// Scaling Variables
@use "sass:math";

$golden: 1.618;
$minor-second: 1.067;
$major-second: 1.125;
$minor-third: 1.2;
$major-third: 1.25;
$perfect-fourth: 1.333;
$augmented-fourth: 1.414;
$perfect-fifth: 1.5;
$minor-sixth: 1.6;
$major-sixth: 1.667;
$minor-seventh: 1.778;
$major-seventh: 1.875;
$octave: 2;
$major-tenth: 2.5;
$major-eleventh: 2.667;
$major-twelfth: 3;
$double-octave: 4;

$modular-scale-ratio: $perfect-fourth !default;
$modular-scale-base: em($em-base) !default;

@function modular-scale($increment, $value: $modular-scale-base, $ratio: $modular-scale-ratio) {
    $v1: nth($value, 1);
    $v2: nth($value, length($value));
    $value: $v1;

    // scale $v2 to just above $v1
    @while $v2 > $v1 {
        $v2: math.div($v2, $ratio); // will be off-by-1
    }
    @while $v2 < $v1 {
        $v2: ($v2 * $ratio); // will fix off-by-1
    }

    // check AFTER scaling $v2 to prevent double-counting corner-case
    $double-stranded: $v2 > $v1;

    @if $increment > 0 {
        @for $i from 1 through $increment {
            @if $double-stranded and ($v1 * $ratio) > $v2 {
                $value: $v2;
                $v2: ($v2 * $ratio);
            } @else {
                $v1: ($v1 * $ratio);
                $value: $v1;
            }
        }
    }

    @if $increment < 0 {
        // adjust $v2 to just below $v1
        @if $double-stranded {
            $v2: math.div($v2, $ratio);
        }

        @for $i from $increment through -1 {
            @if $double-stranded and math.div($v1, $ratio) < $v2 {
                $value: $v2;
                $v2: math.div($v2, $ratio);
            } @else {
                $v1: math.div($v1, $ratio);
                $value: $v1;
            }
        }
    }

    @return $value;
}