Compass/compass

@import "compass/utilities/color/brightness";

$contrasted-dark-default:   #000 !default;
$contrasted-light-default:  #fff !default;

// Returns either the `$light` or `$dark` color
// by deciding which contrasts more with `$color`.
//
// E.g. This can be used to select the more readable foreground color
// for a given background color.
//
// `$dark` defaults to black and `$light` defaults to white.
//
// When `$color` is `null`, this function returns `null`.
@function contrast-color(
  $color,
  $dark: $contrasted-dark-default,
  $light: $contrasted-light-default,
  $threshold: null
) {
  @if $threshold {
    // Deprecated in Compass 0.13
    @warn "The $threshold argment to contrast-color is no longer needed and will be removed in the next release."
  }
  @if $color == null {
    @return null;
  }
  @else {
    $color-brightness: brightness($color);
    $dark-text-brightness: brightness($dark);
    $light-text-brightness: brightness($light);

    @return if(abs($color-brightness - $light-text-brightness) > abs($color-brightness - $dark-text-brightness), $light, $dark);
  }
}

// Sets the specified background color and calculates a dark or light
// contrasted text color.  The arguments are passed through to the
// [contrast-color function](#function-contrast-color).
@mixin contrasted(
  $background-color,
  $dark: $contrasted-dark-default,
  $light: $contrasted-light-default,
  $threshold: null
) {
  @if $threshold {
    // Deprecated in Compass 0.13
    @warn "The $threshold argment to contrasted is no longer needed and will be removed in the next release."
  }
  background-color: $background-color;
  color: contrast-color($background-color, $dark, $light);
}