1 files changed, 36 insertions, 0 deletions
diff --git a/src/lib/color.ts b/src/lib/color.ts
new file mode 100644
index 0000000..59b320d
--- /dev/null
+++ b/src/lib/color.ts
@@ -0,0 +1,36 @@
+interface Color {
+  red: number,
+  green: number,
+  blue: number,
+}
+
+export function parse(str: string): Color {
+  return {
+    red: parseInt(str.slice(1,3), 16),
+    green: parseInt(str.slice(3,5), 16),
+    blue: parseInt(str.slice(5,7), 16),
+  }
+}
+
+// https://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrastratio
+export function contrastRatio(c1: Color, c2: Color): number {
+  const r1 = relativeLuminance(c1)
+  const r2 = relativeLuminance(c2)
+
+  return r1 > r2
+    ? (r1 + 0.05) / (r2 + 0.05)
+    : (r2 + 0.05) / (r1 + 0.05)
+}
+
+function relativeLuminance(c: Color): number {
+  return (
+    0.2126 * fromSRGB(c.red / 255) 
+    + 0.7152 * fromSRGB(c.green / 255) 
+    + 0.0722 * fromSRGB(c.blue / 255))
+}
+
+function fromSRGB(sRGB: number): number {
+  return sRGB <= 0.03928
+    ? sRGB / 12.92
+    : Math.pow(((sRGB + 0.055) / 1.055), 2.4)
+}