/**
 * Task Service
 *
 * Central service for managing worker tasks with:
 * - Atomic task claiming (per-store locking)
 * - Task lifecycle management
 * - Auto-chaining of related tasks
 * - Capacity planning metrics
 */

import { pool } from '../db/pool';
import { isTaskPoolPaused } from './task-pool-state';

// Helper to check if a table exists
async function tableExists(tableName: string): Promise<boolean> {
  const result = await pool.query(`
    SELECT EXISTS (
      SELECT FROM information_schema.tables
      WHERE table_name = $1
    ) as exists
  `, [tableName]);
  return result.rows[0].exists;
}

// Per TASK_WORKFLOW_2024-12-10.md: Task roles
// payload_fetch: Hits Dutchie API, saves raw payload to filesystem
// product_refresh: Reads local payload, normalizes, upserts to DB
export type TaskRole =
  | 'store_discovery'
  | 'entry_point_discovery'
  | 'product_discovery'
  | 'payload_fetch'      // NEW: Fetches from API, saves to disk
  | 'product_refresh'    // CHANGED: Now reads from local payload
  | 'analytics_refresh';

export type TaskStatus =
  | 'pending'
  | 'claimed'
  | 'running'
  | 'completed'
  | 'failed'
  | 'stale';

export interface WorkerTask {
  id: number;
  role: TaskRole;
  dispensary_id: number | null;
  dispensary_name?: string;  // JOINed from dispensaries
  dispensary_slug?: string;  // JOINed from dispensaries
  platform: string | null;
  status: TaskStatus;
  priority: number;
  scheduled_for: Date | null;
  worker_id: string | null;
  claimed_at: Date | null;
  started_at: Date | null;
  completed_at: Date | null;
  last_heartbeat_at: Date | null;
  result: Record<string, unknown> | null;
  error_message: string | null;
  retry_count: number;
  max_retries: number;
  payload: Record<string, unknown> | null;  // Per TASK_WORKFLOW_2024-12-10.md: Task chaining data
  created_at: Date;
  updated_at: Date;
}

export interface CreateTaskParams {
  role: TaskRole;
  dispensary_id?: number;
  platform?: string;
  priority?: number;
  scheduled_for?: Date;
  payload?: Record<string, unknown>;  // Per TASK_WORKFLOW_2024-12-10.md: For task chaining data
}

export interface CapacityMetrics {
  role: string;
  pending_tasks: number;
  ready_tasks: number;
  claimed_tasks: number;
  running_tasks: number;
  completed_last_hour: number;
  failed_last_hour: number;
  active_workers: number;
  avg_duration_sec: number | null;
  tasks_per_worker_hour: number | null;
  estimated_hours_to_drain: number | null;
}

export interface TaskFilter {
  role?: TaskRole;
  status?: TaskStatus | TaskStatus[];
  dispensary_id?: number;
  worker_id?: string;
  limit?: number;
  offset?: number;
}

class TaskService {
  /**
   * Create a new task
   */
  async createTask(params: CreateTaskParams): Promise<WorkerTask> {
    const result = await pool.query(
      `INSERT INTO worker_tasks (role, dispensary_id, platform, priority, scheduled_for, payload)
       VALUES ($1, $2, $3, $4, $5, $6)
       RETURNING *`,
      [
        params.role,
        params.dispensary_id ?? null,
        params.platform ?? null,
        params.priority ?? 0,
        params.scheduled_for ?? null,
        params.payload ? JSON.stringify(params.payload) : null,
      ]
    );
    return result.rows[0] as WorkerTask;
  }

  /**
   * Create multiple tasks in a batch
   */
  async createTasks(tasks: CreateTaskParams[]): Promise<number> {
    if (tasks.length === 0) return 0;

    const values = tasks.map((t, i) => {
      const base = i * 5;
      return `($${base + 1}, $${base + 2}, $${base + 3}, $${base + 4}, $${base + 5})`;
    });

    const params = tasks.flatMap((t) => [
      t.role,
      t.dispensary_id ?? null,
      t.platform ?? null,
      t.priority ?? 0,
      t.scheduled_for ?? null,
    ]);

    const result = await pool.query(
      `INSERT INTO worker_tasks (role, dispensary_id, platform, priority, scheduled_for)
       VALUES ${values.join(', ')}
       ON CONFLICT DO NOTHING`,
      params
    );

    return result.rowCount ?? 0;
  }

  /**
   * Claim a task atomically for a worker
   * If role is null, claims ANY available task (role-agnostic worker)
   * Returns null if task pool is paused.
   */
  async claimTask(role: TaskRole | null, workerId: string): Promise<WorkerTask | null> {
    // Check if task pool is paused - don't claim any tasks
    if (isTaskPoolPaused()) {
      return null;
    }

    if (role) {
      // Role-specific claiming - use the SQL function
      const result = await pool.query(
        `SELECT * FROM claim_task($1, $2)`,
        [role, workerId]
      );
      return (result.rows[0] as WorkerTask) || null;
    }

    // Role-agnostic claiming - claim ANY pending task
    const result = await pool.query(`
      UPDATE worker_tasks
      SET
        status = 'claimed',
        worker_id = $1,
        claimed_at = NOW()
      WHERE id = (
        SELECT id FROM worker_tasks
        WHERE status = 'pending'
          AND (scheduled_for IS NULL OR scheduled_for <= NOW())
          -- Exclude stores that already have an active task
          AND (dispensary_id IS NULL OR dispensary_id NOT IN (
            SELECT dispensary_id FROM worker_tasks
            WHERE status IN ('claimed', 'running')
            AND dispensary_id IS NOT NULL
          ))
        ORDER BY priority DESC, created_at ASC
        LIMIT 1
        FOR UPDATE SKIP LOCKED
      )
      RETURNING *
    `, [workerId]);

    return (result.rows[0] as WorkerTask) || null;
  }

  /**
   * Mark a task as running (worker started processing)
   */
  async startTask(taskId: number): Promise<void> {
    await pool.query(
      `UPDATE worker_tasks
       SET status = 'running', started_at = NOW(), last_heartbeat_at = NOW()
       WHERE id = $1`,
      [taskId]
    );
  }

  /**
   * Update heartbeat to prevent stale detection
   */
  async heartbeat(taskId: number): Promise<void> {
    await pool.query(
      `UPDATE worker_tasks
       SET last_heartbeat_at = NOW()
       WHERE id = $1 AND status = 'running'`,
      [taskId]
    );
  }

  /**
   * Mark a task as completed
   */
  async completeTask(taskId: number, result?: Record<string, unknown>): Promise<void> {
    await pool.query(
      `UPDATE worker_tasks
       SET status = 'completed', completed_at = NOW(), result = $2
       WHERE id = $1`,
      [taskId, result ? JSON.stringify(result) : null]
    );
  }

  /**
   * Mark a task as failed, with auto-retry if under max_retries
   * Returns true if task was re-queued for retry, false if permanently failed
   */
  async failTask(taskId: number, errorMessage: string): Promise<boolean> {
    // Get current retry state
    const result = await pool.query(
      `SELECT retry_count, max_retries FROM worker_tasks WHERE id = $1`,
      [taskId]
    );

    if (result.rows.length === 0) {
      return false;
    }

    const { retry_count, max_retries } = result.rows[0];
    const newRetryCount = (retry_count || 0) + 1;

    if (newRetryCount < (max_retries || 3)) {
      // Re-queue for retry - reset to pending with incremented retry_count
      await pool.query(
        `UPDATE worker_tasks
         SET status = 'pending',
             worker_id = NULL,
             claimed_at = NULL,
             started_at = NULL,
             retry_count = $2,
             error_message = $3,
             updated_at = NOW()
         WHERE id = $1`,
        [taskId, newRetryCount, `Retry ${newRetryCount}: ${errorMessage}`]
      );
      console.log(`[TaskService] Task ${taskId} queued for retry ${newRetryCount}/${max_retries || 3}`);
      return true;
    }

    // Max retries exceeded - mark as permanently failed
    await pool.query(
      `UPDATE worker_tasks
       SET status = 'failed',
           completed_at = NOW(),
           retry_count = $2,
           error_message = $3
       WHERE id = $1`,
      [taskId, newRetryCount, `Failed after ${newRetryCount} attempts: ${errorMessage}`]
    );
    console.log(`[TaskService] Task ${taskId} permanently failed after ${newRetryCount} attempts`);
    return false;
  }

  /**
   * Get a task by ID
   */
  async getTask(taskId: number): Promise<WorkerTask | null> {
    const result = await pool.query(
      `SELECT * FROM worker_tasks WHERE id = $1`,
      [taskId]
    );
    return (result.rows[0] as WorkerTask) || null;
  }

  /**
   * List tasks with filters
   */
  async listTasks(filter: TaskFilter = {}): Promise<WorkerTask[]> {
    // Return empty list if table doesn't exist
    if (!await tableExists('worker_tasks')) {
      return [];
    }

    const conditions: string[] = [];
    const params: (string | number | string[])[] = [];
    let paramIndex = 1;

    if (filter.role) {
      conditions.push(`t.role = $${paramIndex++}`);
      params.push(filter.role);
    }

    if (filter.status) {
      if (Array.isArray(filter.status)) {
        conditions.push(`t.status = ANY($${paramIndex++})`);
        params.push(filter.status);
      } else {
        conditions.push(`t.status = $${paramIndex++}`);
        params.push(filter.status);
      }
    }

    if (filter.dispensary_id) {
      conditions.push(`t.dispensary_id = $${paramIndex++}`);
      params.push(filter.dispensary_id);
    }

    if (filter.worker_id) {
      conditions.push(`t.worker_id = $${paramIndex++}`);
      params.push(filter.worker_id);
    }

    const whereClause = conditions.length > 0 ? `WHERE ${conditions.join(' AND ')}` : '';
    const limit = filter.limit ?? 100;
    const offset = filter.offset ?? 0;

    const result = await pool.query(
      `SELECT
         t.*,
         d.name as dispensary_name,
         d.slug as dispensary_slug
       FROM worker_tasks t
       LEFT JOIN dispensaries d ON d.id = t.dispensary_id
       ${whereClause}
       ORDER BY t.created_at DESC
       LIMIT ${limit} OFFSET ${offset}`,
      params
    );

    return result.rows as WorkerTask[];
  }

  /**
   * Get capacity metrics for all roles
   */
  async getCapacityMetrics(): Promise<CapacityMetrics[]> {
    // Return empty metrics if worker_tasks table doesn't exist
    if (!await tableExists('worker_tasks')) {
      return [];
    }

    try {
      const result = await pool.query(
        `SELECT * FROM v_worker_capacity`
      );
      return result.rows as CapacityMetrics[];
    } catch {
      // View may not exist
      return [];
    }
  }

  /**
   * Get capacity metrics for a specific role
   */
  async getRoleCapacity(role: TaskRole): Promise<CapacityMetrics | null> {
    // Return null if worker_tasks table doesn't exist
    if (!await tableExists('worker_tasks')) {
      return null;
    }

    try {
      const result = await pool.query(
        `SELECT * FROM v_worker_capacity WHERE role = $1`,
        [role]
      );
      return (result.rows[0] as CapacityMetrics) || null;
    } catch {
      // View may not exist
      return null;
    }
  }

  /**
   * Recover stale tasks from dead workers
   */
  async recoverStaleTasks(staleThresholdMinutes = 10): Promise<number> {
    const result = await pool.query(
      `SELECT recover_stale_tasks($1)`,
      [staleThresholdMinutes]
    );
    return (result.rows[0] as { recover_stale_tasks: number })?.recover_stale_tasks ?? 0;
  }

  /**
   * Generate daily resync tasks for all active stores
   */
  async generateDailyResyncTasks(batchesPerDay = 6, date?: Date): Promise<number> {
    const result = await pool.query(
      `SELECT generate_resync_tasks($1, $2)`,
      [batchesPerDay, date ?? new Date()]
    );
    return (result.rows[0] as { generate_resync_tasks: number })?.generate_resync_tasks ?? 0;
  }

  /**
   * Chain next task after completion
   * Called automatically when a task completes successfully
   *
   * Per TASK_WORKFLOW_2024-12-10.md: Task chaining flow:
   *
   * Discovery flow (new stores):
   *   store_discovery → product_discovery → payload_fetch → product_refresh
   *
   * Scheduled flow (existing stores):
   *   payload_fetch → product_refresh
   *
   * Note: entry_point_discovery is deprecated since platform_dispensary_id
   * is now resolved during store promotion.
   */
  async chainNextTask(completedTask: WorkerTask): Promise<WorkerTask | null> {
    if (completedTask.status !== 'completed') {
      return null;
    }

    switch (completedTask.role) {
      case 'store_discovery': {
        // Per TASK_WORKFLOW_2024-12-10.md: New stores discovered -> create product_discovery tasks
        // Skip entry_point_discovery since platform_dispensary_id is set during promotion
        const newStoreIds = (completedTask.result as { newStoreIds?: number[] })?.newStoreIds;
        if (newStoreIds && newStoreIds.length > 0) {
          console.log(`[TaskService] Chaining ${newStoreIds.length} product_discovery tasks for new stores`);
          for (const storeId of newStoreIds) {
            await this.createTask({
              role: 'product_discovery',
              dispensary_id: storeId,
              platform: completedTask.platform ?? undefined,
              priority: 10, // High priority for new stores
            });
          }
        }
        break;
      }

      case 'entry_point_discovery': {
        // DEPRECATED: Entry point resolution now happens during store promotion
        // Kept for backward compatibility with any in-flight tasks
        const success = (completedTask.result as { success?: boolean })?.success;
        if (success && completedTask.dispensary_id) {
          return this.createTask({
            role: 'product_discovery',
            dispensary_id: completedTask.dispensary_id,
            platform: completedTask.platform ?? undefined,
            priority: 10,
          });
        }
        break;
      }

      case 'product_discovery': {
        // Per TASK_WORKFLOW_2024-12-10.md: Product discovery chains internally to payload_fetch
        // No external chaining needed - handleProductDiscovery calls handlePayloadFetch directly
        break;
      }

      case 'payload_fetch': {
        // Per TASK_WORKFLOW_2024-12-10.md: payload_fetch chains to product_refresh
        // This is handled internally by the payload_fetch handler via taskService.createTask
        // No external chaining needed here
        break;
      }
    }

    return null;
  }

  /**
   * Create store discovery task for a platform/state
   */
  async createStoreDiscoveryTask(
    platform: string,
    stateCode?: string,
    priority = 0
  ): Promise<WorkerTask> {
    return this.createTask({
      role: 'store_discovery',
      platform,
      priority,
    });
  }

  /**
   * Create entry point discovery task for a specific store
   */
  async createEntryPointTask(
    dispensaryId: number,
    platform: string,
    priority = 10
  ): Promise<WorkerTask> {
    return this.createTask({
      role: 'entry_point_discovery',
      dispensary_id: dispensaryId,
      platform,
      priority,
    });
  }

  /**
   * Create product discovery task for a specific store
   */
  async createProductDiscoveryTask(
    dispensaryId: number,
    platform: string,
    priority = 10
  ): Promise<WorkerTask> {
    return this.createTask({
      role: 'product_discovery',
      dispensary_id: dispensaryId,
      platform,
      priority,
    });
  }

  /**
   * Get task counts by status for dashboard
   */
  async getTaskCounts(): Promise<Record<TaskStatus, number>> {
    const counts: Record<TaskStatus, number> = {
      pending: 0,
      claimed: 0,
      running: 0,
      completed: 0,
      failed: 0,
      stale: 0,
    };

    // Return empty counts if table doesn't exist
    if (!await tableExists('worker_tasks')) {
      return counts;
    }

    const result = await pool.query(
      `SELECT status, COUNT(*) as count
       FROM worker_tasks
       GROUP BY status`
    );

    for (const row of result.rows) {
      const typedRow = row as { status: TaskStatus; count: string };
      counts[typedRow.status] = parseInt(typedRow.count, 10);
    }

    return counts;
  }

  /**
   * Get recent task completions for a role
   */
  async getRecentCompletions(role: TaskRole, limit = 10): Promise<WorkerTask[]> {
    const result = await pool.query(
      `SELECT * FROM worker_tasks
       WHERE role = $1 AND status = 'completed'
       ORDER BY completed_at DESC
       LIMIT $2`,
      [role, limit]
    );
    return result.rows as WorkerTask[];
  }

  /**
   * Check if a store has any active tasks
   */
  async hasActiveTask(dispensaryId: number): Promise<boolean> {
    const result = await pool.query(
      `SELECT EXISTS(
        SELECT 1 FROM worker_tasks
        WHERE dispensary_id = $1
        AND status IN ('claimed', 'running')
      ) as exists`,
      [dispensaryId]
    );
    return (result.rows[0] as { exists: boolean })?.exists ?? false;
  }

  /**
   * Get the last completion time for a role
   */
  async getLastCompletion(role: TaskRole): Promise<Date | null> {
    const result = await pool.query(
      `SELECT MAX(completed_at) as completed_at
       FROM worker_tasks
       WHERE role = $1 AND status = 'completed'`,
      [role]
    );
    return (result.rows[0] as { completed_at: Date | null })?.completed_at ?? null;
  }

  /**
   * Calculate workers needed to complete tasks within SLA
   */
  async calculateWorkersNeeded(role: TaskRole, slaHours: number): Promise<number> {
    const capacity = await this.getRoleCapacity(role);
    if (!capacity || !capacity.tasks_per_worker_hour) {
      return 1; // Default to 1 worker if no data
    }

    const pendingTasks = capacity.pending_tasks;
    const tasksPerWorkerHour = capacity.tasks_per_worker_hour;
    const totalTaskCapacityNeeded = pendingTasks / slaHours;

    return Math.ceil(totalTaskCapacityNeeded / tasksPerWorkerHour);
  }
}

export const taskService = new TaskService();