//
// Copyright 2017 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

@import "./constants";

// Calculate the luminance for a color.
// See https://www.w3.org/TR/WCAG20-TECHS/G17.html#G17-tests
@function mdc-theme-luminance($color) {
  $red: nth($mdc-theme-linear-channel-values, red($color) + 1);
  $green: nth($mdc-theme-linear-channel-values, green($color) + 1);
  $blue: nth($mdc-theme-linear-channel-values, blue($color) + 1);

  @return .2126 * $red + .7152 * $green + .0722 * $blue;
}

// Calculate the contrast ratio between two colors.
// See https://www.w3.org/TR/WCAG20-TECHS/G17.html#G17-tests
@function mdc-theme-contrast($back, $front) {
  $backLum: mdc-theme-luminance($back) + .05;
  $foreLum: mdc-theme-luminance($front) + .05;

  @return max($backLum, $foreLum) / min($backLum, $foreLum);
}

// Determine whether the color is "light" or "dark".
@function mdc-theme-tone($color) {
  @if $color == "dark" or $color == "light" {
    @return $color;
  }

  $minimumContrast: 3.1;

  $lightContrast: mdc-theme-contrast($color, white);
  $darkContrast: mdc-theme-contrast($color, rgba(black, .87));

  @if ($lightContrast < $minimumContrast) and ($darkContrast > $lightContrast) {
    @return "light";
  } @else {
    @return "dark";
  }
}

// Determine whether to use dark or light text on top of given color to meet accessibility standards for contrast.
// Returns "dark" if the given color is light and "light" if the given color is dark.
@function mdc-theme-contrast-tone($color) {
  @return if(mdc-theme-tone($color) == "dark", "light", "dark");
}