@use 'sass:math';
@use 'sass:meta';
@use 'sass:string';
@use '../../functions/is-alias' as *;
@use '../../functions/is-length' as *;
@use '../../functions/is-number' as *;
@use '../../functions/is-string' as *;

/// Creates an inner box-shadow for only one side of an element.
///
/// @param {String} $side ['bottom'] - The inner side of the element where the
/// shadow is supposed to appear. Can be `top`, `left`, `right` or `bottom`.
/// @param {Number} $size [20px] - The width of the shadow on the target side.
/// Used in combination with $side to calculate all the values for the box-shadow.
/// @param {Color} $color [hsl(0, 0%, 0%, 0.33] - The color of the shadow.
///
/// @group Utilities
/// @require {function} is-alias
/// @require {function} is-length
/// @require {function} is-number
/// @require {function} is-string
/// @since 0.8.1 - Was not working in previous versions.
///
/// @throw Invalid $side value error. Must be either `top`, `right`, `bottom`,
/// or `left`.
/// @throw Invalid $size value error. Must be a length or a unitless number.
@mixin inner-side-shadow(
  $side: 'bottom',
  $size: 20px,
  $color: hsla(0, 0%, 0%, 0.33)
) {
  $helper: 0;

  @if $side and is-string($side) {
    $side: string.to-lower-case($side);
  }

  @if $size and is-number($size) and $size != 0 {
    @if math.is-unitless($size) {
      $size: $size * 1px;
    }

    @if not is-length($size) {
      @error 'Invalid $size input for the [ inner-side-shadow() ] mixin. ' +
          'The value for $size should either be a valid length or a unitless ' +
          'number (would be converted to pixels).';
    }
  }

  $helper: math.round($size * 0.65);

  @if is-alias('top', $side) {
    box-shadow: inset 0 $helper $size (-1) * $helper $color;
  } @else if is-alias('left', $side) {
    box-shadow: inset $helper 0 $size (-1) * $helper $color;
  } @else if is-alias('right', $side) {
    box-shadow: inset (-1) * $helper 0 $size (-1) * $helper $color;
  } @else if is-alias('bottom', $side) {
    box-shadow: inset 0 (-1) * $helper $size (-1) * $helper $color;
  } @else {
    @error 'Invalid $side value of #{meta.inspect($side)} for the ' +
        '[ inner-side-shadow() ] mixin. Accepted values are `top`, `right`, ' +
        '`bottom`, and `left`.';
  }
}