//************************************************************************//
// Background property for adding multiple backgrounds using shorthand
// notation.
//************************************************************************//

@mixin background(
  $background-1       , $background-2: null,
  $background-3: null, $background-4: null,
  $background-5: null, $background-6: null,
  $background-7: null, $background-8: null,
  $background-9: null, $background-10: null,
  $fallback: null
) {
  $backgrounds: $background-1, $background-2,
                $background-3, $background-4,
                $background-5, $background-6,
                $background-7, $background-8,
                $background-9, $background-10;

  $fallback-color: false;
  @if (type-of($fallback) == color) or ($fallback == "transparent") {
    $fallback-color: $fallback;
  }
  @else {
    $fallback-color: _extract-background-color($backgrounds);
  }

  @if $fallback-color {
    background-color: $fallback-color;
  }
  background: _background-add-prefix($backgrounds, webkit);
  background: _background-add-prefix($backgrounds);
}

@function _extract-background-color($backgrounds) {
  $final-bg-layer: nth($backgrounds, length($backgrounds));
  @if type-of($final-bg-layer) == list {
    @for $i from 1 through length($final-bg-layer) {
      $value: nth($final-bg-layer, $i);
      @if type-of($value) == color {
        @return $value;
      }
    }
  }
  @return false;
}

@function _background-add-prefix($backgrounds, $vendor: false) {
  $backgrounds-prefixed: ();

  @for $i from 1 through length($backgrounds) {
    $shorthand: nth($backgrounds, $i); // Get member for current index
    $type: type-of($shorthand); // Get type of variable - List (gradient) or String (image)

    // If shorthand is a list (gradient)
    @if $type == list {
      $first-member: nth($shorthand, 1); // Get first member of shorthand

      // Linear Gradient
      @if index(linear radial, nth($first-member, 1)) {
        $gradient-type: nth($first-member, 1); // linear || radial
        $gradient-args:      false;
        $gradient-positions: false;
        $shorthand-start:    false;
        @if type-of($first-member) == list { // Linear gradient plus additional shorthand values - lg(red,orange)repeat,...
          $gradient-positions: nth($first-member, 2);
          $gradient-args:      nth($first-member, 3);
          $shorthand-start: 2;
        }
        @else { // Linear gradient only - lg(red,orange),...
          $gradient-positions: nth($shorthand, 2);
          $gradient-args:      nth($shorthand, 3); // Get gradient (red, blue)
        }

        $gradient-positions: _gradient-positions-parser($gradient-type, $gradient-positions);
        $gradient: _render-gradients($gradient-positions, $gradient-args, $gradient-type, $vendor);

        // Append any additional shorthand args to gradient
        @if $shorthand-start {
          @for $j from $shorthand-start through length($shorthand) {
            $gradient: join($gradient, nth($shorthand, $j), space);
          }
        }
        $backgrounds-prefixed: append($backgrounds-prefixed, $gradient, comma);
      }
      // Image with additional properties
      @else {
        $backgrounds-prefixed: append($backgrounds-prefixed, $shorthand, comma);
      }
    }
    // If shorthand is a simple string (color or image)
    @else if $type == string {
      $backgrounds-prefixed: join($backgrounds-prefixed, $shorthand, comma);
    }
  }
  @return $backgrounds-prefixed;
}

//Examples:
  //@include background(linear-gradient(top, orange, red));
  //@include background(radial-gradient(circle at 40% 40%, orange, red));
  //@include background(url("/images/a.png") no-repeat, linear-gradient(orange, red));
  //@include background(url("image.png") center center, linear-gradient(orange, red), url("image.png"));
