// The list of browsers you want to support.
// Defaults to all.
$supported-browsers: browsers() !default;

// The browser usage threshold for features that gracefully degrade
// Defaults to 1 user in 1,000.
$graceful-usage-threshold: 0.1 !default;

// The browser usage threshold for features that cannot degrade gracefully
// Defaults to 1 user in 10,000.
$critical-usage-threshold: 0.01 !default;

// Set this to true to generate comments that will explain why a prefix was included or omitted.
$debug-browser-support: false !default;

// Minimum browser versions that must be supported.
// The keys of this map are any valid browser according to `browsers()`.
// The values of this map are the min version that is valid for that browser
// according to `browser-versions($browser)`
$browser-minimum-versions: (
  'chrome':  null,
  'firefox': null,
  'ie':      null,
  'safari':  null,
  'opera':   null
) !default;


// @private
$default-capability-options: (
  (full-support: true),
  (partial-support: true)
);

// When a prefix in in context, but there is no current prefix
// That context is recorded here so other prefixes can be avoided.
$prefix-context: null;

// When a prefix is in a selector or directive scope, this is set to the
// current prefix value.  When `null`, either there is no prefix in scope
// or the official prefix is being rendered. The `$prefix-context`
// variable can be used to make that distinction.
$current-prefix: null;

// When in a context that only exists in a particular version
// this variable is set to those versions.
$current-browser-versions: ();

// The legacy support CSS 2.1 Selectors.
// Defaults to the $critical-usage-threshold.
$css-sel2-support-threshold: $critical-usage-threshold !default;

// Check if the browser is in scope given the current prefix minimums.
@function browser-out-of-scope($browser, $version: null) {
  @if not ($current-prefix == null or $current-prefix == browser-prefix($browser)) {
    @if $debug-browser-support {
      @return "#{$browser} #{$version} is incompatible with #{$current-prefix}."
    } @else {
      @return true;
    }
  }
  $current-range: map-get($current-browser-versions, $browser);
  $current-min: if($current-range, nth($current-range, 1), null);
  $current-max: if($current-range, nth($current-range, 2), null);
  @if not ($version and $current-max) {
    // We don't have any versions to compare
    @return false;
  } @else {
    // If the version is less than the current min, it is not supported
    $too-old: compare-browser-versions($browser, $version, $current-max) < 0;
    @if $too-old {
      @if $debug-browser-support {
        @return "The current scope only works with #{display-browser-range($browser, $current-min, $current-max)}.";
      } @else {
        @return true;
      }
    } @else {
      @return false;
    }
  }
}

// Check whether the browser is supported according to the declared minimum support
// and usage thresholds.
@function support-legacy-browser($browser, $min-version, $max-version: null, $threshold: $critical-usage-threshold) {
  // Check agaist usage stats and declared minimums
  $min-required-version: map-get($browser-minimum-versions, $browser);
  $usage: if($max-version,
             omitted-usage($browser, $min-version, $max-version),
             omitted-usage($browser, $min-version));
  @return $usage > $threshold or
          ($min-required-version and
           compare-browser-versions($browser, $max-version or $min-version, $min-required-version) >= 0);
}

// Include content for a legacy browser
// Version can be a single version string or a list of versions ordered from oldest to newest.
@mixin for-legacy-browser($browser, $min-version, $max-version: $min-version,
                          $threshold: $critical-usage-threshold,
                          $ranges: ($browser: $min-version $max-version)) {
  @if not browser-out-of-scope($browser, $max-version) and
      support-legacy-browser($browser, $min-version, $max-version, $threshold)
  {
    @if $debug-browser-support {
      /* Content for #{$browser} #{$version}.
      Min version: #{map-get($browser-minimum-versions, $browser) or unspecified}.
      User threshold to keep: #{$threshold}%. If #{$browser} #{$version} and below are omitted: #{omitted-usage($browser, $version)}%. */
    }
    @include with-browser-ranges(intersect-browser-ranges($current-browser-versions, $ranges)) {
      @content;
    }
  } @else if $debug-browser-support and browser-out-of-scope($browser, $max-version) {
    /* Content for #{display-browser-range($browser, $min-version, $max-version)} omitted.
       Not allowed in the current scope: #{browser-out-of-scope($browser, $max-version)} */
  } @else if $debug-browser-support and not
  support-legacy-browser($browser, $min-version, $max-version, $threshold) {
    @if omitted-usage($browser, $min-version, $max-version) > $threshold {
      /* Content for #{display-browser-range($browser, $min-version, $max-version)} omitted.
         User threshold to keep: #{$threshold}%. If #{display-browser-range($browser, $min-version, $max-version)} and below are omitted: #{omitted-usage($browser, $min-version, $max-version)}%. */
    } @else {
      /* Content for #{display-browser-range($browser, $min-version, $max-version)} omitted.
         Minimum support is #{map-get($browser-minimum-versions, $browser)}. */
    }
  }
}

@function display-browser-range($browser, $min-version, $max-version: $min-version) {
  @return "#{unquote($browser)} #{unquote($min-version)}#{if($max-version != $min-version, unquote(' -') unquote($max-version), null)}";
}


// Renders the content once if any of the legacy browsers are supported.
// $browsers is a map of browser name to version ranges
@mixin for-legacy-browsers($browsers, $threshold: $critical-usage-threshold) {
  $rendered: false;
  @each $browser, $range in $browsers {
    @if not $rendered {
      @include for-legacy-browser($browser, $range..., $threshold: $threshold, $ranges: $browsers) {
        $rendered: true;
        @content;
      }
    }
  }
}

// If there's a prefix context in scope, this will only output the content if the prefix matches.
// Otherwise, sets the current prefix scope and outputs the content.
@mixin with-prefix($prefix) {
  @if $current-prefix or $prefix-context {
    @if $current-prefix == $prefix or $prefix-context == $prefix {
      @if $debug-browser-support {
        @if $prefix {
          /* content for #{$prefix} because #{$current-prefix or $prefix-context} is already in scope. */
        } @else {
          /* unprefixed content. #{$current-prefix or $prefix-context} is already in scope. */
        }
      }
      $old-prefix-context: $prefix-context;
      $old-prefix: $current-prefix;
      $prefix-context: $prefix-context or $current-prefix !global;
      $current-prefix: $prefix !global;
      @content;
      $prefix-context: $old-prefix-context !global;
      $current-prefix: $old-prefix !global;
    } @else if $prefix == null {
      $old-prefix-context: $prefix-context;
      $prefix-context: $prefix-context or $current-prefix !global;
      $current-prefix: null !global;
      @if $debug-browser-support {
        /* Content for official syntax. Prefix context is still #{$prefix-context}. */
      }
      @content;
      $current-prefix: $prefix-context !global;
      $prefix-context: $old-prefix-context !global;
    } @else if $debug-browser-support {
      /* Omitting content for #{$prefix} because #{$current-prefix} is already in scope. */
    }
  } @else {
    @if $debug-browser-support and $prefix {
      /* Creating new #{$prefix} context. */
    }
    $prefix-context: $prefix !global;
    $current-prefix: $prefix !global;
    @content;
    $current-prefix: null !global;
    $prefix-context: null !global;
  }
}

@function prefixes-for-capability($capability, $threshold, $capability-options: $default-capability-options) {
  $result: ();
  @each $prefix in browser-prefixes($supported-browsers) {
    $result: map-merge($result,
                      ($prefix: use-prefix($prefix, $capability, $threshold, $capability-options)));
  }
  @return $result;
}

// Yields to the mixin content once for each prefix required.
// The current prefix is set to the $current-prefix global for use by the included content.
// Also yields to the content once with $current-prefix set to null for the official version
// as long as there's not already a prefix in scope.
@mixin with-each-prefix($capability, $threshold, $capability-options: $default-capability-options) {
  @each $prefix, $should-use-prefix in prefixes-for-capability($capability, $threshold, $capability-options) {
    @if $should-use-prefix {
      @if $debug-browser-support and type-of($should-use-prefix) == list {
        /* Capability #{$capability} is prefixed with #{$prefix} because #{$should-use-prefix} is required. */
      } @else if $debug-browser-support and type-of($should-use-prefix) == number {
        /* Capability #{$capability} is prefixed with #{$prefix} because #{$should-use-prefix}% of users need it which is more than the threshold of #{$threshold}%. */
      }
      @include with-prefix($prefix) {
        @include with-browser-ranges($capability) {
          @content;
        }
      }
    } @else if $debug-browser-support {
      /* Capability #{$capability} is not prefixed with #{$prefix} because #{prefix-usage($prefix, $capability, $capability-options)}% of users are affected which is less than the threshold of #{$threshold}. */
    }
  }
  @include with-prefix(null) {
    @include with-browser-ranges($capability) {
      @content;
    }
  }
}

// Returns true if at least one browser-version pair in $subset-ranges
// is a higher (or same) version than the browser-version pairs in
// $ranges.
@function has-browser-subset($ranges, $subset-ranges) {
  $found-mismatch: false;
  @each $browser, $subset-range in $subset-ranges {
    $range: map-get($ranges, $browser);
    @if $range {
      $min-1: nth($subset-range, 1);
      $max-1: nth($subset-range, 2);
      $min-2: nth($range, 1);
      $max-2: nth($range, 2);
      @if (compare-browser-versions($browser, $min-2, $min-1) <= 0 and
           compare-browser-versions($browser, $min-1, $max-2) <= 0) or
          (compare-browser-versions($browser, $min-2, $max-1) <= 0 and
           compare-browser-versions($browser, $max-1, $max-2) <= 0) or
          (compare-browser-versions($browser, $min-1, $min-2) <= 0 and
           compare-browser-versions($browser, $max-1, $max-2) >= 0) or
          (compare-browser-versions($browser, $min-1, $min-2) >= 0 and
           compare-browser-versions($browser, $max-1, $max-2) <= 0) {
        @return true;
      } @else {
        $found-mismatch: true
      }
    }
  }
  @return not $found-mismatch;
}

// When the same browser is in both maps, then the minimum will be set
// to the maximum of the two minimum versions, and the maximum will be
// set to the minmum of the two maximum versions.
@function intersect-browser-ranges($ranges, $new-ranges) {
  @each $browser, $new-range in $new-ranges {
    $old-range: map-get($ranges, $browser);
    @if $old-range {
      $old-min: nth($old-range, 1);
      $old-max: nth($old-range, 2);
      $new-min: nth($new-range, 1);
      $new-max: nth($new-range, 2);
      $maximin: if(compare-browser-versions($browser, $old-min, $new-min) > 0,
                   $old-min, $new-min);
      $minimax: if(compare-browser-versions($browser, $old-max, $new-max) < 0,
                   $old-max, $new-max);
      $ranges: map-merge($ranges, ($browser: $maximin $minimax));
    } @else {
      $ranges: map-merge($ranges, ($browser: $new-range));
    }
  }
  @return $ranges;
}

// If passed a map, that will be the new browser ranges.
// Otherwise a range map will be created based on the given capability and prefix
// using the `browser-ranges($capability, $prefix)` function.
//
// If there are current ranges in scope and the new ranges have some overlap
// with the current, 
//
// If there is no overlap, then the content will not be rendered.
@mixin with-browser-ranges($capability, $prefix: $current-prefix) {
  $new-ranges: null;
  @if type-of($capability) == map {
    $new-ranges: $capability;
  } @else {
    $new-ranges: browser-ranges($capability, $prefix);
  }

  @if has-browser-subset($current-browser-versions, $new-ranges) {
    $old-ranges: $current-browser-versions;
    $current-browser-versions: intersect-browser-ranges($old-ranges, $new-ranges) !global;
    @content;
    $current-browser-versions: $old-ranges !global;
  } @else if $debug-browser-support {
    /* Excluding content because #{inspect($new-ranges)} is not included within
       #{inspect($current-browser-versions)} */
  }
}

// Returns true if the prefixed usage stats for the capability exceed the threshold
// or if the minimum version for a supported browser would require a prefix for the capability.
@function use-prefix($prefix, $capability, $threshold, $capability-options: $default-capability-options) {
  $usage: prefix-usage($prefix, $capability, $capability-options);
  @if $usage > $threshold {
    @return $usage;
  } @else {
    @each $browser in browsers($prefix) {
      @if index($supported-browsers, $browser) {
        $min-version: map-get($browser-minimum-versions, $browser);
        @if $min-version {
          $actual-prefix: browser-requires-prefix($browser, $min-version, $capability, $capability-options);
          @if $actual-prefix and $prefix == $actual-prefix {
            @return $browser $min-version;
          }
        }
      }
    }
  }
  @return false;
}

@function prefix-identifier($ident, $prefix: $current-prefix) {
  @return unquote("#{$prefix}#{if($prefix, '-', null)}#{$ident}");
}

// Output a property and value using the current prefix.
// It will be unprefixed if $current-prefix is null.
@mixin prefix-prop($property, $value, $prefix: $current-prefix) {
  #{prefix-identifier($property, $prefix)}: $value;
}

// Emit a set of properties with the prefix governed by the capability and usage threshold given.
//
// Example:
//
//     @include prefixed-properties(css-animation, $animation-support-threshold,
//       (animation-name: foo, animation-duration: 2s)
//     );
@mixin prefixed-properties($capability, $threshold, $properties, $capability-options: $default-capability-options) {
  @include with-each-prefix($capability, $threshold, $capability-options) {
    @each $prop, $value in $properties {
      @include prefix-prop($prop, $value);
    }
  }
}


// @private
@function warn-about-old-variables() {
  $old-variables-in-use: ();
  @each $old-variable-name in
        (legacy-support-for-ie, legacy-support-for-ie6, legacy-support-for-ie7,
         legacy-support-for-ie8, legacy-support-for-mozilla, legacy-support-for-webkit,
         experimental-support-for-mozilla, experimental-support-for-webkit,
         experimental-support-for-opera, experimental-support-for-microsoft,
         experimental-support-for-khtml, experimental-support-for-svg)
  {
    @if global-variable-exists($old-variable-name) {
      $old-variables-in-use: append($old-variables-in-use,
                                    unquote("$#{$old-variable-name}"), comma);
    }
  }
  @if length($old-variables-in-use) > 0 {
    @warn "Compass has changed how browser support is configured. " +
          "See the CHANGELOG for more details. The following configuration variables " +
          "are no longer supported: #{$old-variables-in-use}."
  }
  @return $old-variables-in-use;
}

// @private
@function warn-about-pie-removal() {
  @if global-variable-exists(experimental-support-for-pie) {
    @warn "Compass no longer supports css3pie.";
  }
  @return true;
}

// Enable browser support debugging within the content block.
// Or you can enable it for the whole stylesheet by setting `$debug-browser-support` to true.
@mixin with-browser-support-debugging {
  $current-status: $debug-browser-support;
  $debug-browser-support: true !global;
  @content;
  $debug-browser-support: $current-status !global;
}

// Set a default value if the given arglist is empty
@function set-arglist-default($arglist, $default) {
  $default-index: index($arglist, default);
  @if $default-index {
    $arglist: set-nth($arglist, $default-index, $default)
  }
  @return if(length($arglist) > 0, $arglist, $default);
}


// @private
$old-variable-warnings-issued: warn-about-old-variables() !default;

// @private
$pie-removal-warnging-issued: warn-about-pie-removal() !default;

// @private
@function warn-about-useless-prefix-arguments($moz: null, $webkit: null, $o: null, $khtml: null, $official: null) {
  @if $moz != null or $webkit != null or $o != null or $khtml != null or $official != null {
    @warn "Browser prefix arguments to this mixin are no longer used and " +
          "will be removed in the next release.";
  }
  @return true;
}

// coerce a list to be comma delimited or make a new, empty comma delimited list.
@function comma-list($list: ()) {
  @return join((), $list, comma);
}

// @private Returns the legacy value for a given box-model
// - Used by background-clip and -origin.
@function legacy-box($box) {
  $box: unquote($box);
  @if $box == padding-box { $box: padding; }
  @if $box == border-box { $box: border; }
  @if $box == content-box { $box: content; }
  @return $box;
}