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

/// Changes a color to have the required luminance
/// @since 1.12.0 - The Sith
/// @param {Color} $color - Color to be modified
/// @param {Number} $target-luminance - a number between 0 and 1
/// @return {Color} - modified color
/// @todo DRY out the checks on line 36-49
@function scale-luminance($color, $target-luminance) {
	// First, scale the channels by the required amount
	$scale: $target-luminance / luminance($color);

	// And clip them, so we don't end up dividing by zero... among other things I forget
	$red: clip(xyz(red($color))) * $scale;
	$green: clip(xyz(green($color))) * $scale;
	$blue: clip(xyz(blue($color))) * $scale;

	// Sometimes, that's not enough and one channel hits #ff or #0. We'll need to scale the other channels to compensate
	$red-passes: in-bounds($red);
	$green-passes: in-bounds($green);
	$blue-passes: in-bounds($blue);

	@if (not $red-passes or not $green-passes or not $blue-passes) {
		// First, pick a channel to be a baseline, so the rest can be expressed as ratios
		$baseline: min($red, $green, $blue);

		// Then set up the variables expressed in terms of the baseline
		$r: $red / $baseline;
		$g: $green / $baseline;
		$b: $blue / $baseline;

		// Subtract any channel no longer in bounds
		@if (not $red-passes) {
			$target-luminance: $target-luminance - .2126;
			$r: 0;
		}
		@if (not $green-passes) {
			$target-luminance: $target-luminance - .7152;
			$g: 0;
		}
		@if (not $blue-passes) {
			$target-luminance: $target-luminance - .0722;
			$b: 0;
		}

		// Now get the required difference by using the luminance() formula
		$x: $target-luminance / ($r * .2126 + $g * .7152 + $b * .722);

		// And multiply the channels by this new per-channel luminance
		@if ($red-passes) {
			$red: $r * $x;
		}
		@if ($green-passes) {
			$green: $g * $x;
		}
		@if ($blue-passes) {
			$blue: $b * $x;
		}
	}

	// Return the new color
	@return rgb(srgb($red), srgb($green), srgb($blue));
}