// Support the last 4 versions of all browsers except IE.
$support-for: (
  chrome:  -4,
  edge:    25, // Current Windows Server & Xbox One version.
  firefox: 45, // Version 45 has "extended support" until June 13, 2017.
  ie:      9,
  opera:   -4,
  safari:  -4,
  '*':     -4,
) !default;

// Set the current version number for all browsers. As of: 2016-10-17
$support-for-current-browser-version: (
  chrome:  54, // https://en.wikipedia.org/wiki/Google_Chrome_release_history
  edge:    38, // https://en.wikipedia.org/wiki/Microsoft_Edge
  firefox: 49, // https://en.wikipedia.org/wiki/Firefox_version_history#Firefox_45.4_ESR
  ie:      11, // https://en.wikipedia.org/wiki/Internet_Explorer_versions
  opera:   40, // https://en.wikipedia.org/wiki/Opera_(web_browser)
  safari:  10, // https://en.wikipedia.org/wiki/Safari_version_history
) !default;


// support-for()
//
// Determines if the project has declared a minimum supported version number for
// the specified browser.
//
// If configured, this is a wrapper function that uses Compass'
// support-legacy-browser().
// @see http://compass-style.org/reference/compass/support/#function-support-legacy-browser
//
@function support-for($browser, $version) {
  // Ensure $version is an integer (or null).
  @if not (type-of($version) == "null" or type-of($version) == "number" and round($version) == $version) {
    @error "The $version parameter of support-for() must be an integer; #{type-of($version)} given.";
  }

  // Check against declared minimums.
  $min-version: null;
  @if map-has-key($support-for, $browser) {
    $min-version: map-get($support-for, $browser);
  }
  @else if map-has-key($support-for, '*') {
    $min-version: map-get($support-for, '*');
  }

  // Ensure $min-version is an integer (or null).
  @if type-of($min-version) != "null" and type-of($min-version) != "number" {
    @error "$support-for: (#{$browser}: #{$min-version}) must be set to an integer (or null); #{$min-version} is a #{type-of($min-version)}.";
  }
  @elseif type-of($min-version) == "number" and round($min-version) != $min-version {
    @error "$support-for: (#{$browser}: #{$min-version}) must be set to an integer (or null); #{$min-version} is not an integer.";
  }

  // Negative $min-version means "X most recent versions".
  @if type-of($min-version) == "number" and $min-version < 0 {
    @if not map-has-key($support-for-current-browser-version, $browser) {
      @error "#{$browser} not found in $support-for-current-browser-version map; it must be set to an integer.";
    }
    $min-version: map-get($support-for-current-browser-version, $browser) + $min-version + 1;
  }

  @return if(($min-version and ($version >= $min-version)), true, false);
}