# Frontend Architecture

## Component Architecture

### Component Organization

```
frontend/src/
├── components/
│   ├── layout/
│   │   ├── Header.jsx
│   │   ├── Footer.jsx
│   │   └── Layout.jsx
│   ├── books/
│   │   ├── BookCard.jsx
│   │   ├── BookList.jsx
│   │   ├── BookSearchResults.jsx
│   │   └── AddBookForm.jsx
│   ├── progress/
│   │   ├── LogProgressModal.jsx
│   │   ├── ProgressDisplay.jsx
│   │   └── StatusIndicator.jsx
│   ├── calendar/
│   │   ├── Calendar.jsx
│   │   ├── CalendarDay.jsx
│   │   └── CalendarLegend.jsx
│   └── common/
│       ├── Button.jsx
│       ├── Input.jsx
│       ├── Modal.jsx
│       ├── Loading.jsx
│       └── ErrorMessage.jsx
├── pages/
│   ├── Home.jsx
│   ├── AddBook.jsx
│   ├── BookDetail.jsx
│   └── CalendarView.jsx
├── hooks/
│   ├── useBooks.js
│   ├── useProgress.js
│   └── useLogs.js
├── services/
│   ├── api.js (API client setup)
│   ├── booksService.js
│   └── logsService.js
├── context/
│   └── AppContext.jsx
├── utils/
│   ├── dateUtils.js
│   ├── paceUtils.js
│   └── validation.js
├── styles/
│   └── index.css (Tailwind directives)
└── App.jsx
```

### Component Template

```typescript
// Example: BookCard.jsx
import React from 'react';
import { useNavigate } from 'react-router-dom';
import StatusIndicator from '../progress/StatusIndicator';
import { formatDate } from '../../utils/dateUtils';

/**
 * BookCard - Displays a single book with progress metrics
 * @param {Object} book - Book object with progress data
 * @param {Function} onLogProgress - Handler for log progress action
 */
function BookCard({ book, onLogProgress }) {
  const navigate = useNavigate();

  const handleCardClick = () => {
    navigate(`/books/${book.id}`);
  };

  const handleLogClick = (e) => {
    e.stopPropagation(); // Prevent navigation when clicking log button
    onLogProgress(book);
  };

  return (
    <div
      onClick={handleCardClick}
      className="bg-white rounded-lg shadow-md p-4 cursor-pointer hover:shadow-lg transition-shadow"
    >
      {/* Book cover and title */}
      <div className="flex gap-4">
        {book.coverUrl ? (
          <img
            src={book.coverUrl}
            alt={book.title}
            className="w-16 h-24 object-cover rounded"
          />
        ) : (
          <div className="w-16 h-24 bg-gray-200 rounded flex items-center justify-center">
            <span className="text-gray-400 text-xs">No cover</span>
          </div>
        )}

        <div className="flex-1">
          <h3 className="font-bold text-lg">{book.title}</h3>
          {book.author && <p className="text-gray-600 text-sm">{book.author}</p>}
          <p className="text-gray-500 text-xs mt-1">
            Due: {formatDate(book.deadlineDate)}
          </p>
        </div>
      </div>

      {/* Progress metrics */}
      <div className="mt-4 space-y-2">
        <StatusIndicator status={book.status} />
        <div className="text-sm">
          <p><strong>Target:</strong> {book.requiredPace.toFixed(1)} pages/day</p>
          <p>
            <strong>Your pace:</strong> {' '}
            {book.actualPace ? `${book.actualPace.toFixed(1)} pages/day` : 'No data yet'}
          </p>
          <p className="text-gray-600">
            {book.pagesRemaining} pages left, {book.daysRemaining} days
          </p>
        </div>
      </div>

      {/* Log progress button */}
      <button
        onClick={handleLogClick}
        className="mt-4 w-full bg-blue-500 text-white py-2 px-4 rounded hover:bg-blue-600 transition-colors"
      >
        Log Progress
      </button>
    </div>
  );
}

export default BookCard;
```

## State Management Architecture

### State Structure

```typescript
// context/AppContext.jsx
import React, { createContext, useContext, useState, useEffect } from 'react';
import { booksService } from '../services/booksService';

const AppContext = createContext();

export function AppProvider({ children }) {
  const [books, setBooks] = useState([]);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  // Fetch books on mount
  useEffect(() => {
    loadBooks();
  }, []);

  const loadBooks = async () => {
    setLoading(true);
    setError(null);
    try {
      const data = await booksService.getActiveBooks();
      setBooks(data.books);
    } catch (err) {
      setError(err.message);
    } finally {
      setLoading(false);
    }
  };

  const addBook = async (bookData) => {
    const newBook = await booksService.addBook(bookData);
    setBooks(prev => [...prev, newBook]);
    return newBook;
  };

  const deleteBook = async (bookId) => {
    await booksService.deleteBook(bookId);
    setBooks(prev => prev.filter(b => b.id !== bookId));
  };

  const logProgress = async (bookId, currentPage, logDate) => {
    await booksService.logProgress(bookId, currentPage, logDate);
    // Refresh books to get updated progress
    await loadBooks();
  };

  const value = {
    books,
    loading,
    error,
    loadBooks,
    addBook,
    deleteBook,
    logProgress,
  };

  return <AppContext.Provider value={value}>{children}</AppContext.Provider>;
}

export function useApp() {
  const context = useContext(AppContext);
  if (!context) {
    throw new Error('useApp must be used within AppProvider');
  }
  return context;
}
```

### State Management Patterns

- **Global State:** Books list, loading states, errors (via React Context)
- **Local Component State:** Form inputs, modal open/closed, UI-only state (via useState)
- **Server State:** Fetched data cached in Context, refetch on mutations
- **No External State Library:** Context API sufficient for MVP (books list + UI state)
- **State Updates:** Optimistic UI updates followed by data refetch for consistency

## Routing Architecture

### Route Organization

```
Routes:
/                    → Home (Book List Screen)
/add-book            → Add Book Screen
/books/:bookId       → Book Detail Screen
/calendar            → Calendar View Screen (optional, may be in Book Detail)
/*                   → 404 Not Found
```

### Protected Route Pattern

```typescript
// App.jsx with React Router
import React from 'react';
import { BrowserRouter, Routes, Route } from 'react-router-dom';
import { AppProvider } from './context/AppContext';
import Layout from './components/layout/Layout';
import Home from './pages/Home';
import AddBook from './pages/AddBook';
import BookDetail from './pages/BookDetail';
import CalendarView from './pages/CalendarView';
import NotFound from './pages/NotFound';

function App() {
  return (
    <BrowserRouter>
      <AppProvider>
        <Layout>
          <Routes>
            <Route path="/" element={<Home />} />
            <Route path="/add-book" element={<AddBook />} />
            <Route path="/books/:bookId" element={<BookDetail />} />
            <Route path="/calendar" element={<CalendarView />} />
            <Route path="*" element={<NotFound />} />
          </Routes>
        </Layout>
      </AppProvider>
    </BrowserRouter>
  );
}

export default App;
```

**Note:** No protected routes needed for MVP (single-user, no authentication). Add in v1.1 if multi-user support is needed.

## Frontend Services Layer

### API Client Setup

```typescript
// services/api.js
const API_BASE_URL = import.meta.env.VITE_API_URL || 'http://localhost:3000/api';

class ApiClient {
  async request(endpoint, options = {}) {
    const url = `${API_BASE_URL}${endpoint}`;
    const config = {
      headers: {
        'Content-Type': 'application/json',
        ...options.headers,
      },
      ...options,
    };

    try {
      const response = await fetch(url, config);

      // Handle non-JSON responses (like 204 No Content)
      if (response.status === 204) {
        return null;
      }

      const data = await response.json();

      if (!response.ok) {
        throw new Error(data.error || 'Request failed');
      }

      return data;
    } catch (error) {
      console.error('API request failed:', error);
      throw error;
    }
  }

  get(endpoint) {
    return this.request(endpoint, { method: 'GET' });
  }

  post(endpoint, body) {
    return this.request(endpoint, {
      method: 'POST',
      body: JSON.stringify(body),
    });
  }

  put(endpoint, body) {
    return this.request(endpoint, {
      method: 'PUT',
      body: JSON.stringify(body),
    });
  }

  delete(endpoint) {
    return this.request(endpoint, { method: 'DELETE' });
  }
}

export const apiClient = new ApiClient();
```

### Service Example

```typescript
// services/booksService.js
import { apiClient } from './api';

export const booksService = {
  // Search books via Open Library
  async searchBooks(query) {
    return apiClient.get(`/books/search?q=${encodeURIComponent(query)}`);
  },

  // Get all active books with progress
  async getActiveBooks() {
    return apiClient.get('/books');
  },

  // Add a new book
  async addBook(bookData) {
    return apiClient.post('/books', bookData);
  },

  // Get single book
  async getBook(bookId) {
    return apiClient.get(`/books/${bookId}`);
  },

  // Delete book
  async deleteBook(bookId) {
    return apiClient.delete(`/books/${bookId}`);
  },

  // Get book progress
  async getProgress(bookId) {
    return apiClient.get(`/books/${bookId}/progress`);
  },

  // Get reading logs
  async getLogs(bookId) {
    return apiClient.get(`/books/${bookId}/logs`);
  },

  // Log progress
  async logProgress(bookId, currentPage, logDate = null) {
    return apiClient.post(`/books/${bookId}/logs`, {
      currentPage,
      ...(logDate && { logDate }),
    });
  },
};
```

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