// Black transparent background
@function black($opacity){
    @return rgba(0, 0, 0, $opacity);
}

// White transparent background
@function white($opacity){
    @return rgba(255, 255, 255, $opacity);
}

// Take a list of classes and generate a selector list
@function join-classes($classes, $inherit: true) {
    $selectors: ();

    @each $class in $classes {
        @if str-index($class, ".") != 0 {
            $class: "." + $class;
        }

        @if $inherit {
            $selectors: append($selectors, unquote("&" + $class), "comma");
        } @else {
            $selectors: append($selectors, unquote($class), "comma");
        }
    }

    @return $selectors;
}

// Remove the first selector character (#, ., etc) from the class name or ID
@function remove-selector($selector) {
    @return str-slice($selector, 2, str-length($selector));
}

// Generate a class name and apply an optional prefix
@function class-name($class, $prefix: $namespace, $selector: ".") {
    $name: $class;

    @if str_slice($class, 1, 1) == $selector {
        $name: remove-selector($name);
    }

    @if $prefix != "" {
        $name: $prefix + $name;
    }

    @return $selector + $name;
}

// Format a class name into the BEM format
@function bem($block: "", $element: "", $modifier: "", $element-separator: $bem-element-separator, $modifier-separator: $bem-modifier-separator) {
    $name: $block;

    @if $element != "" {
        $name: $name + $element-separator + $element;
    }

    @if $modifier != "" {
        $name: $name + $modifier-separator + $modifier;
    }

    @return $name;
}

// Calculate the gutter spacing as a percentage.
// Use the max width of the grid to calculate against.
@function gutter($width, $gutter) {
    @return if($gutter, ((to-pixel($gutter) / to-pixel($width)) * 100 * 1%), 0%);
}

// Calculate the width of an individual element within a row.
// Take into account max widths and gutters.
@function span-width($n, $columns, $width, $gutter) {
    $row-width: 100%;
    $gutter-width: 0%;

    // If a gutter is set, remove width based on the sum of the gutter columns
    @if $gutter {
        $gutter-width: gutter($width, $gutter);
        $row-width: $row-width - ($gutter-width * ($columns - 1));
    }

    // The column width should span a division of the total width
    $span-width: ($row-width / $columns) * $n;

    // If a gutter is set, increase the column width to fill in the missing gaps
    @if $gutter and $n > 1 {
        $span-width: $span-width + (($n - 1) * $gutter-width);
    }

    @return $span-width;
}