection?: Selection;
+  private clipboardData?: AudioBuffer;
+  private pastePosition?: number;
+  private onApply: (buffer: AudioBuffer) => void;
+
+  constructor(params: EditCommandParams) {
+    super();
+    this.type = params.type;
+    this.beforeBuffer = params.beforeBuffer;
+    this.afterBuffer = params.afterBuffer;
+    this.selection = params.selection;
+    this.clipboardData = params.clipboardData;
+    this.pastePosition = params.pastePosition;
+    this.onApply = params.onApply;
+  }
+
+  execute(): void {
+    this.onApply(this.afterBuffer);
+  }
+
+  undo(): void {
+    this.onApply(this.beforeBuffer);
+  }
+
+  getDescription(): string {
+    switch (this.type) {
+      case 'cut':
+        return 'Cut';
+      case 'delete':
+        return 'Delete';
+      case 'paste':
+        return 'Paste';
+      case 'trim':
+        return 'Trim';
+      default:
+        return 'Edit';
+    }
+  }
+
+  /**
+   * Get the type of edit operation
+   */
+  getType(): EditCommandType {
+    return this.type;
+  }
+
+  /**
+   * Get the selection that was affected
+   */
+  getSelection(): Selection | undefined {
+    return this.selection;
+  }
+}
+
+/**
+ * Factory functions to create edit commands
+ */
+
+export function createCutCommand(
+  buffer: AudioBuffer,
+  selection: Selection,
+  onApply: (buffer: AudioBuffer) => void
+): EditCommand {
+  const afterBuffer = deleteBufferSegment(buffer, selection.start, selection.end);
+
+  return new EditCommand({
+    type: 'cut',
+    beforeBuffer: buffer,
+    afterBuffer,
+    selection,
+    onApply,
+  });
+}
+
+export function createDeleteCommand(
+  buffer: AudioBuffer,
+  selection: Selection,
+  onApply: (buffer: AudioBuffer) => void
+): EditCommand {
+  const afterBuffer = deleteBufferSegment(buffer, selection.start, selection.end);
+
+  return new EditCommand({
+    type: 'delete',
+    beforeBuffer: buffer,
+    afterBuffer,
+    selection,
+    onApply,
+  });
+}
+
+export function createPasteCommand(
+  buffer: AudioBuffer,
+  clipboardData: AudioBuffer,
+  pastePosition: number,
+  onApply: (buffer: AudioBuffer) => void
+): EditCommand {
+  const afterBuffer = insertBufferSegment(buffer, clipboardData, pastePosition);
+
+  return new EditCommand({
+    type: 'paste',
+    beforeBuffer: buffer,
+    afterBuffer,
+    clipboardData,
+    pastePosition,
+    onApply,
+  });
+}
+
+export function createTrimCommand(
+  buffer: AudioBuffer,
+  selection: Selection,
+  onApply: (buffer: AudioBuffer) => void
+): EditCommand {
+  const afterBuffer = trimBuffer(buffer, selection.start, selection.end);
+
+  return new EditCommand({
+    type: 'trim',
+    beforeBuffer: buffer,
+    afterBuffer,
+    selection,
+    onApply,
+  });
+}

lib/history/history-manager.ts

@@ -0,0 +1,156 @@
+/**
+ * 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();
+  }
+}

lib/hooks/useHistory.ts

@@ -0,0 +1,54 @@
+'use client';
+
+import * as React from 'react';
+import { HistoryManager } from '@/lib/history/history-manager';
+import type { HistoryState } from '@/lib/history/history-manager';
+import type { Command } from '@/lib/history/command';
+
+export interface UseHistoryReturn {
+  execute: (command: Command) => void;
+  undo: () => boolean;
+  redo: () => boolean;
+  clear: () => void;
+  state: HistoryState;
+}
+
+export function useHistory(maxHistorySize: number = 50): UseHistoryReturn {
+  const [manager] = React.useState(() => new HistoryManager(maxHistorySize));
+  const [state, setState] = React.useState<HistoryState>(manager.getState());
+
+  React.useEffect(() => {
+    const unsubscribe = manager.subscribe(() => {
+      setState(manager.getState());
+    });
+
+    return unsubscribe;
+  }, [manager]);
+
+  const execute = React.useCallback(
+    (command: Command) => {
+      manager.execute(command);
+    },
+    [manager]
+  );
+
+  const undo = React.useCallback(() => {
+    return manager.undo();
+  }, [manager]);
+
+  const redo = React.useCallback(() => {
+    return manager.redo();
+  }, [manager]);
+
+  const clear = React.useCallback(() => {
+    manager.clear();
+  }, [manager]);
+
+  return {
+    execute,
+    undo,
+    redo,
+    clear,
+    state,
+  };
+}