/**
 * Database Queries
 *
 * Prepared statements for CRUD operations on the knowledge graph.
 */

import Database from 'better-sqlite3';
import {
  Node,
  Edge,
  FileRecord,
  UnresolvedReference,
  NodeKind,
  EdgeKind,
  Language,
  GraphStats,
  SearchOptions,
  SearchResult,
} from '../types';

/**
 * Database row types (snake_case from SQLite)
 */
interface NodeRow {
  id: string;
  kind: string;
  name: string;
  qualified_name: string;
  file_path: string;
  language: string;
  start_line: number;
  end_line: number;
  start_column: number;
  end_column: number;
  docstring: string | null;
  signature: string | null;
  visibility: string | null;
  is_exported: number;
  is_async: number;
  is_static: number;
  is_abstract: number;
  decorators: string | null;
  type_parameters: string | null;
  updated_at: number;
}

interface EdgeRow {
  id: number;
  source: string;
  target: string;
  kind: string;
  metadata: string | null;
  line: number | null;
  col: number | null;
}

interface FileRow {
  path: string;
  content_hash: string;
  language: string;
  size: number;
  modified_at: number;
  indexed_at: number;
  node_count: number;
  errors: string | null;
}

interface UnresolvedRefRow {
  id: number;
  from_node_id: string;
  reference_name: string;
  reference_kind: string;
  line: number;
  col: number;
  candidates: string | null;
}

/**
 * Convert database row to Node object
 */
function rowToNode(row: NodeRow): Node {
  return {
    id: row.id,
    kind: row.kind as NodeKind,
    name: row.name,
    qualifiedName: row.qualified_name,
    filePath: row.file_path,
    language: row.language as Language,
    startLine: row.start_line,
    endLine: row.end_line,
    startColumn: row.start_column,
    endColumn: row.end_column,
    docstring: row.docstring ?? undefined,
    signature: row.signature ?? undefined,
    visibility: row.visibility as Node['visibility'],
    isExported: row.is_exported === 1,
    isAsync: row.is_async === 1,
    isStatic: row.is_static === 1,
    isAbstract: row.is_abstract === 1,
    decorators: row.decorators ? JSON.parse(row.decorators) : undefined,
    typeParameters: row.type_parameters ? JSON.parse(row.type_parameters) : undefined,
    updatedAt: row.updated_at,
  };
}

/**
 * Convert database row to Edge object
 */
function rowToEdge(row: EdgeRow): Edge {
  return {
    source: row.source,
    target: row.target,
    kind: row.kind as EdgeKind,
    metadata: row.metadata ? JSON.parse(row.metadata) : undefined,
    line: row.line ?? undefined,
    column: row.col ?? undefined,
  };
}

/**
 * Convert database row to FileRecord object
 */
function rowToFileRecord(row: FileRow): FileRecord {
  return {
    path: row.path,
    contentHash: row.content_hash,
    language: row.language as Language,
    size: row.size,
    modifiedAt: row.modified_at,
    indexedAt: row.indexed_at,
    nodeCount: row.node_count,
    errors: row.errors ? JSON.parse(row.errors) : undefined,
  };
}

/**
 * Query builder for the knowledge graph database
 */
export class QueryBuilder {
  private db: Database.Database;

  // Node cache for frequently accessed nodes (LRU-style, max 1000 entries)
  private nodeCache: Map<string, Node> = new Map();
  private readonly maxCacheSize = 1000;

  // Prepared statements (lazily initialized)
  private stmts: {
    insertNode?: Database.Statement;
    updateNode?: Database.Statement;
    deleteNode?: Database.Statement;
    deleteNodesByFile?: Database.Statement;
    getNodeById?: Database.Statement;
    getNodesByFile?: Database.Statement;
    getNodesByKind?: Database.Statement;
    insertEdge?: Database.Statement;
    upsertFile?: Database.Statement;
    deleteEdgesBySource?: Database.Statement;
    deleteEdgesByTarget?: Database.Statement;
    getEdgesBySource?: Database.Statement;
    getEdgesByTarget?: Database.Statement;
    insertFile?: Database.Statement;
    updateFile?: Database.Statement;
    deleteFile?: Database.Statement;
    getFileByPath?: Database.Statement;
    getAllFiles?: Database.Statement;
    insertUnresolved?: Database.Statement;
    deleteUnresolvedByNode?: Database.Statement;
    getUnresolvedByName?: Database.Statement;
  } = {};

  constructor(db: Database.Database) {
    this.db = db;
  }

  // ===========================================================================
  // Node Operations
  // ===========================================================================

  /**
   * Insert a new node
   */
  insertNode(node: Node): void {
    if (!this.stmts.insertNode) {
      this.stmts.insertNode = this.db.prepare(`
        INSERT INTO nodes (
          id, kind, name, qualified_name, file_path, language,
          start_line, end_line, start_column, end_column,
          docstring, signature, visibility,
          is_exported, is_async, is_static, is_abstract,
          decorators, type_parameters, updated_at
        ) VALUES (
          @id, @kind, @name, @qualifiedName, @filePath, @language,
          @startLine, @endLine, @startColumn, @endColumn,
          @docstring, @signature, @visibility,
          @isExported, @isAsync, @isStatic, @isAbstract,
          @decorators, @typeParameters, @updatedAt
        )
      `);
    }

    this.stmts.insertNode.run({
      id: node.id,
      kind: node.kind,
      name: node.name,
      qualifiedName: node.qualifiedName,
      filePath: node.filePath,
      language: node.language,
      startLine: node.startLine,
      endLine: node.endLine,
      startColumn: node.startColumn,
      endColumn: node.endColumn,
      docstring: node.docstring ?? null,
      signature: node.signature ?? null,
      visibility: node.visibility ?? null,
      isExported: node.isExported ? 1 : 0,
      isAsync: node.isAsync ? 1 : 0,
      isStatic: node.isStatic ? 1 : 0,
      isAbstract: node.isAbstract ? 1 : 0,
      decorators: node.decorators ? JSON.stringify(node.decorators) : null,
      typeParameters: node.typeParameters ? JSON.stringify(node.typeParameters) : null,
      updatedAt: node.updatedAt,
    });
  }

  /**
   * Insert multiple nodes in a transaction
   */
  insertNodes(nodes: Node[]): void {
    this.db.transaction(() => {
      for (const node of nodes) {
        this.insertNode(node);
      }
    })();
  }

  /**
   * Update an existing node
   */
  updateNode(node: Node): void {
    if (!this.stmts.updateNode) {
      this.stmts.updateNode = this.db.prepare(`
        UPDATE nodes SET
          kind = @kind,
          name = @name,
          qualified_name = @qualifiedName,
          file_path = @filePath,
          language = @language,
          start_line = @startLine,
          end_line = @endLine,
          start_column = @startColumn,
          end_column = @endColumn,
          docstring = @docstring,
          signature = @signature,
          visibility = @visibility,
          is_exported = @isExported,
          is_async = @isAsync,
          is_static = @isStatic,
          is_abstract = @isAbstract,
          decorators = @decorators,
          type_parameters = @typeParameters,
          updated_at = @updatedAt
        WHERE id = @id
      `);
    }

    // Invalidate cache before update
    this.nodeCache.delete(node.id);

    this.stmts.updateNode.run({
      id: node.id,
      kind: node.kind,
      name: node.name,
      qualifiedName: node.qualifiedName,
      filePath: node.filePath,
      language: node.language,
      startLine: node.startLine,
      endLine: node.endLine,
      startColumn: node.startColumn,
      endColumn: node.endColumn,
      docstring: node.docstring ?? null,
      signature: node.signature ?? null,
      visibility: node.visibility ?? null,
      isExported: node.isExported ? 1 : 0,
      isAsync: node.isAsync ? 1 : 0,
      isStatic: node.isStatic ? 1 : 0,
      isAbstract: node.isAbstract ? 1 : 0,
      decorators: node.decorators ? JSON.stringify(node.decorators) : null,
      typeParameters: node.typeParameters ? JSON.stringify(node.typeParameters) : null,
      updatedAt: node.updatedAt,
    });
  }

  /**
   * Delete a node by ID
   */
  deleteNode(id: string): void {
    if (!this.stmts.deleteNode) {
      this.stmts.deleteNode = this.db.prepare('DELETE FROM nodes WHERE id = ?');
    }
    // Invalidate cache
    this.nodeCache.delete(id);
    this.stmts.deleteNode.run(id);
  }

  /**
   * Delete all nodes for a file
   */
  deleteNodesByFile(filePath: string): void {
    if (!this.stmts.deleteNodesByFile) {
      this.stmts.deleteNodesByFile = this.db.prepare('DELETE FROM nodes WHERE file_path = ?');
    }
    // Invalidate cache for nodes in this file
    for (const [id, node] of this.nodeCache) {
      if (node.filePath === filePath) {
        this.nodeCache.delete(id);
      }
    }
    this.stmts.deleteNodesByFile.run(filePath);
  }

  /**
   * Get a node by ID
   */
  getNodeById(id: string): Node | null {
    // Check cache first
    if (this.nodeCache.has(id)) {
      const cached = this.nodeCache.get(id)!;
      // Move to end to implement LRU (delete and re-add)
      this.nodeCache.delete(id);
      this.nodeCache.set(id, cached);
      return cached;
    }

    if (!this.stmts.getNodeById) {
      this.stmts.getNodeById = this.db.prepare('SELECT * FROM nodes WHERE id = ?');
    }
    const row = this.stmts.getNodeById.get(id) as NodeRow | undefined;
    if (!row) {
      return null;
    }

    const node = rowToNode(row);
    this.cacheNode(node);
    return node;
  }

  /**
   * Add a node to the cache, evicting oldest if needed
   */
  private cacheNode(node: Node): void {
    if (this.nodeCache.size >= this.maxCacheSize) {
      // Evict oldest (first) entry
      const firstKey = this.nodeCache.keys().next().value;
      if (firstKey) {
        this.nodeCache.delete(firstKey);
      }
    }
    this.nodeCache.set(node.id, node);
  }

  /**
   * Clear the node cache
   */
  clearCache(): void {
    this.nodeCache.clear();
  }

  /**
   * Get all nodes in a file
   */
  getNodesByFile(filePath: string): Node[] {
    if (!this.stmts.getNodesByFile) {
      this.stmts.getNodesByFile = this.db.prepare(
        'SELECT * FROM nodes WHERE file_path = ? ORDER BY start_line'
      );
    }
    const rows = this.stmts.getNodesByFile.all(filePath) as NodeRow[];
    return rows.map(rowToNode);
  }

  /**
   * Get all nodes of a specific kind
   */
  getNodesByKind(kind: NodeKind): Node[] {
    if (!this.stmts.getNodesByKind) {
      this.stmts.getNodesByKind = this.db.prepare('SELECT * FROM nodes WHERE kind = ?');
    }
    const rows = this.stmts.getNodesByKind.all(kind) as NodeRow[];
    return rows.map(rowToNode);
  }

  /**
   * Search nodes by name using FTS
   */
  searchNodes(query: string, options: SearchOptions = {}): SearchResult[] {
    const { kinds, languages, limit = 100, offset = 0 } = options;

    let sql = `
      SELECT nodes.*, bm25(nodes_fts) as score
      FROM nodes_fts
      JOIN nodes ON nodes_fts.id = nodes.id
      WHERE nodes_fts MATCH ?
    `;

    const params: (string | number)[] = [query];

    if (kinds && kinds.length > 0) {
      sql += ` AND nodes.kind IN (${kinds.map(() => '?').join(',')})`;
      params.push(...kinds);
    }

    if (languages && languages.length > 0) {
      sql += ` AND nodes.language IN (${languages.map(() => '?').join(',')})`;
      params.push(...languages);
    }

    sql += ' ORDER BY score LIMIT ? OFFSET ?';
    params.push(limit, offset);

    const rows = this.db.prepare(sql).all(...params) as (NodeRow & { score: number })[];

    return rows.map((row) => ({
      node: rowToNode(row),
      score: Math.abs(row.score), // bm25 returns negative scores
    }));
  }

  // ===========================================================================
  // Edge Operations
  // ===========================================================================

  /**
   * Insert a new edge
   */
  insertEdge(edge: Edge): void {
    if (!this.stmts.insertEdge) {
      this.stmts.insertEdge = this.db.prepare(`
        INSERT INTO edges (source, target, kind, metadata, line, col)
        VALUES (@source, @target, @kind, @metadata, @line, @col)
      `);
    }

    this.stmts.insertEdge.run({
      source: edge.source,
      target: edge.target,
      kind: edge.kind,
      metadata: edge.metadata ? JSON.stringify(edge.metadata) : null,
      line: edge.line ?? null,
      col: edge.column ?? null,
    });
  }

  /**
   * Insert multiple edges in a transaction
   */
  insertEdges(edges: Edge[]): void {
    this.db.transaction(() => {
      for (const edge of edges) {
        this.insertEdge(edge);
      }
    })();
  }

  /**
   * Delete all edges from a source node
   */
  deleteEdgesBySource(sourceId: string): void {
    if (!this.stmts.deleteEdgesBySource) {
      this.stmts.deleteEdgesBySource = this.db.prepare('DELETE FROM edges WHERE source = ?');
    }
    this.stmts.deleteEdgesBySource.run(sourceId);
  }

  /**
   * Get outgoing edges from a node
   */
  getOutgoingEdges(sourceId: string, kinds?: EdgeKind[]): Edge[] {
    if (kinds && kinds.length > 0) {
      const sql = `SELECT * FROM edges WHERE source = ? AND kind IN (${kinds.map(() => '?').join(',')})`;
      const rows = this.db.prepare(sql).all(sourceId, ...kinds) as EdgeRow[];
      return rows.map(rowToEdge);
    }

    if (!this.stmts.getEdgesBySource) {
      this.stmts.getEdgesBySource = this.db.prepare('SELECT * FROM edges WHERE source = ?');
    }
    const rows = this.stmts.getEdgesBySource.all(sourceId) as EdgeRow[];
    return rows.map(rowToEdge);
  }

  /**
   * Get incoming edges to a node
   */
  getIncomingEdges(targetId: string, kinds?: EdgeKind[]): Edge[] {
    if (kinds && kinds.length > 0) {
      const sql = `SELECT * FROM edges WHERE target = ? AND kind IN (${kinds.map(() => '?').join(',')})`;
      const rows = this.db.prepare(sql).all(targetId, ...kinds) as EdgeRow[];
      return rows.map(rowToEdge);
    }

    if (!this.stmts.getEdgesByTarget) {
      this.stmts.getEdgesByTarget = this.db.prepare('SELECT * FROM edges WHERE target = ?');
    }
    const rows = this.stmts.getEdgesByTarget.all(targetId) as EdgeRow[];
    return rows.map(rowToEdge);
  }

  // ===========================================================================
  // File Operations
  // ===========================================================================

  /**
   * Insert or update a file record
   */
  upsertFile(file: FileRecord): void {
    if (!this.stmts.upsertFile) {
      this.stmts.upsertFile = this.db.prepare(`
        INSERT INTO files (path, content_hash, language, size, modified_at, indexed_at, node_count, errors)
        VALUES (@path, @contentHash, @language, @size, @modifiedAt, @indexedAt, @nodeCount, @errors)
        ON CONFLICT(path) DO UPDATE SET
          content_hash = @contentHash,
          language = @language,
          size = @size,
          modified_at = @modifiedAt,
          indexed_at = @indexedAt,
          node_count = @nodeCount,
          errors = @errors
      `);
    }

    this.stmts.upsertFile.run({
      path: file.path,
      contentHash: file.contentHash,
      language: file.language,
      size: file.size,
      modifiedAt: file.modifiedAt,
      indexedAt: file.indexedAt,
      nodeCount: file.nodeCount,
      errors: file.errors ? JSON.stringify(file.errors) : null,
    });
  }

  /**
   * Delete a file record and its nodes
   */
  deleteFile(filePath: string): void {
    this.db.transaction(() => {
      this.deleteNodesByFile(filePath);
      if (!this.stmts.deleteFile) {
        this.stmts.deleteFile = this.db.prepare('DELETE FROM files WHERE path = ?');
      }
      this.stmts.deleteFile.run(filePath);
    })();
  }

  /**
   * Get a file record by path
   */
  getFileByPath(filePath: string): FileRecord | null {
    if (!this.stmts.getFileByPath) {
      this.stmts.getFileByPath = this.db.prepare('SELECT * FROM files WHERE path = ?');
    }
    const row = this.stmts.getFileByPath.get(filePath) as FileRow | undefined;
    return row ? rowToFileRecord(row) : null;
  }

  /**
   * Get all tracked files
   */
  getAllFiles(): FileRecord[] {
    if (!this.stmts.getAllFiles) {
      this.stmts.getAllFiles = this.db.prepare('SELECT * FROM files ORDER BY path');
    }
    const rows = this.stmts.getAllFiles.all() as FileRow[];
    return rows.map(rowToFileRecord);
  }

  /**
   * Get files that need re-indexing (hash changed)
   */
  getStaleFiles(currentHashes: Map<string, string>): FileRecord[] {
    const files = this.getAllFiles();
    return files.filter((f) => {
      const currentHash = currentHashes.get(f.path);
      return currentHash && currentHash !== f.contentHash;
    });
  }

  // ===========================================================================
  // Unresolved References
  // ===========================================================================

  /**
   * Insert an unresolved reference
   */
  insertUnresolvedRef(ref: UnresolvedReference): void {
    if (!this.stmts.insertUnresolved) {
      this.stmts.insertUnresolved = this.db.prepare(`
        INSERT INTO unresolved_refs (from_node_id, reference_name, reference_kind, line, col, candidates)
        VALUES (@fromNodeId, @referenceName, @referenceKind, @line, @col, @candidates)
      `);
    }

    this.stmts.insertUnresolved.run({
      fromNodeId: ref.fromNodeId,
      referenceName: ref.referenceName,
      referenceKind: ref.referenceKind,
      line: ref.line,
      col: ref.column,
      candidates: ref.candidates ? JSON.stringify(ref.candidates) : null,
    });
  }

  /**
   * Delete unresolved references from a node
   */
  deleteUnresolvedByNode(nodeId: string): void {
    if (!this.stmts.deleteUnresolvedByNode) {
      this.stmts.deleteUnresolvedByNode = this.db.prepare(
        'DELETE FROM unresolved_refs WHERE from_node_id = ?'
      );
    }
    this.stmts.deleteUnresolvedByNode.run(nodeId);
  }

  /**
   * Get unresolved references by name (for resolution)
   */
  getUnresolvedByName(name: string): UnresolvedReference[] {
    if (!this.stmts.getUnresolvedByName) {
      this.stmts.getUnresolvedByName = this.db.prepare(
        'SELECT * FROM unresolved_refs WHERE reference_name = ?'
      );
    }
    const rows = this.stmts.getUnresolvedByName.all(name) as UnresolvedRefRow[];
    return rows.map((row) => ({
      fromNodeId: row.from_node_id,
      referenceName: row.reference_name,
      referenceKind: row.reference_kind as EdgeKind,
      line: row.line,
      column: row.col,
      candidates: row.candidates ? JSON.parse(row.candidates) : undefined,
    }));
  }

  /**
   * Get all unresolved references
   */
  getUnresolvedReferences(): UnresolvedReference[] {
    const rows = this.db.prepare('SELECT * FROM unresolved_refs').all() as UnresolvedRefRow[];
    return rows.map((row) => ({
      fromNodeId: row.from_node_id,
      referenceName: row.reference_name,
      referenceKind: row.reference_kind as EdgeKind,
      line: row.line,
      column: row.col,
      candidates: row.candidates ? JSON.parse(row.candidates) : undefined,
    }));
  }

  /**
   * Delete all unresolved references (after resolution)
   */
  clearUnresolvedReferences(): void {
    this.db.exec('DELETE FROM unresolved_refs');
  }

  /**
   * Delete resolved references by their IDs
   */
  deleteResolvedReferences(fromNodeIds: string[]): void {
    if (fromNodeIds.length === 0) return;
    const placeholders = fromNodeIds.map(() => '?').join(',');
    this.db.prepare(`DELETE FROM unresolved_refs WHERE from_node_id IN (${placeholders})`).run(...fromNodeIds);
  }

  // ===========================================================================
  // Statistics
  // ===========================================================================

  /**
   * Get graph statistics
   */
  getStats(): GraphStats {
    const nodeCount = (
      this.db.prepare('SELECT COUNT(*) as count FROM nodes').get() as { count: number }
    ).count;

    const edgeCount = (
      this.db.prepare('SELECT COUNT(*) as count FROM edges').get() as { count: number }
    ).count;

    const fileCount = (
      this.db.prepare('SELECT COUNT(*) as count FROM files').get() as { count: number }
    ).count;

    const nodesByKind = {} as Record<NodeKind, number>;
    const nodeKindRows = this.db
      .prepare('SELECT kind, COUNT(*) as count FROM nodes GROUP BY kind')
      .all() as Array<{ kind: string; count: number }>;
    for (const row of nodeKindRows) {
      nodesByKind[row.kind as NodeKind] = row.count;
    }

    const edgesByKind = {} as Record<EdgeKind, number>;
    const edgeKindRows = this.db
      .prepare('SELECT kind, COUNT(*) as count FROM edges GROUP BY kind')
      .all() as Array<{ kind: string; count: number }>;
    for (const row of edgeKindRows) {
      edgesByKind[row.kind as EdgeKind] = row.count;
    }

    const filesByLanguage = {} as Record<Language, number>;
    const languageRows = this.db
      .prepare('SELECT language, COUNT(*) as count FROM files GROUP BY language')
      .all() as Array<{ language: string; count: number }>;
    for (const row of languageRows) {
      filesByLanguage[row.language as Language] = row.count;
    }

    return {
      nodeCount,
      edgeCount,
      fileCount,
      nodesByKind,
      edgesByKind,
      filesByLanguage,
      dbSizeBytes: 0, // Set by caller using DatabaseConnection.getSize()
      lastUpdated: Date.now(),
    };
  }

  /**
   * Clear all data from the database
   */
  clear(): void {
    this.nodeCache.clear();
    this.db.transaction(() => {
      this.db.exec('DELETE FROM unresolved_refs');
      this.db.exec('DELETE FROM vectors');
      this.db.exec('DELETE FROM edges');
      this.db.exec('DELETE FROM nodes');
      this.db.exec('DELETE FROM files');
    })();
  }
}