// ST-BME: 外部 Embedding API 封装 + 向量检索
// 支持 OpenAI 兼容的 /v1/embeddings 接口

/**
 * Embedding 服务
 * 调用外部 API 获取文本向量，并提供暴力搜索 cosine 相似度
 */

import { extension_settings } from "../../../extensions.js";

const MODULE_NAME = "st_bme";
const EMBEDDING_REQUEST_TIMEOUT_MS = 300000;

function getConfiguredTimeoutMs(
  settings = extension_settings[MODULE_NAME] || {},
) {
  const timeoutMs = Number(settings?.timeoutMs);
  return Number.isFinite(timeoutMs) && timeoutMs > 0
    ? timeoutMs
    : EMBEDDING_REQUEST_TIMEOUT_MS;
}

function isAbortError(error) {
  return error?.name === "AbortError";
}

function normalizeOpenAICompatibleBaseUrl(value) {
  return String(value || "")
    .trim()
    .replace(/\/+(chat\/completions|embeddings)$/i, "")
    .replace(/\/+$/, "");
}

function createCombinedAbortSignal(...signals) {
  const validSignals = signals.filter(Boolean);
  if (validSignals.length <= 1) {
    return validSignals[0] || undefined;
  }

  if (
    typeof AbortSignal !== "undefined" &&
    typeof AbortSignal.any === "function"
  ) {
    return AbortSignal.any(validSignals);
  }

  const controller = new AbortController();
  for (const signal of validSignals) {
    if (signal.aborted) {
      controller.abort(signal.reason);
      return controller.signal;
    }
    signal.addEventListener("abort", () => controller.abort(signal.reason), {
      once: true,
    });
  }
  return controller.signal;
}

async function fetchWithTimeout(
  url,
  options = {},
  timeoutMs = EMBEDDING_REQUEST_TIMEOUT_MS,
) {
  const controller = new AbortController();
  const timeout = setTimeout(
    () =>
      controller.abort(
        new DOMException(
          `Embedding 请求超时 (${Math.round(timeoutMs / 1000)}s)`,
          "AbortError",
        ),
      ),
    timeoutMs,
  );
  const signal = options.signal
    ? createCombinedAbortSignal(options.signal, controller.signal)
    : controller.signal;

  try {
    return await fetch(url, {
      ...options,
      signal,
    });
  } finally {
    clearTimeout(timeout);
  }
}

/**
 * 调用外部 Embedding API
 *
 * @param {string} text - 要嵌入的文本
 * @param {object} config - API 配置
 * @param {string} config.apiUrl - API 基地址（如 https://api.openai.com/v1）
 * @param {string} config.apiKey - API Key
 * @param {string} config.model - 模型名（如 text-embedding-3-small）
 * @returns {Promise<Float64Array|null>} 向量或 null
 */
export async function embedText(text, config, { signal } = {}) {
  const apiUrl = normalizeOpenAICompatibleBaseUrl(config?.apiUrl);
  if (!text || !apiUrl || !config?.model) {
    console.warn("[ST-BME] Embedding 配置不完整，跳过");
    return null;
  }

  try {
    const response = await fetchWithTimeout(
      `${apiUrl}/embeddings`,
      {
        method: "POST",
        headers: {
          "Content-Type": "application/json",
          ...(config.apiKey
            ? { Authorization: `Bearer ${config.apiKey}` }
            : {}),
        },
        signal,
        body: JSON.stringify({
          model: config.model,
          input: text,
        }),
      },
      getConfiguredTimeoutMs(),
    );

    if (!response.ok) {
      const errorText = await response.text();
      console.error(
        `[ST-BME] Embedding API 错误 (${response.status}):`,
        errorText,
      );
      return null;
    }

    const data = await response.json();
    const vector = data?.data?.[0]?.embedding;

    if (!vector || !Array.isArray(vector)) {
      console.error("[ST-BME] Embedding API 返回格式异常:", data);
      return null;
    }

    return new Float64Array(vector);
  } catch (e) {
    if (isAbortError(e)) {
      throw e;
    }
    console.error("[ST-BME] Embedding API 调用失败:", e);
    return null;
  }
}

/**
 * 批量嵌入文本
 *
 * @param {string[]} texts
 * @param {object} config
 * @returns {Promise<(Float64Array|null)[]>}
 */
export async function embedBatch(texts, config, { signal } = {}) {
  const apiUrl = normalizeOpenAICompatibleBaseUrl(config?.apiUrl);
  if (!texts.length || !apiUrl || !config?.model) {
    return texts.map(() => null);
  }

  try {
    const response = await fetchWithTimeout(
      `${apiUrl}/embeddings`,
      {
        method: "POST",
        headers: {
          "Content-Type": "application/json",
          ...(config.apiKey
            ? { Authorization: `Bearer ${config.apiKey}` }
            : {}),
        },
        signal,
        body: JSON.stringify({
          model: config.model,
          input: texts,
        }),
      },
      getConfiguredTimeoutMs(),
    );

    if (!response.ok) {
      const errorText = await response.text();
      console.error(
        `[ST-BME] Embedding API 批量错误 (${response.status}):`,
        errorText,
      );
      return texts.map(() => null);
    }

    const data = await response.json();
    const embeddings = data?.data;

    if (!Array.isArray(embeddings)) {
      return texts.map(() => null);
    }

    // 按 index 排序（API 可能不保证顺序）
    embeddings.sort((a, b) => a.index - b.index);

    return embeddings.map((item) => {
      if (item?.embedding && Array.isArray(item.embedding)) {
        return new Float64Array(item.embedding);
      }
      return null;
    });
  } catch (e) {
    if (isAbortError(e)) {
      throw e;
    }
    console.error("[ST-BME] Embedding API 批量调用失败:", e);
    return texts.map(() => null);
  }
}

/**
 * 计算两个向量的 cosine 相似度
 *
 * @param {Float64Array|number[]} vecA
 * @param {Float64Array|number[]} vecB
 * @returns {number} 相似度 [-1, 1]
 */
export function cosineSimilarity(vecA, vecB) {
  if (!vecA || !vecB || vecA.length !== vecB.length || vecA.length === 0) {
    return 0;
  }

  let dotProduct = 0;
  let normA = 0;
  let normB = 0;

  for (let i = 0; i < vecA.length; i++) {
    dotProduct += vecA[i] * vecB[i];
    normA += vecA[i] * vecA[i];
    normB += vecB[i] * vecB[i];
  }

  const denominator = Math.sqrt(normA) * Math.sqrt(normB);
  if (denominator === 0) return 0;

  return dotProduct / denominator;
}

/**
 * 暴力搜索：找出与查询向量最相似的 Top-K 节点
 * PeroCore 的向量引擎也是暴力搜索（<1000 节点时比 HNSW 更快）
 *
 * @param {Float64Array|number[]} queryVec - 查询向量
 * @param {Array<{nodeId: string, embedding: Float64Array|number[]}>} candidates - 候选节点
 * @param {number} topK - 返回数量
 * @returns {Array<{nodeId: string, score: number}>} 按相似度降序
 */
export function searchSimilar(queryVec, candidates, topK = 20) {
  if (!queryVec || candidates.length === 0) return [];

  const scored = candidates
    .filter((c) => c.embedding && c.embedding.length > 0)
    .map((c) => ({
      nodeId: c.nodeId,
      score: cosineSimilarity(queryVec, c.embedding),
    }))
    .filter((item) => item.score > 0);

  scored.sort((a, b) => b.score - a.score);

  return scored.slice(0, topK);
}

/**
 * 测试 Embedding API 连通性
 *
 * @param {object} config - API 配置
 * @returns {Promise<{success: boolean, dimensions: number, error: string}>}
 */
export async function testConnection(config) {
  try {
    const vec = await embedText("test connection", config);
    if (vec) {
      return { success: true, dimensions: vec.length, error: "" };
    }
    return { success: false, dimensions: 0, error: "API 返回空结果" };
  } catch (e) {
    return { success: false, dimensions: 0, error: String(e) };
  }
}