Shift node color's brightness for light mode (#123)

* Shift node color's brightness for light mode

* nit

* Fix test

src/utils/colorUtil.ts

@@ -0,0 +1,100 @@
+type RGB = { r: number; g: number; b: number };
+type HSL = { h: number; s: number; l: number };
+
+function rgbToHsl({ r, g, b }: RGB): HSL {
+  (r /= 255), (g /= 255), (b /= 255);
+  const max = Math.max(r, g, b),
+    min = Math.min(r, g, b);
+  let h: number,
+    s: number,
+    l: number = (max + min) / 2;
+
+  if (max === min) {
+    h = s = 0; // achromatic
+  } else {
+    const d = max - min;
+    s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
+    switch (max) {
+      case r:
+        h = (g - b) / d + (g < b ? 6 : 0);
+        break;
+      case g:
+        h = (b - r) / d + 2;
+        break;
+      case b:
+        h = (r - g) / d + 4;
+        break;
+    }
+    h /= 6;
+  }
+
+  return { h, s, l };
+}
+
+function hslToRgb({ h, s, l }: HSL): RGB {
+  let r: number, g: number, b: number;
+
+  if (s === 0) {
+    r = g = b = l; // achromatic
+  } else {
+    const hue2rgb = (p: number, q: number, t: number) => {
+      if (t < 0) t += 1;
+      if (t > 1) t -= 1;
+      if (t < 1 / 6) return p + (q - p) * 6 * t;
+      if (t < 1 / 2) return q;
+      if (t < 2 / 3) return p + (q - p) * (2 / 3 - t) * 6;
+      return p;
+    };
+
+    const q = l < 0.5 ? l * (1 + s) : l + s - l * s;
+    const p = 2 * l - q;
+    r = hue2rgb(p, q, h + 1 / 3);
+    g = hue2rgb(p, q, h);
+    b = hue2rgb(p, q, h - 1 / 3);
+  }
+
+  return {
+    r: Math.round(r * 255),
+    g: Math.round(g * 255),
+    b: Math.round(b * 255),
+  };
+}
+
+function hexToRgb(hex: string): RGB {
+  let r = 0,
+    g = 0,
+    b = 0;
+  // 3 digits
+  if (hex.length == 4) {
+    r = parseInt(hex[1] + hex[1], 16);
+    g = parseInt(hex[2] + hex[2], 16);
+    b = parseInt(hex[3] + hex[3], 16);
+  }
+  // 6 digits
+  else if (hex.length == 7) {
+    r = parseInt(hex.slice(1, 3), 16);
+    g = parseInt(hex.slice(3, 5), 16);
+    b = parseInt(hex.slice(5, 7), 16);
+  }
+  return { r, g, b };
+}
+
+function rgbToHex({ r, g, b }: RGB): string {
+  return (
+    "#" +
+    [r, g, b]
+      .map((x) => {
+        const hex = x.toString(16);
+        return hex.length === 1 ? "0" + hex : hex;
+      })
+      .join("")
+  );
+}
+
+export function lightenColor(hex: string, amount: number): string {
+  let rgb = hexToRgb(hex);
+  let hsl = rgbToHsl(rgb);
+  hsl.l = Math.min(1, hsl.l + amount);
+  rgb = hslToRgb(hsl);
+  return rgbToHex(rgb);
+}