import * as plugins from '../plugins.js';
import type { IStorageAdapter } from '../storage/IStorageAdapter.js';

// Simple B-Tree implementation for range queries
// Since sorted-btree has ESM/CJS interop issues, we use a simple custom implementation
class SimpleBTree<K, V> {
  private entries: Map<string, { key: K; value: V }> = new Map();
  private sortedKeys: K[] = [];
  private comparator: (a: K, b: K) => number;

  constructor(_unused?: undefined, comparator?: (a: K, b: K) => number) {
    this.comparator = comparator || ((a: K, b: K) => {
      if (a < b) return -1;
      if (a > b) return 1;
      return 0;
    });
  }

  private keyToString(key: K): string {
    return JSON.stringify(key);
  }

  set(key: K, value: V): boolean {
    const keyStr = this.keyToString(key);
    const existed = this.entries.has(keyStr);
    this.entries.set(keyStr, { key, value });

    if (!existed) {
      // Insert in sorted order
      const idx = this.sortedKeys.findIndex(k => this.comparator(k, key) > 0);
      if (idx === -1) {
        this.sortedKeys.push(key);
      } else {
        this.sortedKeys.splice(idx, 0, key);
      }
    }
    return !existed;
  }

  get(key: K): V | undefined {
    const entry = this.entries.get(this.keyToString(key));
    return entry?.value;
  }

  delete(key: K): boolean {
    const keyStr = this.keyToString(key);
    if (this.entries.has(keyStr)) {
      this.entries.delete(keyStr);
      const idx = this.sortedKeys.findIndex(k => this.comparator(k, key) === 0);
      if (idx !== -1) {
        this.sortedKeys.splice(idx, 1);
      }
      return true;
    }
    return false;
  }

  forRange(
    lowKey: K | undefined,
    highKey: K | undefined,
    lowInclusive: boolean,
    highInclusive: boolean,
    callback: (value: V, key: K) => void
  ): void {
    for (const key of this.sortedKeys) {
      // Check low bound
      if (lowKey !== undefined) {
        const cmp = this.comparator(key, lowKey);
        if (cmp < 0) continue;
        if (cmp === 0 && !lowInclusive) continue;
      }

      // Check high bound
      if (highKey !== undefined) {
        const cmp = this.comparator(key, highKey);
        if (cmp > 0) break;
        if (cmp === 0 && !highInclusive) break;
      }

      const entry = this.entries.get(this.keyToString(key));
      if (entry) {
        callback(entry.value, key);
      }
    }
  }
}
import type {
  Document,
  IStoredDocument,
  IIndexSpecification,
  IIndexInfo,
  ICreateIndexOptions,
} from '../types/interfaces.js';
import { TsmdbDuplicateKeyError, TsmdbIndexError } from '../errors/TsmdbErrors.js';
import { QueryEngine } from './QueryEngine.js';

/**
 * Comparator for B-Tree that handles mixed types consistently
 */
function indexKeyComparator(a: any, b: any): number {
  // Handle null/undefined
  if (a === null || a === undefined) {
    if (b === null || b === undefined) return 0;
    return -1;
  }
  if (b === null || b === undefined) return 1;

  // Handle arrays (compound keys)
  if (Array.isArray(a) && Array.isArray(b)) {
    for (let i = 0; i < Math.max(a.length, b.length); i++) {
      const cmp = indexKeyComparator(a[i], b[i]);
      if (cmp !== 0) return cmp;
    }
    return 0;
  }

  // Handle ObjectId
  if (a instanceof plugins.bson.ObjectId && b instanceof plugins.bson.ObjectId) {
    return a.toHexString().localeCompare(b.toHexString());
  }

  // Handle Date
  if (a instanceof Date && b instanceof Date) {
    return a.getTime() - b.getTime();
  }

  // Handle different types - use type ordering (null < number < string < object)
  const typeOrder = (v: any): number => {
    if (v === null || v === undefined) return 0;
    if (typeof v === 'number') return 1;
    if (typeof v === 'string') return 2;
    if (typeof v === 'boolean') return 3;
    if (v instanceof Date) return 4;
    if (v instanceof plugins.bson.ObjectId) return 5;
    return 6;
  };

  const typeA = typeOrder(a);
  const typeB = typeOrder(b);
  if (typeA !== typeB) return typeA - typeB;

  // Same type comparison
  if (typeof a === 'number') return a - b;
  if (typeof a === 'string') return a.localeCompare(b);
  if (typeof a === 'boolean') return (a ? 1 : 0) - (b ? 1 : 0);

  // Fallback to string comparison
  return String(a).localeCompare(String(b));
}

/**
 * Index data structure using B-Tree for range queries
 */
interface IIndexData {
  name: string;
  key: Record<string, 1 | -1 | string>;
  unique: boolean;
  sparse: boolean;
  expireAfterSeconds?: number;
  // B-Tree for ordered index lookups (supports range queries)
  btree: SimpleBTree<any, Set<string>>;
  // Hash map for fast equality lookups
  hashMap: Map<string, Set<string>>;
}

/**
 * Index engine for managing indexes and query optimization
 */
export class IndexEngine {
  private dbName: string;
  private collName: string;
  private storage: IStorageAdapter;
  private indexes: Map<string, IIndexData> = new Map();
  private initialized = false;

  constructor(dbName: string, collName: string, storage: IStorageAdapter) {
    this.dbName = dbName;
    this.collName = collName;
    this.storage = storage;
  }

  /**
   * Initialize indexes from storage
   */
  async initialize(): Promise<void> {
    if (this.initialized) return;

    const storedIndexes = await this.storage.getIndexes(this.dbName, this.collName);
    const documents = await this.storage.findAll(this.dbName, this.collName);

    for (const indexSpec of storedIndexes) {
      const indexData: IIndexData = {
        name: indexSpec.name,
        key: indexSpec.key,
        unique: indexSpec.unique || false,
        sparse: indexSpec.sparse || false,
        expireAfterSeconds: indexSpec.expireAfterSeconds,
        btree: new SimpleBTree<any, Set<string>>(undefined, indexKeyComparator),
        hashMap: new Map(),
      };

      // Build index entries
      for (const doc of documents) {
        const keyValue = this.extractKeyValue(doc, indexSpec.key);
        if (keyValue !== null || !indexData.sparse) {
          const keyStr = JSON.stringify(keyValue);

          // Add to hash map
          if (!indexData.hashMap.has(keyStr)) {
            indexData.hashMap.set(keyStr, new Set());
          }
          indexData.hashMap.get(keyStr)!.add(doc._id.toHexString());

          // Add to B-tree
          const existing = indexData.btree.get(keyValue);
          if (existing) {
            existing.add(doc._id.toHexString());
          } else {
            indexData.btree.set(keyValue, new Set([doc._id.toHexString()]));
          }
        }
      }

      this.indexes.set(indexSpec.name, indexData);
    }

    this.initialized = true;
  }

  /**
   * Create a new index
   */
  async createIndex(
    key: Record<string, 1 | -1 | 'text' | '2dsphere'>,
    options?: ICreateIndexOptions
  ): Promise<string> {
    await this.initialize();

    // Generate index name if not provided
    const name = options?.name || this.generateIndexName(key);

    // Check if index already exists
    if (this.indexes.has(name)) {
      return name;
    }

    // Create index data structure
    const indexData: IIndexData = {
      name,
      key: key as Record<string, 1 | -1 | string>,
      unique: options?.unique || false,
      sparse: options?.sparse || false,
      expireAfterSeconds: options?.expireAfterSeconds,
      btree: new SimpleBTree<any, Set<string>>(undefined, indexKeyComparator),
      hashMap: new Map(),
    };

    // Build index from existing documents
    const documents = await this.storage.findAll(this.dbName, this.collName);

    for (const doc of documents) {
      const keyValue = this.extractKeyValue(doc, key);

      if (keyValue === null && indexData.sparse) {
        continue;
      }

      const keyStr = JSON.stringify(keyValue);

      if (indexData.unique && indexData.hashMap.has(keyStr)) {
        throw new TsmdbDuplicateKeyError(
          `E11000 duplicate key error index: ${this.dbName}.${this.collName}.$${name}`,
          key as Record<string, 1>,
          keyValue
        );
      }

      // Add to hash map
      if (!indexData.hashMap.has(keyStr)) {
        indexData.hashMap.set(keyStr, new Set());
      }
      indexData.hashMap.get(keyStr)!.add(doc._id.toHexString());

      // Add to B-tree
      const existing = indexData.btree.get(keyValue);
      if (existing) {
        existing.add(doc._id.toHexString());
      } else {
        indexData.btree.set(keyValue, new Set([doc._id.toHexString()]));
      }
    }

    // Store index
    this.indexes.set(name, indexData);
    await this.storage.saveIndex(this.dbName, this.collName, name, {
      key,
      unique: options?.unique,
      sparse: options?.sparse,
      expireAfterSeconds: options?.expireAfterSeconds,
    });

    return name;
  }

  /**
   * Drop an index
   */
  async dropIndex(name: string): Promise<void> {
    await this.initialize();

    if (name === '_id_') {
      throw new TsmdbIndexError('cannot drop _id index');
    }

    if (!this.indexes.has(name)) {
      throw new TsmdbIndexError(`index not found: ${name}`);
    }

    this.indexes.delete(name);
    await this.storage.dropIndex(this.dbName, this.collName, name);
  }

  /**
   * Drop all indexes except _id
   */
  async dropAllIndexes(): Promise<void> {
    await this.initialize();

    const names = Array.from(this.indexes.keys()).filter(n => n !== '_id_');
    for (const name of names) {
      this.indexes.delete(name);
      await this.storage.dropIndex(this.dbName, this.collName, name);
    }
  }

  /**
   * List all indexes
   */
  async listIndexes(): Promise<IIndexInfo[]> {
    await this.initialize();

    return Array.from(this.indexes.values()).map(idx => ({
      v: 2,
      key: idx.key,
      name: idx.name,
      unique: idx.unique || undefined,
      sparse: idx.sparse || undefined,
      expireAfterSeconds: idx.expireAfterSeconds,
    }));
  }

  /**
   * Check if an index exists
   */
  async indexExists(name: string): Promise<boolean> {
    await this.initialize();
    return this.indexes.has(name);
  }

  /**
   * Update index entries after document insert
   */
  async onInsert(doc: IStoredDocument): Promise<void> {
    await this.initialize();

    for (const [name, indexData] of this.indexes) {
      const keyValue = this.extractKeyValue(doc, indexData.key);

      if (keyValue === null && indexData.sparse) {
        continue;
      }

      const keyStr = JSON.stringify(keyValue);

      // Check unique constraint
      if (indexData.unique) {
        const existing = indexData.hashMap.get(keyStr);
        if (existing && existing.size > 0) {
          throw new TsmdbDuplicateKeyError(
            `E11000 duplicate key error collection: ${this.dbName}.${this.collName} index: ${name}`,
            indexData.key as Record<string, 1>,
            keyValue
          );
        }
      }

      // Add to hash map
      if (!indexData.hashMap.has(keyStr)) {
        indexData.hashMap.set(keyStr, new Set());
      }
      indexData.hashMap.get(keyStr)!.add(doc._id.toHexString());

      // Add to B-tree
      const btreeSet = indexData.btree.get(keyValue);
      if (btreeSet) {
        btreeSet.add(doc._id.toHexString());
      } else {
        indexData.btree.set(keyValue, new Set([doc._id.toHexString()]));
      }
    }
  }

  /**
   * Update index entries after document update
   */
  async onUpdate(oldDoc: IStoredDocument, newDoc: IStoredDocument): Promise<void> {
    await this.initialize();

    for (const [name, indexData] of this.indexes) {
      const oldKeyValue = this.extractKeyValue(oldDoc, indexData.key);
      const newKeyValue = this.extractKeyValue(newDoc, indexData.key);
      const oldKeyStr = JSON.stringify(oldKeyValue);
      const newKeyStr = JSON.stringify(newKeyValue);

      // Remove old entry if key changed
      if (oldKeyStr !== newKeyStr) {
        if (oldKeyValue !== null || !indexData.sparse) {
          // Remove from hash map
          const oldHashSet = indexData.hashMap.get(oldKeyStr);
          if (oldHashSet) {
            oldHashSet.delete(oldDoc._id.toHexString());
            if (oldHashSet.size === 0) {
              indexData.hashMap.delete(oldKeyStr);
            }
          }

          // Remove from B-tree
          const oldBtreeSet = indexData.btree.get(oldKeyValue);
          if (oldBtreeSet) {
            oldBtreeSet.delete(oldDoc._id.toHexString());
            if (oldBtreeSet.size === 0) {
              indexData.btree.delete(oldKeyValue);
            }
          }
        }

        // Add new entry
        if (newKeyValue !== null || !indexData.sparse) {
          // Check unique constraint
          if (indexData.unique) {
            const existing = indexData.hashMap.get(newKeyStr);
            if (existing && existing.size > 0) {
              throw new TsmdbDuplicateKeyError(
                `E11000 duplicate key error collection: ${this.dbName}.${this.collName} index: ${name}`,
                indexData.key as Record<string, 1>,
                newKeyValue
              );
            }
          }

          // Add to hash map
          if (!indexData.hashMap.has(newKeyStr)) {
            indexData.hashMap.set(newKeyStr, new Set());
          }
          indexData.hashMap.get(newKeyStr)!.add(newDoc._id.toHexString());

          // Add to B-tree
          const newBtreeSet = indexData.btree.get(newKeyValue);
          if (newBtreeSet) {
            newBtreeSet.add(newDoc._id.toHexString());
          } else {
            indexData.btree.set(newKeyValue, new Set([newDoc._id.toHexString()]));
          }
        }
      }
    }
  }

  /**
   * Update index entries after document delete
   */
  async onDelete(doc: IStoredDocument): Promise<void> {
    await this.initialize();

    for (const indexData of this.indexes.values()) {
      const keyValue = this.extractKeyValue(doc, indexData.key);

      if (keyValue === null && indexData.sparse) {
        continue;
      }

      const keyStr = JSON.stringify(keyValue);

      // Remove from hash map
      const hashSet = indexData.hashMap.get(keyStr);
      if (hashSet) {
        hashSet.delete(doc._id.toHexString());
        if (hashSet.size === 0) {
          indexData.hashMap.delete(keyStr);
        }
      }

      // Remove from B-tree
      const btreeSet = indexData.btree.get(keyValue);
      if (btreeSet) {
        btreeSet.delete(doc._id.toHexString());
        if (btreeSet.size === 0) {
          indexData.btree.delete(keyValue);
        }
      }
    }
  }

  /**
   * Find the best index for a query
   */
  selectIndex(filter: Document): { name: string; data: IIndexData } | null {
    if (!filter || Object.keys(filter).length === 0) {
      return null;
    }

    // Get filter fields and operators
    const filterInfo = this.analyzeFilter(filter);

    // Score each index
    let bestIndex: { name: string; data: IIndexData } | null = null;
    let bestScore = 0;

    for (const [name, indexData] of this.indexes) {
      const indexFields = Object.keys(indexData.key);
      let score = 0;

      // Count how many index fields can be used
      for (const field of indexFields) {
        const info = filterInfo.get(field);
        if (!info) break;

        // Equality is best
        if (info.equality) {
          score += 2;
        } else if (info.range) {
          // Range queries can use B-tree
          score += 1;
        } else if (info.in) {
          score += 1.5;
        } else {
          break;
        }
      }

      // Prefer unique indexes
      if (indexData.unique && score > 0) {
        score += 0.5;
      }

      if (score > bestScore) {
        bestScore = score;
        bestIndex = { name, data: indexData };
      }
    }

    return bestIndex;
  }

  /**
   * Analyze filter to extract field operators
   */
  private analyzeFilter(filter: Document): Map<string, { equality: boolean; range: boolean; in: boolean; ops: Record<string, any> }> {
    const result = new Map<string, { equality: boolean; range: boolean; in: boolean; ops: Record<string, any> }>();

    for (const [key, value] of Object.entries(filter)) {
      if (key.startsWith('$')) continue;

      const info = { equality: false, range: false, in: false, ops: {} as Record<string, any> };

      if (typeof value !== 'object' || value === null || value instanceof plugins.bson.ObjectId || value instanceof Date) {
        info.equality = true;
        info.ops['$eq'] = value;
      } else {
        const ops = value as Record<string, any>;
        if (ops.$eq !== undefined) {
          info.equality = true;
          info.ops['$eq'] = ops.$eq;
        }
        if (ops.$in !== undefined) {
          info.in = true;
          info.ops['$in'] = ops.$in;
        }
        if (ops.$gt !== undefined || ops.$gte !== undefined || ops.$lt !== undefined || ops.$lte !== undefined) {
          info.range = true;
          if (ops.$gt !== undefined) info.ops['$gt'] = ops.$gt;
          if (ops.$gte !== undefined) info.ops['$gte'] = ops.$gte;
          if (ops.$lt !== undefined) info.ops['$lt'] = ops.$lt;
          if (ops.$lte !== undefined) info.ops['$lte'] = ops.$lte;
        }
      }

      result.set(key, info);
    }

    return result;
  }

  /**
   * Use index to find candidate document IDs (supports range queries with B-tree)
   */
  async findCandidateIds(filter: Document): Promise<Set<string> | null> {
    await this.initialize();

    const index = this.selectIndex(filter);
    if (!index) return null;

    const filterInfo = this.analyzeFilter(filter);
    const indexFields = Object.keys(index.data.key);

    // For single-field indexes with range queries, use B-tree
    if (indexFields.length === 1) {
      const field = indexFields[0];
      const info = filterInfo.get(field);

      if (info) {
        // Handle equality using hash map (faster)
        if (info.equality) {
          const keyStr = JSON.stringify(info.ops['$eq']);
          return index.data.hashMap.get(keyStr) || new Set();
        }

        // Handle $in using hash map
        if (info.in) {
          const results = new Set<string>();
          for (const val of info.ops['$in']) {
            const keyStr = JSON.stringify(val);
            const ids = index.data.hashMap.get(keyStr);
            if (ids) {
              for (const id of ids) {
                results.add(id);
              }
            }
          }
          return results;
        }

        // Handle range queries using B-tree
        if (info.range) {
          return this.findRangeCandidates(index.data, info.ops);
        }
      }
    } else {
      // For compound indexes, use hash map with partial key matching
      const equalityValues: Record<string, any> = {};

      for (const field of indexFields) {
        const info = filterInfo.get(field);
        if (!info) break;

        if (info.equality) {
          equalityValues[field] = info.ops['$eq'];
        } else if (info.in) {
          // Handle $in with multiple lookups
          const results = new Set<string>();
          for (const val of info.ops['$in']) {
            equalityValues[field] = val;
            const keyStr = JSON.stringify(this.buildKeyValue(equalityValues, index.data.key));
            const ids = index.data.hashMap.get(keyStr);
            if (ids) {
              for (const id of ids) {
                results.add(id);
              }
            }
          }
          return results;
        } else {
          break; // Non-equality/in operator, stop here
        }
      }

      if (Object.keys(equalityValues).length > 0) {
        const keyStr = JSON.stringify(this.buildKeyValue(equalityValues, index.data.key));
        return index.data.hashMap.get(keyStr) || new Set();
      }
    }

    return null;
  }

  /**
   * Find candidates using B-tree range scan
   */
  private findRangeCandidates(indexData: IIndexData, ops: Record<string, any>): Set<string> {
    const results = new Set<string>();

    let lowKey: any = undefined;
    let highKey: any = undefined;
    let lowInclusive = true;
    let highInclusive = true;

    if (ops['$gt'] !== undefined) {
      lowKey = ops['$gt'];
      lowInclusive = false;
    }
    if (ops['$gte'] !== undefined) {
      lowKey = ops['$gte'];
      lowInclusive = true;
    }
    if (ops['$lt'] !== undefined) {
      highKey = ops['$lt'];
      highInclusive = false;
    }
    if (ops['$lte'] !== undefined) {
      highKey = ops['$lte'];
      highInclusive = true;
    }

    // Use B-tree range iteration
    indexData.btree.forRange(lowKey, highKey, lowInclusive, highInclusive, (value, key) => {
      if (value) {
        for (const id of value) {
          results.add(id);
        }
      }
    });

    return results;
  }

  // ============================================================================
  // Helper Methods
  // ============================================================================

  private generateIndexName(key: Record<string, any>): string {
    return Object.entries(key)
      .map(([field, dir]) => `${field}_${dir}`)
      .join('_');
  }

  private extractKeyValue(doc: Document, key: Record<string, any>): any {
    const values: any[] = [];

    for (const field of Object.keys(key)) {
      const value = QueryEngine.getNestedValue(doc, field);
      values.push(value === undefined ? null : value);
    }

    // For single-field index, return the value directly
    if (values.length === 1) {
      return values[0];
    }

    return values;
  }

  private buildKeyValue(values: Record<string, any>, key: Record<string, any>): any {
    const result: any[] = [];

    for (const field of Object.keys(key)) {
      result.push(values[field] !== undefined ? values[field] : null);
    }

    if (result.length === 1) {
      return result[0];
    }

    return result;
  }

  private getFilterFields(filter: Document, prefix = ''): string[] {
    const fields: string[] = [];

    for (const [key, value] of Object.entries(filter)) {
      if (key.startsWith('$')) {
        // Logical operator
        if (key === '$and' || key === '$or' || key === '$nor') {
          for (const subFilter of value as Document[]) {
            fields.push(...this.getFilterFields(subFilter, prefix));
          }
        }
      } else {
        const fullKey = prefix ? `${prefix}.${key}` : key;
        fields.push(fullKey);

        // Check for nested filters
        if (typeof value === 'object' && value !== null && !Array.isArray(value)) {
          const subKeys = Object.keys(value);
          if (subKeys.length > 0 && !subKeys[0].startsWith('$')) {
            fields.push(...this.getFilterFields(value, fullKey));
          }
        }
      }
    }

    return fields;
  }

  private getFilterValue(filter: Document, field: string): any {
    // Handle dot notation
    const parts = field.split('.');
    let current: any = filter;

    for (const part of parts) {
      if (current === null || current === undefined) {
        return undefined;
      }
      current = current[part];
    }

    return current;
  }
}