update shift to pop

reducing time complexity to `O(2n)`

src/index.ts

@@ -279,8 +279,12 @@ export function sendDistributionMetric(name: string, value: number, ...tags: str
 }
 
 function sendQueueMetrics(listener: MetricsListener) {
+  // Reverse the queue to send metrics in order.
+  // This is necessary because the "queue" is a stack,
+  // and we want to send metrics in the order they were added.
+  _metricsQueue.reverse();
   while (_metricsQueue.length > 0) {
-    const metric = _metricsQueue.shift()!; // This will always exist.
+    const metric = _metricsQueue.pop()!; // This will always exist.
     const { name, value, metricTime, tags } = metric;
     if (metricTime !== undefined) {
       listener.sendDistributionMetricWithDate(name, value, metricTime, false, ...tags);

src/metrics/queue.spec.ts

@@ -37,20 +37,28 @@ describe("MetricsQueue", () => {
     });
   });
 
-  describe("shift", () => {
+  describe("pop", () => {
     it("returns undefined when queue is empty", () => {
       const queue = new MetricsQueue();
-      expect(queue.shift()).toBeUndefined();
+      expect(queue.pop()).toBeUndefined();
     });
 
     it("returns the first element in the queue", () => {
       const queue = new MetricsQueue();
       queue.push({ name: "metric", tags: [], value: 1 });
       queue.push({ name: "metric", tags: [], value: 2 });
-      expect(queue.shift()).toEqual({ name: "metric", tags: [], value: 1 });
+      expect(queue.pop()).toEqual({ name: "metric", tags: [], value: 2 });
     });
   });
 
+  it("reverses the queue", () => {
+    const queue = new MetricsQueue();
+    queue.push({ name: "metric", tags: [], value: 1 });
+    queue.push({ name: "metric", tags: [], value: 2 });
+    queue.reverse();
+    expect(queue.pop()).toEqual({ name: "metric", tags: [], value: 1 });
+  });
+
   it("resets the queue", () => {
     const queue = new MetricsQueue();
     queue.push({ name: "metric", tags: [], value: 1 });

src/metrics/queue.ts

@@ -36,14 +36,18 @@ export class MetricsQueue {
     this.queue.push(metric);
   }
 
-  public shift() {
+  public pop() {
     if (this.queue.length > 0) {
-      return this.queue.shift();
+      return this.queue.pop();
     }
 
     return undefined;
   }
 
+  public reverse() {
+    this.queue.reverse();
+  }
+
   public reset() {
     this.queue = [];
   }