import { Injectable, Logger } from '@nestjs/common';
import type { EmbeddingProvider } from '@mosaicstack/memory';

// ---------------------------------------------------------------------------
// Environment-driven configuration
//
//   EMBEDDING_PROVIDER      — 'ollama' (default) | 'openai'
//   EMBEDDING_MODEL         — model id, defaults differ per provider
//   EMBEDDING_DIMENSIONS    — integer, defaults differ per provider
//   OLLAMA_BASE_URL         — base URL for Ollama (used when provider=ollama)
//   EMBEDDING_API_URL       — full base URL for OpenAI-compatible API
//   OPENAI_API_KEY          — required for OpenAI provider
// ---------------------------------------------------------------------------

const OLLAMA_DEFAULT_MODEL = 'nomic-embed-text';
const OLLAMA_DEFAULT_DIMENSIONS = 768;

const OPENAI_DEFAULT_MODEL = 'text-embedding-3-small';
const OPENAI_DEFAULT_DIMENSIONS = 1536;

/** Known dimension mismatch: warn if pgvector column likely has wrong size */
const PGVECTOR_SCHEMA_DIMENSIONS = 1536;

type EmbeddingBackend = 'ollama' | 'openai';

interface OllamaEmbeddingResponse {
  embedding: number[];
}

interface OpenAIEmbeddingResponse {
  data: Array<{ embedding: number[]; index: number }>;
  model: string;
  usage: { prompt_tokens: number; total_tokens: number };
}

/**
 * Provider-agnostic embedding service.
 *
 * Defaults to Ollama's native embedding API using nomic-embed-text (768 dims).
 * Falls back to the OpenAI-compatible API when EMBEDDING_PROVIDER=openai or
 * when OPENAI_API_KEY is set and EMBEDDING_PROVIDER is not explicitly set to ollama.
 *
 * Dimension mismatch detection: if the configured dimensions differ from the
 * pgvector schema (1536), a warning is logged with re-embedding instructions.
 */
@Injectable()
export class EmbeddingService implements EmbeddingProvider {
  private readonly logger = new Logger(EmbeddingService.name);
  private readonly backend: EmbeddingBackend;
  private readonly model: string;
  readonly dimensions: number;

  // Ollama-specific
  private readonly ollamaBaseUrl: string | undefined;

  // OpenAI-compatible
  private readonly openaiApiKey: string | undefined;
  private readonly openaiBaseUrl: string;

  constructor() {
    // Determine backend
    const providerEnv = process.env['EMBEDDING_PROVIDER'];
    const openaiKey = process.env['OPENAI_API_KEY'];
    const ollamaUrl = process.env['OLLAMA_BASE_URL'] ?? process.env['OLLAMA_HOST'];

    if (providerEnv === 'openai') {
      this.backend = 'openai';
    } else if (providerEnv === 'ollama') {
      this.backend = 'ollama';
    } else if (process.env['EMBEDDING_API_URL']) {
      // Legacy: explicit API URL configured → use openai-compat path
      this.backend = 'openai';
    } else if (ollamaUrl) {
      // Ollama available and no explicit override → prefer Ollama
      this.backend = 'ollama';
    } else if (openaiKey) {
      // OpenAI key present → use OpenAI
      this.backend = 'openai';
    } else {
      // Nothing configured — default to ollama (will return zeros when unavailable)
      this.backend = 'ollama';
    }

    // Set model and dimension defaults based on backend
    if (this.backend === 'ollama') {
      this.model = process.env['EMBEDDING_MODEL'] ?? OLLAMA_DEFAULT_MODEL;
      this.dimensions =
        parseInt(process.env['EMBEDDING_DIMENSIONS'] ?? '', 10) || OLLAMA_DEFAULT_DIMENSIONS;
      this.ollamaBaseUrl = ollamaUrl;
      this.openaiApiKey = undefined;
      this.openaiBaseUrl = '';
    } else {
      this.model = process.env['EMBEDDING_MODEL'] ?? OPENAI_DEFAULT_MODEL;
      this.dimensions =
        parseInt(process.env['EMBEDDING_DIMENSIONS'] ?? '', 10) || OPENAI_DEFAULT_DIMENSIONS;
      this.ollamaBaseUrl = undefined;
      this.openaiApiKey = openaiKey;
      this.openaiBaseUrl = process.env['EMBEDDING_API_URL'] ?? 'https://api.openai.com/v1';
    }

    // Warn on dimension mismatch with the current schema
    if (this.dimensions !== PGVECTOR_SCHEMA_DIMENSIONS) {
      this.logger.warn(
        `Embedding dimensions (${this.dimensions}) differ from pgvector schema (${PGVECTOR_SCHEMA_DIMENSIONS}). ` +
          `If insights already contain ${PGVECTOR_SCHEMA_DIMENSIONS}-dim vectors, similarity search will fail. ` +
          `To fix: truncate the insights table and re-embed, or run a migration to ALTER COLUMN embedding TYPE vector(${this.dimensions}).`,
      );
    }

    this.logger.log(
      `EmbeddingService initialized: backend=${this.backend}, model=${this.model}, dimensions=${this.dimensions}`,
    );
  }

  get available(): boolean {
    if (this.backend === 'ollama') {
      return !!this.ollamaBaseUrl;
    }
    return !!this.openaiApiKey;
  }

  async embed(text: string): Promise<number[]> {
    const results = await this.embedBatch([text]);
    return results[0]!;
  }

  async embedBatch(texts: string[]): Promise<number[][]> {
    if (!this.available) {
      const reason =
        this.backend === 'ollama'
          ? 'OLLAMA_BASE_URL not configured'
          : 'No OPENAI_API_KEY configured';
      this.logger.warn(`${reason} — returning zero vectors`);
      return texts.map(() => new Array<number>(this.dimensions).fill(0));
    }

    if (this.backend === 'ollama') {
      return this.embedBatchOllama(texts);
    }
    return this.embedBatchOpenAI(texts);
  }

  // ---------------------------------------------------------------------------
  // Ollama backend
  // ---------------------------------------------------------------------------

  private async embedBatchOllama(texts: string[]): Promise<number[][]> {
    const baseUrl = this.ollamaBaseUrl!;
    const results: number[][] = [];

    // Ollama's /api/embeddings endpoint processes one text at a time
    for (const text of texts) {
      const response = await fetch(`${baseUrl}/api/embeddings`, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ model: this.model, prompt: text }),
      });

      if (!response.ok) {
        const body = await response.text();
        this.logger.error(`Ollama embedding API error: ${response.status} ${body}`);
        throw new Error(`Ollama embedding API returned ${response.status}`);
      }

      const json = (await response.json()) as OllamaEmbeddingResponse;
      results.push(json.embedding);
    }

    return results;
  }

  // ---------------------------------------------------------------------------
  // OpenAI-compatible backend
  // ---------------------------------------------------------------------------

  private async embedBatchOpenAI(texts: string[]): Promise<number[][]> {
    const response = await fetch(`${this.openaiBaseUrl}/embeddings`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        Authorization: `Bearer ${this.openaiApiKey}`,
      },
      body: JSON.stringify({
        model: this.model,
        input: texts,
        dimensions: this.dimensions,
      }),
    });

    if (!response.ok) {
      const body = await response.text();
      this.logger.error(`Embedding API error: ${response.status} ${body}`);
      throw new Error(`Embedding API returned ${response.status}`);
    }

    const json = (await response.json()) as OpenAIEmbeddingResponse;
    return json.data.sort((a, b) => a.index - b.index).map((d) => d.embedding);
  }
}