// Adds $value at $index in $list
// -------------------------------------------------------------------------------
// @documentation http://sassylists.com/documentation/#insert-nth
// -------------------------------------------------------------------------------
// @example insert-nth(a b c,  2, z) => a z d c
// @example insert-nth(a b c,  0, z) => error
// @example insert-nth(a b c, -1, z) => error
// @example insert-nth(a b c, 10, z) => a b c z
// -------------------------------------------------------------------------------
// @param $list [List] : list
// @param $index [Number] : index to add
// @param $value [Literal] : value to add
// -------------------------------------------------------------------------------
// @raise [Error] if $index isn't an integer
// @raise [Error] if $index is strictly lesser than 1
// @raise [Error] if $index is strictly greater than length of $list
// -------------------------------------------------------------------------------
// @return [List] | false

@function insert-nth($list, $index, $value) {
    $result: false;

    @if type-of($index) != number {
        @warn "List index #{$index} is not a number for `insert-nth`.";
        @return $result;
    }

    @else if $index < 1 {
        @warn "List index #{$index} must be a non-zero integer for `insert-nth`";
        @return $result;
    }

    @else if $index > length($list) {
        @return append($list, $value);
    }

    @else {
        $result: ();

        @for $i from 1 through length($list) {
            @if $i == $index {
                @if $value and $value != "" and $value != () {
                    $result: append($result, $value);
                }
            }

            $result: append($result, nth($list, $i));
        }
    }

    @return $result;
}