SCSS @mixin for choosing a `font-family` and optional `font-display`

font-family()

/// @type List
$font-stack-primary: Georgia, serif !default;

/// @type List
$font-stack-secondary: Arial, sans-serif !default;

/// @type List
$font-stack-tertiary: Tahoma, sans-serif !default;

/// @type Map
/// @prop {String} key - Font Family name
/// @prop {Number} value - Font Family value
$font-families: (
    "primary":   $font-stack-primary,
    "secondary": $font-stack-secondary,
    "tertiary":  $font-stack-tertiary
}


///
/// Specify font-family and associated font-display
///
/// @param {String} $family - Font Family value
/// @param {String} $display - Font Display value
///
/// @require {Variable} $font-families
///
/// @example scss
///   @include font-family(primary);
///   // font-family: Georgia, serif;
///
/// @example scss
///   @include font-family(secondary, swap);
///   // font-family: Arial, sans-serif;
///   // font-display: swap;
///
/// @throw Error if no parameters are passed.
///
@mixin font-family($family, $display) {

    @if( length($family) == 0 ) {
        @error "font-family() expects at least one parameter."
    }

    @if not map-has-key($font-families, $family) {
        @error "There is no font-family named `#{$family}` in $font-families. Font Family should be one of #{map-keys($font-families)}.";
    }

    font-family: map-get($font-families, $family);

    @if( length($display) != 0 ) {
        font-display: $display;
    }

}