//
// Copyright 2017 Google Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions://
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.//
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//

@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");
}