/**
 * @fileoverview This file sets up and runs the HTTP server that acts as a
 * proxy between an OpenAI-compatible client and the Gemini API.
 */
import consola from 'consola';
import http from 'http';
import { listModels, sendChat, sendChatStream } from './chatwrapper';
import { mapRequest, mapResponse, mapStreamChunk } from './mapper.js';
import { RequestBody, GeminiResponse, GeminiStreamChunk, Part } from './types';
import { config } from './config';
import { isAuthorized } from './auth';

// ==================================================================
// Server Configuration
// ==================================================================
const PORT = config.PORT;
const VERBOSE = config.VERBOSE;

// ==================================================================
// Logger Setup
// ==================================================================
if (VERBOSE) {
  consola.level = 5;
  consola.info('Verbose logging enabled');
}

consola.info('Google CLI OpenAI proxy');

// ==================================================================
// HTTP Server Helpers
// ==================================================================

/**
 * Sets CORS headers to allow cross-origin requests.
 * @param res - The HTTP server response object.
 */
function allowCors(res: http.ServerResponse) {
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Headers', '*');
  res.setHeader('Access-Control-Allow-Methods', 'GET,POST,OPTIONS');
}

/**
 * Reads and parses a JSON request body.
 * @param req - The HTTP incoming message object.
 * @param res - The HTTP server response object.
 * @returns A promise that resolves to the parsed request body
 * or null if invalid.
 */
function readJSON(
  req: http.IncomingMessage,
  res: http.ServerResponse,
): Promise<RequestBody | null> {
  return new Promise((resolve) => {
    let data = '';
    req.on('data', (c) => (data += c));
    req.on('end', () => {
      if (!data) {
        if (req.method === 'POST') {
          res.writeHead(400, { 'Content-Type': 'application/json' });
          res.end(
            JSON.stringify({
              error: { message: 'Request body is missing for POST request' },
            }),
          );
          resolve(null);
          return;
        }
        resolve(null);
        return;
      }
      try {
        resolve(JSON.parse(data) as RequestBody);
      } catch {
        // Handle malformed JSON.
        res.writeHead(400, { 'Content-Type': 'application/json' });
        res.end(JSON.stringify({ error: { message: 'Malformed JSON' } }));
        resolve(null);
        return;
      }
    });
  });
}

// ==================================================================
// Main Server Logic
// ==================================================================
http
  .createServer(async (req, res) => {
    allowCors(res);
    const url = new URL(req.url ?? '/', `http://${req.headers.host}`);
    const pathname = url.pathname.replace(/\/$/, '') || '/';
    consola.info(`${req.method} ${url.pathname}`);

    // Handle pre-flight CORS requests.
    if (req.method === 'OPTIONS') {
      res.writeHead(204).end();
      return;
    }

    if (!isAuthorized(req, res)) {
      return;
    }

    // Route for listing available models.
    if (pathname === '/v1/models' || pathname === '/models') {
      res.writeHead(200, { 'Content-Type': 'application/json' });
      res.end(
        JSON.stringify({
          data: listModels(),
        }),
      );
      return;
    }

    // Route for chat completions.
    if (
      (pathname === '/chat/completions' ||
        pathname === '/v1/chat/completions') &&
      req.method === 'POST'
    ) {
      const body = await readJSON(req, res);
      if (!body) return;

      try {
        const { geminiReq, tools } = await mapRequest(body);

        if (body.stream) {
          res.writeHead(200, {
            'Content-Type': 'text/event-stream',
            'Cache-Control': 'no-cache',
            Connection: 'keep-alive',
          });

          for await (const chunk of sendChatStream({ ...geminiReq, tools })) {
            // Transform the chunk to match the expected stream format.
            const transformedParts =
              chunk.candidates?.[0]?.content?.parts?.map((part) => {
                const transformedPart: Part = {
                  text: part.text,
                  thought: part.text?.startsWith?.('<think>') ?? false,
                };

                if (part.inlineData?.data) {
                  transformedPart.inlineData = {
                    mimeType: part.inlineData.mimeType ?? 'text/plain',
                    data: part.inlineData.data,
                  };
                }

                return transformedPart;
              }) ?? [];

            const streamChunk: GeminiStreamChunk = {
              candidates: [
                {
                  content: {
                    parts: transformedParts,
                  },
                },
              ],
            };

            res.write(
              `data: ${JSON.stringify(mapStreamChunk(streamChunk))}\n\n`,
            );
          }
          res.end('data: [DONE]\n\n');
        } else {
          const gResp: GeminiResponse = await sendChat({ ...geminiReq, tools });
          res.writeHead(200, { 'Content-Type': 'application/json' });
          res.end(JSON.stringify(mapResponse(gResp, body)));
        }
      } catch (err) {
        const error = err as Error;
        consola.error('Proxy error ➜', error);
        
        // Handle errors, sending them in the appropriate format for streaming
        // or non-streaming responses.
        if (body.stream && res.headersSent) {
          res.write(
            `data: ${JSON.stringify({
              error: {
                message: error.message,
                type: 'error',
              },
            })}\n\n`,
          );
          res.end('data: [DONE]\n\n');
          return;
        } else {
          res.writeHead(500, { 'Content-Type': 'application/json' });
          res.end(JSON.stringify({ error: { message: error.message } }));
        }
      }
    }
  })
  .listen(PORT, () => {
    consola.info(`Listening on port :${PORT}`);
  });