From 7b5855e18fd3caa6cc6cb9ba6dcd214e2b2e06fe Mon Sep 17 00:00:00 2001
From: Christoph Diehl <cdiehl@mozilla.com>
Date: Thu, 6 Apr 2017 18:12:24 +0200
Subject: [PATCH] Add random utility class

---
 random/random.js | 140 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 140 insertions(+)
 create mode 100644 random/random.js

diff --git a/random/random.js b/random/random.js
new file mode 100644
index 0000000..e47fb3d
--- /dev/null
+++ b/random/random.js
@@ -0,0 +1,140 @@
+var Random = {
+  twister: null,
+
+  init: function (seed) {
+    if (seed == null || seed === undefined) {
+      seed = new Date().getTime();
+    }
+    this.twister = new MersenneTwister();
+    this.twister.seed(seed);
+  },
+  number: function (limit) {
+    // Returns an integer in [0, limit]. Uniform distribution.
+    if (limit == 0) {
+      return limit;
+    }
+    if (limit == null || limit === undefined) {
+      limit = 0xffffffff;
+    }
+    return (this.twister.int32() >>> 0) % limit;
+  },
+  float: function () {
+    // Returns a float in [0, 1]. Uniform distribution.
+    return this.twister.real2() >>> 0;
+  },
+  range: function (start, limit) {
+    // Returns an integer in [start, limit]. Uniform distribution.
+    if (isNaN(start) || isNaN(limit)) {
+      Utils.traceback();
+      throw new TypeError("Random.range() received a non number type: '" + start + "', '" + limit + "')");
+    }
+    return Random.number(limit - start + 1) + start;
+  },
+  ludOneTo: function(limit) {
+    // Returns a float in [1, limit]. The logarithm has uniform distribution.
+    return Math.exp(Random.float() * Math.log(limit));
+  },
+  index: function (list) {
+    if (!(list instanceof Array || (typeof list != "string" && "length" in list))) {
+      Utils.traceback();
+      throw new TypeError("Random.index() received a non array type: '" + list + "'");
+    }
+    return list[this.number(list.length)];
+  },
+  key: function (obj) {
+    var list = [];
+    for (var i in obj) {
+      list.push(i);
+    }
+    return this.index(list);
+  },
+  bool: function () {
+    return this.index([true, false]);
+  },
+  pick: function (obj) {
+    if (typeof obj == "function") {
+      return obj();
+    }
+    if (obj instanceof Array) {
+      return this.pick(this.index(obj));
+    }
+    return obj;
+  },
+  chance: function (limit) {
+    if (limit == null || limit === undefined) {
+      limit = 2;
+    }
+    if (isNaN(limit)) {
+      Utils.traceback();
+      throw new TypeError("Random.chance() received a non number type: '" + limit + "'");
+    }
+    return this.number(limit) == 1;
+  },
+  choose: function (list, flat) {
+    if (!(list instanceof Array)) {
+      Utils.traceback();
+      throw new TypeError("Random.choose() received a non-array type: '" + list + "'");
+    }
+    var total = 0;
+    for (var i = 0; i < list.length; i++) {
+      total += list[i][0];
+    }
+    var n = this.number(total);
+    for (var i = 0; i < list.length; i++) {
+      if (n < list[i][0]) {
+        if (flat == true) {
+          return list[i][1];
+        } else {
+          return this.pick([list[i][1]]);
+        }
+      }
+      n = n - list[i][0];
+    }
+    if (flat == true) {
+      return list[0][1];
+    }
+    return this.pick([list[0][1]]);
+  },
+  weighted: function (wa) {
+    // More memory-hungry but hopefully faster than Random.choose$flat
+    var a = [];
+    for (var i = 0; i < wa.length; ++i) {
+      for (var j = 0; j < wa[i].w; ++j) {
+        a.push(wa[i].v);
+      }
+    }
+    return a;
+  },
+  use: function (obj) {
+    return Random.bool() ? obj : "";
+  },
+  shuffle: function (arr) {
+    var len = arr.length;
+    var i = len;
+    while (i--) {
+      var p = Random.number(i + 1);
+      var t = arr[i];
+      arr[i] = arr[p];
+      arr[p] = t;
+    }
+  },
+  shuffled: function (arr) {
+    var newArray = arr.slice();
+    Random.shuffle(newArray);
+    return newArray;
+  },
+  some: function (list, limit) {
+    if (!(list instanceof Array)) {
+      Utils.traceback();
+      throw new TypeError("Random.some() received a non-array type: '" + list + "'");
+    }
+    if (typeof limit == 'number') {
+      limit = this.range(0, list.length);
+    }
+    var result = [];
+    for (var i = 0; i < limit; i++) {
+      result.push(this.pick(list));
+    }
+    return result;
+  }
+};