2 files changed, 134 insertions, 0 deletions
diff --git a/src/utils/set_utils.js b/src/utils/set_utils.js
new file mode 100644
index 0000000..88e8fea
--- /dev/null
+++ b/src/utils/set_utils.js
@@ -0,0 +1,81 @@
+/**
+ * Operations on sets.
+ * @module app/utils/set_utils
+ */
+
+/**
+ * Determine if `set` contains `subset`
+ * @param  {Set}  set       the superset
+ * @param  {Set}  subset    the subset
+ * @return {Boolean}        true if set contains subset
+ */
+export function isSuperset(set, subset) {
+  for (let elem of subset) {
+    if (!set.has(elem)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+/**
+ * Return the union (A or B) of two sets
+ * @param  {Set}  setA      a set
+ * @param  {Set}  setB      a set
+ * @return {Boolean}        the union of the sets
+ */
+export function union(setA, setB) {
+  let _union = new Set(setA);
+  for (let elem of setB) {
+    _union.add(elem);
+  }
+  return _union;
+}
+
+/**
+ * Return the intersection (A and B) of two sets
+ * @param  {Set}  setA      a set
+ * @param  {Set}  setB      a set
+ * @return {Boolean}        the intersection of the sets
+ */
+export function intersection(setA, setB) {
+  let _intersection = new Set();
+  for (let elem of setB) {
+    if (setA.has(elem)) {
+      _intersection.add(elem);
+    }
+  }
+  return _intersection;
+}
+
+/**
+ * Return the symmetric difference (A xor B) of two sets
+ * @param  {Set}  setA      a set
+ * @param  {Set}  setB      a set
+ * @return {Boolean}        the symmetric difference of the sets
+ */
+export function symmetricDifference(setA, setB) {
+  let _difference = new Set(setA);
+  for (let elem of setB) {
+    if (_difference.has(elem)) {
+      _difference.delete(elem);
+    } else {
+      _difference.add(elem);
+    }
+  }
+  return _difference;
+}
+
+/**
+ * Return the difference (A not B) of two sets
+ * @param  {Set}  setA      a set
+ * @param  {Set}  setB      a set
+ * @return {Boolean}        the difference of the sets
+ */
+export function difference(setA, setB) {
+  let _difference = new Set(setA);
+  for (let elem of setB) {
+    _difference.delete(elem);
+  }
+  return _difference;
+}
diff --git a/src/utils/stars.js b/src/utils/stars.js
new file mode 100644
index 0000000..516a359
--- /dev/null
+++ b/src/utils/stars.js
@@ -0,0 +1,53 @@
+export default function stars() {
+  var canvas = document.createElement("canvas"),
+    ctx = canvas.getContext("2d");
+  document.body.appendChild(canvas);
+  canvas.style.width = "100%";
+  canvas.style.height = "100%";
+  canvas.style.position = "absolute";
+  canvas.style.top = "0px";
+  canvas.style.left = "0px";
+  canvas.style.zIndex = 1;
+  canvas.style.opacity = 0.6;
+  canvas.style.pointerEvents = "none";
+  document.body.addEventListener("resize", go);
+  document.body.parentNode.style.backgroundColor = "black";
+  ctx.strokeStyle = "white";
+  var s = Math.sin,
+    c = Math.cos;
+  go();
+  function ri(n) {
+    return Math.random() * n;
+  }
+  function rr(a, b) {
+    return (b - a) * Math.random() + a;
+  }
+  function go() {
+    var w = (canvas.width = window.innerWidth);
+    var h = (canvas.height = window.innerHeight);
+    ctx.clearRect(0, 0, w, h);
+    var n = Math.sqrt(w * h) | 0;
+    while (n--) {
+      var x = ri(w);
+      var y = ri(h);
+      var r0 = rr(0, 1);
+      var r1 = rr(0, 1);
+      var r2 = rr(0, 1);
+      var t0 = ri(2 * Math.PI);
+      var t1 = ri(2 * Math.PI);
+      var t2 = ri(2 * Math.PI);
+      var x0 = x + c(t0) * r0;
+      var y0 = y + s(t0) * r0;
+      var x1 = x + c(t1) * r1;
+      var y1 = y + s(t1) * r1;
+      var x2 = x + c(t2) * r2;
+      var y2 = y + s(t2) * r2;
+      ctx.beginPath();
+      ctx.moveTo(x, y);
+      ctx.bezierCurveTo(x0, y0, x1, y1, x2, y2);
+      var color = rr(0, 255) | 0;
+      ctx.strokeStyle = "rgb(" + color + "," + color + "," + color + ")";
+      ctx.stroke();
+    }
+  }
+}