add base file

README.md

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+# Simple Todo Application
+
+A command-line todo list manager with persistent JSON storage.
+
+## Overview
+
+This is a simple yet complete todo application that demonstrates:
+- Functional requirements implementation (CRUD operations)
+- Non-functional requirements (persistence, validation, performance, error handling)
+- Clean code architecture with proper error handling
+- Data persistence using JSON
+
+## Requirements Implemented
+
+### Functional Requirements
+
+- **REQ-001**: Create Todo Items - Add new todos with title and optional description
+- **REQ-002**: List Todo Items - Display all todos with status and metadata
+- **REQ-003**: Mark Todo as Complete - Toggle completion status on/off
+- **REQ-004**: Delete Todo Items - Remove todos from the list permanently
+- **REQ-005**: Edit Todo Items - Update title and description of existing todos
+
+### Non-Functional Requirements
+
+- **REQ-006**: Data Persistence - All todos saved to `todos.json` file
+- **REQ-007**: Input Validation - Titles validated (non-empty, max 200 chars)
+- **REQ-008**: Performance - All operations complete within 100ms
+- **REQ-009**: Code Quality - Comprehensive error handling with descriptive messages
+- **REQ-010**: User Interface - Simple CLI with menu-driven interface
+
+## Features
+
+✅ Create, Read, Update, Delete (CRUD) todos
+✅ Toggle completion status
+✅ Persistent storage (JSON)
+✅ Input validation
+✅ Error handling
+✅ Clear CLI interface
+✅ Timestamps for created/updated dates
+
+## Usage
+
+```bash
+python app.py
+```
+
+### Menu Options
+
+```
+1. Create new todo          - Add a new todo item
+2. List all todos          - View all todos with status
+3. Mark todo complete      - Toggle todo completion status
+4. Edit todo               - Update title or description
+5. Delete todo             - Remove a todo permanently
+6. Exit                    - Save and quit application
+```
+
+## Data Storage
+
+All todos are persisted in `todos.json` with the following structure:
+
+```json
+[
+  {
+    "id": 1,
+    "title": "Buy groceries",
+    "description": "Milk, eggs, bread",
+    "completed": false,
+    "created_at": "2025-12-09T10:30:00",
+    "updated_at": "2025-12-09T10:30:00"
+  }
+]
+```
+
+## File Structure
+
+```
+simple_app/
+├── requirements.md    - 10 requirements for the application
+├── app.py            - Main application implementation
+└── README.md         - This file
+```
+
+## Requirements Traceability
+
+Each requirement is implemented and can be traced in the code:
+
+| REQ ID | Feature | Implementation | Status |
+|--------|---------|-----------------|--------|
+| REQ-001 | Create todos | `create_todo()` method | ✅ |
+| REQ-002 | List todos | `list_todos()` method | ✅ |
+| REQ-003 | Mark complete | `mark_complete()` method | ✅ |
+| REQ-004 | Delete todos | `delete_todo()` method | ✅ |
+| REQ-005 | Edit todos | `edit_todo()` method | ✅ |
+| REQ-006 | Data persistence | `_load_todos()`, `_save_todos()` | ✅ |
+| REQ-007 | Input validation | `_validate_title()` method | ✅ |
+| REQ-008 | Performance | JSON operations, efficient filtering | ✅ |
+| REQ-009 | Error handling | Try-except blocks, error messages | ✅ |
+| REQ-010 | CLI interface | `show_menu()`, `run()` methods | ✅ |
+
+## Example Session
+
+```
+🚀 Welcome to the Simple Todo Application!
+
+════════════════════════════════════════════════════════════════════
+📝 Todo Application
+════════════════════════════════════════════════════════════════════
+1. Create new todo
+2. List all todos
+3. Mark todo complete/incomplete
+4. Edit todo
+5. Delete todo
+6. Exit
+════════════════════════════════════════════════════════════════════
+Enter your choice (1-6): 1
+Enter todo title: Buy groceries
+Enter description (optional): Milk, eggs, bread
+✅ Todo created: 'Buy groceries'
+
+📋 Your Todos:
+════════════════════════════════════════════════════════════════════
+
+  ○ [1] [TODO] Buy groceries
+      Description: Milk, eggs, bread
+      Created: 2025-12-09
+
+════════════════════════════════════════════════════════════════════
+```
+
+## Error Handling
+
+The application provides clear error messages for:
+- Empty titles
+- Titles exceeding 200 characters
+- Invalid todo IDs
+- File I/O errors
+- Invalid menu selections
+
+## Performance
+
+All operations are optimized:
+- JSON file read on startup only
+- Linear search for todo lookups (acceptable for typical use)
+- Single file write per operation
+- No external dependencies
+
+## Code Quality
+
+- Type hints for all function parameters
+- Comprehensive docstrings
+- Clear variable names
+- Proper error handling throughout
+- Separation of concerns (UI, data, logic)

app.py

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+#!/usr/bin/env python3
+"""
+Simple Todo Application
+
+This application implements a command-line todo list manager that persists
+data to JSON and provides full CRUD operations with validation.
+
+Implements requirements: REQ-001 through REQ-010
+"""
+
+import json
+import os
+import sys
+from pathlib import Path
+from typing import Optional, List, Dict, Any
+from datetime import datetime
+
+
+class TodoApp:
+    """
+    Simple Todo Application with persistent storage.
+    
+    Implements all 10 requirements:
+    - REQ-001: Create todo items
+    - REQ-002: List todo items
+    - REQ-003: Mark complete/incomplete
+    - REQ-004: Delete todo items
+    - REQ-005: Edit todo items
+    - REQ-006: Data persistence (JSON)
+    - REQ-007: Input validation
+    - REQ-008: Performance optimization
+    - REQ-009: Error handling
+    - REQ-010: CLI user interface
+    """
+    
+    DATA_FILE = "todos.json"
+    MAX_TITLE_LENGTH = 200
+    
+    def __init__(self):
+        """Initialize the application with data persistence."""
+        self.todos: List[Dict[str, Any]] = []
+        self._load_todos()
+    
+    def _load_todos(self) -> None:
+        """Load todos from JSON file if it exists. REQ-006: Data Persistence."""
+        try:
+            if Path(self.DATA_FILE).exists():
+                with open(self.DATA_FILE, 'r') as f:
+                    self.todos = json.load(f)
+        except (json.JSONDecodeError, IOError) as e:
+            print(f"⚠️  Could not load todos: {e}. Starting with empty list.")
+            self.todos = []
+    
+    def _save_todos(self) -> None:
+        """Save todos to JSON file. REQ-006: Data Persistence."""
+        try:
+            with open(self.DATA_FILE, 'w') as f:
+                json.dump(self.todos, f, indent=2)
+        except IOError as e:
+            raise RuntimeError(f"Failed to save todos: {e}")  # REQ-009: Error handling
+    
+    def _validate_title(self, title: str) -> bool:
+        """
+        Validate todo title. REQ-007: Input Validation.
+        
+        Args:
+            title: The title to validate
+            
+        Returns:
+            bool: True if valid, False otherwise
+        """
+        if not title or not title.strip():
+            print("❌ Error: Title cannot be empty")
+            return False
+        
+        if len(title) > self.MAX_TITLE_LENGTH:
+            print(f"❌ Error: Title cannot exceed {self.MAX_TITLE_LENGTH} characters")
+            return False
+        
+        return True
+    
+    def create_todo(self, title: str, description: str = "") -> bool:
+        """
+        Create a new todo item. REQ-001: Create Todo Items.
+        REQ-007: Input Validation. REQ-009: Error handling.
+        
+        Args:
+            title: The todo title
+            description: Optional todo description
+            
+        Returns:
+            bool: True if created successfully
+        """
+        if not self._validate_title(title):
+            return False
+        
+        try:
+            todo = {
+                "id": len(self.todos) + 1,
+                "title": title.strip(),
+                "description": description.strip(),
+                "completed": False,
+                "created_at": datetime.now().isoformat(),
+                "updated_at": datetime.now().isoformat()
+            }
+            self.todos.append(todo)
+            self._save_todos()
+            print(f"✅ Todo created: '{title}'")
+            return True
+        except Exception as e:
+            print(f"❌ Error creating todo: {e}")  # REQ-009: Error handling
+            return False
+    
+    def list_todos(self) -> None:
+        """
+        Display all todos in a formatted list. REQ-002: List Todo Items.
+        REQ-010: CLI user interface.
+        """
+        if not self.todos:
+            print("\n📋 No todos yet. Create one to get started!")
+            return
+        
+        print("\n📋 Your Todos:")
+        print("=" * 70)
+        
+        for todo in self.todos:
+            status = "✓" if todo["completed"] else "○"
+            completed_text = "[DONE]" if todo["completed"] else "[TODO]"
+            
+            print(f"\n  {status} [{todo['id']}] {completed_text} {todo['title']}")
+            
+            if todo["description"]:
+                print(f"      Description: {todo['description']}")
+            
+            print(f"      Created: {todo['created_at'][:10]}")
+        
+        print("\n" + "=" * 70)
+    
+    def mark_complete(self, todo_id: int) -> bool:
+        """
+        Mark a todo as complete or toggle completion status.
+        REQ-003: Mark Todo as Complete. REQ-009: Error handling.
+        
+        Args:
+            todo_id: The ID of the todo to mark complete
+            
+        Returns:
+            bool: True if successful
+        """
+        try:
+            for todo in self.todos:
+                if todo["id"] == todo_id:
+                    todo["completed"] = not todo["completed"]
+                    todo["updated_at"] = datetime.now().isoformat()
+                    self._save_todos()
+                    
+                    status = "completed" if todo["completed"] else "reopened"
+                    print(f"✅ Todo {status}: '{todo['title']}'")
+                    return True
+            
+            print(f"❌ Error: Todo with ID {todo_id} not found")
+            return False
+        except Exception as e:
+            print(f"❌ Error marking todo: {e}")  # REQ-009: Error handling
+            return False
+    
+    def delete_todo(self, todo_id: int) -> bool:
+        """
+        Delete a todo item. REQ-004: Delete Todo Items.
+        REQ-009: Error handling.
+        
+        Args:
+            todo_id: The ID of the todo to delete
+            
+        Returns:
+            bool: True if successful
+        """
+        try:
+            original_length = len(self.todos)
+            self.todos = [t for t in self.todos if t["id"] != todo_id]
+            
+            if len(self.todos) < original_length:
+                self._save_todos()
+                print(f"✅ Todo deleted")
+                return True
+            else:
+                print(f"❌ Error: Todo with ID {todo_id} not found")
+                return False
+        except Exception as e:
+            print(f"❌ Error deleting todo: {e}")  # REQ-009: Error handling
+            return False
+    
+    def edit_todo(self, todo_id: int, title: Optional[str] = None, 
+                  description: Optional[str] = None) -> bool:
+        """
+        Edit an existing todo item. REQ-005: Edit Todo Items.
+        REQ-007: Input Validation. REQ-009: Error handling.
+        
+        Args:
+            todo_id: The ID of the todo to edit
+            title: New title (optional)
+            description: New description (optional)
+            
+        Returns:
+            bool: True if successful
+        """
+        try:
+            for todo in self.todos:
+                if todo["id"] == todo_id:
+                    if title is not None:
+                        if not self._validate_title(title):
+                            return False
+                        todo["title"] = title.strip()
+                    
+                    if description is not None:
+                        todo["description"] = description.strip()
+                    
+                    todo["updated_at"] = datetime.now().isoformat()
+                    self._save_todos()
+                    print(f"✅ Todo updated: '{todo['title']}'")
+                    return True
+            
+            print(f"❌ Error: Todo with ID {todo_id} not found")
+            return False
+        except Exception as e:
+            print(f"❌ Error editing todo: {e}")  # REQ-009: Error handling
+            return False
+    
+    def show_menu(self) -> None:
+        """Display the main menu. REQ-010: CLI user interface."""
+        print("\n" + "=" * 70)
+        print("📝 Todo Application")
+        print("=" * 70)
+        print("1. Create new todo")
+        print("2. List all todos")
+        print("3. Mark todo complete/incomplete")
+        print("4. Edit todo")
+        print("5. Delete todo")
+        print("6. Exit")
+        print("=" * 70)
+    
+    def run(self) -> None:
+        """Main application loop. REQ-010: CLI user interface."""
+        print("\n🚀 Welcome to the Simple Todo Application!")
+        
+        while True:
+            self.show_menu()
+            choice = input("Enter your choice (1-6): ").strip()
+            
+            if choice == "1":
+                # REQ-001: Create Todo Items
+                title = input("Enter todo title: ").strip()
+                description = input("Enter description (optional): ").strip()
+                self.create_todo(title, description)
+            
+            elif choice == "2":
+                # REQ-002: List Todo Items
+                self.list_todos()
+            
+            elif choice == "3":
+                # REQ-003: Mark Todo as Complete
+                self.list_todos()
+                try:
+                    todo_id = int(input("Enter todo ID to toggle: "))
+                    self.mark_complete(todo_id)
+                except ValueError:
+                    print("❌ Error: Please enter a valid ID number")
+            
+            elif choice == "4":
+                # REQ-005: Edit Todo Items
+                self.list_todos()
+                try:
+                    todo_id = int(input("Enter todo ID to edit: "))
+                    title = input("Enter new title (leave empty to skip): ").strip()
+                    description = input("Enter new description (leave empty to skip): ").strip()
+                    
+                    new_title = title if title else None
+                    new_description = description if description else None
+                    
+                    self.edit_todo(todo_id, new_title, new_description)
+                except ValueError:
+                    print("❌ Error: Please enter a valid ID number")
+            
+            elif choice == "5":
+                # REQ-004: Delete Todo Items
+                self.list_todos()
+                try:
+                    todo_id = int(input("Enter todo ID to delete: "))
+                    confirm = input(f"Are you sure? (yes/no): ").strip().lower()
+                    if confirm == "yes":
+                        self.delete_todo(todo_id)
+                except ValueError:
+                    print("❌ Error: Please enter a valid ID number")
+            
+            elif choice == "6":
+                # REQ-010: CLI user interface - graceful exit
+                print("\n👋 Goodbye! Your todos have been saved.")
+                break
+            
+            else:
+                print("❌ Error: Invalid choice. Please enter 1-6.")
+
+
+if __name__ == "__main__":
+    app = TodoApp()
+    app.run()

requirements.md

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+# Simple Todo Application - Requirements
+
+## Functional Requirements
+
+### REQ-001: Create Todo Items
+The application shall allow users to create new todo items with a title and optional description.
+
+### REQ-002: List Todo Items
+The application shall display all created todo items in a list format with their current status.
+
+### REQ-003: Mark Todo as Complete
+The application shall provide functionality to mark a todo item as complete or incomplete with a toggle action.
+
+### REQ-004: Delete Todo Items
+The application shall allow users to delete todo items from the list permanently.
+
+### REQ-005: Edit Todo Items
+The application shall allow users to edit the title and description of existing todo items.
+
+## Non-Functional Requirements
+
+### REQ-006: Data Persistence
+The application shall persist all todo items to a JSON file so that data remains available after application restart.
+
+### REQ-007: Input Validation
+The application shall validate that todo titles are not empty and are no longer than 200 characters.
+
+### REQ-008: Performance
+The application shall complete all todo operations (create, read, update, delete) within 100 milliseconds.
+
+### REQ-009: Code Quality
+The application shall implement proper error handling with descriptive error messages for all operations.
+
+### REQ-010: User Interface
+The application shall provide a simple command-line interface with clear menu options and status feedback for user actions.