// Viewer-request function for the substandard.blog distribution
// (aws_cloudfront_function.trailing_slash in main.tf).
//
// Astro builds with trailingSlash "never" but emits directory output: the
// page at /posts/x is the S3 object posts/x/index.html. Extensionless URIs
// are rewritten to that object, and trailing-slash URIs are 301-redirected
// to the no-slash address — standard.site document records claim the
// no-slash address as canonical, so /posts/x/ and /posts/x must stay one
// page.

function handler(event) {
  var request = event.request;
  var uri = request.uri;

  if (uri === '/') {
    // default_root_object serves index.html at the distribution root.
    return request;
  }

  if (uri.endsWith('/')) {
    var canonical = uri.replace(/\/+$/, '') || '/';
    return {
      statusCode: 301,
      statusDescription: 'Moved Permanently',
      headers: { location: { value: canonical + search(request.querystring) } },
    };
  }

  if (!uri.split('/').pop().includes('.')) {
    request.uri = uri + '/index.html';
  }

  return request;
}

// Rebuild the query string for the redirect Location header; the event
// carries it as an object, not on the uri.
function search(querystring) {
  var parts = [];
  Object.keys(querystring).forEach(function (key) {
    var values = querystring[key].multiValue || [querystring[key]];
    values.forEach(function (entry) {
      parts.push(entry.value === '' ? key : key + '=' + entry.value);
    });
  });
  return parts.length ? '?' + parts.join('&') : '';
}