/// Calculating Levenshtein distance between strings `$a` and `$b`.
/// @since 1.2.0
/// @param {String} $a - first string
/// @param {String} $b - second string
/// @return {Number}
@function _ss-levenshtein($a, $b) {
  $a: to-lower-case($a);
  $b: to-lower-case($b);

  $n: str-length($a);
  $m: str-length($b);

  $matrix: _ss-matrix($n + 1, $m + 1);
  $cost: _ss-matrix($n, $m);

  @if $a == $b { @return 0; }
  @if $n == 0  { @return $m; }
  @if $m == 0  { @return $n; }

  @for $i from 0 through $n  {
    @for $j from 0 through $m  {
      $v: if($i == 0, $j, if($j == 0, $i, 0));
      @if $v != 0 {
        $matrix: _ss-set-matrix($matrix, $i + 1, $j + 1, $v);
      }
      @if $i != 0 and $j != 0 {
        $v: if(str-slice($a, $i, $i) == str-slice($b, $j, $j), 0, 1);
        @if $v != 0 {
          $cost: _ss-set-matrix($cost, $i, $j, $v);
        }
      }
    }
  }

  @for $i from 2 through length($matrix) {
    @for $j from 2 through length(nth($matrix, $i)) {
      $matrix: _ss-set-matrix($matrix, $i, $j, min(_ss-e($matrix, $i - 1, $j) + 1, _ss-e($matrix, $i, $j - 1) + 1, _ss-e($matrix, $i - 1, $j - 1) + _ss-e($cost, $i - 1, $j - 1)));
    }
  }

  @return _ss-e($matrix, length($matrix), length(nth($matrix, 1)));
}

/// Helper to target an element in a matrix
/// @access private
/// @param {Number} $m - matrix
/// @param {Number} $x - x coord
/// @param {Number} $y - y coord
/// @return {Number}
@function _ss-e($m, $x, $y) {
  @return nth(nth($m, $x), $y);
}

/// Helper instanciation a matrix of $x by $y
/// @access private
/// @param {Number} $x - number of cols
/// @param {Number} $y - number of lines
/// @return {List}
@function _ss-matrix($x, $y) {
  $matrix: ();

  @for $i from 1 through $x {
    $tmp: ();

    @for $y from 1 through $y {
      $tmp: append($tmp, 0)
    }

    $matrix: append($matrix, $tmp);
  }

  @return $matrix;
}

/// Helper assigning $value at $matrix[$x, $y]
/// @access private
/// @param {Number} $matrix - matrix to update
/// @param {Number} $x      - x coord
/// @param {Number} $y      - y coord
/// @param {Number} $value  - value to assign at $matrix[$x, $y]
/// @return {List}
@function _ss-set-matrix($matrix, $x, $y, $value) {
    @return set-nth($matrix, $x, set-nth(nth($matrix, $x), $y, $value));
}