const fs = require('fs');
const path = require('path');

const DATA_DIR = path.join(__dirname, 'data');
const TASKS_FILE = path.join(DATA_DIR, 'tasks.json');
const CONFIG_FILE = path.join(DATA_DIR, 'config.json');

// In-memory cache to avoid read-modify-write race conditions
let tasksCache = null;

// Write throttling
let writePending = false;
let writeTimer = null;

function ensureDir() {
  if (!fs.existsSync(DATA_DIR)) {
    fs.mkdirSync(DATA_DIR, { recursive: true });
  }
}

// Load tasks into memory cache (lazy load)
function loadTasksCache() {
  if (tasksCache === null) {
    try {
      if (fs.existsSync(TASKS_FILE)) {
        const content = fs.readFileSync(TASKS_FILE, 'utf-8');
        const data = JSON.parse(content);
        tasksCache = data.tasks || {};
      } else {
        tasksCache = {};
      }
    } catch (e) {
      console.error('Error loading tasks:', e.message);
      tasksCache = {};
    }
  }
  return tasksCache;
}

// Throttled write - batch writes within 100ms
function scheduleWrite() {
  if (!writePending) {
    writePending = true;
    if (writeTimer) {
      clearTimeout(writeTimer);
    }
    writeTimer = setTimeout(() => {
      writePending = false;
      writeTimer = null;
      try {
        ensureDir();
        fs.writeFileSync(TASKS_FILE, JSON.stringify({ tasks: tasksCache }, null, 2), 'utf-8');
      } catch (e) {
        console.error('Write error:', e.message);
      }
    }, 100);
  }
}

// Immediate write (for critical operations)
function flushWrite() {
  if (writeTimer) {
    clearTimeout(writeTimer);
    writeTimer = null;
  }
  if (tasksCache !== null) {
    try {
      ensureDir();
      fs.writeFileSync(TASKS_FILE, JSON.stringify({ tasks: tasksCache }, null, 2), 'utf-8');
    } catch (e) {
      console.error('Flush write error:', e.message);
    }
  }
  writePending = false;
}

// Read JSON helper for other files
function readJSON(file, defaultValue = {}) {
  try {
    if (fs.existsSync(file)) {
      const content = fs.readFileSync(file, 'utf-8');
      return JSON.parse(content);
    }
  } catch (e) {
    console.error(`Error reading ${file}:`, e.message);
  }
  return defaultValue;
}

// Task persistence - all operations use in-memory cache
function loadTasks() {
  return { tasks: loadTasksCache() };
}

function saveTasks(tasks) {
  tasksCache = tasks;
  scheduleWrite();
}

function getTask(taskId) {
  const cache = loadTasksCache();
  return cache[taskId] || null;
}

function saveTask(taskId, taskData) {
  const cache = loadTasksCache();
  cache[taskId] = taskData;
  scheduleWrite();
}

function deleteTask(taskId) {
  const cache = loadTasksCache();
  delete cache[taskId];
  scheduleWrite();
}

function getAllTasks() {
  return loadTasksCache();
}

// Config persistence
function loadConfig() {
  return readJSON(CONFIG_FILE, {});
}

function saveConfig(config) {
  ensureDir();
  fs.writeFileSync(CONFIG_FILE, JSON.stringify(config, null, 2), 'utf-8');
}

// Raw tasks.json operations (for config editor)
function getTasksRaw() {
  flushWrite(); // Ensure latest data is written
  return readJSON(TASKS_FILE, { tasks: {} });
}

function saveTasksRaw(content) {
  // Parse and validate
  const data = JSON.parse(content);
  
  // Update cache and write immediately
  tasksCache = data.tasks || {};
  flushWrite();
}

// Check if any task is running
function hasRunningTasks() {
  const tasks = getAllTasks();
  return Object.values(tasks).some(t => t.status === 'running' || t.status === 'paused');
}

// Check if there's pending data to write
function hasPendingWrite() {
  return writePending || writeTimer !== null;
}

// Graceful shutdown - flush all pending data
function shutdown() {
  if (writeTimer) {
    clearTimeout(writeTimer);
    writeTimer = null;
  }
  if (tasksCache !== null && writePending) {
    try {
      ensureDir();
      fs.writeFileSync(TASKS_FILE, JSON.stringify({ tasks: tasksCache }, null, 2), 'utf-8');
      console.log('[Storage] Data flushed on shutdown');
    } catch (e) {
      console.error('[Storage] Shutdown flush error:', e.message);
    }
  }
  writePending = false;
}

module.exports = {
  loadTasks,
  saveTasks,
  getTask,
  saveTask,
  deleteTask,
  getAllTasks,
  loadConfig,
  saveConfig,
  getTasksRaw,
  saveTasksRaw,
  hasRunningTasks,
  flushTasks: flushWrite,
  hasPendingWrite,
  shutdown
};