searcher/server/gallery/color.ts

export type GalleryColorFamily =
    | "black"
    | "blue"
    | "green"
    | "light"
    | "orange"
    | "purple"
    | "red"
    | "yellow";

function hexToRgb(hex: string) {
    const normalized = hex.trim().replace(/^#/, "");

    if (!/^[0-9a-f]{6}$/i.test(normalized)) {
        return null;
    }

    return {
        r: parseInt(normalized.slice(0, 2), 16),
        g: parseInt(normalized.slice(2, 4), 16),
        b: parseInt(normalized.slice(4, 6), 16),
    };
}

export function getGalleryColorFamily(
    color: string | null | undefined,
): GalleryColorFamily | null {
    if (!color) {
        return null;
    }

    const rgb = hexToRgb(color);

    if (!rgb) {
        return null;
    }

    const { r, g, b } = rgb;
    const max = Math.max(r, g, b);
    const min = Math.min(r, g, b);
    const lightness = (max + min) / 510;

    if (lightness > 0.78) {
        return "light";
    }

    if (lightness < 0.2) {
        return "black";
    }

    const delta = max - min;

    if (delta < 24) {
        return lightness > 0.52 ? "light" : "black";
    }

    let hue = 0;

    if (max === r) {
        hue = ((g - b) / delta) % 6;
    } else if (max === g) {
        hue = (b - r) / delta + 2;
    } else {
        hue = (r - g) / delta + 4;
    }

    hue = Math.round(hue * 60);

    if (hue < 0) {
        hue += 360;
    }

    if (hue < 18 || hue >= 345) {
        return "red";
    }
    if (hue < 45) {
        return "orange";
    }
    if (hue < 70) {
        return "yellow";
    }
    if (hue < 170) {
        return "green";
    }
    if (hue < 255) {
        return "blue";
    }
    if (hue < 345) {
        return "purple";
    }

    return null;
}