/// Select all children from the first to `$num`.
/// @param {Number} $num[] First `n` numbers of total children 
@mixin first($num) {
  @if $num == 1 {
    &:first-child {
      @content;
    }
  } @else {
    &:nth-child(-n + #{$num}) {
      @content;
    }
  }
}

/// Select the first exact child
@mixin first-child {
  &:first-of-type {
    @content;
  }
}

/// Select all children from the last to `$num`.
/// @param {Number} $num[] Last `n` numbers of total children 
@mixin last($num) {
  &:nth-last-child(-n + #{$num}) {
    @content;
  }
}

/// Select the last exact child
@mixin last-child {
  &:last-of-type {
    @content;
  }
}

/// Select children every `$num`.
/// @param {Number} $num[] Every `n` number of all children
@mixin every($num) {
  &:nth-child(#{$num}n) {
    @content;
  }
}

/// Select only the first and last child.
@mixin first-last {
  &:first-child,
  &:last-child {
    @content;
  }
}

/// Select all children after the first to `$num`.
/// @param {Number} $num[] After First `n` numbers of total children 
@mixin after-first($num) {
  &:nth-child(n + #{$num + 1}) {
    @content;
  }
}

/// Select all children before `$num` from the last.
/// @param {Number} $num[] From Last `n` numbers of total children 
@mixin from-last($num) {
  &:nth-last-child(#{$num}) {
    @content;
  }
}

/// Select the `$num` child from the first and the `$num` child from the last.
/// @param {Number} $num[] `n` number called from first and last 
@mixin from-first-last($num) {
  &:nth-child(#{$num}),
  &:nth-last-child(#{$num}) {
    @content;
  }
}

/// Select all children but `$num`.
/// @param {Number} $num[] `n` number that should be excluded from all other children 
@mixin all-but($num) {
  &:not(:nth-child(#{$num})) {
    @content;
  }
}

/// Select all children between the `$num` first and the `$num` last.
/// @param {Number} $num[] `n` number excluded from first and last from all other children
@mixin all-but-first-last($num) {
  &:nth-child(n + #{$num}):nth-last-child(n + #{$num}) {
    @content;
  }
}

/// Will only select the child if it's unique. That means that if there are at least 2 children, the style will not be applied.
@mixin unique {
  &:only-child {
    @content;
  }
}

/// Will only select children if they are not unique. That means that if there are at least 2 children, the style will be applied.
@mixin not-unique() {
  &:not(:only-child) {
    @content;
  }
}

/// Select all children between `$first` and `$last`.
/// @param {Number} $first[] First `nth` number
/// @param {Number} $last[] Last `nth` number
@mixin between($first, $last) {
  &:nth-child(n + #{$first}):nth-child(-n + #{$last}) {
    @content;
  }
}

/// Select all even children.
@mixin even {
  &:nth-child(even) {
    @content;
  }
}

/// Select all even children between `$first` and `$last`.
/// @param {Number} $first[] First `nth` number
/// @param {Number} $last[] Last `nth` number
@mixin even-between($first, $last) {
  &:nth-child(even):nth-child(n + #{$first}):nth-child(-n + #{$last}) {
    @content;
  }
}

/// Select all odd children.
@mixin odd {
  &:nth-child(odd) {
    @content;
  }
}

/// Select all odd children between `$first` and `$last`.
/// @param {Number} $first[] First `nth` number
/// @param {Number} $last[] Last `nth` number
@mixin odd-between($first, $last) {
  &:nth-child(odd):nth-child(n + #{$first}):nth-child(-n + #{$last}) {
    @content;
  }
}

/// Select all `$num` children between `$first` and `$last`.
/// @param {Number} $num[] Every `n` number between `$first` and `$last`.
/// @param {Number} $first[] First `n` number
/// @param {Number} $last[] Last `n` number
@mixin number-between($num, $first, $last) {
  &:nth-child(#{$num}n):nth-child(n + #{$first}):nth-child(-n + #{$last}) {
    @content;
  }
}
