/// Select all children from the first to `$num`.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - id of the child
@mixin first($num) {
    &:nth-child(-n + #{$num}) {
        @content;
    }
}

/// Select all children from the last to `$num`.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - id of the child
@mixin last($num) {
    &:nth-last-child(-n + #{$num}) {
        @content;
    }
}

/// Select all children after the first to `$num`.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - id of the child
@mixin after-first($num) {
    &:nth-child(n + #{$num + 1}) {
        @content;
    }
}

/// Select all children before `$num` from the last.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - id of the child
@mixin from-end($num) {
    &:nth-last-child(#{$num}) {
        @content;
    }
}

/// Select all children between `$first` and `$last`.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin between($first, $last) {
    &:nth-child(n + #{$first}):nth-child(-n + #{$last}) {
        @content;
    }
}

/// Select all even children between `$first` and `$last`.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin pair-between($first, $last) {
    &:nth-child(even):nth-child(n + #{$first}):nth-child(-n + #{$last}) {
        @content;
    }
}

/// Select all odd children between `$first` and `$last`.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin impair-between($first, $last) {
    &:nth-child(odd):nth-child(n + #{$first}):nth-child(-n + #{$last}) {
        @content;
    }
}

/// Select all `$num` children between `$first` and `$last`.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin n-between($num, $first, $last) {
    &:nth-child(#{$num}n):nth-child(n + #{$first}):nth-child(-n + #{$last}) {
        @content;
    }
}

/// Select all children but `$num`.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - id of the child
@mixin all-but($num) {
    &:not(:nth-child(#{$num})) {
        @content;
    }
}

/// Select children each `$num`.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - id of the child
/// @alias every
@mixin each($num) {
    &:nth-child(#{$num}n) {
        @content;
    }
}

/// Select children each `$num`.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - id of the child
@mixin every($num) {
    &:nth-child(#{$num}n) {
        @content;
    }
}

/// Select the `$num` child from the start and the `$num` child from the last.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - id of the child
@mixin from-first-last($num) {
    &:nth-child(#{$num}),
    &:nth-last-child(#{$num}) {
        @content;
    }
}

/// Select the item in the middle of `$num` child. Only works with odd number
/// chain.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - id of the child
@mixin middle($num) {
    &:nth-child(#{round($num / 2)}) {
        @content;
    }
}

/// Select all children between the `$num` first and the `$num` last.
/// @group with-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - id of the child
@mixin all-but-first-last($num) {
    &:nth-child(n + #{$num}):nth-last-child(n + #{$num}) {
        @content;
    }
}

/// This I/O mixin will only select the first of `$limit` items. It will not
/// work if there is not as much as item as you set in `$limit`.
/// @group io
/// @param {number} $limit
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin first-of($limit) {
    &:nth-last-child(#{$limit}):first-child {
        @content;
    }
}

/// This I/O mixin will only select the last of `$limit` items. It will not
/// if there is not as much as item as you set in `$limit`.
/// @group io
/// @param {number} $limit
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin last-of($limit) {
    &:nth-of-type(#{$limit}):nth-last-of-type(1) {
        @content;
    }
}

/// Select all even children.
/// @group no-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin even() {
    &:nth-child(even) {
        @content;
    }
}

/// Select all odd children.
/// @group no-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin odd() {
    &:nth-child(odd) {
        @content;
    }
}

/// Select only the first and last child.
/// @group no-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin first-last() {
    &:first-child,
    &:last-child {
        @content;
    }
}

/// Will only select the child if it’s unique.
/// @group no-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @alias only
@mixin unique() {
    &:only-child {
        @content;
    }
}

/// Will only select the child if it’s unique.
/// @group no-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin only() {
    &:only-child {
        @content;
    }
}

/// Will only select children if they are not unique. Meaning if there is at
/// least 2 children, the style is applied.
/// @group no-arguments
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
@mixin not-unique() {
    &:not(:only-child) {
        @content;
    }
}

/// This mixin is used to automatically sort z-index in numerical order. But it
/// can also sort them in anti-numerical order, depending the parameters you use.
/// @group using functions
/// @content [Write the style you want to apply to the children, and it will be added within the @content directive]
/// @param {number} $num - Number of children
/// @param {string} $direction [forward] - Direction of the sort
/// @param {number} $index [0] - Index of the sorting
@mixin child-index($num, $direction: 'forward', $index: 0) {
    @for $i from 1 through $num {
        @if ($direction == 'forward') {
            &:nth-child(#{$i}) {
                z-index: order-index($i, $index);
                @content;
            }
        } @else if ($direction == 'backward') {
            &:nth-last-child(#{$i}) {
                z-index: order-index($i, $index);
                @content;
            }
        }
    }
}

/// Used by the child-index mixin. It will returned the proper sorted numbers
/// depending on the `$index` value.
/// @access private
/// @param {number} $num - Number of children
/// @param {number} $index - Index of the sorting
@function order-index($i, $index) {
    @return ($index + $i);
}
