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// The name of the cookie that will be used to determine which phone number to show
const cookieName = "phone_num_id";

// The list of all phone numbers to use
const phoneNumbers = [
  {
    id: "google-cpc",
    utmSource: "google",
    utmMedium: "cpc",
    phoneNumber: "222-222-2222"
  },
  {
    id: "bing-cpc",
    utmSource: "bing",
    utmMedium: "cpc",
    phoneNumber: "333-333-3333"
  }
];

// This adds a "fetch" event listener which will be called for all incoming requests
addEventListener("fetch", event => {
  event.respondWith(handleRequest(event.request));
});

async function handleRequest(request) {
  // Forward the incoming request and get the original response. If Cloudflare has already cached
  // this request, this will return the cached response, otherwise it will make the request to
  // the origin
  let response = await fetch(request);

  // Check the content type of the response and fallback to an empty string
  // if there is no content-type header
  let contentType = response.headers.get("content-type") || "";

  // We're only interested in changing respones that have a content-type starting
  // with "text/html". Anything else will be returned without any modifications
  if (/^text\/html/.test(contentType)) {
    // `newPhoneNumberData` will be the new phone number to show (if any)
    let newPhoneNumberData;

    // searchParams are the query parameters for this request
    let searchParams = new URL(request.url).searchParams;

    // If the request has a `utm_source` query param, use that to determine which phone number to show
    if (searchParams.has("utm_source")) {
      let utmSource = searchParams.get("utm_source") || "";
      let utmMedium = searchParams.get("utm_medium") || "";
      // Lookup the phone number based on the `utmSource` and `utmMedium`
      newPhoneNumberData = phoneNumbers.find(
        phoneNumber =>
          phoneNumber.utmSource === utmSource &&
          phoneNumber.utmMedium === utmMedium
      );

      // If we found a match, set a cookie so that subsequent requests get the same phone number
      if (newPhoneNumberData) {
        // In order to modify the response headers, we first have to duplicate the response
        // so that it becomes mutable
        response = new Response(response.body, response);

        // Now set a cookie with the id of the new phone number to use. You should modify the properties
        // of the cookie for your use case. See this page for more information:
        // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie
        response.headers.append(
          "Set-Cookie",
          `${cookieName}=${newPhoneNumberData.id}; Max-Age=2147483647`
        );
      }
    }

    // If we weren't able to determine the new phone number based on the query params, try
    // checking the cookies next
    if (!newPhoneNumberData) {
      let cookieHeader = request.headers.get("cookie") || "";

      // split each of the cookies and remove leading/trailing whitespace
      let cookies = cookieHeader.split(";").map(str => str.trim());

      // Find the phone number cookie
      let phoneNumberCookieString = cookies.find(cookieString =>
        cookieString.startsWith(`${cookieName}=`)
      );

      // If the request has the phone number cookie, use that
      if (phoneNumberCookieString) {
        // Extract the phone number id from the cookie
        const phoneNumberId = phoneNumberCookieString.split("=")[1];

        // Lookup the phone number data based on the ID
        newPhoneNumberData = phoneNumbers.find(
          phoneNumber => phoneNumber.id === phoneNumberId
        );
      }
    }

    // If we found a matching phone number to use, now we'll need to replace all occurences
    // of the original phone number with the new one before returning the response
    if (newPhoneNumberData) {
      // Get the original response body
      let responseBody = await response.text();

      // Use a regex with the `g` flag to find/replace all occurences of the original phone number.
      // This would look for a phone number like "(111)-111-1111" but you can modify this to fit
      // however your original phone number appears
      responseBody = responseBody.replace(
        /\(?111\)?[-\s]*111[-\s]*1111/g,
        newPhoneNumberData.phoneNumber
      );

      // Create a new response with the updated responseBody. We also pass the original `response` as the
      // second argument in order to copy all other properties from the original response (status, headers, etc)
      response = new Response(responseBody, response);
    }
  }

  return response;
}