node_modules/mdl-ext/src/_functions.scss

///
/// Returns the opposite direction of each direction in a list
/// Modified from: https://css-tricks.com/snippets/sass/opposite-direction-function/
/// @author Hugo Giraudel
/// @param {List} $directions - List of initial directions
/// @return {List} - List of opposite directions
@function mdlext-opposite-direction($directions) {
  $opposite-directions: ();
  $direction-map: (
    'top':    'bottom',
    'right':  'left',
    'bottom': 'top',
    'left':   'right',
    'center': 'center',
    'ltr':    'rtl',
    'rtl':    'ltr'
  );

  @each $direction in $directions {
    $direction: to-lower-case($direction);

    @if map-has-key($direction-map, $direction) {
      $opposite-directions: append($opposite-directions, unquote(map-get($direction-map, $direction)));
    }
    @else {
      @warn "No opposite direction can be found for `#{$direction}`. Direction omitted.";
    }
  }

  @return $opposite-directions;
}

///
/// Strip unit from value
/// @author Hugo Giraudel
/// http://hugogiraudel.com/2013/08/12/sass-functions/
/// https://css-tricks.com/snippets/sass/strip-unit-function/
/// @param {Number} $number - Number to remove unit from
/// @return {Number} - Unitless number

@function strip-unit($number) {
  @return if(type-of($number) == 'number' and not unitless($number), $number / ($number * 0 + 1), $number);
}

///
/// Clamping a number means restricting it between min and max values.
///    4 clamped to 1-3 equals 3.
///   -5 clamped to 1-10 equals 1.
///   42 clamped to 10-100 equals 42.
/// @author Hugo Giraudel
/// http://hugogiraudel.com/2013/08/12/sass-functions/
/// @param {Number} $value - The value to clamp
/// @param {Number} $min - min value in range
/// @param {Number} $max - Max value in range
/// @return {Number} - The clamped value

@function clamp($value, $min, $max) {
  @return if($value > $max, $max, if($value < $min, $min, $value));
}

///
/// Convert one unit into another
/// @author Hugo Giraudel
/// http://www.sitepoint.com/understanding-sass-units/
/// @param {Number} $value - Initial value
/// @param {String} $unit - Desired unit
/// @return {Number}
/// @throw Error if `$unit` does not exist or if units are incompatible.

/* stylelint-disable */
@function convert-unit($value, $unit) {
  $units: (
    'px'  : 0px,
    'cm'  : 0cm,
    'mm'  : 0mm,
    '%'   : 0%,
    'ch'  : 0ch,
    'in'  : 0in,
    'em'  : 0em,
    'rem' : 0rem,
    'pt'  : 0pt,
    'pc'  : 0pc,
    'ex'  : 0ex,
    'vw'  : 0vw,
    'vh'  : 0vh,
    'vmin': 0vmin,
    'vmax': 0vmax,
    'deg' : 0deg,
    'turn': 0turn,
    'rad' : 0rad,
    'grad': 0grad,
    's'   : 0s,
    'ms'  : 0ms,
    'Hz'  : 0Hz,
    'kHz' : 0kHz,
    'dppx': 0dppx,
    'dpcm': 0dpcm,
    'dpi' : 0dpi,
  );

  @if map-has-key($units, $unit) {
    @return map-get($units, $unit) + $value;
  }

  @error "Unknown unit `#{$unit}`.";
}
/* stylelint-enable */


///
/// Replace `$search` with `$replace` in `$string`
/// @author Hugo Giraudel, http://hugogiraudel.com/2014/01/13/sass-string-replacement-function/
/// @param {String} $string - Initial string
/// @param {String} $search - Substring to replace
/// @param {String} $replace ('') - New value
/// @return {String} - Updated string
@function str-replace($string, $search, $replace: '') {
  $index: str-index($string, $search);

  @if $index {
    @return str-slice($string, 1, $index - 1) + $replace + str-replace(str-slice($string, $index + str-length($search)), $search, $replace);
  }
  @return $string;
}

///
/// @function explode() -- split a string into a list of strings
/// @author https://gist.github.com/danielpchen/3677421ea15dcf2579ff
///  {string} $string: the string to be split
///  {string} $delimiter: the boundary string
///  @return {list} the result list
@function explode($string, $delimiter: ',') {
  $result: ();
  @if $delimiter == "" {
    @for $i from 1 through str-length($string) {
      $result: append($result, str-slice($string, $i, $i));
    }
    @return $result;
  }
  $exploding: true;
  @while $exploding {
    $d-index: str-index($string, $delimiter);
    @if $d-index {
      @if $d-index > 1 {
        $result: append($result, str-slice($string, 1, $d-index - 1));
        $string: str-slice($string, $d-index + str-length($delimiter));
      }
      @else if $d-index == 1 {
        $string: str-slice($string, 1, $d-index + str-length($delimiter));
      }
      @else {
        $result: append($result, $string);
        $exploding: false;
      }
    }
    @else {
      $result: append($result, $string);
      $exploding: false;
    }
  }
  @return $result;
}

///
/// Add `$unit` to `$value`
/// @author Hugo Giraudel
///
/// @param {Number} $value - Value to add unit to
/// @param {String} $unit - String representation of the unit
///
/// @return {Number} - `$value` expressed in `$unit`
/// @throw Error if `$unit` does not exist or if units are incompatible.
///
@function to-length($value, $unit) {
  $units: (
    'px'  : 1px,
    'cm'  : 1cm,
    'mm'  : 1mm,
    '%'   : 1%,
    'ch'  : 1ch,
    'pc'  : 1pc,
    'in'  : 1in,
    'em'  : 1em,
    'rem' : 1rem,
    'pt'  : 1pt,
    'ex'  : 1ex,
    'vw'  : 1vw,
    'vh'  : 1vh,
    'vmin': 1vmin,
    'vmax': 1vmax
  );

  @if not index(map-keys($units), $unit) {
    @error('Invalid unit `#{$unit}`.');
  }

  @return $value * map-get($units, $unit);
}

///
/// Casts a string into a number
///
/// @author Hugo Giraudel
// @param {String | Number} $value - Value to be parsed
///
/// @return {Number}
/// @throw Error if `$value` is not a number or a string.
///
@function to-number($value) {
  @if type-of($value) == 'number' {
    @return $value;
  }
  @else if type-of($value) != 'string' {
    @error('Value for `to-number` should be a number or a string.');
  }

  $result: 0;
  $digits: 0;
  $minus: str-slice($value, 1, 1) == '-';
  $numbers: ('0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9);

  @for $i from if($minus, 2, 1) through str-length($value) {
    $character: str-slice($value, $i, $i);

    @if not (index(map-keys($numbers), $character) or $character == '.') {
      @return to-length(if($minus, -$result, $result), str-slice($value, $i));
    }

    @if $character == '.' {
      $digits: 1;
    }
    @else if $digits == 0 {
      $result: $result * 10 + map-get($numbers, $character);
    }
    @else {
      $digits: $digits * 10;
      $result: $result + map-get($numbers, $character) / $digits;
    }
  }

  @return if($minus, -$result, $result);
}

///
/// Convert `$rgb-string` to a number list
/// @author Leif Olsen
/// @param {String | Number} $value - Value to be parsed
/// @return {list} the rgb number list
/// @throw Error if `$value` is not a number, color or a string.
@function rgb-string-to-numbers($value) {
  @if type-of($value) == 'number' or type-of($value) == 'color' {
    @return $value;
  }
  @else if type-of($value) != 'string' {
    @error('Value for `rgb-string-to-numbers` should be a number or a string.');
  }

  $s: str-replace($value, "rgba");
  $s: str-replace($s, "rgb");
  $s: str-replace($s, "(");
  $s: str-replace($s, ")");
  $s: str-replace($s, " ");
  $l: explode($s);
  $result: ();
  @for $i from 1 through length($l) {
    $result: append($result, to-number(nth($l, $i)));
  }
  @return $result;
}

///
/// Convert `$rgb-string` to a corresponding hex value
/// @author Leif Olsen
/// @param {String | Number} $value - Value to be parsed
/// @return {number} the rgb hex value
/// @throw Error if `$value` is not a number, color or a string.
@function rgb-string-to-hex($value) {
  @if type-of($value) == 'number' or type-of($value) == 'color' {
    @return $value;
  }
  @else if type-of($value) != 'string' {
    @error('Value for `rgb-string-to-numbers` should be a number or a string.');
  }
  $l: rgb-string-to-numbers($value);
  @return rgb(nth($l, 1), nth($l, 2), nth($l, 3));
}


///
/// Convert hex color to a coresponding `$rgb-string`
/// @author https://github.com/google/material-design-lite/issues/1689
/// @param {Number} $hexColor - Value to convert
/// @return {String} the rgb string value
///
/// @example - $color-primary: hex-to-string(#333);
@function hex-to-rgb-string($hexColor) {
  // 0.999999 val in alpha actually compiles to 1.0
  $rgbaVal:  inspect(rgba($hexColor, 0.9999999));

  // slice substring between 'rgba(' and '1.0)'
  @return str-slice($rgbaVal, 6, str-length($rgbaVal)-4);
}