Implement MultiFileEditor component for managing multiple files

[nullcoder]

Description

Implement the MultiFileEditor component that manages multiple FileEditor instances in a vertical layout, following GitHub Gist's UX pattern.

Requirements

• Vertical layout: All files displayed vertically on one page (NO TABS)
• Each file editor is stacked below the previous one
• Add new file button at the bottom of all files
• Auto-scroll to newly added files with smooth animation
• Delete file functionality with inline remove button
• Minimum 1 file, maximum 20 files
• Generate default filenames (file1.txt, file2.txt, etc.)
• Prevent duplicate filenames across all files
• Total size validation (5MB limit for entire gist)
• Individual file size validation (500KB per file)
• Responsive design for mobile
• Proper focus management when adding/removing files

Acceptance Criteria

• Files are displayed vertically, all visible at once
• Can add new files up to 20 file limit
• New files appear at the bottom with auto-scroll
• Focus moves to new file's filename input
• Can delete files (except when only 1 remains)
• Remove button hidden when only 1 file exists
• Confirmation dialog for non-empty file deletion
• Default filenames are auto-generated sequentially
• Duplicate filenames are prevented with error message
• Total size limit is enforced (5MB) with clear indicator
• Individual file warnings at 400KB, errors at 500KB
• Component is fully typed with TypeScript
• Works well on mobile devices
• Keyboard shortcuts work (Ctrl+Enter for new file)
• Accessible with screen readers

State Interface

interface FileData {
  id: string; // nanoid for React keys
  name: string;
  content: string;
  language?: string;
}

interface MultiFileEditorProps {
  initialFiles?: FileData[];
  onChange: (files: FileData[]) => void;
  readOnly?: boolean;
  maxFiles?: number; // Default 20
  maxTotalSize?: number; // Default 5MB
  maxFileSize?: number; // Default 500KB
}

UI Layout

┌─ MultiFileEditor Container ─────────────┐
│                                         │
│ Total: 3 files, 126 KB / 5 MB          │
│                                         │
│ [FileEditor 1]                          │
│   filename.js | JavaScript ▼ | ✕       │
│   // code...                            │
│                                         │
│ [FileEditor 2]                          │
│   styles.css | CSS ▼ | ✕               │
│   /* code... */                         │
│                                         │
│ [FileEditor 3]                          │
│   data.json | JSON ▼                   │
│   { "data": "..." }                     │
│                                         │
│ ┌─────────────────────────────────────┐ │
│ │      ➕ Add another file            │ │
│ └─────────────────────────────────────┘ │
└─────────────────────────────────────────┘

File Management Logic

// Generate unique default filename
function generateFilename(existingFiles: FileData[]): string {
  let counter = 1;
  let filename = `file${counter}.txt`;
  
  while (existingFiles.some(f => f.name === filename)) {
    counter++;
    filename = `file${counter}.txt`;
  }
  
  return filename;
}

// Calculate total size
function calculateTotalSize(files: FileData[]): number {
  return files.reduce((sum, file) => 
    sum + new Blob([file.content]).size, 0
  );
}

Technical Notes

• Follow the design in docs/MULTI_FILE_EDITOR_DESIGN.md
• Use array state management for files
• Each file needs unique ID (use nanoid)
• Implement proper memoization to prevent unnecessary re-renders
• Use React.memo for FileEditor components
• Consider virtualization for many files (future enhancement)
• File operations should update state immutably
• Use requestAnimationFrame for smooth scrolling
• Debounce size calculations for performance

Keyboard Shortcuts

• Ctrl/Cmd + Enter: Add new file
• Delete/Backspace: Remove file (when focused on remove button)
• Tab: Navigate between file editors
• Shift + Tab: Navigate backwards

Related

• Depends on Implement FileEditor component for single file editing #55 (FileEditor component)
• Uses design from docs/MULTI_FILE_EDITOR_DESIGN.md
• Part of Phase 4 UI Components
• Core component for create page functionality

[nullcoder]

📝 Important Design Note: This component should follow the GitHub Gist-style vertical layout as documented in .

Key points:

• NO TABS - all files visible vertically
• Each file editor stacked below the previous
• Add file button at the bottom
• Similar to how GitHub Gists display multiple files

Please review the design document before implementation.

[nullcoder]

📝 Important Design Note: This component should follow the GitHub Gist-style vertical layout as documented in docs/MULTI_FILE_EDITOR_DESIGN.md.

Key points:

• NO TABS - all files visible vertically
• Each file editor stacked below the previous
• Add file button at the bottom
• Similar to how GitHub Gists display multiple files

Please review the design document before implementation.