import * as plugins from '../../congodb.plugins.js';
import type { ICommandHandler, IHandlerContext, ICursorState } from '../CommandRouter.js';
import { AggregationEngine } from '../../engine/AggregationEngine.js';

/**
 * AggregateHandler - Handles aggregate command
 */
export class AggregateHandler implements ICommandHandler {
  private cursors: Map<bigint, ICursorState>;
  private nextCursorId: () => bigint;

  constructor(
    cursors: Map<bigint, ICursorState>,
    nextCursorId: () => bigint
  ) {
    this.cursors = cursors;
    this.nextCursorId = nextCursorId;
  }

  async handle(context: IHandlerContext): Promise<plugins.bson.Document> {
    const { storage, database, command } = context;

    const collection = command.aggregate;
    const pipeline = command.pipeline || [];
    const cursor = command.cursor || {};
    const batchSize = cursor.batchSize || 101;

    // Validate
    if (typeof collection !== 'string' && collection !== 1) {
      return {
        ok: 0,
        errmsg: 'aggregate command requires a collection name or 1',
        code: 2,
        codeName: 'BadValue',
      };
    }

    if (!Array.isArray(pipeline)) {
      return {
        ok: 0,
        errmsg: 'pipeline must be an array',
        code: 2,
        codeName: 'BadValue',
      };
    }

    try {
      // Get source documents
      let documents: plugins.bson.Document[] = [];

      if (collection === 1 || collection === '1') {
        // Database-level aggregation (e.g., $listLocalSessions)
        documents = [];
      } else {
        // Collection-level aggregation
        const exists = await storage.collectionExists(database, collection);
        if (exists) {
          documents = await storage.findAll(database, collection);
        }
      }

      // Handle $lookup and $graphLookup stages that reference other collections
      const processedPipeline = await this.preprocessPipeline(
        storage,
        database,
        pipeline,
        documents
      );

      // Run aggregation
      let results: plugins.bson.Document[];

      // Check for special stages that we handle manually
      if (this.hasSpecialStages(pipeline)) {
        results = await this.executeWithSpecialStages(
          storage,
          database,
          documents,
          pipeline
        );
      } else {
        results = AggregationEngine.aggregate(documents as any, processedPipeline);
      }

      // Handle $out and $merge stages
      const lastStage = pipeline[pipeline.length - 1];
      if (lastStage && lastStage.$out) {
        await this.handleOut(storage, database, results, lastStage.$out);
        return { ok: 1, cursor: { id: plugins.bson.Long.fromNumber(0), ns: `${database}.${collection}`, firstBatch: [] } };
      }

      if (lastStage && lastStage.$merge) {
        await this.handleMerge(storage, database, results, lastStage.$merge);
        return { ok: 1, cursor: { id: plugins.bson.Long.fromNumber(0), ns: `${database}.${collection}`, firstBatch: [] } };
      }

      // Build cursor response
      const effectiveBatchSize = Math.min(batchSize, results.length);
      const firstBatch = results.slice(0, effectiveBatchSize);
      const remaining = results.slice(effectiveBatchSize);

      let cursorId = BigInt(0);
      if (remaining.length > 0) {
        cursorId = this.nextCursorId();
        this.cursors.set(cursorId, {
          id: cursorId,
          database,
          collection: typeof collection === 'string' ? collection : '$cmd.aggregate',
          documents: remaining,
          position: 0,
          batchSize,
          createdAt: new Date(),
        });
      }

      return {
        ok: 1,
        cursor: {
          id: plugins.bson.Long.fromBigInt(cursorId),
          ns: `${database}.${typeof collection === 'string' ? collection : '$cmd.aggregate'}`,
          firstBatch,
        },
      };
    } catch (error: any) {
      return {
        ok: 0,
        errmsg: error.message || 'Aggregation failed',
        code: 1,
        codeName: 'InternalError',
      };
    }
  }

  /**
   * Preprocess pipeline to handle cross-collection lookups
   */
  private async preprocessPipeline(
    storage: any,
    database: string,
    pipeline: plugins.bson.Document[],
    documents: plugins.bson.Document[]
  ): Promise<plugins.bson.Document[]> {
    // For now, return the pipeline as-is
    // Cross-collection lookups are handled in executeWithSpecialStages
    return pipeline;
  }

  /**
   * Check if pipeline has stages that need special handling
   */
  private hasSpecialStages(pipeline: plugins.bson.Document[]): boolean {
    return pipeline.some(stage =>
      stage.$lookup ||
      stage.$graphLookup ||
      stage.$unionWith
    );
  }

  /**
   * Execute pipeline with special stage handling
   */
  private async executeWithSpecialStages(
    storage: any,
    database: string,
    documents: plugins.bson.Document[],
    pipeline: plugins.bson.Document[]
  ): Promise<plugins.bson.Document[]> {
    let results: plugins.bson.Document[] = [...documents];

    for (const stage of pipeline) {
      if (stage.$lookup) {
        const lookupSpec = stage.$lookup;
        const fromCollection = lookupSpec.from;

        // Get foreign collection documents
        const foreignExists = await storage.collectionExists(database, fromCollection);
        const foreignDocs = foreignExists
          ? await storage.findAll(database, fromCollection)
          : [];

        results = AggregationEngine.executeLookup(results as any, lookupSpec, foreignDocs);
      } else if (stage.$graphLookup) {
        const graphLookupSpec = stage.$graphLookup;
        const fromCollection = graphLookupSpec.from;

        const foreignExists = await storage.collectionExists(database, fromCollection);
        const foreignDocs = foreignExists
          ? await storage.findAll(database, fromCollection)
          : [];

        results = AggregationEngine.executeGraphLookup(results as any, graphLookupSpec, foreignDocs);
      } else if (stage.$unionWith) {
        let unionSpec = stage.$unionWith;
        let unionColl: string;
        let unionPipeline: plugins.bson.Document[] | undefined;

        if (typeof unionSpec === 'string') {
          unionColl = unionSpec;
        } else {
          unionColl = unionSpec.coll;
          unionPipeline = unionSpec.pipeline;
        }

        const unionExists = await storage.collectionExists(database, unionColl);
        const unionDocs = unionExists
          ? await storage.findAll(database, unionColl)
          : [];

        results = AggregationEngine.executeUnionWith(results as any, unionDocs, unionPipeline);
      } else if (stage.$facet) {
        // Execute each facet pipeline separately
        const facetResults: plugins.bson.Document = {};

        for (const [facetName, facetPipeline] of Object.entries(stage.$facet)) {
          const facetDocs = await this.executeWithSpecialStages(
            storage,
            database,
            results,
            facetPipeline as plugins.bson.Document[]
          );
          facetResults[facetName] = facetDocs;
        }

        results = [facetResults];
      } else {
        // Regular stage - pass to mingo
        results = AggregationEngine.aggregate(results as any, [stage]);
      }
    }

    return results;
  }

  /**
   * Handle $out stage - write results to a collection
   */
  private async handleOut(
    storage: any,
    database: string,
    results: plugins.bson.Document[],
    outSpec: string | { db?: string; coll: string }
  ): Promise<void> {
    let targetDb = database;
    let targetColl: string;

    if (typeof outSpec === 'string') {
      targetColl = outSpec;
    } else {
      targetDb = outSpec.db || database;
      targetColl = outSpec.coll;
    }

    // Drop existing collection
    await storage.dropCollection(targetDb, targetColl);

    // Create new collection and insert results
    await storage.createCollection(targetDb, targetColl);

    for (const doc of results) {
      if (!doc._id) {
        doc._id = new plugins.bson.ObjectId();
      }
      await storage.insertOne(targetDb, targetColl, doc);
    }
  }

  /**
   * Handle $merge stage - merge results into a collection
   */
  private async handleMerge(
    storage: any,
    database: string,
    results: plugins.bson.Document[],
    mergeSpec: any
  ): Promise<void> {
    let targetDb = database;
    let targetColl: string;

    if (typeof mergeSpec === 'string') {
      targetColl = mergeSpec;
    } else if (typeof mergeSpec.into === 'string') {
      targetColl = mergeSpec.into;
    } else {
      targetDb = mergeSpec.into.db || database;
      targetColl = mergeSpec.into.coll;
    }

    const on = mergeSpec.on || '_id';
    const whenMatched = mergeSpec.whenMatched || 'merge';
    const whenNotMatched = mergeSpec.whenNotMatched || 'insert';

    // Ensure target collection exists
    await storage.createCollection(targetDb, targetColl);

    for (const doc of results) {
      // Find matching document
      const existingDocs = await storage.findAll(targetDb, targetColl);
      const onFields = Array.isArray(on) ? on : [on];

      let matchingDoc = null;
      for (const existing of existingDocs) {
        let matches = true;
        for (const field of onFields) {
          if (JSON.stringify(existing[field]) !== JSON.stringify(doc[field])) {
            matches = false;
            break;
          }
        }
        if (matches) {
          matchingDoc = existing;
          break;
        }
      }

      if (matchingDoc) {
        // Handle whenMatched
        if (whenMatched === 'replace') {
          await storage.updateById(targetDb, targetColl, matchingDoc._id, doc);
        } else if (whenMatched === 'keepExisting') {
          // Do nothing
        } else if (whenMatched === 'merge') {
          const merged = { ...matchingDoc, ...doc };
          await storage.updateById(targetDb, targetColl, matchingDoc._id, merged);
        } else if (whenMatched === 'fail') {
          throw new Error('Document matched but whenMatched is fail');
        }
      } else {
        // Handle whenNotMatched
        if (whenNotMatched === 'insert') {
          if (!doc._id) {
            doc._id = new plugins.bson.ObjectId();
          }
          await storage.insertOne(targetDb, targetColl, doc);
        } else if (whenNotMatched === 'discard') {
          // Do nothing
        } else if (whenNotMatched === 'fail') {
          throw new Error('Document not matched but whenNotMatched is fail');
        }
      }
    }
  }
}