import { db } from '../config/database'
import axios from 'axios'
import crypto from 'crypto'
import { logger } from '../utils/logger'

interface SyncPayload {
  type: 'employees' | 'skills' | 'users' | 'settings'
  action: 'create' | 'update' | 'delete'
  data: any
  timestamp: string
  nodeId: string
  checksum: string
}

interface SyncResult {
  success: boolean
  syncedItems: number
  conflicts: any[]
  errors: any[]
}

export class SyncService {
  private static instance: SyncService
  private syncQueue: SyncPayload[] = []
  private isSyncing = false

  private constructor() {
    // Initialize sync tables
    this.initializeSyncTables()
  }

  static getInstance(): SyncService {
    if (!SyncService.instance) {
      SyncService.instance = new SyncService()
    }
    return SyncService.instance
  }

  private initializeSyncTables() {
    // Sync log table to track all sync operations
    db.exec(`
      CREATE TABLE IF NOT EXISTS sync_log (
        id TEXT PRIMARY KEY,
        node_id TEXT NOT NULL,
        sync_type TEXT NOT NULL,
        sync_action TEXT NOT NULL,
        entity_id TEXT NOT NULL,
        entity_type TEXT NOT NULL,
        payload TEXT NOT NULL,
        checksum TEXT NOT NULL,
        status TEXT CHECK(status IN ('pending', 'completed', 'failed', 'conflict')) NOT NULL,
        error_message TEXT,
        created_at TEXT NOT NULL,
        completed_at TEXT
      )
    `)

    // Conflict resolution table
    db.exec(`
      CREATE TABLE IF NOT EXISTS sync_conflicts (
        id TEXT PRIMARY KEY,
        entity_id TEXT NOT NULL,
        entity_type TEXT NOT NULL,
        local_data TEXT NOT NULL,
        remote_data TEXT NOT NULL,
        conflict_type TEXT NOT NULL,
        resolution_status TEXT CHECK(resolution_status IN ('pending', 'resolved', 'ignored')) DEFAULT 'pending',
        resolved_by TEXT,
        resolved_at TEXT,
        created_at TEXT NOT NULL
      )
    `)

    // Sync metadata table
    db.exec(`
      CREATE TABLE IF NOT EXISTS sync_metadata (
        node_id TEXT PRIMARY KEY,
        last_sync_at TEXT,
        last_successful_sync TEXT,
        sync_version INTEGER DEFAULT 1,
        total_synced_items INTEGER DEFAULT 0,
        total_conflicts INTEGER DEFAULT 0,
        total_errors INTEGER DEFAULT 0
      )
    `)
  }

  // Generate checksum for data integrity
  private generateChecksum(data: any): string {
    const hash = crypto.createHash('sha256')
    hash.update(JSON.stringify(data))
    return hash.digest('hex')
  }

  // Add item to sync queue
  async queueSync(type: SyncPayload['type'], action: SyncPayload['action'], data: any) {
    const nodeId = this.getNodeId()
    const payload: SyncPayload = {
      type,
      action,
      data,
      timestamp: new Date().toISOString(),
      nodeId,
      checksum: this.generateChecksum(data)
    }

    this.syncQueue.push(payload)

    // Log to sync_log
    db.prepare(`
      INSERT INTO sync_log (
        id, node_id, sync_type, sync_action, entity_id, entity_type,
        payload, checksum, status, created_at
      ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
    `).run(
      crypto.randomUUID(),
      nodeId,
      type,
      action,
      data.id || 'unknown',
      type,
      JSON.stringify(payload),
      payload.checksum,
      'pending',
      payload.timestamp
    )

    // Trigger sync if auto-sync is enabled
    const syncSettings = this.getSyncSettings()
    if (syncSettings.autoSyncInterval !== 'disabled') {
      this.triggerSync()
    }
  }

  // Sync with remote nodes
  async syncWithNode(targetNodeId: string): Promise<SyncResult> {
    const result: SyncResult = {
      success: false,
      syncedItems: 0,
      conflicts: [],
      errors: []
    }

    try {
      const targetNode = this.getNodeInfo(targetNodeId)
      if (!targetNode) {
        throw new Error('Target node not found')
      }

      // Get pending sync items
      const pendingItems = db.prepare(`
        SELECT * FROM sync_log 
        WHERE status = 'pending' 
        ORDER BY created_at ASC
      `).all() as any[]

      for (const item of pendingItems) {
        try {
          const payload = JSON.parse(item.payload)
          
          // Send to target node
          const response = await axios.post(
            `http://${targetNode.ip_address}:${targetNode.port}/api/sync/receive`,
            payload,
            {
              headers: {
                'Authorization': `Bearer ${targetNode.api_key}`,
                'X-Node-Id': this.getNodeId()
              },
              timeout: 30000
            }
          )

          if (response.data.success) {
            // Mark as completed
            db.prepare(`
              UPDATE sync_log 
              SET status = 'completed', completed_at = ? 
              WHERE id = ?
            `).run(new Date().toISOString(), item.id)

            result.syncedItems++
          } else if (response.data.conflict) {
            // Handle conflict
            this.handleConflict(item, response.data.conflictData)
            result.conflicts.push({
              itemId: item.id,
              conflict: response.data.conflictData
            })
          }
        } catch (error: any) {
          logger.error(`Sync error for item ${item.id}:`, error)
          
          // Mark as failed
          db.prepare(`
            UPDATE sync_log 
            SET status = 'failed', error_message = ? 
            WHERE id = ?
          `).run(error.message, item.id)

          result.errors.push({
            itemId: item.id,
            error: error.message
          })
        }
      }

      // Update sync metadata
      this.updateSyncMetadata(targetNodeId, result)
      result.success = result.errors.length === 0

    } catch (error: any) {
      logger.error('Sync failed:', error)
      result.errors.push({ error: error.message })
    }

    return result
  }

  // Receive sync from remote node
  async receiveSync(payload: SyncPayload): Promise<any> {
    try {
      // Verify checksum
      const calculatedChecksum = this.generateChecksum(payload.data)
      if (calculatedChecksum !== payload.checksum) {
        throw new Error('Checksum mismatch - data integrity error')
      }

      // Check for conflicts
      const conflict = await this.checkForConflicts(payload)
      if (conflict) {
        return {
          success: false,
          conflict: true,
          conflictData: conflict
        }
      }

      // Apply changes based on type and action
      await this.applyChanges(payload)

      return { success: true }
    } catch (error: any) {
      logger.error('Error receiving sync:', error)
      return {
        success: false,
        error: error.message
      }
    }
  }

  // Check for conflicts
  private async checkForConflicts(payload: SyncPayload): Promise<any> {
    const { type, action, data } = payload

    if (action === 'create') {
      // Check if entity already exists
      let exists = false
      
      switch (type) {
        case 'employees':
          exists = !!db.prepare('SELECT id FROM employees WHERE id = ?').get(data.id)
          break
        case 'skills':
          exists = !!db.prepare('SELECT id FROM skills WHERE id = ?').get(data.id)
          break
        case 'users':
          exists = !!db.prepare('SELECT id FROM users WHERE id = ?').get(data.id)
          break
      }

      if (exists) {
        return {
          type: 'already_exists',
          entityId: data.id,
          entityType: type
        }
      }
    } else if (action === 'update') {
      // Check if local version is newer
      let localEntity: any = null
      
      switch (type) {
        case 'employees':
          localEntity = db.prepare('SELECT * FROM employees WHERE id = ?').get(data.id)
          break
        case 'skills':
          localEntity = db.prepare('SELECT * FROM skills WHERE id = ?').get(data.id)
          break
        case 'users':
          localEntity = db.prepare('SELECT * FROM users WHERE id = ?').get(data.id)
          break
      }

      if (localEntity && new Date(localEntity.updated_at) > new Date(data.updatedAt)) {
        return {
          type: 'newer_version',
          entityId: data.id,
          entityType: type,
          localVersion: localEntity,
          remoteVersion: data
        }
      }
    }

    return null
  }

  // Apply changes to local database
  private async applyChanges(payload: SyncPayload) {
    const { type, action, data } = payload

    switch (type) {
      case 'employees':
        await this.syncEmployee(action, data)
        break
      case 'skills':
        await this.syncSkill(action, data)
        break
      case 'users':
        await this.syncUser(action, data)
        break
      case 'settings':
        await this.syncSettings(action, data)
        break
    }
  }

  // Sync employee data
  private async syncEmployee(action: string, data: any) {
    switch (action) {
      case 'create':
        db.prepare(`
          INSERT INTO employees (
            id, first_name, last_name, employee_number, photo, position,
            department, email, phone, mobile, office, availability,
            clearance_level, clearance_valid_until, clearance_issued_date,
            created_at, updated_at, created_by
          ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
        `).run(
          data.id, data.firstName, data.lastName, data.employeeNumber,
          data.photo, data.position, data.department, data.email,
          data.phone, data.mobile, data.office, data.availability,
          data.clearance?.level, data.clearance?.validUntil,
          data.clearance?.issuedDate, data.createdAt, data.updatedAt,
          data.createdBy
        )

        // Sync skills
        if (data.skills) {
          for (const skill of data.skills) {
            db.prepare(`
              INSERT INTO employee_skills (employee_id, skill_id, level, verified, verified_by, verified_date)
              VALUES (?, ?, ?, ?, ?, ?)
            `).run(
              data.id, skill.id, skill.level,
              skill.verified ? 1 : 0, skill.verifiedBy, skill.verifiedDate
            )
          }
        }
        break

      case 'update':
        db.prepare(`
          UPDATE employees SET
            first_name = ?, last_name = ?, position = ?, department = ?,
            email = ?, phone = ?, mobile = ?, office = ?, availability = ?,
            updated_at = ?, updated_by = ?
          WHERE id = ?
        `).run(
          data.firstName, data.lastName, data.position, data.department,
          data.email, data.phone, data.mobile, data.office, data.availability,
          data.updatedAt, data.updatedBy, data.id
        )
        break

      case 'delete':
        db.prepare('DELETE FROM employees WHERE id = ?').run(data.id)
        db.prepare('DELETE FROM employee_skills WHERE employee_id = ?').run(data.id)
        db.prepare('DELETE FROM language_skills WHERE employee_id = ?').run(data.id)
        db.prepare('DELETE FROM specializations WHERE employee_id = ?').run(data.id)
        break
    }
  }

  // Sync skill data
  private async syncSkill(action: string, data: any) {
    switch (action) {
      case 'create':
        db.prepare(`
          INSERT INTO skills (id, name, category, description, requires_certification, expires_after)
          VALUES (?, ?, ?, ?, ?, ?)
        `).run(
          data.id, data.name, data.category, data.description,
          data.requiresCertification ? 1 : 0, data.expiresAfter
        )
        break

      case 'update':
        db.prepare(`
          UPDATE skills SET name = ?, category = ?, description = ?
          WHERE id = ?
        `).run(data.name, data.category, data.description, data.id)
        break

      case 'delete':
        db.prepare('DELETE FROM skills WHERE id = ?').run(data.id)
        break
    }
  }

  // Sync user data
  private async syncUser(action: string, data: any) {
    // Implementation for user sync
    logger.info(`Syncing user: ${action}`, data)
  }

  // Sync settings
  private async syncSettings(action: string, data: any) {
    // Implementation for settings sync
    logger.info(`Syncing settings: ${action}`, data)
  }

  // Handle conflicts
  private handleConflict(syncItem: any, conflictData: any) {
    const conflictId = crypto.randomUUID()
    
    db.prepare(`
      INSERT INTO sync_conflicts (
        id, entity_id, entity_type, local_data, remote_data,
        conflict_type, created_at
      ) VALUES (?, ?, ?, ?, ?, ?, ?)
    `).run(
      conflictId,
      conflictData.entityId,
      conflictData.entityType,
      JSON.stringify(conflictData.localVersion || {}),
      JSON.stringify(conflictData.remoteVersion || {}),
      conflictData.type,
      new Date().toISOString()
    )

    // Apply conflict resolution strategy
    const settings = this.getSyncSettings()
    if (settings.conflictResolution === 'admin') {
      // Admin wins - apply remote changes if from admin node
      const remoteNode = this.getNodeInfo(syncItem.node_id)
      if (remoteNode?.type === 'admin') {
        this.applyChanges(JSON.parse(syncItem.payload))
      }
    } else if (settings.conflictResolution === 'newest') {
      // Newest wins - compare timestamps
      const localTime = new Date(conflictData.localVersion?.updatedAt || 0)
      const remoteTime = new Date(conflictData.remoteVersion?.updatedAt || 0)
      if (remoteTime > localTime) {
        this.applyChanges(JSON.parse(syncItem.payload))
      }
    }
    // Manual resolution - do nothing, let admin resolve
  }

  // Get sync settings
  private getSyncSettings(): any {
    const settings = db.prepare('SELECT * FROM sync_settings WHERE id = ?').get('default') as any
    return settings || {
      autoSyncInterval: 'disabled',
      conflictResolution: 'admin'
    }
  }

  // Get node information
  private getNodeInfo(nodeId: string): any {
    return db.prepare('SELECT * FROM network_nodes WHERE id = ?').get(nodeId)
  }

  // Get current node ID
  private getNodeId(): string {
    // Get from environment or generate
    return process.env.NODE_ID || 'local-node'
  }

  // Update sync metadata
  private updateSyncMetadata(nodeId: string, result: SyncResult) {
    const existing = db.prepare('SELECT * FROM sync_metadata WHERE node_id = ?').get(nodeId) as any

    if (existing) {
      db.prepare(`
        UPDATE sync_metadata SET
          last_sync_at = ?,
          last_successful_sync = ?,
          total_synced_items = total_synced_items + ?,
          total_conflicts = total_conflicts + ?,
          total_errors = total_errors + ?
        WHERE node_id = ?
      `).run(
        new Date().toISOString(),
        result.success ? new Date().toISOString() : existing.last_successful_sync,
        result.syncedItems,
        result.conflicts.length,
        result.errors.length,
        nodeId
      )
    } else {
      db.prepare(`
        INSERT INTO sync_metadata (
          node_id, last_sync_at, last_successful_sync,
          total_synced_items, total_conflicts, total_errors
        ) VALUES (?, ?, ?, ?, ?, ?)
      `).run(
        nodeId,
        new Date().toISOString(),
        result.success ? new Date().toISOString() : null,
        result.syncedItems,
        result.conflicts.length,
        result.errors.length
      )
    }
  }

  // Trigger sync process
  async triggerSync() {
    if (this.isSyncing) {
      logger.info('Sync already in progress')
      return
    }

    this.isSyncing = true

    try {
      // Get all active nodes
      const nodes = db.prepare(`
        SELECT * FROM network_nodes 
        WHERE is_online = 1 AND id != ?
      `).all(this.getNodeId()) as any[]

      for (const node of nodes) {
        logger.info(`Syncing with node: ${node.name}`)
        await this.syncWithNode(node.id)
      }
    } catch (error) {
      logger.error('Sync trigger failed:', error)
    } finally {
      this.isSyncing = false
    }
  }

  // Get sync status
  getSyncStatus(): any {
    const pendingCount = db.prepare(
      'SELECT COUNT(*) as count FROM sync_log WHERE status = ?'
    ).get('pending') as any

    const recentSync = db.prepare(`
      SELECT * FROM sync_log 
      ORDER BY created_at DESC 
      LIMIT 10
    `).all()

    const conflicts = db.prepare(`
      SELECT COUNT(*) as count FROM sync_conflicts 
      WHERE resolution_status = ?
    `).get('pending') as any

    return {
      pendingItems: pendingCount.count,
      recentSync,
      pendingConflicts: conflicts.count,
      isSyncing: this.isSyncing
    }
  }
}

export const syncService = SyncService.getInstance()