// Taken from: https://css-tricks.com/programming-sass-to-create-accessible-color-combinations/


// From https://github.com/material-components/material-components-web/blob/master/packages/mdc-theme/_constants.scss
//
// 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.
//

// Precomputed linear color channel values, for use in contrast calculations.
// See https://www.w3.org/TR/WCAG20-TECHS/G17.html#G17-tests
//
// Algorithm, for c in 0 to 255:
// f(c) {
//   c = c / 255;
//   return c < 0.03928 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4);
// }
//
// This lookup table is needed since there is no `pow` in SASS.
$linear-channel-values:
  0
  .0003035269835488375
  .000607053967097675
  .0009105809506465125
  .00121410793419535
  .0015176349177441874
  .001821161901293025
  .0021246888848418626
  .0024282158683907
  .0027317428519395373
  .003035269835488375
  .003346535763899161
  .003676507324047436
  .004024717018496307
  .004391442037410293
  .004776953480693729
  .005181516702338386
  .005605391624202723
  .006048833022857054
  .006512090792594475
  .006995410187265387
  .007499032043226175
  .008023192985384994
  .008568125618069307
  .009134058702220787
  .00972121732023785
  .010329823029626936
  .010960094006488246
  .011612245179743885
  .012286488356915872
  .012983032342173012
  .013702083047289686
  .014443843596092545
  .01520851442291271
  .01599629336550963
  .016807375752887384
  .017641954488384078
  .018500220128379697
  .019382360956935723
  .0202885630566524
  .021219010376003555
  .022173884793387385
  .02315336617811041
  .024157632448504756
  .02518685962736163
  .026241221894849898
  .027320891639074894
  .028426039504420793
  .0295568344378088
  .030713443732993635
  .03189603307301153
  .033104766570885055
  .03433980680868217
  .03560131487502034
  .03688945040110004
  .0382043715953465
  .03954623527673284
  .04091519690685319
  .042311410620809675
  .043735029256973465
  .04518620438567554
  .046665086336880095
  .04817182422688942
  .04970656598412723
  .05126945837404324
  .052860647023180246
  .05448027644244237
  .05612849004960009
  .05780543019106723
  .0595112381629812
  .06124605423161761
  .06301001765316767
  .06480326669290577
  .06662593864377289
  .06847816984440017
  .07036009569659588
  .07227185068231748
  .07421356838014963
  .07618538148130785
  .07818742180518633
  .08021982031446832
  .0822827071298148
  .08437621154414882
  .08650046203654976
  .08865558628577294
  .09084171118340768
  .09305896284668745
  .0953074666309647
  .09758734714186246
  .09989872824711389
  .10224173308810132
  .10461648409110419
  .10702310297826761
  .10946171077829933
  .1119324278369056
  .11443537382697373
  .11697066775851084
  .11953842798834562
  .12213877222960187
  .12477181756095049
  .12743768043564743
  .1301364766903643
  .13286832155381798
  .13563332965520566
  .13843161503245183
  .14126329114027164
  .14412847085805777
  .14702726649759498
  .14995978981060856
  .15292615199615017
  .1559264637078274
  .1589608350608804
  .162029375639111
  .1651321945016676
  .16826940018969075
  .1714411007328226
  .17464740365558504
  .17788841598362912
  .18116424424986022
  .184474994500441
  .18782077230067787
  .19120168274079138
  .1946178304415758
  .19806931955994886
  .20155625379439707
  .20507873639031693
  .20863687014525575
  .21223075741405523
  .21586050011389926
  .2195261997292692
  .2232279573168085
  .22696587351009836
  .23074004852434915
  .23455058216100522
  .238397573812271
  .24228112246555486
  .24620132670783548
  .25015828472995344
  .25415209433082675
  .2581828529215958
  .26225065752969623
  .26635560480286247
  .2704977910130658
  .27467731206038465
  .2788942634768104
  .2831487404299921
  .2874408377269175
  .29177064981753587
  .2961382707983211
  .3005437944157765
  .3049873140698863
  .30946892281750854
  .31398871337571754
  .31854677812509186
  .32314320911295075
  .3277780980565422
  .33245153634617935
  .33716361504833037
  .3419144249086609
  .3467040563550296
  .35153259950043936
  .3564001441459435
  .3613067797835095
  .3662525955988395
  .3712376804741491
  .3762621229909065
  .38132601143253014
  .386429433787049
  .39157247774972326
  .39675523072562685
  .4019777798321958
  .4072402119017367
  .41254261348390375
  .4178850708481375
  .4232676699860717
  .4286904966139066
  .43415363617474895
  .4396571738409188
  .44520119451622786
  .45078578283822346
  .45641102318040466
  .4620769996544071
  .467783796112159
  .47353149614800955
  .4793201831008268
  .4851499400560704
  .4910208498478356
  .4969329950608704
  .5028864580325687
  .5088813208549338
  .5149176653765214
  .5209955732043543
  .5271151257058131
  .5332764040105052
  .5394794890121072
  .5457244613701866
  .5520114015120001
  .5583403896342679
  .5647115057049292
  .5711248294648731
  .5775804404296506
  .5840784178911641
  .5906188409193369
  .5972017883637634
  .6038273388553378
  .6104955708078648
  .6172065624196511
  .6239603916750761
  .6307571363461468
  .6375968739940326
  .6444796819705821
  .6514056374198242
  .6583748172794485
  .665387298282272
  .6724431569576875
  .6795424696330938
  .6866853124353135
  .6938717612919899
  .7011018919329731
  .7083757798916868
  .7156935005064807
  .7230551289219693
  .7304607400903537
  .7379104087727308
  .7454042095403874
  .7529422167760779
  .7605245046752924
  .768151147247507
  .7758222183174236
  .7835377915261935
  .7912979403326302
  .799102738014409
  .8069522576692516
  .8148465722161012
  .8227857543962835
  .8307698767746546
  .83879901174074
  .846873231509858
  .8549926081242338
  .8631572134541023
  .8713671191987972
  .8796223968878317
  .8879231178819663
  .8962693533742664
  .9046611743911496
  .9130986517934192
  .9215818562772946
  .9301108583754237
  .938685728457888
  .9473065367331999
  .9559733532492861
  .9646862478944651
  .9734452903984125
  .9822505503331171
  .9911020971138298
  1;

// luminance($color)
// @requires $linear-channel-values [list]
// Helper: Calculate Luminance of a single color
// Adapted from: https://medium.com/dev-channel/using-sass-to-automatically-pick-text-colors-4ba7645d2796
// White luminance is 1, Black luminance is 0
// To be used in other functions or mixins — creates non-standard CSS output:
// Usage: 
// .sample { luminance: luminance(#c00); }
// Output:
// .sample { luminance: 0.1283736922; }
//
@function luminance($color) {
  // $linear-channel-values are our Lookup Table of constants
  $red: nth($linear-channel-values, red($color) + 1);
  $green: nth($linear-channel-values, green($color) + 1);
  $blue: nth($linear-channel-values, blue($color) + 1);
  $calculation: .2126 * $red + .7152 * $green + .0722 * $blue;
  @return $calculation;
}

// color-contrast($fg, $bg)
// Helper: Calculate "readability" as defined by WCAG 2.1
// Adapted from: https://github.com/LeaVerou/contrast-ratio/blob/gh-pages/color.js
// Formula: http://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef
// To be used in other functions or mixins — creates non-standard CSS output:
// Usage: 
// .sample { color-contrast: color-contrast(#c00, #fff); }
// Output:
// .sample { color-contrast: 5.89; }
//
@function color-contrast($fg, $bg) {
  $luminance1: luminance($fg) + 0.05;
  $luminance2: luminance($bg) + 0.05;
  $ratio: $luminance1 / $luminance2;
  @if $luminance2 > $luminance1 {
    $ratio: 1 / $ratio;
  }
  // Round to a hundreth because 6.96 should not pass a ratio of 7.0
  $ratio: round($ratio * 100) / 100;
  @return $ratio;
}