bf: ZENKO-1144 add sorted set support StatsModel

Changes in this commit:
- Helper method _normalizeTimestampByHour normalizes date to
  nearest hour
- Helper method _setDateToPreviousHour sets date back 1 hour
- method getSortedSetHours returns list of 24 normalized
  hourly timestamps
- method getSortedSetCurrentHour returns normalized
  hourly timestamp based on epoch passed
- method addToSortedSet adds to a sorted set and applies
  expiry if adding to new sorted set

lib/metrics/RedisClient.js

@@ -204,6 +204,16 @@ class RedisClient {
         return this._client.zrangebyscore(key, min, max, cb);
     }
 
+    /**
+     * get TTL or expiration in seconds
+     * @param {string} key - name of key
+     * @param {function} cb - callback
+     * @return {undefined}
+     */
+    ttl(key, cb) {
+        return this._client.ttl(key, cb);
+    }
+
     clear(cb) {
         return this._client.flushdb(cb);
     }

lib/metrics/StatsModel.js

@@ -143,6 +143,86 @@ class StatsModel extends StatsClient {
             return cb(null, statsRes);
         });
     }
+
+    /**
+     * normalize date timestamp to the nearest hour
+     * @param {Date} d - Date instance
+     * @return {number} timestamp - normalized to the nearest hour
+     */
+    _normalizeTimestampByHour(d) {
+        return d.setMinutes(0, 0, 0);
+    }
+
+    /**
+     * get previous hour to date given
+     * @param {Date} d - Date instance
+     * @return {number} timestamp - one hour prior to date passed
+     */
+    _getDatePreviousHour(d) {
+        return d.setHours(d.getHours() - 1);
+    }
+
+    /**
+     * get list of sorted set key timestamps
+     * @param {number} epoch - epoch time
+     * @return {array} array of sorted set key timestamps
+     */
+    getSortedSetHours(epoch) {
+        const timestamps = [];
+        let date = this._normalizeTimestampByHour(new Date(epoch));
+        while (timestamps.length < 24) {
+            timestamps.push(date);
+            date = this._getDatePreviousHour(new Date(date));
+        }
+        return timestamps;
+    }
+
+    /**
+     * get the normalized hour timestamp for given epoch time
+     * @param {number} epoch - epoch time
+     * @return {string} normalized hour timestamp for given time
+     */
+    getSortedSetCurrentHour(epoch) {
+        return this._normalizeTimestampByHour(new Date(epoch));
+    }
+
+    /**
+     * helper method to add element to a sorted set, applying TTL if new set
+     * @param {string} key - name of key
+     * @param {integer} score - score used to order set
+     * @param {string} value - value to store
+     * @param {callback} cb - callback
+     * @return {undefined}
+     */
+    addToSortedSet(key, score, value, cb) {
+        this._redis.exists(key, (err, resCode) => {
+            if (err) {
+                return cb(err);
+            }
+            if (resCode === 0) {
+                // milliseconds in a day
+                const msInADay = 24 * 60 * 60 * 1000;
+                const nearestHour = this._normalizeTimestampByHour(new Date());
+                const ttl = msInADay - (Date.now() - nearestHour);
+                const cmds = [
+                    ['zadd', key, score, value],
+                    ['expire', key, ttl],
+                ];
+                return this._redis.batch(cmds, (err, res) => {
+                    if (err) {
+                        return cb(err);
+                    }
+                    const cmdErr = res.find(r => r[0] !== null);
+                    if (cmdErr) {
+                        return cb(cmdErr);
+                    }
+                    const successResponse = res[0][1];
+                    return cb(null, successResponse);
+                });
+            }
+            return this._redis.zadd(key, score, value, cb);
+        });
+    }
 }
 
 module.exports = StatsModel;

tests/functional/metrics/StatsModel.js

@@ -243,4 +243,66 @@ describe('StatsModel class', () => {
             },
         ], done);
     });
+
+    it('should normalize to the nearest hour using _normalizeTimestampByHour',
+    () => {
+        const date = new Date('2018-09-13T23:30:59.195Z');
+        const newDate = new Date(statsModel._normalizeTimestampByHour(date));
+
+        assert.strictEqual(date.getHours(), newDate.getHours());
+        assert.strictEqual(newDate.getMinutes(), 0);
+        assert.strictEqual(newDate.getSeconds(), 0);
+        assert.strictEqual(newDate.getMilliseconds(), 0);
+    });
+
+    it('should get previous hour using _getDatePreviousHour', () => {
+        const date = new Date('2018-09-13T23:30:59.195Z');
+        const newDate = statsModel._getDatePreviousHour(new Date(date));
+
+        const millisecondsInOneHour = 3600000;
+        assert.strictEqual(date - newDate, millisecondsInOneHour);
+    });
+
+    it('should get an array of hourly timestamps using getSortedSetHours',
+    () => {
+        const epoch = 1536882476501;
+        const millisecondsInOneHour = 3600000;
+
+        const expected = [];
+        let dateInMilliseconds = statsModel._normalizeTimestampByHour(
+            new Date(epoch));
+
+        for (let i = 0; i < 24; i++) {
+            expected.push(dateInMilliseconds);
+            dateInMilliseconds -= millisecondsInOneHour;
+        }
+        const res = statsModel.getSortedSetHours(epoch);
+
+        assert.deepStrictEqual(res, expected);
+    });
+
+    it('should apply TTL on a new sorted set using addToSortedSet', done => {
+        const key = 'a-test-key';
+        const score = 100;
+        const value = 'a-value';
+
+        statsModel.addToSortedSet(key, score, value, (err, res) => {
+            assert.ifError(err);
+            // check both a "zadd" and "expire" occurred
+            assert.equal(res.length, 2);
+
+            const responses = res.map(i => i[1]);
+            responses.forEach(r => {
+                // assert an action occurred for both
+                assert.equal(r, 1);
+            });
+
+            // check TTL applied
+            redisClient.ttl(key, (err, res) => {
+                assert.ifError(err);
+                assert(res > 0);
+                done();
+            });
+        });
+    });
 });