/**
 * Cloudflare Worker to cache a URL on all US Edge servers
 * 
 * This worker:
 * 1. Accepts a target URL via query parameter or POST body
 * 2. Fetches the URL using Cloudflare's fetch API
 * 3. Forces caching by setting appropriate cache headers
 * 4. Can be configured to cache on specific US regions or all of them
 */

// Define US Cloudflare regions (These are the major US colo locations)
const US_REGIONS = [
  "IAD", // Washington DC (Northern Virginia)
  "EWR", // Newark, NJ
  "ATL", // Atlanta, GA
  "MIA", // Miami, FL
  "ORD", // Chicago, IL
  "DFW", // Dallas, TX
  "DEN", // Denver, CO
  "SEA", // Seattle, WA
  "LAX", // Los Angeles, CA
  "SJC", // San Jose, CA
  "PHX"  // Phoenix, AZ
];

export default {
  async fetch(request, env, ctx) {
    // Create the response headers with CORS support
    const headers = new Headers({
      "Access-Control-Allow-Origin": "*",
      "Access-Control-Allow-Methods": "GET, POST, OPTIONS",
      "Access-Control-Allow-Headers": "Content-Type",
      "Content-Type": "application/json"
    });
    
    // Handle OPTIONS requests (pre-flight for CORS)
    if (request.method === "OPTIONS") {
      return new Response(null, { headers });
    }
    
    // Get the target URL from query params or POST body
    let targetUrl;
    if (request.method === "POST") {
      try {
        const body = await request.json();
        targetUrl = body.url;
      } catch (error) {
        return new Response(
          JSON.stringify({ error: "Invalid JSON body" }),
          { headers, status: 400 }
        );
      }
    } else {
      const url = new URL(request.url);
      targetUrl = url.searchParams.get("url");
    }
    
    // Validate the target URL
    if (!targetUrl) {
      return new Response(
        JSON.stringify({ error: "Missing 'url' parameter" }),
        { headers, status: 400 }
      );
    }
    
    try {
      new URL(targetUrl); // Validate URL format
    } catch (error) {
      return new Response(
        JSON.stringify({ error: "Invalid URL format" }),
        { headers, status: 400 }
      );
    }
    
    // Process all regions in parallel
    const results = await Promise.allSettled(US_REGIONS.map(async (region) => {
      return await cacheInRegion(targetUrl, region);
    }));
    
    // Compile results
    const response = {
      url: targetUrl,
      cached: true,
      regionResults: results.map((result, index) => ({
        region: US_REGIONS[index],
        success: result.status === "fulfilled",
        status: result.status === "fulfilled" ? result.value.status : null,
        error: result.status === "rejected" ? result.reason.message : null
      }))
    };
    
    return new Response(JSON.stringify(response, null, 2), { headers });
  }
};

/**
 * Attempts to cache the URL in a specific Cloudflare region
 * 
 * @param {string} url - The URL to cache
 * @param {string} region - The Cloudflare region code
 * @returns {Promise<Object>} - The fetch response details
 */
async function cacheInRegion(url, region) {
  // Create fetch request with cache control headers
  const cacheRequest = new Request(url, {
    headers: {
      // CF-specific header to route to a specific region
      "CF-Worker-Request-Region": region,
      // Headers to encourage caching
      "Cache-Control": "public, max-age=86400",
      // Tell Cloudflare that we're a cache warmer
      "User-Agent": "Cloudflare-Cache-Warmer/1.0"
    },
    cf: {
      // Force caching even if origin has no-store
      cacheEverything: true,
      // Cache for 1 day
      cacheTtl: 86400,
      // Attempt to resolve through the specified region
      resolveOverride: region
    }
  });
  
  // Perform the fetch
  const response = await fetch(cacheRequest);
  
  return {
    status: response.status,
    cached: response.headers.get("CF-Cache-Status") === "HIT" || 
            response.headers.get("CF-Cache-Status") === "MISS", // MISS on first cache, but still stored
    headers: {
      "CF-Cache-Status": response.headers.get("CF-Cache-Status"),
      "CF-Ray": response.headers.get("CF-Ray")
    }
  };
}