sheets-injected.js

const enableAutoDarkMode = true;

(function () {
    'use strict';

    var invert

    invert = enableAutoDarkMode && window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches;

    function updateDarkMode(isDark) {
        invert = isDark
    }

    function changeHue(rgb, degree) {
        var hsl = rgbToHSL(rgb);
        hsl.h += degree;
        if (hsl.h > 360) {
            hsl.h -= 360;
        }
        else if (hsl.h < 0) {
            hsl.h += 360;
        }
        return hslToRGB(hsl);
    }
    
    // exepcts a string and returns an object
    function rgbToHSL(rgb) {
        // strip the leading # if it's there
        rgb = rgb.replace(/^\s*#|\s*$/g, '');
    
        // convert 3 char codes --> 6, e.g. `E0F` --> `EE00FF`
        if(rgb.length == 3){
            rgb = rgb.replace(/(.)/g, '$1$1');
        }
    
        var r = parseInt(rgb.substr(0, 2), 16) / 255,
            g = parseInt(rgb.substr(2, 2), 16) / 255,
            b = parseInt(rgb.substr(4, 2), 16) / 255,
            cMax = Math.max(r, g, b),
            cMin = Math.min(r, g, b),
            delta = cMax - cMin,
            l = (cMax + cMin) / 2,
            h = 0,
            s = 0;
    
        if (delta == 0) {
            h = 0;
        }
        else if (cMax == r) {
            h = 60 * (((g - b) / delta) % 6);
        }
        else if (cMax == g) {
            h = 60 * (((b - r) / delta) + 2);
        }
        else {
            h = 60 * (((r - g) / delta) + 4);
        }
    
        if (delta == 0) {
            s = 0;
        }
        else {
            s = (delta/(1-Math.abs(2*l - 1)))
        }
    
        return {
            h: h,
            s: s,
            l: l
        }
    }
    
    // expects an object and returns a string
    function hslToRGB(hsl) {
        var h = hsl.h,
            s = hsl.s,
            l = hsl.l,
            c = (1 - Math.abs(2*l - 1)) * s,
            x = c * ( 1 - Math.abs((h / 60 ) % 2 - 1 )),
            m = l - c/ 2,
            r, g, b;
    
        if (h < 60) {
            r = c;
            g = x;
            b = 0;
        }
        else if (h < 120) {
            r = x;
            g = c;
            b = 0;
        }
        else if (h < 180) {
            r = 0;
            g = c;
            b = x;
        }
        else if (h < 240) {
            r = 0;
            g = x;
            b = c;
        }
        else if (h < 300) {
            r = x;
            g = 0;
            b = c;
        }
        else {
            r = c;
            g = 0;
            b = x;
        }
    
        r = normalize_rgb_value(r, m);
        g = normalize_rgb_value(g, m);
        b = normalize_rgb_value(b, m);
    
        return rgbToHex(r,g,b);
    }
    
    function normalize_rgb_value(color, m) {
        color = Math.floor((color + m) * 255);
        if (color < 0) {
            color = 0;
        }
        return color;
    }
    
    function rgbToHex(r, g, b) {
        return "#" + ((1 << 24) + (r << 16) + (g << 8) + b).toString(16).slice(1);
    }

    // Set black text to white if in dark mode
    if (enableAutoDarkMode) {
        CanvasRenderingContext2D.prototype.fillRect = function (orig) {
            return function (type) {
                var prevFillStyle = this.fillStyle;
                this.fillStyle = invert ? changeHue(this.fillStyle, 180): prevFillStyle;
                var out = orig.apply(this, arguments);
                this.fillStyle = prevFillStyle;
                return out
            }
        }(CanvasRenderingContext2D.prototype.fillRect)
    }
    updateDarkMode(invert);

    // Listen for changes
    if (enableAutoDarkMode) {
    window
        .matchMedia("(prefers-color-scheme: dark)")
        .addEventListener("change", function (e) {
            const colorScheme = e.matches ? "dark" : "light";

            if (colorScheme === "dark") {
                updateDarkMode(true)
            } else {
                updateDarkMode(false)
            }
        });
    }
})();