sp-codes.de/bower_components/foundation-sites/scss/util/_breakpoint.scss

// Foundation for Sites by ZURB
// foundation.zurb.com
// Licensed under MIT Open Source

////
/// @group breakpoints
////

// scss-lint:disable ZeroUnit

/// A list of named breakpoints. You can use these with the `breakpoint()` mixin to quickly create media queries.
/// @type Map
$breakpoints: (
  small: 0,
  medium: 640px,
  large: 1024px,
  xlarge: 1200px,
  xxlarge: 1440px,
) !default;

$-zf-zero-breakpoint: small !default;

@if nth(map-values($breakpoints), 1) != 0 {
  @error 'Your smallest breakpoint (defined in $breakpoints) must be set to "0".';
}
@else {
  $-zf-zero-breakpoint: nth(map-keys($breakpoints), 1);
}

/// All of the names in this list will be output as classes in your CSS, like `.small-12`, `.medium-6`, and so on. Each value in this list must also be in the `$breakpoints` map.
/// @type List
$breakpoint-classes: (small medium large) !default;

/// Generates a media query string matching the input value. Refer to the documentation for the `breakpoint()` mixin to see what the possible inputs are.
///
/// @param {Keyword|Number} $val [small] - Breakpoint name, or px, rem, or em value to process.
@function breakpoint($val: $-zf-zero-breakpoint) {
  // Size or keyword
  $bp: nth($val, 1);
  // Value for max-width media queries
  $bp-max: 0;
  // Direction of media query (up, down, or only)
  $dir: if(length($val) > 1, nth($val, 2), up);
  // Eventual output
  $str: '';
  // Is it a named media query?
  $named: false;

  // Orientation media queries have a unique syntax
  @if $bp == 'landscape' or $bp == 'portrait' {
    @return '(orientation: #{$bp})';
  }
  @else if $bp == 'retina' {
    @return '(-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi)';
  }

  // Try to pull a named breakpoint out of the $breakpoints map
  @if type-of($bp) == 'string' {
    @if map-has-key($breakpoints, $bp) {
      @if $dir == 'only' or $dir == 'down' {
        $bp-max: -zf-map-next($breakpoints, $bp);
      }

      $bp: map-get($breakpoints, $bp);
      $named: true;
    }
    @else {
      $bp: 0;
      @warn 'breakpoint(): "#{$val}" is not defined in your $breakpoints setting.';
    }
  }

  // Convert any pixel, rem, or unitless value to em
  $bp: -zf-bp-to-em($bp);
  @if $bp-max {
    $bp-max: -zf-bp-to-em($bp-max) - (1/16);
  }

  // Conditions to skip media query creation
  // - It's a named breakpoint that resolved to "0 down" or "0 up"
  // - It's a numeric breakpoint that resolved to "0 " + anything
  @if $bp > 0em or $dir == 'only' or $dir == 'down' {
    // `only` ranges use the format `(min-width: n) and (max-width: n)`
    @if $dir == 'only' {
      // Only named media queries can have an "only" range
      @if $named == true {
        // Only use "min-width" if the floor is greater than 0
        @if $bp > 0em {
          $str: $str + '(min-width: #{$bp})';

          // Only add "and" to the media query if there's a ceiling
          @if $bp-max != null {
            $str: $str + ' and ';
          }
        }

        // Only use "max-width" if there's a ceiling
        @if $bp-max != null {
          $str: $str + '(max-width: #{$bp-max})';
        }
      }
      @else {
        @warn 'breakpoint(): Only named media queries can have an `only` range.';
      }
    }

    // `down` ranges use the format `(max-width: n)`
    @else if $dir == 'down' {
      $max: if($named, $bp-max, $bp);

      // Skip media query creation if input value is exactly "0 down",
      // unless the function was called as "small down", in which case it's just "small only"
      @if $named or $bp > 0em {
        @if $max != null {
          $str: $str + '(max-width: #{$max})';
        }
      }
    }

    // `up` ranges use the format `(min-width: n)`
    @else if $bp > 0em {
      $str: $str + '(min-width: #{$bp})';
    }
  }

  @return $str;
}

/// Wraps a media query around the content you put inside the mixin. This mixin accepts a number of values:
///  - If a string is passed, the mixin will look for it in the `$breakpoints` map, and use a media query there.
///  - If a pixel value is passed, it will be converted to an em value using `$global-font-size` as the base.
///  - If a rem value is passed, the unit will be changed to em.
///  - If an em value is passed, the value will be used as-is.
///
/// @param {Keyword|Number} $value - Breakpoint name, or px, rem, or em value to process.
///
/// @output If the breakpoint is "0px and larger", outputs the content as-is. Otherwise, outputs the content wrapped in a media query.
@mixin breakpoint($value) {
  $str: breakpoint($value);

  // If $str is still an empty string, no media query is needed
  @if $str == '' {
    @content;
  }

  // Otherwise, wrap the content in a media query
  @else {
    @media screen and #{$str} {
      @content;
    }
  }
}

/// Convers the breakpoints map to a URL-encoded string, like this: `key1=value1&key2=value2`. The value is then dropped into the CSS for a special `<meta>` tag, which is read by the Foundation JavaScript. This is how we transfer values from Sass to JavaScript, so they can be defined in one place.
/// @access private
///
/// @param {Map} $map - Map to convert.
///
/// @returns {String} A string containing the map's contents.
@function -zf-bp-serialize($map) {
  $str: '';
  @each $key, $value in $map {
    $str: $str + $key + '=' + -zf-bp-to-em($value) + '&';
  }
  $str: str-slice($str, 1, -2);

  @return $str;
}

/// Find the next key in a map.
/// @access private
///
/// @param {Map} $map - Map to traverse.
/// @param {Mixed} $key - Key to use as a starting point.
///
/// @returns {Mixed} The value for the key after `$key`, if `$key` was found. If `$key` was not found, or `$key` was the last value in the map, returns `null`.
@function -zf-map-next($map, $key) {
  // Store the values of the map as a list, so we can access them with nth
  $values: map-values($map);

  // Ghetto for loop
  $i: 1;
  $found: false;
  @each $val in map-keys($map) {
    @if $found == false {
      @if ($key == $val) {
        $found: true;
      }
      $i: $i + 1;
    }
  }

  // If the key doesn't exist, or it's the last key in the map, return null
  @if $i > length($map) {
    @return null;
  }
  // Otherwise, return the value
  @else {
    @return nth($values, $i);
  }
}

/// Get a value for a breakpoint from a responsive config map. If the config map has the key `$value`, the exact breakpoint value is returned. If the config map does *not* have the breakpoint, the value matching the next lowest breakpoint in the config map is returned.
/// @access private
///
/// @param {Map} $map - Input config map.
/// @param {Keyword} $value - Breakpoint name to use.
///
/// @return {Mixed} The corresponding breakpoint value.
@function -zf-get-bp-val($map, $value) {
  // Check if the breakpoint name exists globally
  @if not map-has-key($breakpoints, $value) {
    @return null;
  }
  // Check if the breakpoint name exists in the local config map
  @else if map-has-key($map, $value) {
    // If it does, just return the value
    @return map-get($map, $value);
  }
  // Otherwise, find the next lowest breakpoint and return that value
  @else {
    $anchor: null;
    $found: false;

    @each $key, $val in $breakpoints {
      @if not $found {
        @if map-has-key($map, $key) {
          $anchor: $key;
        }
        @if $key == $value {
          $found: true;
        }
      }
    }

    @return map-get($map, $anchor);
  }
}

// Legacy breakpoint variables
// These will be removed in 6.3
$small-up: null;
$small-only: null;
$medium-up: null;
$medium-only: null;
$large-up: null;
$large-only: null;
$xlarge-up: null;
$xlarge-only: null;
$xxlarge-up: null;
$xxlarge-only: null;

@if map-has-key($breakpoints, small) {
  $small-up: screen;
  $small-only: unquote('screen and #{breakpoint(small only)}');
}

@if map-has-key($breakpoints, medium) {
  $medium-up: unquote('screen and #{breakpoint(medium)}');
  $medium-only: unquote('screen and #{breakpoint(medium only)}');
}

@if map-has-key($breakpoints, large) {
  $large-up: unquote('screen and #{breakpoint(large)}');
  $large-only: unquote('screen and #{breakpoint(large only)}');
}

@if map-has-key($breakpoints, xlarge) {
  $xlarge-up: unquote('screen and #{breakpoint(xlarge)}');
  $xlarge-only: unquote('screen and #{breakpoint(xlarge only)}');
}

@if map-has-key($breakpoints, xxlarge) {
  $xxlarge-up: unquote('screen and #{breakpoint(xxlarge)}');
}