/**
 * TaskDispatcher — Automatic task queue dispatcher for RemoteTurtle
 *
 * Periodically polls the task_queue for pending tasks, matches them to
 * available (idle + connected) turtles, maps task_type to state machine
 * states, and drives the turtle state machine.  Handles turtle disconnection
 * mid-task (re-queues) and completion callbacks.
 *
 * Task type → State machine mapping:
 *   mine_area    → mining   (requires bounds in task_data)
 *   explore      → exploring (requires target/area in task_data)
 *   gather       → extracting (requires blockName in task_data)
 *   build        → building  (requires plan in task_data)
 *   transport    → moving    (requires target position)
 *   clear_area   → mining    (same as mine_area)
 *   scan         → scanning  (requires area/range)
 *   farm         → farming   (requires area)
 *   autocraft    → autocrafting (requires recipe)
 */

// Map task_type values from the TaskPanel UI to turtle state machine state names + data mappers
const TASK_TYPE_MAP = {
  mine_area:  { state: 'mining',      mapData: d => ({ bounds: d.bounds || d, ...d }) },
  explore:    { state: 'exploring',   mapData: d => ({ target: d.target || d, ...d }) },
  gather:     { state: 'extracting',  mapData: d => ({ blockName: d.blockName, count: d.count, ...d }) },
  build:      { state: 'building',    mapData: d => ({ plan: d.plan, origin: d.origin, ...d }) },
  transport:  { state: 'moving',      mapData: d => ({ target: d.target || d.destination || d, ...d }) },
  clear_area: { state: 'mining',      mapData: d => ({ bounds: d.bounds || d, ...d }) },
  scan:       { state: 'scanning',    mapData: d => ({ area: d.area, ...d }) },
  farm:       { state: 'farming',     mapData: d => ({ area: d.area, ...d }) },
  autocraft:  { state: 'autocrafting', mapData: d => ({ recipe: d.recipe, count: d.count, ...d }) },
};

export class TaskDispatcher {
  /**
   * @param {Object} opts
   * @param {Map<number, import('./Turtle.js').Turtle>} opts.turtles - Live turtle map
   * @param {Object} opts.db - Database module (server/database.js)
   * @param {Function} opts.broadcastToClients - WebSocket broadcaster
   * @param {number} [opts.pollInterval=5000] - ms between dispatch cycles
   */
  constructor({ turtles, db, broadcastToClients, pollInterval = 5000 }) {
    this._turtles = turtles;
    this._db = db;
    this._broadcast = broadcastToClients;
    this._pollInterval = pollInterval;
    this._timer = null;
    this._enabled = true;

    // Track which tasks are actively being executed by which turtles
    //   turtleId -> { taskId, taskType }
    this._activeTasks = new Map();

    // Reverse lookup: taskId -> turtleId
    this._taskToTurtle = new Map();
  }

  /** Start the dispatch loop */
  start() {
    if (this._timer) return;
    console.log(`🚀 TaskDispatcher started (poll every ${this._pollInterval}ms)`);
    this._timer = setInterval(() => this._tick(), this._pollInterval);
    // Run immediately on start
    this._tick();
  }

  /** Stop the dispatch loop */
  stop() {
    if (this._timer) {
      clearInterval(this._timer);
      this._timer = null;
      console.log('🛑 TaskDispatcher stopped');
    }
  }

  /** Enable/disable automatic dispatching (tasks still tracked when disabled) */
  set enabled(val) {
    this._enabled = !!val;
    console.log(`TaskDispatcher: auto-dispatch ${this._enabled ? 'enabled' : 'disabled'}`);
  }

  get enabled() {
    return this._enabled;
  }

  /** Get dispatcher status for the API */
  status() {
    return {
      enabled: this._enabled,
      activeTasks: Array.from(this._activeTasks.entries()).map(([turtleId, info]) => ({
        turtleId,
        ...info,
      })),
      pollInterval: this._pollInterval,
    };
  }

  // ========== Internal ==========

  /**
   * One dispatch cycle:
   *  1. Reconcile active tasks (detect turtle disconnects, state completions)
   *  2. If enabled, find pending tasks and assign to idle turtles
   */
  _tick() {
    try {
      this._reconcile();
      if (this._enabled) {
        this._dispatch();
      }
    } catch (err) {
      console.error('[TaskDispatcher] tick error:', err.message);
    }
  }

  /**
   * Reconcile: check if turtles executing tasks have finished or disconnected.
   */
  _reconcile() {
    for (const [turtleId, info] of this._activeTasks) {
      const turtle = this._turtles.get(turtleId);

      // Turtle removed from server
      if (!turtle) {
        this._handleTaskFailure(info.taskId, turtleId, 'Turtle no longer exists');
        continue;
      }

      // Turtle disconnected mid-task
      if (!turtle.connected) {
        this._handleTaskFailure(info.taskId, turtleId, 'Turtle disconnected');
        continue;
      }

      // Turtle transitioned to idle → task completed
      if (turtle.stateName === 'idle') {
        this._handleTaskCompletion(info.taskId, turtleId);
        continue;
      }

      // Turtle errored out
      if (turtle._error) {
        this._handleTaskFailure(info.taskId, turtleId, turtle._error);
        continue;
      }
    }
  }

  /**
   * Dispatch: find pending (unassigned or assigned-but-not-started) tasks,
   * match to available turtles, and start them.
   */
  _dispatch() {
    // Get all pending tasks (sorted by priority DESC, created_at ASC via DB)
    let pendingTasks;
    try {
      pendingTasks = this._db.getAllTasks('pending');
    } catch (e) {
      return;
    }

    if (!pendingTasks || pendingTasks.length === 0) return;

    // Find idle, connected turtles not already executing a task
    const availableTurtles = this._getAvailableTurtles();
    if (availableTurtles.length === 0) return;

    for (const task of pendingTasks) {
      if (availableTurtles.length === 0) break;

      const mapping = TASK_TYPE_MAP[task.task_type];
      if (!mapping) {
        console.warn(`[TaskDispatcher] Unknown task type: ${task.task_type} (task #${task.id})`);
        continue;
      }

      // If task has a specific turtle assignment, respect it
      let turtle = null;
      if (task.assigned_turtle_id) {
        turtle = this._turtles.get(task.assigned_turtle_id);
        if (!turtle || !turtle.connected || turtle.stateName !== 'idle') {
          // Assigned turtle not available — skip this task for now
          continue;
        }
        // Remove from available pool
        const idx = availableTurtles.indexOf(turtle);
        if (idx !== -1) availableTurtles.splice(idx, 1);
      } else {
        // Pick the best available turtle (closest to target if we have coords, else first)
        turtle = this._pickBestTurtle(availableTurtles, task.task_data);
        const idx = availableTurtles.indexOf(turtle);
        if (idx !== -1) availableTurtles.splice(idx, 1);
      }

      if (!turtle) continue;

      // Dispatch!
      this._startTask(task, turtle, mapping);
    }
  }

  /**
   * Start a task on a turtle.
   */
  _startTask(task, turtle, mapping) {
    const taskId = task.id;
    const turtleId = turtle.id;

    console.log(`[TaskDispatcher] Assigning task #${taskId} (${task.task_type}) → Turtle #${turtleId}`);

    // Map task_data to state data
    const stateData = mapping.mapData(task.task_data || {});

    // Update DB: assign + set in_progress
    try {
      this._db.assignTask(taskId, turtleId);
      this._db.updateTaskStatus(taskId, 'in_progress');
    } catch (e) {
      console.error(`[TaskDispatcher] DB error assigning task #${taskId}:`, e.message);
      return;
    }

    // Track
    this._activeTasks.set(turtleId, { taskId, taskType: task.task_type });
    this._taskToTurtle.set(taskId, turtleId);

    // Broadcast updates
    this._broadcast({ type: 'task_assigned', taskId, turtleId });
    this._broadcast({ type: 'task_updated', taskId, status: 'in_progress' });

    // Set the turtle's state machine
    turtle.setState(mapping.state, stateData);
  }

  /**
   * Handle task completion (turtle went back to idle after executing).
   */
  _handleTaskCompletion(taskId, turtleId) {
    console.log(`[TaskDispatcher] Task #${taskId} completed by Turtle #${turtleId}`);

    try {
      this._db.completeTask(taskId);
    } catch (e) {
      console.error(`[TaskDispatcher] DB error completing task #${taskId}:`, e.message);
    }

    this._activeTasks.delete(turtleId);
    this._taskToTurtle.delete(taskId);

    this._broadcast({ type: 'task_completed', taskId });
  }

  /**
   * Handle task failure (turtle disconnected, errored, etc.).
   * Re-queues the task as pending so another turtle can pick it up.
   */
  _handleTaskFailure(taskId, turtleId, reason) {
    console.warn(`[TaskDispatcher] Task #${taskId} failed on Turtle #${turtleId}: ${reason}`);

    try {
      // Re-queue: set back to pending, clear assignment
      this._db.updateTaskStatus(taskId, 'pending', reason);
      this._db.assignTask(taskId, null);
    } catch (e) {
      console.error(`[TaskDispatcher] DB error re-queuing task #${taskId}:`, e.message);
    }

    this._activeTasks.delete(turtleId);
    this._taskToTurtle.delete(taskId);

    this._broadcast({ type: 'task_updated', taskId, status: 'pending' });
  }

  /**
   * Manually cancel a running task (called via API).
   */
  cancelTask(taskId) {
    const turtleId = this._taskToTurtle.get(taskId);
    if (turtleId !== undefined) {
      const turtle = this._turtles.get(turtleId);
      if (turtle) {
        turtle.setState('idle');
      }
      this._activeTasks.delete(turtleId);
      this._taskToTurtle.delete(taskId);
    }

    try {
      this._db.updateTaskStatus(taskId, 'cancelled');
    } catch (e) {
      console.error(`[TaskDispatcher] DB error cancelling task #${taskId}:`, e.message);
    }

    this._broadcast({ type: 'task_updated', taskId, status: 'cancelled' });
  }

  /**
   * Check if a specific task is currently being executed.
   */
  isTaskActive(taskId) {
    return this._taskToTurtle.has(taskId);
  }

  // ========== Helpers ==========

  /**
   * Get connected, idle turtles not currently executing a dispatched task.
   */
  _getAvailableTurtles() {
    const available = [];
    for (const [id, turtle] of this._turtles) {
      if (
        turtle.connected &&
        turtle.stateName === 'idle' &&
        !this._activeTasks.has(id)
      ) {
        available.push(turtle);
      }
    }
    return available;
  }

  /**
   * Pick the best turtle for a task.
   * If task_data has coordinates, pick the closest turtle with a known position.
   * Otherwise, pick the turtle with the most fuel.
   */
  _pickBestTurtle(candidates, taskData) {
    if (candidates.length === 0) return null;
    if (candidates.length === 1) return candidates[0];

    // Try to extract a target position from task data
    const target = this._extractTarget(taskData);

    if (target) {
      // Sort by Manhattan distance to target
      let bestTurtle = candidates[0];
      let bestDist = Infinity;

      for (const t of candidates) {
        if (t.position) {
          const dist = Math.abs(t.position.x - target.x)
                     + Math.abs(t.position.y - target.y)
                     + Math.abs(t.position.z - target.z);
          if (dist < bestDist) {
            bestDist = dist;
            bestTurtle = t;
          }
        }
      }
      return bestTurtle;
    }

    // No target — pick turtle with highest fuel
    return candidates.reduce((best, t) => (t._fuel > best._fuel ? t : best), candidates[0]);
  }

  /**
   * Try to extract a target {x,y,z} from task_data.
   */
  _extractTarget(data) {
    if (!data) return null;

    // Direct target
    if (data.target && typeof data.target.x === 'number') return data.target;
    if (data.destination && typeof data.destination.x === 'number') return data.destination;

    // Bounds — use center
    if (data.bounds) {
      const b = data.bounds;
      if (typeof b.minX === 'number' && typeof b.maxX === 'number') {
        return {
          x: Math.floor((b.minX + b.maxX) / 2),
          y: Math.floor((b.minY + b.maxY) / 2),
          z: Math.floor((b.minZ + b.maxZ) / 2),
        };
      }
    }

    // Coordinate pair (from TaskPanel)
    if (typeof data.startX === 'number' && typeof data.startZ === 'number') {
      return { x: data.startX, y: data.startY || 64, z: data.startZ };
    }

    return null;
  }
}