@use 'sass:math';
@use 'sass:map';
@use 'sass:meta';

// from compass
// https://github.com/Compass/compass/blob/d5df161d0df7edc686e576b22412f437dd0590cc/core/stylesheets/compass/typography/_units.scss

// @private Default font-size for all browsers
$browser-default-font-size: 16px;

// Base font size in pixels, if not already defined.
// Should be the same as the font-size of the html element.
$base-font-size: 16px !default;

// Whether to output fallback values in px when outputting rems.
$rem-with-px-fallback: true !default;

// Convert any CSS <length> or <percentage> value to any another.
//
// @param $length
//   A css <length> or <percentage> value
//
// @param $to-unit
//   String matching a css unit keyword, e.g. 'em', '%', etc.
//
// @param $from-context
//   When converting from relative units, the absolute length (in px) to
//   which $length refers (e.g. for $lengths in em units, would normally be the
//   font-size of the current element).
//
// @param $to-context
//   For converting to relative units, the absolute length in px to which the
//   output value will refer. Defaults to the same as $from-context, since it is
//   rarely needed.
@function convert-length(
  $length,
  $to-unit,
  $from-context: $base-font-size,
  $to-context: $from-context
) {
  $from-unit: math.unit($length);

  // Optimize for cases where `from` and `to` units are accidentally the same.
  @if $from-unit == $to-unit {
    @return $length;
  }

  // Context values must be in px so we can determine a conversion ratio for
  // relative units.
  @if math.unit($from-context) != 'px' {
    @warn "Paremeter $from-context must resolve to a value in pixel units.";
  }
  @if math.unit($to-context) != 'px' {
    @warn "Parameter $to-context must resolve to a value in pixel units.";
  }

  // Convert input length to pixels
  $px-length: $length;

  @if $from-unit != 'px' {
    // Convert relative units using the from-context parameter.
    @if $from-unit == 'em' {
      $px-length: $length * $from-context / 1em;
    } @else if $from-unit == 'rem' {
      $px-length: $length * $base-font-size / 1rem;
    } @else if $from-unit == '%' {
      $px-length: $length * $from-context / 100%;
    } @else if $from-unit == 'ex' {
      $px-length: $length * $from-context / 2ex;
    }
    // Convert absolute units using Sass' conversion table.
    @else if
      $from-unit ==
      'in' or
      $from-unit ==
      'mm' or
      $from-unit ==
      'cm' or
      $from-unit ==
      'pt' or
      $from-unit ==
      'pc'
    {
      $px-length: 0px + $length;
    }
    // Certain units can't be converted.
    @else if
      $from-unit ==
      'ch' or
      $from-unit ==
      'vw' or
      $from-unit ==
      'vh' or
      $from-unit ==
      'vmin'
    {
      @warn "#{$from-unit} units can't be reliably converted; Returning original value.";
      @return $length;
    } @else {
      @warn "#{$from-unit} is an unknown length unit. Returning original value.";
      @return $length;
    }
  }

  // Convert length in pixels to the output unit
  $output-length: $px-length;
  @if $to-unit != 'px' {
    // Relative units
    @if $to-unit == 'em' {
      $output-length: $px-length * 1em / $to-context;
    } @else if $to-unit == 'rem' {
      $output-length: math.div($px-length * 1rem, $base-font-size);
    } @else if $to-unit == '%' {
      $output-length: $px-length * 100% / $to-context;
    } @else if $to-unit == 'ex' {
      $output-length: $px-length * 2ex / $to-context;
    }
    // Absolute units
    @else if $to-unit == 'in' {
      $output-length: 0in + $px-length;
    } @else if $to-unit == 'mm' {
      $output-length: 0mm + $px-length;
    } @else if $to-unit == 'cm' {
      $output-length: 0cm + $px-length;
    } @else if $to-unit == 'pt' {
      $output-length: 0pt + $px-length;
    } @else if $to-unit == 'pc' {
      $output-length: 0pc + $px-length;
    }
    // Non-convertible units
    @else if
      $to-unit ==
      'ch' or
      $to-unit ==
      'vw' or
      $to-unit ==
      'vh' or
      $to-unit ==
      'vmin'
    {
      @warn "#{$to-unit} units can't be reliably converted; Returning original value.";
      @return $length;
    } @else {
      @warn "#{$to-unit} is an unknown length unit. Returning original value.";
      @return $length;
    }
  }

  @return $output-length;
}

// @private Get the px/rem versions of a value.
@function rem-fallback-values($value) {
  $_return: (
    px: $value,
    rem: $value
  );

  @if meta.type-of($value) == number and not math.is-unitless($value) {
    @if math.unit($value) == rem {
      $_return: map.merge(
        $_return,
        (
          px: math.round(convert-length($value, px))
        )
      );
    } @else if math.unit($value) == px {
      $_return: map.merge(
        $_return,
        (
          px: math.round($value),
          rem: convert-length($value, rem)
        )
      );
    }
  }

  @return $_return;
}

// @private Get the px/rem versions of a list (or nested lists).
@function list-convert-rems($value) {
  $_empty: (
    px: (),
    rem: ()
  );
  $_return: $_empty;
  $_sep: null;

  @if meta.type-of($value) == list {
    $_sep: list-separator($value);
    @each $sub in $value {
      $_this: list-convert-rems($sub);
      $_return: (
        px: append(map.get($_return, px), map.get($_this, px), $_sep),
        rem: append(map.get($_return, rem), map.get($_this, rem), $_sep)
      );
    }
  } @else {
    $_this: rem-fallback-values($value);
    $_return: map.merge($_return, $_this);
  }

  @return $_return;
}

// Output a given style rule containing rem values along with an (optional)
// fallback rule for older browsers (with rem values converted to px).
//
// @param $property
//   The css property name.
//
// @param $values
//   The value or list of values for the property.
//
// @param $use-px-fallback
//   [ true | false ]
//
@mixin rem($property, $values, $use-px-fallback: $rem-with-px-fallback) {
  // get converted values.
  $values: list-convert-rems($values);
  $px-values: map.get($values, px);
  $values: map.get($values, rem);

  // Use pixel fallback for browsers that don't understand rem units.
  @if $use-px-fallback and $px-values != $values {
    #{$property}: $px-values;
  }

  // Use rem values for everyone else (overrides pixel values).
  #{$property}: $values;
}
