import { Exa } from "exa-js";
import { serializeMcpClientMetadata } from "../utils/mcpClientMetadata.js";

function encodeIntegrationSource(source: string): string {
  return Array.from(new TextEncoder().encode(source), (byte) =>
    byte <= 127
      ? String.fromCharCode(byte)
      : `%${byte.toString(16).toUpperCase().padStart(2, "0")}`,
  ).join("");
}

// Build Exa reporting headers, appending x-exa-source if present
export function integrationHeaders(tool: string, config?: Record<string, unknown>) {
  const source = config?.exaSource;
  const mcpSessionId = config?.mcpSessionId;
  const mcpClient = serializeMcpClientMetadata(config?.mcpClient);
  const oauthAccessToken = config?.oauthAccessToken;
  const headers: Record<string, string> = {
    "x-exa-integration":
      typeof source === "string" ? `${tool}:${encodeIntegrationSource(source)}` : tool,
  };

  if (typeof oauthAccessToken === "string" && oauthAccessToken.length > 0) {
    headers["Authorization"] = `Bearer ${oauthAccessToken}`;
  }

  if (typeof mcpSessionId === "string" && mcpSessionId.length > 0) {
    headers["x-exa-mcp-session-id"] = mcpSessionId;
  }

  if (mcpClient) {
    headers["x-exa-mcp-client"] = mcpClient;
  }

  return headers;
}

export function createExaClient(config?: Record<string, unknown>, tool?: string) {
  const exa = createBaseExaClient(config);
  if (tool) {
    applyClientHeaders(exa, integrationHeaders(tool, config));
  }
  return exa;
}

function createBaseExaClient(config?: Record<string, unknown>) {
  const oauthAccessToken = config?.oauthAccessToken;
  if (typeof oauthAccessToken === "string" && oauthAccessToken.length > 0) {
    const exa = new Exa("oauth");
    (exa as unknown as { headers: Headers }).headers.delete("x-api-key");
    return exa;
  }
  const exaApiKey = config?.exaApiKey;
  return new Exa(
    typeof exaApiKey === "string" && exaApiKey.length > 0
      ? exaApiKey
      : process.env.EXA_API_KEY || "",
  );
}

function applyClientHeaders(exa: Exa, headers: Record<string, string>) {
  const client = exa as unknown as { headers: Headers | Record<string, string> };
  const headerBag = client.headers as Headers;
  if (typeof headerBag.set === "function") {
    Object.entries(headers).forEach(([key, value]) => headerBag.set(key, value));
    return;
  }

  client.headers = {
    ...client.headers,
    ...headers,
  };
}

// Configuration for API
export const API_CONFIG = {
  ENDPOINTS: {
    SEARCH: "/search",
    RESEARCH: "/research/v1",
  },
  TOOL_TIMEOUTS: {
    SEARCH_MS: 60_000,
    FETCH_MS: 60_000,
    ADVANCED_SEARCH_MS: 300_000,
  },
  DEFAULT_NUM_RESULTS: 10,
  DEFAULT_MAX_CHARACTERS: 3000,
} as const;