todo-list

import fs from 'fs';
import path from 'path';

export interface TodoItem {
  id: number;
  task: string;
  completed: boolean;
}

export class TodoManager {
  private todos: TodoItem[] = [];
  private filePath: string;

  constructor() {
    this.filePath = path.join(__dirname, '../todos.json');
    this.load();
  }

  private load() {
    if (fs.existsSync(this.filePath)) {
      try {
        const data = fs.readFileSync(this.filePath, 'utf-8');
        this.todos = JSON.parse(data);
        // Safety: Ensure IDs are actually numbers if JSON got messed up
        this.todos.forEach(t => t.id = Number(t.id));
      } catch (e) {
        console.error("Failed to parse todos.json", e);
        this.todos = [];
      }
    } else {
      this.todos = [];
    }
  }

  private save() {
    try {
      fs.writeFileSync(this.filePath, JSON.stringify(this.todos, null, 2));
    } catch (e) {
      console.error("Failed to save todos.json", e);
    }
  }

  add(task: string): string {
    // Generate safe sequential ID
    const maxId = this.todos.length > 0 ? Math.max(...this.todos.map(t => t.id)) : 0;
    const id = maxId + 1;
    
    this.todos.push({ id, task, completed: false });
    this.save();
    return `Success: Added task #${id}: "${task}"`;
  }

  complete(id: number): string {
    // Robust finding: coerce both to string to be safe, then strict compare
    const todo = this.todos.find(t => t.id === Number(id));
    
    if (!todo) {
      return `Error: Task #${id} not found. Available IDs: ${this.todos.map(t => t.id).join(", ")}`;
    }
    
    todo.completed = true;
    this.save();
    return `Success: Task #${id} marked as COMPLETED.`;
  }

  remove(id: number): string {
    const startCount = this.todos.length;
    this.todos = this.todos.filter(t => t.id !== Number(id));
    
    if (this.todos.length === startCount) {
        return `Error: Task #${id} not found.`;
    }
    
    this.save();
    return `Success: Task #${id} deleted from list.`;
  }

  clear(): string {
    const count = this.todos.length;
    this.todos = [];
    this.save();
    return `Success: Cleared all ${count} tasks. The list is empty.`;
  }

  list(): string {
    if (this.todos.length === 0) return "Status: The todo list is empty.";

    const pending = this.todos.filter(t => !t.completed);
    const done = this.todos.filter(t => t.completed);

    let output = "";

    if (pending.length > 0) {
        output += "--- PENDING TASKS ---\n";
        output += pending.map(t => `[ ] #${t.id}: ${t.task}`).join('\n');
    } else {
        output += "--- NO PENDING TASKS --- (Good job!)";
    }

    if (done.length > 0) {
        output += "\n\n--- COMPLETED ---\n";
        output += done.map(t => `[x] #${t.id}: ${t.task}`).join('\n');
    }

    return output;
  }
}