@function __is-space($char-code) {
    @return $char-code == ' ';
}


@function __chars-index($string, $chars, $direction) {
    $index: 1;
    $length: str-length($string);
    $direction-map: ('right': -1, 'left': 1);
    $increment: map-get($direction-map, $direction);

    @while str-index($chars, __char-at($string, $index))
    and $index <= $length {
        $index: $index + $increment;
    }

    @return $index;
}


@function __chars-left-index($string, $chars) {
    @return __chars-index($string, $chars, $direction: left);
}


@function __chars-right-index($string, $chars) {
    @return __chars-index($string, $chars, $direction: right);
}


@function __get-char-code($char, $args...) {
    $chars: __const('ASCII_PRINTABLE');
    $char: __to-string($char);

    @if not $char or $char == '' {
        @return null;
    }

    @each $char-code, $char-value in $chars {
        @if $char == $char-value {
            @return $char-code;
        }
    }

    @return null;
}


@function __char-at-callback($string, $args...) {
    @return __get-char-code(str-slice($string, 1, 1));
}


@function __char-at($string, $index: 1) {
    @return str-slice($string, $index, $index);
}


@function __char-code-at($string, $index: 1) {
    @return __get-char-code(__char-at($string, $index));
}


/// Gets the character at `$index` of a string.
/// 
/// @access public
/// @group String
/// @param {String} $string - Source string.
/// @param {Number} $index [1] - Character index in string.
/// @returns {number} Returns character at string index, or `null` if index is not in string.
/// @example scss
/// $foo: _char-at('coffee', 4);
/// // => 'f'

@function _char-at($args...) {
    @return call(get-function('__char-at'), $args...);
}


/// Gets the ASCII char code of a character at `$index` of a string.
/// 
/// @access public
/// @group String
/// @param {String} $string - Source string.
/// @param {number} $index [1] - Character index in string.
/// @returns {number} Returns char code of character at given string index.
/// @example scss
/// $foo: _char-code-at('beach', 3);
/// // => 97

@function _char-code-at($args...) {
    @return call(get-function('__char-code-at'), $args...);
}


/// Gets the ASCII char code of a given character.
/// 
/// @access public
/// @group String
/// @param {String} $char - Source character.
/// @returns {number} Returns char code of given character.
/// @example scss
/// $foo: _get-char-code('a');
/// // => 97

@function _get-char-code($args...) {
    @return call(get-function('__get-char-code'), $args...);
}


/// @alias _get-char-code

@function _char-code($args...) {
    @return call(get-function('__get-char-code'), $args...);
}