import type { Client as ElasticClient } from '@elastic/elasticsearch';
import {
  BatchOperation,
  BatchResult,
  DocumentOperation,
  SessionConfig,
} from './types.js';
import { Logger } from '../../core/observability/logger.js';
import { BulkOperationError } from '../../core/errors/elasticsearch-error.js';

/**
 * Document session for managing document lifecycle
 *
 * Tracks documents during a session and can clean up stale ones at the end.
 */
export class DocumentSession<T = unknown> {
  private operations: BatchOperation<T>[] = [];
  private seenDocuments = new Set<string>();
  private config: Required<SessionConfig>;
  private startTimestamp: Date;
  private isActive = false;

  constructor(
    private client: ElasticClient,
    private index: string,
    private logger: Logger,
    config: SessionConfig = {}
  ) {
    this.config = {
      onlyNew: config.onlyNew || false,
      fromTimestamp: config.fromTimestamp || new Date(),
      cleanupStale: config.cleanupStale !== false,
      batchSize: config.batchSize || 1000,
    };
    this.startTimestamp = new Date();
  }

  /**
   * Start the session
   */
  start(): this {
    if (this.isActive) {
      throw new Error('Session already active');
    }

    this.isActive = true;
    this.operations = [];
    this.seenDocuments.clear();
    this.startTimestamp = new Date();

    this.logger.debug('Document session started', {
      index: this.index,
      config: this.config,
    });

    return this;
  }

  /**
   * Add a document (upsert - create or update)
   */
  upsert(documentId: string, document: T): this {
    this.ensureActive();

    this.operations.push({
      operation: DocumentOperation.UPSERT,
      documentId,
      document,
    });

    this.seenDocuments.add(documentId);
    return this;
  }

  /**
   * Create a document (fails if exists)
   */
  create(documentId: string, document: T): this {
    this.ensureActive();

    this.operations.push({
      operation: DocumentOperation.CREATE,
      documentId,
      document,
    });

    this.seenDocuments.add(documentId);
    return this;
  }

  /**
   * Update a document (fails if doesn't exist)
   */
  update(documentId: string, document: T, version?: { seqNo: number; primaryTerm: number }): this {
    this.ensureActive();

    this.operations.push({
      operation: DocumentOperation.UPDATE,
      documentId,
      document,
      ...(version && {
        seqNo: version.seqNo,
        primaryTerm: version.primaryTerm,
      }),
    });

    this.seenDocuments.add(documentId);
    return this;
  }

  /**
   * Delete a document
   */
  delete(documentId: string): this {
    this.ensureActive();

    this.operations.push({
      operation: DocumentOperation.DELETE,
      documentId,
    });

    return this;
  }

  /**
   * Commit the session and execute all operations
   */
  async commit(): Promise<BatchResult> {
    this.ensureActive();

    try {
      // Execute batched operations
      const result = await this.executeBatch();

      // Clean up stale documents if configured
      if (this.config.cleanupStale) {
        await this.cleanupStaleDocuments();
      }

      this.isActive = false;

      this.logger.info('Session committed', {
        index: this.index,
        successful: result.successful,
        failed: result.failed,
        duration: Date.now() - this.startTimestamp.getTime(),
      });

      return result;
    } catch (error) {
      this.logger.error('Session commit failed', error as Error, {
        index: this.index,
        operationCount: this.operations.length,
      });
      throw error;
    }
  }

  /**
   * Rollback the session (discard all operations)
   */
  rollback(): void {
    this.operations = [];
    this.seenDocuments.clear();
    this.isActive = false;

    this.logger.debug('Session rolled back', { index: this.index });
  }

  /**
   * Execute batch operations
   */
  private async executeBatch(): Promise<BatchResult> {
    if (this.operations.length === 0) {
      return {
        successful: 0,
        failed: 0,
        errors: [],
        took: 0,
      };
    }

    const startTime = Date.now();
    const bulkBody: any[] = [];

    // Build bulk request body
    for (const op of this.operations) {
      switch (op.operation) {
        case DocumentOperation.CREATE:
          bulkBody.push({ create: { _index: this.index, _id: op.documentId } });
          bulkBody.push(op.document);
          break;

        case DocumentOperation.UPDATE:
          bulkBody.push({
            update: {
              _index: this.index,
              _id: op.documentId,
              ...(op.seqNo !== undefined && { if_seq_no: op.seqNo }),
              ...(op.primaryTerm !== undefined && { if_primary_term: op.primaryTerm }),
            },
          });
          bulkBody.push({ doc: op.document });
          break;

        case DocumentOperation.UPSERT:
          bulkBody.push({ index: { _index: this.index, _id: op.documentId } });
          bulkBody.push(op.document);
          break;

        case DocumentOperation.DELETE:
          bulkBody.push({ delete: { _index: this.index, _id: op.documentId } });
          break;
      }
    }

    // Execute bulk request
    const response = await this.client.bulk({
      body: bulkBody,
      refresh: true, // Make changes immediately visible
    });

    const took = Date.now() - startTime;

    // Process results
    let successful = 0;
    let failed = 0;
    const errors: Array<{
      documentId: string;
      operation: DocumentOperation;
      error: string;
      statusCode: number;
    }> = [];

    if (response.errors) {
      for (let i = 0; i < response.items.length; i++) {
        const item = response.items[i];
        const operation = this.operations[i];

        const action = Object.keys(item)[0];
        const result = item[action as keyof typeof item] as any;

        if (result.error) {
          failed++;
          errors.push({
            documentId: operation.documentId,
            operation: operation.operation,
            error: result.error.reason || result.error,
            statusCode: result.status,
          });
        } else {
          successful++;
        }
      }
    } else {
      successful = response.items.length;
    }

    const result: BatchResult = {
      successful,
      failed,
      errors,
      took,
    };

    if (failed > 0) {
      this.logger.warn('Batch operation had failures', {
        successful,
        failed,
        errors: errors.slice(0, 5), // Log first 5 errors
      });

      if (failed === this.operations.length) {
        // Complete failure
        throw new BulkOperationError(
          'All bulk operations failed',
          successful,
          failed,
          errors
        );
      }
    }

    return result;
  }

  /**
   * Clean up documents not seen in this session
   */
  private async cleanupStaleDocuments(): Promise<void> {
    if (this.seenDocuments.size === 0) {
      return; // No documents to keep, skip cleanup
    }

    this.logger.debug('Cleaning up stale documents', {
      index: this.index,
      seenCount: this.seenDocuments.size,
    });

    try {
      // Use deleteByQuery to remove documents not in seen set
      // This is more efficient than the old scroll-and-compare approach
      const seenIds = Array.from(this.seenDocuments);

      await this.client.deleteByQuery({
        index: this.index,
        body: {
          query: {
            bool: {
              must_not: {
                ids: {
                  values: seenIds,
                },
              },
            },
          },
        },
        refresh: true,
      });

      this.logger.debug('Stale documents cleaned up', { index: this.index });
    } catch (error) {
      this.logger.warn('Failed to cleanup stale documents', undefined, {
        index: this.index,
        error: (error as Error).message,
      });
      // Don't throw - cleanup is best-effort
    }
  }

  /**
   * Ensure session is active
   */
  private ensureActive(): void {
    if (!this.isActive) {
      throw new Error('Session not active. Call start() first.');
    }
  }

  /**
   * Get session statistics
   */
  getStats(): {
    isActive: boolean;
    operationCount: number;
    seenDocumentCount: number;
    startTime: Date;
  } {
    return {
      isActive: this.isActive,
      operationCount: this.operations.length,
      seenDocumentCount: this.seenDocuments.size,
      startTime: this.startTimestamp,
    };
  }
}