<?php
header('Content-Type: application/json; charset=utf-8');
date_default_timezone_set('Asia/Ho_Chi_Minh');

$todoFile = __DIR__ . '/todos.json';

if (!file_exists($todoFile)) {
    file_put_contents($todoFile, json_encode([], JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE));
}

$todos = json_decode(file_get_contents($todoFile), true);
if (!is_array($todos)) {
    $todos = [];
}

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $raw = file_get_contents('php://input');
    $body = json_decode($raw, true);

    $action = $_POST['action'] ?? ($body['action'] ?? '');

    if ($action === 'add') {
        $title = trim($_POST['title'] ?? ($body['title'] ?? ''));
        if ($title !== '') {
            $maxId = 0;
            foreach ($todos as $t) {
                if (($t['id'] ?? 0) > $maxId) {
                    $maxId = $t['id'];
                }
            }
            $todos[] = [
                'id' => $maxId + 1,
                'title' => $title,
                'completed' => false,
                'created_at' => date('H:i d/m/Y')
            ];
            file_put_contents($todoFile, json_encode($todos, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE), LOCK_EX);
        }
    } elseif ($action === 'toggle') {
        $id = (int)($_POST['id'] ?? ($body['id'] ?? 0));
        foreach ($todos as &$t) {
            if ((int)$t['id'] === $id) {
                $t['completed'] = !$t['completed'];
                break;
            }
        }
        unset($t);
        file_put_contents($todoFile, json_encode($todos, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE), LOCK_EX);
    } elseif ($action === 'delete') {
        $id = (int)($_POST['id'] ?? ($body['id'] ?? 0));
        $todos = array_values(array_filter($todos, function ($t) use ($id) {
            return (int)$t['id'] !== $id;
        }));
        file_put_contents($todoFile, json_encode($todos, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE), LOCK_EX);
    } elseif ($action === 'clear_completed') {
        $todos = array_values(array_filter($todos, function ($t) {
            return empty($t['completed']);
        }));
        file_put_contents($todoFile, json_encode($todos, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE), LOCK_EX);
    }
}

echo json_encode([
    'status' => 'success',
    'todos' => $todos
], JSON_UNESCAPED_UNICODE);