1use kmeans_colors::get_kmeans_hamerly;
2use palette::{color_difference::Wcag21RelativeContrast, FromColor, Lab, Srgb};
3
4pub fn find_dominant_colors(lab: &Vec<Lab>, max_colors: usize) -> Vec<Lab> {
5    // This is based on code from the kmeans-colors binary, but with a bunch of
6    // the options stripped out.
7    // See https://github.com/okaneco/kmeans-colors/blob/0.5.0/src/bin/kmeans_colors/app.rs
8    let max_iterations = 20;
9    let converge = 1.0;
10    let verbose = false;
11    let seed: u64 = 0;
12
13    assert!(lab.len() > 0);
14
15    let result = get_kmeans_hamerly(max_colors, max_iterations, converge, verbose, lab, seed);
16
17    result.centroids
18}
19
20pub fn choose_best_color_for_bg(colors: Vec<Lab>, background: &Srgb<u8>) -> Vec<Lab> {
21    // Start by adding black and white to the list of candidate colors.
22    //
23    // They're boring, but any background colour will always have sufficient
24    // contrast with at least one of them.
25    let black = Srgb::new(0.0, 0.0, 0.0);
26    let white = Srgb::new(1.0, 1.0, 1.0);
27
28    // I suspect this is not the most "technically correct" way to convert
29    // an Srgb<u8> to a Srgb<f32>, but it's good enough for my purposes.
30    let mut extended_colors: Vec<Srgb<f32>> =
31        colors.iter().map(|c| Srgb::<f32>::from_color(*c)).collect();
32
33    extended_colors.push(black);
34    extended_colors.push(white);
35
36    let background: Srgb<f32> = Srgb::new(
37        background.red as f32 / 255.0,
38        background.green as f32 / 255.0,
39        background.blue as f32 / 255.0,
40    );
41
42    // Filter for colors which meet the min contrast ratio
43    let allowed_colors: Vec<Srgb<f32>> = extended_colors
44        .into_iter()
45        .filter(|c| background.has_min_contrast_graphics(*c))
46        .collect();
47
48    // Now pick the color with the highest saturation among the remaining.
49    let best_color: Srgb<f32> = allowed_colors
50        .into_iter()
51        .max_by(|color_a, color_b| {
52            saturation(color_a)
53                .partial_cmp(&saturation(color_b))
54                .unwrap()
55        })
56        .unwrap();
57
58    vec![Lab::from_color(best_color)]
59}
60
61// Based on https://filmentor.academy/en/blogs/news/die-wunderbare-welt-der-mathematik-fur-farben
62fn saturation(c: &Srgb<f32>) -> f32 {
63    let min_rgb: f32 = vec![c.red, c.green, c.blue]
64        .into_iter()
65        .min_by(|a, b| a.partial_cmp(b).unwrap())
66        .unwrap();
67    let max_rgb: f32 = vec![c.red, c.green, c.blue]
68        .into_iter()
69        .max_by(|a, b| a.partial_cmp(b).unwrap())
70        .unwrap();
71
72    if min_rgb == max_rgb {
73        return 0.0;
74    }
75
76    let luminosity: f32 = 0.5 * (min_rgb + max_rgb);
77
78    if luminosity == 1.0 {
79        0.0
80    } else {
81        (max_rgb - min_rgb) / (1.0 - (2.0 * luminosity - 1.0).abs())
82    }
83}