/*
 * Copyright 2020 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import {MetricType, MetricRatingThresholds} from '../types.js';

const getRating = (
  value: number,
  thresholds: MetricRatingThresholds,
): MetricType['rating'] => {
  if (value > thresholds[1]) {
    return 'poor';
  }
  if (value > thresholds[0]) {
    return 'needs-improvement';
  }
  return 'good';
};

export const bindReporter = <MetricName extends MetricType['name']>(
  callback: (metric: Extract<MetricType, {name: MetricName}>) => void,
  metric: Extract<MetricType, {name: MetricName}>,
  thresholds: MetricRatingThresholds,
  reportAllChanges?: boolean,
) => {
  let prevValue: number;
  let delta: number;
  return (forceReport?: boolean) => {
    if (metric.value >= 0) {
      if (forceReport || reportAllChanges) {
        delta = metric.value - (prevValue || 0);

        // Report the metric if there's a non-zero delta or if no previous
        // value exists (which can happen in the case of the document becoming
        // hidden when the metric value is 0).
        // See: https://github.com/GoogleChrome/web-vitals/issues/14
        if (delta || prevValue === undefined) {
          prevValue = metric.value;
          metric.delta = delta;
          metric.rating = getRating(metric.value, thresholds);
          callback(metric);
        }
      }
    }
  };
};