@function __string-index-of($string, $target, $position: 0) {
    $string: str-slice($string, $position);
    $string-index: str-index($string, $target);

    @if not $string-index {
        @return -1;
    }

    @return $string-index + $position - 1;
}


@function __string-last-index-of($string, $target, $position: 0) {
    $current-index: __string-index-of($string, $target, $position);
    $last-index: -1;

    @while $current-index != -1 {
        $last-index: $current-index;
        $current-index: __string-index-of($string, $target, $last-index + 1);
    }

    @return $last-index;
}


@function __base-index-of($list, $value, $from-index: 1) {
    $length: length($list);
    $index: $from-index;

    @if __is-falsey($index) {
        $index: 1;
    }

    @while $index <= $length {
        @if nth($list, $index) == $value {
            @return $index;
        }

        $index: $index + 1;
    }

    @return -1;
}


@function __index-of($list, $value: $__undefined__, $from-index: 1) {
    $length: if($list, length($list), 0);

    @if ($length == 0) {
        @return -1;
    }

    @if __is-number($from-index) {
        $from-index: if($from-index < 0, max($length + $from-index, 0), $from-index);
    } @else if not (__is-falsey($from-index)) {
        $index: __binary-index($list, $value);
        $other: nth($list, $index);

        @return if($value == $other, $index, -1);
    }

    @return __base-index-of($list, $value, $from-index);
}


@function __last-index-of($list, $value: null, $from-index: length($list)) {
    $length: if($list, length($list), 0);

    @if (__is-falsey($length)) {
        @return -1;
    }

    $index: $length;

    @if __is-number($from-index) {
        $index: if($from-index < 0, max($length + $from-index, 0), min($from-index - 1, $length - 1)) + 1;
    } @else if not (__is-falsey($from-index)) {
        $index: __binary-index($list, $value, true) - 1;

        $other: nth($list, $index);

        @return if($value == other, $index, -1);
    }

    @while ($index > 0) {
        @if (nth($list, $index) == $value) {
            @return $index;
        }

        $index: $index - 1;
    }

    @return -1;
}


/// Gets the index at which the first occurrence of `$value` is found in `$list`.
/// If `$from-index` is negative,
/// it is used as the offset from the end of `$list`. If `$list` is sorted
/// providing `true` for `$from-index` performs a faster binary search.
///
///
/// @access public
/// @group List
/// @param {List} $list The list to search.
/// @param {*} $value The value to search for.
/// @param {boolean|number} $from-index [1] - The index to search from or `true`
///  to perform a binary search on a sorted list.
/// @returns {number} Returns the index of the matched value, else `-1`.
/// @example scss
/// $foo: _index-of((1, 2, 1, 2), 2);
/// // => 2
/// 
/// // using `$from-index`
/// $foo: _index-of((1, 2, 1, 2), 2, 3);
/// // => 4
/// 
/// // performing a binary search
/// $foo: _index-of((1, 1, 2, 2), 3, true);
/// // => 3

@function _index-of($args...) {
    @return call(get-function('__index-of'), $args...);
}


/// This method is like `_index-of` except that it iterates over elements of
/// `$list` from right to left.
///
///
/// @access public
/// @group List
/// @param {List} $list The list to search.
/// @param {*} $value The value to search for.
/// @param {boolean|number} $from-index [length($list)] - The index to search from
///  or `true` to perform a binary search on a sorted list.
/// @returns {number} Returns the index of the matched value, else `-1`.
/// @example scss
/// $foo: _last-index-of((1, 2, 1, 2), 2);
/// // => 4
/// 
/// // using `$from-index`
/// $foo: _last-index-of((1, 2, 1, 2), 2, 2);
/// // => 2
/// 
/// // performing a binary search
/// $foo: _last-index-of((1, 1, 2, 2), 2, true);
/// // => 4

@function _last-index-of($args...) {
    @return call(get-function('__last-index-of'), $args...);
}