/**
 * @cc-platform/server/proxy — Cross-service integration proxy
 *
 * Extracted from the reciprocal proxy endpoints in both servers:
 *   remoteturtle: /api/integration/inventory-locate → INVENTORY_SERVER_URL
 *   inventory-manager: /api/integration/turtle-status → TURTLE_SERVER_URL
 *
 * Both use the exact same pattern: check URL configured → fetch → forward JSON.
 *
 * Usage:
 *   const { proxyRequest, createProxyEndpoint } = require('@cc-platform/server/proxy');
 *
 *   // One-off proxy call
 *   const result = await proxyRequest('http://other-server:3001', '/api/items', { q: 'diamond' });
 *
 *   // Register a proxy endpoint on Express
 *   createProxyEndpoint(app, '/api/integration/items', 'INVENTORY_SERVER_URL', '/api/integration/items');
 */

'use strict';

/**
 * Proxy a request to a remote service, returning JSON.
 *
 * @param {string} baseUrl - Base URL of the remote service (e.g. 'http://localhost:3001')
 * @param {string} remotePath - Path on the remote service (e.g. '/api/items')
 * @param {Object} [query={}] - Query parameters to forward
 * @param {Object} [options={}] - Additional options
 * @param {number} [options.timeoutMs=5000] - Request timeout in milliseconds
 * @returns {Promise<Object>} Parsed JSON response, or error/unconfigured object
 */
async function proxyRequest(baseUrl, remotePath, query = {}, options = {}) {
  if (!baseUrl) {
    return {
      configured: false,
      message: 'Integration not configured — remote service URL not set',
    };
  }

  const timeoutMs = options.timeoutMs || 5000;

  try {
    const params = new URLSearchParams(query).toString();
    const url = params
      ? `${baseUrl}${remotePath}?${params}`
      : `${baseUrl}${remotePath}`;

    const resp = await fetch(url, {
      signal: AbortSignal.timeout(timeoutMs),
    });

    if (!resp.ok) {
      return {
        error: `Remote service returned ${resp.status}: ${resp.statusText}`,
        status: resp.status,
      };
    }

    return await resp.json();
  } catch (e) {
    return {
      error: `Integration unavailable: ${e.message}`,
    };
  }
}

/**
 * Register a proxy endpoint on an Express app.
 *
 * Creates a GET endpoint at `localPath` that proxies requests to
 * `remotePath` on the service URL specified by the given environment variable.
 *
 * @param {Express.Application} app - Express app instance
 * @param {string} localPath - Local endpoint path (e.g. '/api/integration/items')
 * @param {string} remoteBaseUrlEnvVar - Env var name for the remote URL (e.g. 'INVENTORY_SERVER_URL')
 * @param {string} remotePath - Path on the remote service (e.g. '/api/integration/items')
 * @param {Object} [options={}] - proxyRequest options
 * @returns {string} The resolved base URL (for logging)
 */
function createProxyEndpoint(app, localPath, remoteBaseUrlEnvVar, remotePath, options = {}) {
  const baseUrl = process.env[remoteBaseUrlEnvVar] || '';

  app.get(localPath, async (req, res) => {
    try {
      const result = await proxyRequest(baseUrl, remotePath, req.query, options);
      res.json(result);
    } catch (e) {
      res.status(500).json({ error: e.message });
    }
  });

  return baseUrl;
}

module.exports = { proxyRequest, createProxyEndpoint };