/* stylelint-disable scss/dollar-variable-pattern */
/* stylelint-disable scss/at-function-pattern */

@use 'sass:color';
@use 'sass:list';
@use 'sass:map';
@use 'sass:math';

$SA98G: (
    mainTRC:     2.4,

    sRco:        .2126729, 
    sGco:        .7151522, 
    sBco:        .072175,

    normBG:      .56, 
    normTXT:     .57,
    revTXT:      .62,
    revBG:       .65,

    blkThrs:     .022,
    blkClmp:     1.414,
    scaleBoW:    1.14,
    scaleWoB:    1.14,
    loBoWoffset: .027,
    loWoBoffset: .027,
    deltaYmin:   .0005,
    loClip:      .0001,

    mFactor:     1.9468554433171,
    mOffsetIn:   .0387393816571401,
    mExpAdj:     .283343396420869,
    mOffsetOut:  .312865795870758,
);

@function apca_sRGB_to_Y($color) {
    $rgb: color.to-space($color, rgb);

    @return map.get($SA98G, sRco) * math.pow(math.div(color.channel($rgb, 'red'), 255), map.get($SA98G, mainTRC)) +
        map.get($SA98G, sGco) * math.pow(math.div(color.channel($rgb, 'green'), 255), map.get($SA98G, mainTRC)) +
        map.get($SA98G, sBco) * math.pow(math.div(color.channel($rgb, 'blue'), 255), map.get($SA98G, mainTRC));
}

@function apca_Y_to_sRGB($y) {
    $c: math.round(math.pow($y, math.div(1, map.get($SA98G, mainTRC))) * 255);
    @return rgb($c, $c, $c);
}

@function apcaContrast($txtY, $bgY) {
    $icp:  1.1;

    @if math.min($txtY, $bgY) < list.nth($icp, 1) or math.max($txtY, $bgY) > list.nth($icp, 2) {
        @return 0;
    }

    @if $txtY <= map.get($SA98G, blkThrs) {
        $txtY: $txtY + math.pow(map.get($SA98G, blkThrs) - $txtY, map.get($SA98G, blkClmp));
    }
    @if $bgY <= map.get($SA98G, blkThrs) {
        $bgY: $bgY + math.pow(map.get($SA98G, blkThrs) - $bgY, map.get($SA98G, blkClmp));
    }

    @if math.abs($bgY - $txtY) < map.get($SA98G, deltaYmin) {
        @return 0;
    }

    $outputContrast: 0;

    @if $bgY > $txtY {
        $SAPC: map.get($SA98G, scaleBoW) * (math.pow($bgY, map.get($SA98G, normBG)) - math.pow($txtY, map.get($SA98G, normTXT)));
        
        @if $SAPC >= map.get($SA98G, loClip) {
            $outputContrast: $SAPC - map.get($SA98G, loBoWoffset);
        }
    } @else {
        $SAPC: map.get($SA98G, scaleWoB) * (math.pow($bgY, map.get($SA98G, revBG)) - math.pow($txtY, map.get($SA98G, revTXT)));
        
        @if $SAPC <= -1 * map.get($SA98G, loClip) {
            $outputContrast: $SAPC + map.get($SA98G, loWoBoffset);
        }
    }

    @return $outputContrast * 100;
}

@function apcaReverse($contrast, $knownY, $knownType: 'bg') {
    $unknownY:   $knownY;

    $knownExp:   0;
    $unknownExp: 0;

    $scale:  map.get($SA98G, if($contrast > 0, scaleBoW, scaleWoB));
    $offset: map.get($SA98G, if($contrast > 0, loBoWoffset, loWoBoffset));

    $contrast: math.div($contrast * .01 + $offset, $scale);

    @if $knownY <= map.get($SA98G, blkThrs) {
        $knownY: $knownY + math.pow(map.get($SA98G, blkThrs) - $knownY, map.get($SA98G, blkClmp));
    }

    @if $knownType == 'bg' {
        $knownExp:   map.get($SA98G, if($contrast > 0, normBG, revBG));
        $unknownExp: map.get($SA98G, if($contrast > 0, normTXT, revTXT));
        $unknownY:   math.pow(math.pow($knownY, $knownExp) - $contrast, math.div(1, $unknownExp));
    } @else {
        $knownExp:   map.get($SA98G, if($contrast > 0, normTXT, revTXT));
        $unknownExp: map.get($SA98G, if($contrast > 0, normBG, revBG));
        $unknownY:   math.pow($contrast + math.pow($knownY, $knownExp), math.div(1, $unknownExp));
    }

    @if '#{$unknownY}' == '#{math.sqrt(-1)}' {
        @return false;
    }

    @if $unknownY > 1.06 or $unknownY < 0 {
        @return false;
    }

    @if $unknownY <= map.get($SA98G, blkThrs) {
        $unknownY: math.pow(($unknownY + map.get($SA98G, mOffsetIn)) * map.get($SA98G, mFactor),
            math.div(map.get($SA98G, mExpAdj), map.get($SA98G, blkClmp))) * math.div(1, map.get($SA98G, mFactor)) - map.get($SA98G, mOffsetOut);
    }

    $unknownY: math.max(math.min($unknownY, 1), 0);

    @return $unknownY;
}