import { readdir, readFile } from 'fs/promises';
import { join, relative } from 'path';
import { createHash } from 'crypto';
import type { FastifyBaseLogger } from 'fastify';
import { RAGRetriever } from './rag-retriever.js';
import { EmbeddingService } from './embedding-service.js';

/**
 * Document metadata stored with each chunk
 */
export interface DocumentMetadata {
  document_id: string;
  chunk_index: number;
  content_hash: string;
  last_updated: number;
  tags: string[];
  heading?: string;
  file_path: string;
}

/**
 * Document chunk with content and metadata
 */
export interface DocumentChunk {
  content: string;
  metadata: DocumentMetadata;
}

/**
 * Document loader configuration
 */
export interface DocumentLoaderConfig {
  knowledgeDir: string;
  maxChunkSize?: number; // in tokens (approximate by chars)
  chunkOverlap?: number; // overlap between chunks
}

/**
 * Global knowledge document loader
 *
 * Loads markdown documents from a directory structure and stores them
 * as global knowledge (user_id="0") in Qdrant for RAG retrieval.
 *
 * Features:
 * - Intelligent chunking by markdown headers
 * - Content hashing for change detection
 * - Metadata extraction (tags, headings)
 * - Automatic embedding generation
 * - Incremental updates (only changed docs)
 *
 * Directory structure:
 * gateway/knowledge/
 *   platform/
 *   trading/
 *   indicators/
 *   strategies/
 */
export class DocumentLoader {
  private config: DocumentLoaderConfig;
  private logger: FastifyBaseLogger;
  private embeddings: EmbeddingService;
  private rag: RAGRetriever;
  private loadedDocs: Map<string, string> = new Map(); // path -> hash

  constructor(
    config: DocumentLoaderConfig,
    embeddings: EmbeddingService,
    rag: RAGRetriever,
    logger: FastifyBaseLogger
  ) {
    this.config = {
      maxChunkSize: 4000, // ~1000 tokens
      chunkOverlap: 200,
      ...config,
    };
    this.embeddings = embeddings;
    this.rag = rag;
    this.logger = logger;
  }

  /**
   * Load all documents from knowledge directory
   */
  async loadAll(): Promise<{ loaded: number; updated: number; skipped: number }> {
    this.logger.info({ dir: this.config.knowledgeDir }, 'Loading knowledge documents');

    const stats = { loaded: 0, updated: 0, skipped: 0 };

    try {
      const files = await this.findMarkdownFiles(this.config.knowledgeDir);

      for (const filePath of files) {
        const result = await this.loadDocument(filePath);

        if (result === 'loaded') stats.loaded++;
        else if (result === 'updated') stats.updated++;
        else stats.skipped++;
      }

      this.logger.info(stats, 'Knowledge documents loaded');
      return stats;
    } catch (error) {
      this.logger.error({ error }, 'Failed to load knowledge documents');
      throw error;
    }
  }

  /**
   * Load a single document
   */
  async loadDocument(filePath: string): Promise<'loaded' | 'updated' | 'skipped'> {
    try {
      // Read file content
      const content = await readFile(filePath, 'utf-8');
      const contentHash = this.hashContent(content);

      // Check if document has changed
      const relativePath = relative(this.config.knowledgeDir, filePath);
      const existingHash = this.loadedDocs.get(relativePath);

      if (existingHash === contentHash) {
        this.logger.debug({ file: relativePath }, 'Document unchanged, skipping');
        return 'skipped';
      }

      const isUpdate = !!existingHash;

      // Parse and chunk document
      const chunks = this.chunkDocument(content, relativePath);

      this.logger.info(
        { file: relativePath, chunks: chunks.length, update: isUpdate },
        'Processing document'
      );

      // Generate embeddings and store chunks
      for (const chunk of chunks) {
        const embedding = await this.embeddings.embed(chunk.content);

        // Create unique ID for this chunk
        const chunkId = `global:${chunk.metadata.document_id}:${chunk.metadata.chunk_index}`;

        // Store in Qdrant as global knowledge
        await this.rag.storeGlobalKnowledge(
          chunkId,
          chunk.content,
          embedding,
          {
            ...chunk.metadata,
            type: 'knowledge_doc',
          }
        );
      }

      // Update loaded docs tracking
      this.loadedDocs.set(relativePath, contentHash);

      return isUpdate ? 'updated' : 'loaded';
    } catch (error) {
      this.logger.error({ error, file: filePath }, 'Failed to load document');
      throw error;
    }
  }

  /**
   * Reload a specific document (for updates)
   */
  async reloadDocument(filePath: string): Promise<void> {
    this.logger.info({ file: filePath }, 'Reloading document');
    await this.loadDocument(filePath);
  }

  /**
   * Chunk document by markdown headers with smart splitting
   */
  private chunkDocument(content: string, documentId: string): DocumentChunk[] {
    const chunks: DocumentChunk[] = [];
    const tags = this.extractTags(content);
    const lastModified = Date.now();

    // Split by headers (## or ###)
    const sections = this.splitByHeaders(content);

    let chunkIndex = 0;

    for (const section of sections) {
      // If section is too large, split it further
      const subChunks = this.splitLargeSection(section.content);

      for (const subContent of subChunks) {
        if (subContent.trim().length === 0) continue;

        chunks.push({
          content: subContent,
          metadata: {
            document_id: documentId,
            chunk_index: chunkIndex++,
            content_hash: this.hashContent(content),
            last_updated: lastModified,
            tags,
            heading: section.heading,
            file_path: documentId,
          },
        });
      }
    }

    return chunks;
  }

  /**
   * Split document by markdown headers
   */
  private splitByHeaders(content: string): Array<{ heading?: string; content: string }> {
    const lines = content.split('\n');
    const sections: Array<{ heading?: string; content: string }> = [];
    let currentSection: string[] = [];
    let currentHeading: string | undefined;

    for (const line of lines) {
      // Check for markdown header (##, ###, ####)
      const headerMatch = line.match(/^(#{2,4})\s+(.+)$/);

      if (headerMatch) {
        // Save previous section
        if (currentSection.length > 0) {
          sections.push({
            heading: currentHeading,
            content: currentSection.join('\n'),
          });
        }

        // Start new section
        currentHeading = headerMatch[2].trim();
        currentSection = [line];
      } else {
        currentSection.push(line);
      }
    }

    // Add final section
    if (currentSection.length > 0) {
      sections.push({
        heading: currentHeading,
        content: currentSection.join('\n'),
      });
    }

    return sections;
  }

  /**
   * Split large sections into smaller chunks
   */
  private splitLargeSection(content: string): string[] {
    const maxSize = this.config.maxChunkSize!;
    const overlap = this.config.chunkOverlap!;

    if (content.length <= maxSize) {
      return [content];
    }

    const chunks: string[] = [];
    let start = 0;

    while (start < content.length) {
      const end = Math.min(start + maxSize, content.length);
      let chunkEnd = end;

      // Try to break at sentence boundary
      if (end < content.length) {
        const sentenceEnd = content.lastIndexOf('.', end);
        const paragraphEnd = content.lastIndexOf('\n\n', end);

        if (paragraphEnd > start + maxSize / 2) {
          chunkEnd = paragraphEnd;
        } else if (sentenceEnd > start + maxSize / 2) {
          chunkEnd = sentenceEnd + 1;
        }
      }

      chunks.push(content.substring(start, chunkEnd));
      start = chunkEnd - overlap;
    }

    return chunks;
  }

  /**
   * Extract tags from document (frontmatter or first heading)
   */
  private extractTags(content: string): string[] {
    const tags: string[] = [];

    // Try to extract from YAML frontmatter
    const frontmatterMatch = content.match(/^---\n([\s\S]*?)\n---/);
    if (frontmatterMatch) {
      const frontmatter = frontmatterMatch[1];
      const tagsMatch = frontmatter.match(/tags:\s*\[([^\]]+)\]/);
      if (tagsMatch) {
        tags.push(...tagsMatch[1].split(',').map((t) => t.trim()));
      }
    }

    // Extract from first heading
    const headingMatch = content.match(/^#\s+(.+)$/m);
    if (headingMatch) {
      tags.push(headingMatch[1].toLowerCase().replace(/\s+/g, '-'));
    }

    return tags;
  }

  /**
   * Hash content for change detection
   */
  private hashContent(content: string): string {
    return createHash('md5').update(content).digest('hex');
  }

  /**
   * Recursively find all markdown files
   */
  private async findMarkdownFiles(dir: string): Promise<string[]> {
    const files: string[] = [];

    try {
      const entries = await readdir(dir, { withFileTypes: true });

      for (const entry of entries) {
        const fullPath = join(dir, entry.name);

        if (entry.isDirectory()) {
          const subFiles = await this.findMarkdownFiles(fullPath);
          files.push(...subFiles);
        } else if (entry.isFile() && entry.name.endsWith('.md')) {
          files.push(fullPath);
        }
      }
    } catch (error) {
      this.logger.warn({ error, dir }, 'Failed to read directory');
    }

    return files;
  }

  /**
   * Get loaded document stats
   */
  getStats(): { totalDocs: number; totalSize: number } {
    return {
      totalDocs: this.loadedDocs.size,
      totalSize: Array.from(this.loadedDocs.values()).reduce((sum, hash) => sum + hash.length, 0),
    };
  }
}