feat(color): add color theme strategies

- add strategy fns:
  - `complementaryStrategy()`
  - `splitComplementaryStrategy()`
  - `monochromeStrategy()`
  - `triadicStrategy()`
  - `tetradicStrategy()`
  - `squareStrategy()`

packages/color/src/strategies.ts

@@ -0,0 +1,60 @@
+import { clamp, clamp01 } from "@thi.ng/math/interval";
+import { lch, LCH } from "./lch/lch.js";
+import { rotate } from "./rotate.js";
+
+const DELTA_L = 0.1;
+const DELTA_C = -0.1;
+
+const $ = (src: LCH, l = DELTA_L, c = DELTA_C) => {
+    src.l = clamp01(src.l + l);
+    src.c = clamp(src.c + c, 0, 1.312);
+    return src;
+};
+
+export const complementaryStrategy = (
+    src: LCH,
+    theta = 1 / 2,
+    deltaL?: number,
+    deltaC?: number
+) => [src, $(<LCH>rotate(lch(), src, theta), deltaL, deltaC)];
+
+export const splitComplementaryStrategy = (
+    src: LCH,
+    theta = 1 / 12,
+    deltaL?: number,
+    deltaC?: number
+) => [
+    src,
+    $(<LCH>rotate(lch(), src, 0.5 - theta), deltaL, deltaC),
+    $(<LCH>rotate(lch(), src, 0.5 + theta), deltaL, deltaC),
+];
+
+export const monochromeStrategy = (src: LCH, deltaC = 0) => {
+    let [_, c, h, a] = src;
+    c = clamp(c + deltaC, 0, 1.312);
+    return [
+        lch(0.025, c, h, a),
+        lch(0.2, c, h, a),
+        lch(0.5, c, h, a),
+        lch(0.75, c, h, a),
+        lch(1, c, h, a),
+    ];
+};
+
+export const triadicStrategy = (src: LCH, deltaL?: number, deltaC?: number) =>
+    splitComplementaryStrategy(src, 1 / 6, deltaL, deltaC);
+
+export const tetradicStrategy = (
+    src: LCH,
+    theta = 1 / 12,
+    deltaL?: number,
+    deltaC?: number
+) => [
+    src,
+    $(<LCH>rotate(lch(), src, theta), deltaL, deltaC),
+    $(<LCH>rotate(lch(), src, 0.5), deltaL, deltaC),
+    $(<LCH>rotate(lch(), src, 0.5 + theta), deltaL, deltaC),
+];
+
+export const squareStrategy = (src: LCH, deltaL?: number, deltaC?: number) =>
+    tetradicStrategy(src, 0.25, deltaL, deltaC);