/*
  This file uses pow(), currently there is no such function
  in sass by default. Pow() can be added via node-sass custom
  functions or via eyeglass + eyeglass-math packages.

  There are a few examples of sass only pow, but they are way
  slower then node based solutions. (last I checked)
*/

@function luma($color){
  // Get sRGB values
  $sR: red($color)/255;
  $sG: green($color)/255;
  $sB: blue($color)/255;

  // Calculate luminance
  $R: if($sR <= 0.03928, $sR/12.92, pow(($sR + 0.055)/1.055, 2.4));
  $G: if($sG <= 0.03928, $sG/12.92, pow(($sG + 0.055)/1.055, 2.4));
  $B: if($sB <= 0.0392,  $sB/12.92, pow(($sB + 0.055)/1.055, 2.4));

  @return (0.2126 * $R + 0.7152 * $G + 0.0722 * $B);
}

@function contrast($color1, $color2: white){
  $luminance1: luma($color1) + .05;
  $luminance2: luma($color2) + .05;
  $ratio: $luminance1 / $luminance2;

  @if $luminance2 > $luminance1 {
    $ratio: 1 / $ratio;
  }

  @return $ratio;
}

@function compliantColor($sample, $against: white, $ratio: 4.5){
  $maxRatio: 21;
  $sampleRatio: contrast($sample, $against);

  @while $sampleRatio < $ratio {
    $sample: darken($sample, 1%);
    $sampleRatio: contrast($sample, $against);
  }

  @return $sample;
}

/*
  Will return a color that is a compliant text color
  against red. In this case the color we are checking is blue.
*/
$compliant: compliantColor(blue, $against: red, $ratio: 4.5);