# all files / src/audits/accessibility/ color-contrast.js

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     /**
     * @license
     * Copyright 2016 Google Inc. All rights reserved.
     *
     * 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
     *
     *     http://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.
     */

    'use strict';

    const Audit = require('../audit');
    const Formatter = require('../../../formatters/formatter');

    class ColorContrast extends Audit {
      /**
       * @override
       */
      static get meta() {
        return {
          category: 'Accessibility',
          name: 'color-contrast',
          description: 'Background and foreground colors have a sufficient contrast ratio',
          requiredArtifacts: ['accessibility']
        };
      }

      /**
       * @param {!Artifacts} artifacts
       * @return {!AuditResult}
       */
      static audit(artifacts) {
        const rule =
            artifacts.accessibility.violations.find(result => result.id === 'color-contrast');

        return ColorContrast.generateAuditResult({
          value: typeof rule === 'undefined',
          debugString: this.createDebugString(rule),
          extendedInfo: {
            formatter: Formatter.SUPPORTED_FORMATS.ACCESSIBILITY,
            value: rule
          }
        });
      }

      static createDebugString(rule) {
        if (typeof rule === 'undefined') {
          return '';
        }

        const elementsStr = rule.nodes.length === 1 ? 'element' : 'elements';
        return `${rule.help} (Failed on ${rule.nodes.length} ${elementsStr})`;
      }
    }

    module.exports = ColorContrast;