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   1  /* global Color */
   2  /* eslint no-unused-vars: off */
   3  /**
   4   * Color Calculations.
   5   *
   6   * @since Twenty Twenty 1.0
   7   *
   8   * @param {string} backgroundColor - The background color.
   9   * @param {number} accentHue - The hue for our accent color.
  10   *
  11   * @return {Object} - this
  12   */
  13  function _twentyTwentyColor( backgroundColor, accentHue ) {
  14      // Set the object properties.
  15      this.backgroundColor = backgroundColor;
  16      this.accentHue = accentHue;
  17      this.bgColorObj = new Color( backgroundColor );
  18      this.textColorObj = this.bgColorObj.getMaxContrastColor();
  19      this.textColor = this.textColorObj.toCSS();
  20      this.isDark = 0.5 > this.bgColorObj.toLuminosity();
  21      this.isLight = ! this.isDark;
  22  
  23      // Return the object.
  24      return this;
  25  }
  26  
  27  /**
  28   * Builds an array of Color objects based on the accent hue.
  29   * For improved performance we only build half the array
  30   * depending on dark/light background-color.
  31   *
  32   * @since Twenty Twenty 1.0
  33   *
  34   * @return {Object} - this
  35   */
  36  _twentyTwentyColor.prototype.setAccentColorsArray = function() {
  37      var self = this,
  38          minSaturation = 65,
  39          maxSaturation = 100,
  40          minLightness = 30,
  41          maxLightness = 80,
  42          stepSaturation = 2,
  43          stepLightness = 2,
  44          pushColor = function() {
  45              var colorObj = new Color( {
  46                      h: self.accentHue,
  47                      s: s,
  48                      l: l
  49                  } ),
  50                  item,
  51                  /**
  52                   * Get a score for this color in contrast to its background color and surrounding text.
  53                   *
  54                   * @since Twenty Twenty 1.0
  55                   *
  56                   * @param {number} contrastBackground - WCAG contrast with the background color.
  57                   * @param {number} contrastSurroundingText - WCAG contrast with surrounding text.
  58                   * @return {number} - 0 is best, higher numbers have bigger difference with the desired scores.
  59                   */
  60                  getScore = function( contrastBackground, contrastSurroundingText ) {
  61                      var diffBackground = ( 7 >= contrastBackground ) ? 0 : 7 - contrastBackground,
  62                          diffSurroundingText = ( 3 >= contrastSurroundingText ) ? 0 : 3 - contrastSurroundingText;
  63  
  64                      return diffBackground + diffSurroundingText;
  65                  };
  66  
  67              item = {
  68                  color: colorObj,
  69                  contrastBackground: colorObj.getDistanceLuminosityFrom( self.bgColorObj ),
  70                  contrastText: colorObj.getDistanceLuminosityFrom( self.textColorObj )
  71              };
  72  
  73              // Check a minimum of 4.5:1 contrast with the background and 3:1 with surrounding text.
  74              if ( 4.5 > item.contrastBackground || 3 > item.contrastText ) {
  75                  return;
  76              }
  77  
  78              // Get a score for this color by multiplying the 2 contrasts.
  79              // We'll use that to sort the array.
  80              item.score = getScore( item.contrastBackground, item.contrastText );
  81  
  82              self.accentColorsArray.push( item );
  83          },
  84          s, l, aaa;
  85  
  86      this.accentColorsArray = [];
  87  
  88      // We're using `for` loops here because they perform marginally better than other loops.
  89      for ( s = minSaturation; s <= maxSaturation; s += stepSaturation ) {
  90          for ( l = minLightness; l <= maxLightness; l += stepLightness ) {
  91              pushColor( s, l );
  92          }
  93      }
  94  
  95      // Check if we have colors that are AAA compliant.
  96      aaa = this.accentColorsArray.filter( function( color ) {
  97          return 7 <= color.contrastBackground;
  98      } );
  99  
 100      // If we have AAA-compliant colors, always prefer them.
 101      if ( aaa.length ) {
 102          this.accentColorsArray = aaa;
 103      }
 104  
 105      // Sort colors by contrast.
 106      this.accentColorsArray.sort( function( a, b ) {
 107          return a.score - b.score;
 108      } );
 109      return this;
 110  };
 111  
 112  /**
 113   * Get accessible text-color.
 114   *
 115   * @since Twenty Twenty 1.0
 116   *
 117   * @return {Color} - Returns a Color object.
 118   */
 119  _twentyTwentyColor.prototype.getTextColor = function() {
 120      return this.textColor;
 121  };
 122  
 123  /**
 124   * Get accessible color for the defined accent-hue and background-color.
 125   *
 126   * @since Twenty Twenty 1.0
 127   *
 128   * @return {Color} - Returns a Color object.
 129   */
 130  _twentyTwentyColor.prototype.getAccentColor = function() {
 131      var fallback;
 132  
 133      // If we have colors returns the 1st one - it has the highest score.
 134      if ( this.accentColorsArray[0] ) {
 135          return this.accentColorsArray[0].color;
 136      }
 137  
 138      // Fallback.
 139      fallback = new Color( 'hsl(' + this.accentHue + ',75%,50%)' );
 140      return fallback.getReadableContrastingColor( this.bgColorObj, 4.5 );
 141  };
 142  
 143  /**
 144   * Return a new instance of the _twentyTwentyColor object.
 145   *
 146   * @since Twenty Twenty 1.0
 147   *
 148   * @param {string} backgroundColor - The background color.
 149   * @param {number} accentHue - The hue for our accent color.
 150   * @return {Object} - this
 151   */
 152  function twentyTwentyColor( backgroundColor, accentHue ) {// jshint ignore:line
 153      var color = new _twentyTwentyColor( backgroundColor, accentHue );
 154      color.setAccentColorsArray();
 155      return color;
 156  }