/**
 * Neo4j Auto-Sync Service
 *
 * Automated synchronization between local Neo4j and AuraDB cloud.
 * Supports full sync, incremental sync, and scheduled execution.
 */

import neo4j, { Driver, Session } from 'neo4j-driver';
import cron from 'node-cron';
import fs from 'fs';
import path from 'path';

export interface SyncConfig {
  local: {
    uri: string;
    user: string;
    password: string;
    database: string;
  };
  cloud: {
    uri: string;
    user: string;
    password: string;
    database: string;
  };
  schedule?: string; // Cron expression
  incrementalEnabled?: boolean;
  batchSize?: number;
}

export interface SyncStatus {
  lastSyncTime: string | null;
  lastSyncType: 'full' | 'incremental' | null;
  lastSyncDuration: number | null;
  nodesSync: number;
  relationshipsSync: number;
  status: 'idle' | 'running' | 'success' | 'error';
  error?: string;
  nextScheduledSync?: string;
}

export interface SyncCheckpoint {
  timestamp: string;
  nodeCount: number;
  relationshipCount: number;
  lastNodeIds: string[];
}

const CHECKPOINT_FILE = path.join(process.cwd(), '.neo4j-sync-checkpoint.json');
const STATUS_FILE = path.join(process.cwd(), '.neo4j-sync-status.json');

export class Neo4jAutoSync {
  private config: SyncConfig;
  private localDriver: Driver | null = null;
  private cloudDriver: Driver | null = null;
  private cronJob: cron.ScheduledTask | null = null;
  private status: SyncStatus = {
    lastSyncTime: null,
    lastSyncType: null,
    lastSyncDuration: null,
    nodesSync: 0,
    relationshipsSync: 0,
    status: 'idle'
  };

  constructor(config?: Partial<SyncConfig>) {
    this.config = {
      local: {
        uri: config?.local?.uri || process.env.NEO4J_LOCAL_URI || 'bolt://localhost:7687',
        user: config?.local?.user || process.env.NEO4J_LOCAL_USER || 'neo4j',
        password: config?.local?.password || process.env.NEO4J_LOCAL_PASSWORD || 'password',
        database: config?.local?.database || process.env.NEO4J_LOCAL_DATABASE || 'neo4j'
      },
      cloud: {
        uri: config?.cloud?.uri || process.env.NEO4J_URI || '',
        user: config?.cloud?.user || process.env.NEO4J_USER || 'neo4j',
        password: config?.cloud?.password || process.env.NEO4J_PASSWORD || '',
        database: config?.cloud?.database || process.env.NEO4J_DATABASE || 'neo4j'
      },
      schedule: config?.schedule || process.env.NEO4J_SYNC_SCHEDULE || '0 */6 * * *', // Every 6 hours
      incrementalEnabled: config?.incrementalEnabled ?? true,
      batchSize: config?.batchSize || 500
    };

    this.loadStatus();
  }

  private loadStatus(): void {
    try {
      if (fs.existsSync(STATUS_FILE)) {
        const data = fs.readFileSync(STATUS_FILE, 'utf-8');
        this.status = JSON.parse(data);
        this.status.status = 'idle'; // Reset running status on restart
      }
    } catch {
      // Ignore errors, use default status
    }
  }

  private saveStatus(): void {
    try {
      fs.writeFileSync(STATUS_FILE, JSON.stringify(this.status, null, 2));
    } catch (error) {
      console.error('Failed to save sync status:', error);
    }
  }

  private loadCheckpoint(): SyncCheckpoint | null {
    try {
      if (fs.existsSync(CHECKPOINT_FILE)) {
        const data = fs.readFileSync(CHECKPOINT_FILE, 'utf-8');
        return JSON.parse(data);
      }
    } catch {
      // Ignore errors
    }
    return null;
  }

  private saveCheckpoint(checkpoint: SyncCheckpoint): void {
    try {
      fs.writeFileSync(CHECKPOINT_FILE, JSON.stringify(checkpoint, null, 2));
    } catch (error) {
      console.error('Failed to save checkpoint:', error);
    }
  }

  async connect(): Promise<void> {
    console.log('📡 Connecting to Neo4j instances...');

    this.localDriver = neo4j.driver(
      this.config.local.uri,
      neo4j.auth.basic(this.config.local.user, this.config.local.password),
      { maxConnectionLifetime: 3 * 60 * 60 * 1000 }
    );
    await this.localDriver.verifyConnectivity();
    console.log('  ✓ Connected to local Neo4j');

    this.cloudDriver = neo4j.driver(
      this.config.cloud.uri,
      neo4j.auth.basic(this.config.cloud.user, this.config.cloud.password),
      { maxConnectionLifetime: 3 * 60 * 60 * 1000 }
    );
    await this.cloudDriver.verifyConnectivity();
    console.log('  ✓ Connected to AuraDB cloud');
  }

  async disconnect(): Promise<void> {
    if (this.localDriver) await this.localDriver.close();
    if (this.cloudDriver) await this.cloudDriver.close();
    this.localDriver = null;
    this.cloudDriver = null;
  }

  /**
   * Start scheduled auto-sync
   */
  startScheduler(): void {
    if (this.cronJob) {
      this.cronJob.stop();
    }

    console.log(`⏰ Starting Neo4j auto-sync scheduler: ${this.config.schedule}`);

    this.cronJob = cron.schedule(this.config.schedule!, async () => {
      console.log(`\n🔄 [${new Date().toISOString()}] Scheduled sync starting...`);
      try {
        await this.sync();
      } catch (error) {
        console.error('Scheduled sync failed:', error);
      }
    });

    // Calculate next run time
    const nextRun = this.getNextScheduledTime();
    this.status.nextScheduledSync = nextRun;
    this.saveStatus();

    console.log(`  Next sync: ${nextRun}`);
  }

  stopScheduler(): void {
    if (this.cronJob) {
      this.cronJob.stop();
      this.cronJob = null;
      console.log('⏹️  Scheduler stopped');
    }
  }

  private getNextScheduledTime(): string {
    // Simple calculation for common cron patterns
    const now = new Date();
    const schedule = this.config.schedule!;

    if (schedule.includes('*/6')) {
      // Every 6 hours
      const nextHour = Math.ceil(now.getHours() / 6) * 6;
      const next = new Date(now);
      next.setHours(nextHour, 0, 0, 0);
      if (next <= now) next.setHours(next.getHours() + 6);
      return next.toISOString();
    }

    return 'See cron expression: ' + schedule;
  }

  /**
   * Perform sync (auto-detects full vs incremental)
   */
  async sync(forceFullSync: boolean = false): Promise<SyncStatus> {
    const startTime = Date.now();
    this.status.status = 'running';
    this.saveStatus();

    try {
      await this.connect();

      const checkpoint = this.loadCheckpoint();
      const shouldDoFullSync = forceFullSync || !checkpoint || !this.config.incrementalEnabled;

      if (shouldDoFullSync) {
        await this.fullSync();
        this.status.lastSyncType = 'full';
      } else {
        const hasChanges = await this.checkForChanges(checkpoint);
        if (hasChanges) {
          await this.incrementalSync(checkpoint);
          this.status.lastSyncType = 'incremental';
        } else {
          console.log('✓ No changes detected, skipping sync');
          this.status.lastSyncType = 'incremental';
        }
      }

      this.status.status = 'success';
      this.status.lastSyncTime = new Date().toISOString();
      this.status.lastSyncDuration = Date.now() - startTime;
      delete this.status.error;

    } catch (error: any) {
      this.status.status = 'error';
      this.status.error = error.message;
      console.error('❌ Sync failed:', error.message);
    } finally {
      await this.disconnect();
      this.saveStatus();
    }

    return this.status;
  }

  private async checkForChanges(checkpoint: SyncCheckpoint): Promise<boolean> {
    const session = this.localDriver!.session({ database: this.config.local.database });
    try {
      // Check node count
      const nodeResult = await session.run('MATCH (n) RETURN count(n) as count');
      const currentNodeCount = nodeResult.records[0].get('count').toNumber();

      // Check relationship count
      const relResult = await session.run('MATCH ()-[r]->() RETURN count(r) as count');
      const currentRelCount = relResult.records[0].get('count').toNumber();

      const hasChanges = currentNodeCount !== checkpoint.nodeCount ||
                        currentRelCount !== checkpoint.relationshipCount;

      if (hasChanges) {
        console.log(`📊 Changes detected: nodes ${checkpoint.nodeCount} → ${currentNodeCount}, rels ${checkpoint.relationshipCount} → ${currentRelCount}`);
      }

      return hasChanges;
    } finally {
      await session.close();
    }
  }

  private async fullSync(): Promise<void> {
    console.log('\n🔄 Starting FULL sync...');

    const localSession = this.localDriver!.session({ database: this.config.local.database });
    const cloudSession = this.cloudDriver!.session({ database: this.config.cloud.database });

    try {
      // Export schema
      const schema = await this.exportSchema(localSession);

      // Export nodes
      const nodes = await this.exportNodes(localSession);

      // Export relationships
      const relationships = await this.exportRelationships(localSession);

      // Clear cloud
      await this.clearCloud(cloudSession);

      // Apply schema
      await this.applySchema(cloudSession, schema);

      // Import nodes
      const elementIdMap = new Map<string, string>();
      await this.importNodes(cloudSession, nodes, elementIdMap);

      // Import relationships
      await this.importRelationships(cloudSession, relationships, elementIdMap, nodes);

      // Save checkpoint
      this.saveCheckpoint({
        timestamp: new Date().toISOString(),
        nodeCount: nodes.length,
        relationshipCount: relationships.length,
        lastNodeIds: nodes.slice(-100).map(n => n.properties.id)
      });

      this.status.nodesSync = nodes.length;
      this.status.relationshipsSync = relationships.length;

      console.log(`\n✅ Full sync complete: ${nodes.length} nodes, ${relationships.length} relationships`);

    } finally {
      await localSession.close();
      await cloudSession.close();
    }
  }

  private async incrementalSync(checkpoint: SyncCheckpoint): Promise<void> {
    console.log('\n🔄 Starting INCREMENTAL sync...');

    const localSession = this.localDriver!.session({ database: this.config.local.database });
    const cloudSession = this.cloudDriver!.session({ database: this.config.cloud.database });

    try {
      // Find new/modified nodes since checkpoint
      const checkpointTime = new Date(checkpoint.timestamp);

      // Get nodes created/modified after checkpoint
      // This requires nodes to have a 'updatedAt' or 'createdAt' property
      const newNodesResult = await localSession.run(`
        MATCH (n)
        WHERE n.createdAt > datetime($checkpointTime)
           OR n.updatedAt > datetime($checkpointTime)
           OR NOT n.id IN $existingIds
        RETURN n, elementId(n) as elementId
        LIMIT 10000
      `, {
        checkpointTime: checkpointTime.toISOString(),
        existingIds: checkpoint.lastNodeIds
      });

      const newNodes: any[] = [];
      for (const record of newNodesResult.records) {
        const node = record.get('n');
        newNodes.push({
          labels: [...node.labels],
          properties: this.convertProperties(node.properties),
          elementId: record.get('elementId')
        });
      }

      if (newNodes.length === 0) {
        console.log('  No new nodes to sync');
        return;
      }

      console.log(`  Found ${newNodes.length} new/modified nodes`);

      // Import new nodes
      const elementIdMap = new Map<string, string>();
      await this.importNodes(cloudSession, newNodes, elementIdMap);

      // Get new relationships for these nodes
      const nodeIds = newNodes.map(n => n.properties.id).filter(Boolean);
      if (nodeIds.length > 0) {
        const newRelsResult = await localSession.run(`
          MATCH (a)-[r]->(b)
          WHERE a.id IN $nodeIds OR b.id IN $nodeIds
          RETURN r, type(r) as type, elementId(a) as startId, elementId(b) as endId
        `, { nodeIds });

        const newRels: any[] = [];
        for (const record of newRelsResult.records) {
          const rel = record.get('r');
          newRels.push({
            type: record.get('type'),
            properties: this.convertProperties(rel.properties),
            startElementId: record.get('startId'),
            endElementId: record.get('endId')
          });
        }

        if (newRels.length > 0) {
          await this.importRelationships(cloudSession, newRels, elementIdMap, newNodes);
        }
      }

      // Update checkpoint
      const nodeCountResult = await localSession.run('MATCH (n) RETURN count(n) as count');
      const relCountResult = await localSession.run('MATCH ()-[r]->() RETURN count(r) as count');

      this.saveCheckpoint({
        timestamp: new Date().toISOString(),
        nodeCount: nodeCountResult.records[0].get('count').toNumber(),
        relationshipCount: relCountResult.records[0].get('count').toNumber(),
        lastNodeIds: [...checkpoint.lastNodeIds, ...nodeIds].slice(-100)
      });

      this.status.nodesSync = newNodes.length;
      this.status.relationshipsSync = 0;

      console.log(`✅ Incremental sync complete: ${newNodes.length} nodes`);

    } finally {
      await localSession.close();
      await cloudSession.close();
    }
  }

  private convertProperties(props: Record<string, any>): Record<string, any> {
    const result: Record<string, any> = {};
    for (const [key, value] of Object.entries(props)) {
      if (value === null || value === undefined) {
        result[key] = value;
      } else if (typeof value === 'object' && value.constructor?.name === 'Integer') {
        result[key] = value.toNumber();
      } else if (typeof value === 'object' && (value.constructor?.name === 'DateTime' || value.constructor?.name === 'Date')) {
        result[key] = value.toString();
      } else if (Array.isArray(value)) {
        result[key] = value.map(v => this.convertProperties({ v }).v);
      } else {
        result[key] = value;
      }
    }
    return result;
  }

  private async exportSchema(session: Session): Promise<any[]> {
    const schema: any[] = [];

    const constraintResult = await session.run('SHOW CONSTRAINTS');
    for (const record of constraintResult.records) {
      const name = record.get('name');
      const type = record.get('type');
      const entityType = record.get('entityType');
      const labelsOrTypes = record.get('labelsOrTypes');
      const properties = record.get('properties');

      if (type === 'UNIQUENESS' && entityType === 'NODE') {
        const label = labelsOrTypes?.[0];
        const prop = properties?.[0];
        if (label && prop) {
          schema.push({
            type: 'constraint',
            name,
            definition: `CREATE CONSTRAINT ${name} IF NOT EXISTS FOR (n:${label}) REQUIRE n.${prop} IS UNIQUE`
          });
        }
      }
    }

    const indexResult = await session.run('SHOW INDEXES');
    for (const record of indexResult.records) {
      const name = record.get('name');
      const type = record.get('type');
      const entityType = record.get('entityType');
      const labelsOrTypes = record.get('labelsOrTypes');
      const properties = record.get('properties');
      const owningConstraint = record.get('owningConstraint');

      if (owningConstraint) continue;

      if (type === 'RANGE' && entityType === 'NODE') {
        const label = labelsOrTypes?.[0];
        const prop = properties?.[0];
        if (label && prop) {
          schema.push({
            type: 'index',
            name,
            definition: `CREATE INDEX ${name} IF NOT EXISTS FOR (n:${label}) ON (n.${prop})`
          });
        }
      }
    }

    return schema;
  }

  private async exportNodes(session: Session): Promise<any[]> {
    console.log('📦 Exporting nodes...');
    const result = await session.run('MATCH (n) RETURN n, elementId(n) as elementId');
    const nodes = result.records.map(record => ({
      labels: [...record.get('n').labels],
      properties: this.convertProperties(record.get('n').properties),
      elementId: record.get('elementId')
    }));
    console.log(`  ✓ Exported ${nodes.length} nodes`);
    return nodes;
  }

  private async exportRelationships(session: Session): Promise<any[]> {
    console.log('🔗 Exporting relationships...');
    const result = await session.run(`
      MATCH (a)-[r]->(b)
      RETURN r, type(r) as type, elementId(a) as startId, elementId(b) as endId
    `);
    const rels = result.records.map(record => ({
      type: record.get('type'),
      properties: this.convertProperties(record.get('r').properties),
      startElementId: record.get('startId'),
      endElementId: record.get('endId')
    }));
    console.log(`  ✓ Exported ${rels.length} relationships`);
    return rels;
  }

  private async clearCloud(session: Session): Promise<void> {
    console.log('🗑️  Clearing cloud database...');
    let deleted = 0;
    do {
      const result = await session.run(`
        MATCH (n) WITH n LIMIT 1000 DETACH DELETE n RETURN count(*) as deleted
      `);
      deleted = result.records[0]?.get('deleted')?.toNumber() || 0;
    } while (deleted > 0);
    console.log('  ✓ Cloud cleared');
  }

  private async applySchema(session: Session, schema: any[]): Promise<void> {
    console.log('📋 Applying schema...');
    for (const item of schema) {
      try {
        await session.run(item.definition);
      } catch (error: any) {
        if (!error.message?.includes('already exists')) {
          console.warn(`  ⚠ ${item.name}: ${error.message?.slice(0, 50)}`);
        }
      }
    }
    console.log(`  ✓ Applied ${schema.length} schema items`);
  }

  private async importNodes(session: Session, nodes: any[], elementIdMap: Map<string, string>): Promise<void> {
    console.log('📦 Importing nodes...');
    let imported = 0;
    const batchSize = this.config.batchSize!;

    for (let i = 0; i < nodes.length; i += batchSize) {
      const batch = nodes.slice(i, i + batchSize);

      for (const node of batch) {
        try {
          const labelStr = node.labels.join(':');
          const nodeId = node.properties.id || `node_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
          node.properties.id = nodeId;

          const result = await session.run(`
            MERGE (n:${labelStr} {id: $nodeId})
            SET n = $props
            RETURN elementId(n) as newElementId
          `, { nodeId, props: node.properties });

          const newElementId = result.records[0]?.get('newElementId');
          if (newElementId) {
            elementIdMap.set(node.elementId, newElementId);
          }
          imported++;
        } catch (error: any) {
          // Continue on error
        }
      }

      if ((i + batchSize) % 5000 === 0 || i + batchSize >= nodes.length) {
        console.log(`  Progress: ${Math.min(i + batchSize, nodes.length)}/${nodes.length} nodes`);
      }
    }

    console.log(`  ✓ Imported ${imported} nodes`);
  }

  private async importRelationships(
    session: Session,
    relationships: any[],
    elementIdMap: Map<string, string>,
    nodes: any[]
  ): Promise<void> {
    console.log('🔗 Importing relationships...');

    const elementIdToNodeId = new Map<string, string>();
    for (const node of nodes) {
      elementIdToNodeId.set(node.elementId, node.properties.id);
    }

    let imported = 0;
    const batchSize = this.config.batchSize!;

    for (let i = 0; i < relationships.length; i += batchSize) {
      const batch = relationships.slice(i, i + batchSize);

      for (const rel of batch) {
        try {
          const startNodeId = elementIdToNodeId.get(rel.startElementId);
          const endNodeId = elementIdToNodeId.get(rel.endElementId);

          if (!startNodeId || !endNodeId) continue;

          await session.run(`
            MATCH (a {id: $startId})
            MATCH (b {id: $endId})
            MERGE (a)-[r:${rel.type}]->(b)
            SET r = $props
          `, { startId: startNodeId, endId: endNodeId, props: rel.properties });

          imported++;
        } catch (error: any) {
          // Continue on error
        }
      }

      if ((i + batchSize) % 50000 === 0 || i + batchSize >= relationships.length) {
        console.log(`  Progress: ${Math.min(i + batchSize, relationships.length)}/${relationships.length} relationships`);
      }
    }

    console.log(`  ✓ Imported ${imported} relationships`);
  }

  getStatus(): SyncStatus {
    return { ...this.status };
  }
}

// Singleton instance
let autoSyncInstance: Neo4jAutoSync | null = null;

export function getNeo4jAutoSync(): Neo4jAutoSync {
  if (!autoSyncInstance) {
    autoSyncInstance = new Neo4jAutoSync();
  }
  return autoSyncInstance;
}