/*
 * Licensed to Elasticsearch B.V. under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch B.V. licenses this file to you 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.
 */

import bluebird, {
  fromNode,
  promisify,
} from 'bluebird';
import Handlebars from 'handlebars';
import fs from 'fs';
import path from 'path';
import imageDiff from 'image-diff';
import mkdirp from 'mkdirp';
import moment from 'moment';
import SimpleGit from 'simple-git';

const readDirAsync = promisify(fs.readdir);
const readFileAsync = promisify(fs.readFile);
const writeFileAsync = promisify(fs.writeFile);

Handlebars.registerHelper('lte', function lessThanEquals(value, threshold, options) {
  if (value <= threshold) {
    return options.fn(this);
  }
  return options.inverse(this);
});

Handlebars.registerHelper('gte', function greaterThanEquals(value, threshold, options) {
  if (value >= threshold) {
    return options.fn(this);
  }
  return options.inverse(this);
});

async function buildGallery(comparisons) {
  const simpleGit = new SimpleGit();
  const asyncBranch = promisify(simpleGit.branch, simpleGit);
  const branch = await asyncBranch();

  const template = Handlebars.compile(await readFileAsync(
    path.resolve('./utilities/templates/visual_regression_gallery.handlebars')
    , 'utf8'));

  const html = template({
    date: moment().format('MMMM Do YYYY, h:mm:ss a'),
    branch: branch.current,
    hiddenThreshold: 0,
    warningThreshold: 0.03,
    comparisons,
  });

  return writeFileAsync(
    path.resolve('./test/functional/screenshots/visual_regression_gallery.html'),
    html
  );
}

async function compareScreenshots() {
  const SCREENSHOTS_DIR = 'test/functional/screenshots';
  const BASELINE_SCREENSHOTS_DIR = path.resolve(SCREENSHOTS_DIR, 'baseline');
  const DIFF_SCREENSHOTS_DIR = path.resolve(SCREENSHOTS_DIR, 'diff');
  const SESSION_SCREENSHOTS_DIR = path.resolve(SCREENSHOTS_DIR, 'session');

  // We don't need to create the baseline dir because it's committed.
  mkdirp.sync(DIFF_SCREENSHOTS_DIR);
  mkdirp.sync(SESSION_SCREENSHOTS_DIR);
  const files = await readDirAsync(SESSION_SCREENSHOTS_DIR);
  const screenshots = files.filter(file => file.indexOf('.png') !== -1);

  // We'll use this data to build a screenshot gallery in HTML.
  return await bluebird.map(screenshots, async screenshot => {
    // We're going to load image data and cache it in this object.
    const comparison = {
      name: screenshot,
      change: undefined,
      percentage: undefined,
      imageData: {
        session: undefined,
        baseline: undefined,
        diff: undefined,
      }
    };

    const sessionImagePath = path.resolve(
      SESSION_SCREENSHOTS_DIR,
      screenshot
    );

    const baselineImagePath = path.resolve(
      BASELINE_SCREENSHOTS_DIR,
      screenshot
    );

    const diffImagePath = path.resolve(
      DIFF_SCREENSHOTS_DIR,
      screenshot
    );

    // Diff the images asynchronously.
    const diffResult = await fromNode((cb) => {
      imageDiff.getFullResult({
        actualImage: sessionImagePath,
        expectedImage: baselineImagePath,
        diffImage: diffImagePath,
        shadow: true,
      }, cb);
    });

    const change = diffResult.percentage;
    const changePercentage = (change * 100).toFixed(2);
    console.log(`(${changePercentage}%) ${screenshot}`);
    comparison.percentage = changePercentage;
    comparison.change = change;

    // Once the images have been diffed, we can load and store the image data.
    comparison.imageData.session =
      await readFileAsync(sessionImagePath, 'base64');

    comparison.imageData.baseline =
      await readFileAsync(baselineImagePath, 'base64');

    comparison.imageData.diff =
      await readFileAsync(diffImagePath, 'base64');

    return comparison;
  });
}

export function run(done) {
  compareScreenshots().then(screenshotComparisons => {
    // Once all of the data has been loaded, we can build the gallery.
    buildGallery(screenshotComparisons).then(() => {
      done();
    });
  }, error => {
    console.error(error);
    done(false);
  });
}