// Nick's web site: SCSS colourmap helpers for automatic light/dark styles.
//
// Copyright © 2022 Nick Bowler
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

// database of colour names
$colourmap: ();

// database of combination CSS properties that should be translated to
// colour-only properties (e.g., border-top -> border-top-color).
$_colourpropmap:
    ( border-top: border-top-color
    , border-bottom: border-bottom-color
    , border-left: border-left-color
    , border-right: border-right-color
    , border: border-color
    );

// Define a named set of colours.  Pass keyword arguments with each keyword
// being a colour name and the argument is a list of one or two colours.
//
// When two colours are specified, the first should be for "light" backgrounds
// and the second for "dark".
//
// For example:
//
//   @include defcolours($bg: white black, $fg: black white);
@mixin defcolours($args...) {
    @each $colour, $list in keywords($args) {
        $colourmap: map-merge($colourmap, ($colour: $list)) !global;
    }
}

// Obtain the colour value for a previously-defined colour name.  By
// default, its primary (light) colour value is returned; this can be
// changed with the $num keyword parameter.
//
// The $pre and $post keyword arguments may be used to supplement the
// result with additional tokens either before or after the colour
// value, respectively, as might be used for combined properties
// such as border, outline, etc.
@function getcolour($colour, $pre: (), $post: (), $num: 1) {
    @return join(append($pre, nth(map-get($colourmap, $colour), $num)), $post);
}

@mixin usecolour_dark_($prop, $colour, $pre: (), $post: ()) {
    @if (length(map-get($colourmap, $colour)) > 1) {
        $transprop: map-get($_colourpropmap, $prop);
        @if $transprop {
            #{$transprop}: getcolour($colour, $num: 2)
        } @else {
            #{$prop}: getcolour($colour, $pre, $post, 2);
        }
    }
}

// Sets the given CSS property to the specified colour name.  The $pre
// and $post keyword arguments may be used to supplement the property
// value, as with the getcolour function.
//
// For two-value colours, the property is set using CSS variables to
// adapt the colour based on the user's preference for a light or dark
// background.  The rules will fall back to the static (light) colour
// if CSS variables are not supported.
//
// For example:
//
//   @include usecolour(border, fg, $pre: solid 1px);
@mixin usecolour($prop, $colour, $pre: (), $post: ()) {
    #{$prop}: getcolour($colour, $pre, $post);
    @at-root {
        @media (prefers-color-scheme: dark) {
            & { @include usecolour_dark_($prop, $colour, $pre, $post); }
        }
    }
}

// Convenience helper to assign multiple colour properties at once, for
// the common case where the $pre and $post arguments to usecolour are
// not required.
//
// Takes any number of keyword arguments with the keyword being the
// property name and the value being the colour name.
//
// For example:
//
//   @include usecolours($background-color: bg, $color: fg);
@mixin usecolours($args...) {
    @each $prop, $colour in keywords($args) {
        #{$prop}: getcolour($colour);
    }
    @at-root {
        @media (prefers-color-scheme: dark) {
            & {
                @each $prop, $colour in keywords($args) {
                    @include usecolour_dark_($prop, $colour);
                }
            }
        }
    }
}