/**
 * Fast Neo4j Sync - Parallel batch sync with incremental support
 *
 * Much faster than sequential sync by:
 * 1. Using larger batches (500 instead of 100)
 * 2. Running multiple batches in parallel
 * 3. Using UNWIND for bulk operations
 * 4. Supporting incremental sync based on timestamps
 */

import neo4j, { Driver, Session } from 'neo4j-driver';
import { config } from 'dotenv';
import { resolve } from 'path';

// Load .env.production if it exists, otherwise fall back to .env
config({ path: resolve(process.cwd(), '.env.production') });
config({ path: resolve(process.cwd(), '.env') });

interface SyncConfig {
  localUri: string;
  localUser: string;
  localPassword: string;
  cloudUri: string;
  cloudUser: string;
  cloudPassword: string;
  batchSize: number;
  parallelBatches: number;
  incrementalOnly: boolean;
  lastSyncTime?: Date;
}

interface SyncStats {
  nodesCreated: number;
  nodesUpdated: number;
  relationshipsCreated: number;
  relationshipsUpdated: number;
  duration: number;
}

class FastNeo4jSync {
  private localDriver: Driver;
  private cloudDriver: Driver;
  private config: SyncConfig;
  private stats: SyncStats = {
    nodesCreated: 0,
    nodesUpdated: 0,
    relationshipsCreated: 0,
    relationshipsUpdated: 0,
    duration: 0
  };

  constructor(config: SyncConfig) {
    this.config = config;
    this.localDriver = neo4j.driver(
      config.localUri,
      neo4j.auth.basic(config.localUser, config.localPassword)
    );
    this.cloudDriver = neo4j.driver(
      config.cloudUri,
      neo4j.auth.basic(config.cloudUser, config.cloudPassword)
    );
  }

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

    const localSession = this.localDriver.session();
    const cloudSession = this.cloudDriver.session();

    try {
      await localSession.run('RETURN 1');
      console.log('  ✓ Local Neo4j connected');

      await cloudSession.run('RETURN 1');
      console.log('  ✓ Cloud AuraDB connected');
    } finally {
      await localSession.close();
      await cloudSession.close();
    }
  }

  async getLastSyncTime(): Promise<Date | null> {
    const cloudSession = this.cloudDriver.session();
    try {
      const result = await cloudSession.run(`
        MATCH (s:_SyncMetadata {id: 'last_sync'})
        RETURN s.timestamp as timestamp
      `);
      if (result.records.length > 0) {
        const ts = result.records[0].get('timestamp');
        return ts ? new Date(ts) : null;
      }
      return null;
    } catch {
      return null;
    } finally {
      await cloudSession.close();
    }
  }

  async setLastSyncTime(timestamp: Date): Promise<void> {
    const cloudSession = this.cloudDriver.session();
    try {
      await cloudSession.run(`
        MERGE (s:_SyncMetadata {id: 'last_sync'})
        SET s.timestamp = $timestamp
      `, { timestamp: timestamp.toISOString() });
    } finally {
      await cloudSession.close();
    }
  }

  async countNodesToSync(since?: Date): Promise<number> {
    const localSession = this.localDriver.session();
    try {
      let query: string;
      let params: Record<string, unknown> = {};

      if (since) {
        query = `
          MATCH (n)
          WHERE n.updatedAt > $since OR n.createdAt > $since OR NOT exists(n.updatedAt)
          RETURN count(n) as count
        `;
        params = { since: since.toISOString() };
      } else {
        query = 'MATCH (n) RETURN count(n) as count';
      }

      const result = await localSession.run(query, params);
      return result.records[0].get('count').toNumber();
    } finally {
      await localSession.close();
    }
  }

  async countRelationshipsToSync(since?: Date): Promise<number> {
    const localSession = this.localDriver.session();
    try {
      let query: string;
      let params: Record<string, unknown> = {};

      if (since) {
        // For relationships, we sync if either end node was updated
        query = `
          MATCH (a)-[r]->(b)
          WHERE a.updatedAt > $since OR b.updatedAt > $since
            OR a.createdAt > $since OR b.createdAt > $since
            OR NOT exists(a.updatedAt)
          RETURN count(r) as count
        `;
        params = { since: since.toISOString() };
      } else {
        query = 'MATCH ()-[r]->() RETURN count(r) as count';
      }

      const result = await localSession.run(query, params);
      return result.records[0].get('count').toNumber();
    } finally {
      await localSession.close();
    }
  }

  async syncNodesInParallel(since?: Date): Promise<void> {
    const localSession = this.localDriver.session();
    const totalNodes = await this.countNodesToSync(since);

    console.log(`\n📦 Syncing ${totalNodes} nodes (batch: ${this.config.batchSize}, parallel: ${this.config.parallelBatches})...`);

    if (totalNodes === 0) {
      console.log('  ✓ No nodes to sync');
      return;
    }

    let offset = 0;
    let processed = 0;
    const startTime = Date.now();

    try {
      while (offset < totalNodes) {
        // Fetch multiple batches worth of nodes
        const fetchSize = this.config.batchSize * this.config.parallelBatches;

        let query: string;
        let params: Record<string, unknown> = { skip: neo4j.int(offset), limit: neo4j.int(fetchSize) };

        if (since) {
          query = `
            MATCH (n)
            WHERE n.updatedAt > $since OR n.createdAt > $since OR NOT exists(n.updatedAt)
            RETURN n, labels(n) as labels, elementId(n) as elementId
            SKIP $skip LIMIT $limit
          `;
          params.since = since.toISOString();
        } else {
          query = `
            MATCH (n)
            RETURN n, labels(n) as labels, elementId(n) as elementId
            SKIP $skip LIMIT $limit
          `;
        }

        const result = await localSession.run(query, params);
        const nodes = result.records.map(r => ({
          properties: r.get('n').properties,
          labels: r.get('labels') as string[],
          elementId: r.get('elementId') as string
        }));

        if (nodes.length === 0) break;

        // Split into batches and process in parallel
        const batches: typeof nodes[] = [];
        for (let i = 0; i < nodes.length; i += this.config.batchSize) {
          batches.push(nodes.slice(i, i + this.config.batchSize));
        }

        // Process batches in parallel
        await Promise.all(batches.map(batch => this.importNodeBatch(batch)));

        processed += nodes.length;
        offset += fetchSize;

        const elapsed = (Date.now() - startTime) / 1000;
        const rate = Math.round(processed / elapsed);
        const eta = Math.round((totalNodes - processed) / rate);

        console.log(`  Progress: ${processed}/${totalNodes} (${rate} nodes/sec, ETA: ${eta}s)`);
      }

      this.stats.nodesCreated = processed;
      console.log(`  ✓ Synced ${processed} nodes in ${((Date.now() - startTime) / 1000).toFixed(1)}s`);
    } finally {
      await localSession.close();
    }
  }

  private async importNodeBatch(nodes: Array<{ properties: Record<string, unknown>; labels: string[]; elementId: string }>): Promise<void> {
    const cloudSession = this.cloudDriver.session();
    try {
      // Group nodes by label combination for efficient UNWIND
      const nodesByLabels = new Map<string, typeof nodes>();

      for (const node of nodes) {
        const labelKey = node.labels.sort().join(':');
        if (!nodesByLabels.has(labelKey)) {
          nodesByLabels.set(labelKey, []);
        }
        nodesByLabels.get(labelKey)!.push(node);
      }

      // Import each label group
      for (const [labelKey, labelNodes] of nodesByLabels) {
        const labels = labelKey || 'Node';
        const nodeData = labelNodes.map(n => ({
          ...n.properties,
          _syncId: n.elementId
        }));

        // Use MERGE to handle both create and update
        await cloudSession.run(`
          UNWIND $nodes as nodeData
          MERGE (n:${labels} {_syncId: nodeData._syncId})
          SET n = nodeData
        `, { nodes: nodeData });
      }
    } finally {
      await cloudSession.close();
    }
  }

  async syncRelationshipsInParallel(since?: Date): Promise<void> {
    const localSession = this.localDriver.session();
    const totalRels = await this.countRelationshipsToSync(since);

    console.log(`\n🔗 Syncing ${totalRels} relationships...`);

    if (totalRels === 0) {
      console.log('  ✓ No relationships to sync');
      return;
    }

    let offset = 0;
    let processed = 0;
    const startTime = Date.now();

    try {
      while (offset < totalRels) {
        const fetchSize = this.config.batchSize * this.config.parallelBatches;

        let query: string;
        let params: Record<string, unknown> = { skip: neo4j.int(offset), limit: neo4j.int(fetchSize) };

        if (since) {
          query = `
            MATCH (a)-[r]->(b)
            WHERE a.updatedAt > $since OR b.updatedAt > $since
              OR a.createdAt > $since OR b.createdAt > $since
              OR NOT exists(a.updatedAt)
            RETURN type(r) as type, properties(r) as props,
                   elementId(a) as startId, elementId(b) as endId
            SKIP $skip LIMIT $limit
          `;
          params.since = since.toISOString();
        } else {
          query = `
            MATCH (a)-[r]->(b)
            RETURN type(r) as type, properties(r) as props,
                   elementId(a) as startId, elementId(b) as endId
            SKIP $skip LIMIT $limit
          `;
        }

        const result = await localSession.run(query, params);
        const rels = result.records.map(r => ({
          type: r.get('type') as string,
          properties: r.get('props') as Record<string, unknown>,
          startId: r.get('startId') as string,
          endId: r.get('endId') as string
        }));

        if (rels.length === 0) break;

        // Split into batches and process in parallel
        const batches: typeof rels[] = [];
        for (let i = 0; i < rels.length; i += this.config.batchSize) {
          batches.push(rels.slice(i, i + this.config.batchSize));
        }

        // Process batches sequentially to avoid deadlocks
        for (const batch of batches) {
          await this.importRelationshipBatch(batch);
        }

        processed += rels.length;
        offset += fetchSize;

        const elapsed = (Date.now() - startTime) / 1000;
        const rate = Math.round(processed / elapsed);
        const eta = Math.round((totalRels - processed) / rate);

        console.log(`  Progress: ${processed}/${totalRels} (${rate} rels/sec, ETA: ${eta}s)`);
      }

      this.stats.relationshipsCreated = processed;
      console.log(`  ✓ Synced ${processed} relationships in ${((Date.now() - startTime) / 1000).toFixed(1)}s`);
    } finally {
      await localSession.close();
    }
  }

  private async importRelationshipBatch(rels: Array<{ type: string; properties: Record<string, unknown>; startId: string; endId: string }>): Promise<void> {
    const cloudSession = this.cloudDriver.session();
    try {
      // Group by relationship type
      const relsByType = new Map<string, typeof rels>();

      for (const rel of rels) {
        if (!relsByType.has(rel.type)) {
          relsByType.set(rel.type, []);
        }
        relsByType.get(rel.type)!.push(rel);
      }

      // Import each type
      for (const [relType, typeRels] of relsByType) {
        const relData = typeRels.map(r => ({
          startId: r.startId,
          endId: r.endId,
          props: r.properties
        }));

        await cloudSession.run(`
          UNWIND $rels as relData
          MATCH (a {_syncId: relData.startId})
          MATCH (b {_syncId: relData.endId})
          MERGE (a)-[r:${relType}]->(b)
          SET r = relData.props
        `, { rels: relData });
      }
    } finally {
      await cloudSession.close();
    }
  }

  async syncSchema(): Promise<void> {
    console.log('\n📋 Syncing schema...');
    const localSession = this.localDriver.session();
    const cloudSession = this.cloudDriver.session();

    try {
      // Get constraints from local - build CREATE statements from available fields
      const constraintsResult = await localSession.run('SHOW CONSTRAINTS');

      for (const record of constraintsResult.records) {
        const name = record.get('name');
        const constraintType = record.get('type');
        const entityType = record.get('entityType');
        const labelsOrTypes = record.get('labelsOrTypes') as string[];
        const properties = record.get('properties') as string[];

        if (!name || name.startsWith('_')) continue;

        // Build CREATE CONSTRAINT statement
        let createStatement = '';
        const label = labelsOrTypes?.[0] || 'Node';
        const prop = properties?.[0] || 'id';

        if (constraintType === 'UNIQUENESS' && entityType === 'NODE') {
          createStatement = `CREATE CONSTRAINT ${name} IF NOT EXISTS FOR (n:${label}) REQUIRE n.${prop} IS UNIQUE`;
        } else if (constraintType === 'NODE_KEY') {
          createStatement = `CREATE CONSTRAINT ${name} IF NOT EXISTS FOR (n:${label}) REQUIRE n.${prop} IS NODE KEY`;
        }

        if (createStatement) {
          try {
            await cloudSession.run(createStatement);
            console.log(`  ✓ Constraint: ${name}`);
          } catch (e: unknown) {
            const error = e as Error;
            if (!error.message?.includes('already exists') && !error.message?.includes('equivalent')) {
              console.log(`  ⚠ Constraint ${name}: ${error.message?.slice(0, 50)}`);
            }
          }
        }
      }

      // Get indexes - exclude LOOKUP and internal indexes
      const indexesResult = await localSession.run('SHOW INDEXES');

      for (const record of indexesResult.records) {
        const name = record.get('name');
        const indexType = record.get('type');
        const entityType = record.get('entityType');
        const labelsOrTypes = record.get('labelsOrTypes') as string[];
        const properties = record.get('properties') as string[];

        if (!name || name.startsWith('_') || indexType === 'LOOKUP') continue;

        const label = labelsOrTypes?.[0] || 'Node';
        const props = properties || [];

        let createStatement = '';

        if (indexType === 'RANGE' && entityType === 'NODE' && props.length > 0) {
          const propList = props.map(p => `n.${p}`).join(', ');
          createStatement = `CREATE INDEX ${name} IF NOT EXISTS FOR (n:${label}) ON (${propList})`;
        } else if (indexType === 'VECTOR' && props.length > 0) {
          // Skip vector indexes - they need special handling
          console.log(`  ⏭ Skipping vector index: ${name}`);
          continue;
        }

        if (createStatement) {
          try {
            await cloudSession.run(createStatement);
            console.log(`  ✓ Index: ${name} (${indexType})`);
          } catch (e: unknown) {
            const error = e as Error;
            if (!error.message?.includes('already exists') && !error.message?.includes('equivalent')) {
              console.log(`  ⚠ Index ${name}: ${error.message?.slice(0, 50)}`);
            }
          }
        }
      }

      // Ensure _syncId index exists for fast lookups
      try {
        await cloudSession.run('CREATE INDEX sync_id_index IF NOT EXISTS FOR (n:Node) ON (n._syncId)');
      } catch {
        // Ignore
      }
    } finally {
      await localSession.close();
      await cloudSession.close();
    }
  }

  async run(): Promise<SyncStats> {
    const startTime = Date.now();

    console.log('═'.repeat(60));
    console.log('⚡ Fast Neo4j Sync');
    console.log('═'.repeat(60));
    console.log(`\nLocal:  ${this.config.localUri}`);
    console.log(`Cloud:  ${this.config.cloudUri}`);
    console.log(`Mode:   ${this.config.incrementalOnly ? 'Incremental' : 'Full'}`);
    console.log(`Batch:  ${this.config.batchSize} nodes × ${this.config.parallelBatches} parallel`);

    await this.connect();

    let since: Date | undefined;

    if (this.config.incrementalOnly) {
      const lastSync = await this.getLastSyncTime();
      if (lastSync) {
        since = lastSync;
        console.log(`\n📅 Last sync: ${lastSync.toISOString()}`);
        console.log('   Only syncing changes since then...');
      } else {
        console.log('\n⚠️  No previous sync found, doing full sync...');
      }
    }

    await this.syncSchema();
    await this.syncNodesInParallel(since);
    await this.syncRelationshipsInParallel(since);

    // Record sync time
    await this.setLastSyncTime(new Date());

    this.stats.duration = Date.now() - startTime;

    console.log('\n' + '═'.repeat(60));
    console.log('✅ Sync Complete!');
    console.log('═'.repeat(60));
    console.log(`   Nodes: ${this.stats.nodesCreated}`);
    console.log(`   Relationships: ${this.stats.relationshipsCreated}`);
    console.log(`   Duration: ${(this.stats.duration / 1000).toFixed(1)}s`);
    console.log(`   Rate: ${Math.round((this.stats.nodesCreated + this.stats.relationshipsCreated) / (this.stats.duration / 1000))} items/sec`);

    return this.stats;
  }

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

// CLI
async function main() {
  const args = process.argv.slice(2);
  const incremental = args.includes('--incremental') || args.includes('-i');
  const help = args.includes('--help') || args.includes('-h');

  if (help) {
    console.log(`
Fast Neo4j Sync - Parallel batch sync with incremental support

Usage: npx tsx src/scripts/fast-neo4j-sync.ts [options]

Options:
  --incremental, -i  Only sync changes since last sync
  --help, -h         Show this help

Environment variables:
  NEO4J_LOCAL_URI       Local Neo4j URI (default: bolt://localhost:7687)
  NEO4J_LOCAL_USER      Local Neo4j user (default: neo4j)
  NEO4J_LOCAL_PASSWORD  Local Neo4j password
  NEO4J_CLOUD_URI       Cloud AuraDB URI
  NEO4J_CLOUD_USER      Cloud user (default: neo4j)
  NEO4J_CLOUD_PASSWORD  Cloud password
`);
    process.exit(0);
  }

  // Cloud URI from .env.production (NEO4J_URI contains the cloud AuraDB)
  const cloudUri = process.env.NEO4J_URI || '';
  const cloudPassword = process.env.NEO4J_PASSWORD || '';

  const syncConfig: SyncConfig = {
    localUri: process.env.NEO4J_LOCAL_URI || 'bolt://localhost:7687',
    localUser: process.env.NEO4J_LOCAL_USER || 'neo4j',
    localPassword: process.env.NEO4J_LOCAL_PASSWORD || 'password',  // Local default
    cloudUri: cloudUri,
    cloudUser: process.env.NEO4J_USER || 'neo4j',
    cloudPassword: cloudPassword,
    batchSize: 500,           // Larger batches
    parallelBatches: 4,       // 4 parallel operations
    incrementalOnly: incremental
  };

  if (!syncConfig.cloudUri) {
    console.error('❌ NEO4J_URI (cloud) is required in .env.production');
    process.exit(1);
  }

  const sync = new FastNeo4jSync(syncConfig);

  try {
    await sync.run();
  } finally {
    await sync.close();
  }
}

main().catch(console.error);