Add function execution rate limiter

earldouglas · Aug 30, 2015 · e3e7171 · e3e7171
1 parent d4830d5
commit e3e7171
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Showing 3 changed files with 105 additions and 7 deletions.
diff --git a/src/teep.ts b/src/teep.ts
@@ -37,6 +37,14 @@ module edc {
     flatMap: <A,B>(xs: Array<A>, f: (A) => Array<B>): Array<B> => {
       return array.flatten(array.map(xs, f));
     },
+    filter: <A>(xs: Array<A>, f: (A) => boolean): Array<A> => {
+      return array.foldr(xs, [], (a: A, as: Array<A>): Array<A> => {
+        if (f(a)) {
+          as.push(a);
+        }
+        return as;
+      });
+    },
   };
 
   var object = {
@@ -104,6 +112,31 @@ module edc {
         };
       };
     },
+    throttle: (limit: number, period: number, interval: number,
+            f: () => any): () => void => {
+      var times = [];
+      var throttled = function () {
+        var now = (new Date()).getTime();
+        times = array.filter(times, function (time) {
+          return now - time < period;
+        });
+        var withinLimit = times.length < limit
+        if (withinLimit) {
+          var newest = Math.max.apply(null, times);
+          var afterInterval = (now - newest) > interval;
+          if (afterInterval) {
+            times.push(now);
+            f();
+          } else {
+            setTimeout(throttled, interval - (now - newest));
+          }
+        } else {
+          var oldest = Math.min.apply(null, times);
+          setTimeout(throttled, period - (now - oldest));
+        }
+      };
+      return throttled;
+    }
   };
 
   export interface Monad<A> {

diff --git a/teep.js b/teep.js
@@ -34,6 +34,14 @@ var edc;
         },
         flatMap: function (xs, f) {
             return array.flatten(array.map(xs, f));
+        },
+        filter: function (xs, f) {
+            return array.foldr(xs, [], function (a, as) {
+                if (f(a)) {
+                    as.push(a);
+                }
+                return as;
+            });
         }
     };
     var object = {
@@ -95,6 +103,32 @@ var edc;
                     get: function () { return fMemo(x); }
                 };
             };
+        },
+        throttle: function (limit, period, interval, f) {
+            var times = [];
+            var throttled = function () {
+                var now = (new Date()).getTime();
+                times = array.filter(times, function (time) {
+                    return now - time < period;
+                });
+                var withinLimit = times.length < limit;
+                if (withinLimit) {
+                    var newest = Math.max.apply(null, times);
+                    var afterInterval = (now - newest) > interval;
+                    if (afterInterval) {
+                        times.push(now);
+                        f();
+                    }
+                    else {
+                        setTimeout(throttled, interval - (now - newest));
+                    }
+                }
+                else {
+                    var oldest = Math.min.apply(null, times);
+                    setTimeout(throttled, period - (now - oldest));
+                }
+            };
+            return throttled;
         }
     };
     var Some = (function () {

diff --git a/test/examples.js b/test/examples.js
@@ -34,6 +34,12 @@ describe('examples', function () {
       var xs = teep.array.flatMap([1,3,5], alsoPlusOne);
       assert.deepEqual([1,2,3,4,5,6], xs);
     });
+    it('filter', function () {
+      var xs = teep.array.filter([1,2,3,4,5,6], function (x) {
+        return x % 2 === 1 || x === 4;
+      });
+      assert.deepEqual([1,3,4,5], xs);
+    });
   });
 
   describe('fn', function () {
@@ -51,9 +57,6 @@ describe('examples', function () {
       assert.equal(nine, 9);
       assert.equal(five, 5);
     });
-  });
-
-  describe('fn', function () {
     it('curry', function () {
       function add(x, y) {
         return x + y;
@@ -71,9 +74,6 @@ describe('examples', function () {
       assert.equal(five, 5);
       assert.equal(fortyTwo, 42);
     });
-  });
-
-  describe('fn', function () {
     it('memoize', function () {
       function expensiveFn(n) {
         for (var i = 0; i < 10000; i++) {
@@ -99,7 +99,6 @@ describe('examples', function () {
       var fast = t3 - t2;
       assert.ok(slow > 10 * fast); // over 10x faster
     });
-
     it('lazy', function () {
       function expensiveFn(n) {
         for (var i = 0; i < 10000; i++) {
@@ -129,6 +128,38 @@ describe('examples', function () {
       var fast = t5 - t4;
       assert.ok(slow > 10 * fast); // over 10x faster
     });
+    it('rate', function (done) {
+      var xs = [];
+      var f = function () {
+        xs.push((new Date()).getTime());
+      };
+
+      var limit = 5;
+      var period = 50;
+      var interval = 5;
+      var count = 101;
+      var f2 = teep.fn.throttle(limit, period, interval, f);
+      for (var i = 0; i < count; i++) {
+        f2();
+      }
+
+      var check = function (above, below) {
+        if (xs.length <= above) {
+          done(Error(xs.length + ' should exceed ' + above));
+        } else if (xs.length > below) {
+          done(Error(xs.length + ' should not exceed ' + below));
+        } else if (xs.length < count) {
+          setTimeout(function () {
+            check(above + limit, below + limit);
+          }, period);
+        } else {
+          done();
+        }
+      };
+
+      setTimeout(function () { check(0, limit); }, period / 2);
+
+    });
   });
 
   describe('option', function () {