////
/// @author Giana Blantin
////

/// Checks if two colors pass minimum contrast requirements
/// @link https://www.w3.org/TR/2016/NOTE-WCAG20-TECHS-20161007/G18#G18-procedure
/// @since 1.12.0 - The Sith
/// @param {Color} $color1 - 1st color to test the contrast against
/// @param {Color} $color2 ["$body-color"] - 2nd color to test the contrast against
/// @param {String | Number} $min-ratio ["AA"] - minimum ratio to test against. Accepted values for this ratio argument are AA and AAALG (4.5:1), AALG (3:1) and AAA (7:1) or a number between 1 and 21.
/// @param {Bool} $return-ratio ["false"] - option to return ratio instead of true/false
/// @return {Number | Bool} - A ratio or boolean if the colors meet the min-ratio
/// @example scss
///   // true/false & using a number as `$min-ratio`
///   check-contrast(#2aaabf, #2b2f31, 3)
///   // true
///
///   // ratio & using a keyword as `$min-ratio`
///   check-contrast(#ffbb9b, #91966d, AAALG, true)
///   // 1.8908
///
///   // if contrast between blue & white passes, use gray, otherwise use #fff
///   .image-caption {
///     color: if( check-contrast(blue, white, AAA), gray, #fff );
///   }
@function check-contrast($color1, $color2, $min-ratio: "AA", $return-ratio: false) {
	// Accept keywords for ratio
	@if ($min-ratio == "AA" or $min-ratio == "AAALG") {
		$min-ratio: 4.5;
	} @elseif ($min-ratio == "AALG") {
		$min-ratio: 3;
	} @elseif ($min-ratio == "AAA") {
		$min-ratio: 7;
	}

	// Check brightness of each color
	$lum1: luminance($color1);
	$lum2: luminance($color2);

	// Measure contrast ratio
	$ratio: (max($lum1, $lum2) + .05) / (min($lum1, $lum2) + .05);

	// Return ratio if option set
	@if ($return-ratio) {
		@return $ratio;
	}

	// Else return boolean
	@return if($ratio >= $min-ratio, true, false);
}