lots of important stuff (#1883)

* lots of important stuff

* Update Constants.js

src/rest/handlers/RequestHandler.js

@@ -0,0 +1,70 @@
+const DiscordAPIError = require('../DiscordAPIError');
+
+class RequestHandler {
+  constructor(manager, handler) {
+    this.manager = manager;
+    this.client = this.manager.client;
+    this.handle = handler.bind(this);
+    this.limit = Infinity;
+    this.resetTime = null;
+    this.remaining = 1;
+    this.timeDifference = 0;
+
+    this.queue = [];
+  }
+
+  get limited() {
+    return this.manager.globallyRateLimited || this.remaining <= 0;
+  }
+
+  set globallyLimited(limited) {
+    this.manager.globallyRateLimited = limited;
+  }
+
+  push(request) {
+    this.queue.push(request);
+    this.handle();
+  }
+
+  execute(item) {
+    return new Promise((resolve, reject) => {
+      const finish = timeout => {
+        // eslint-disable-next-line prefer-promise-reject-errors
+        if (timeout || this.limited) reject({ timeout, limited: this.limited });
+        else resolve();
+      };
+      item.request.gen().end((err, res) => {
+        if (res && res.headers) {
+          if (res.headers['x-ratelimit-global']) this.globallyLimited = true;
+          this.limit = Number(res.headers['x-ratelimit-limit']);
+          this.resetTime = Number(res.headers['x-ratelimit-reset']) * 1000;
+          this.remaining = Number(res.headers['x-ratelimit-remaining']);
+          this.timeDifference = Date.now() - new Date(res.headers.date).getTime();
+        }
+        if (err) {
+          if (err.status === 429) {
+            this.queue.unshift(item);
+            finish(Number(res.headers['retry-after']) + this.client.options.restTimeOffset);
+          } else if (err.status >= 500 && err.status < 600) {
+            this.queue.unshift(item);
+            finish(1e3 + this.client.options.restTimeOffset);
+          } else {
+            item.reject(err.status >= 400 && err.status < 500 ? new DiscordAPIError(res.request.path, res.body) : err);
+            finish();
+          }
+        } else {
+          const data = res && res.body ? res.body : {};
+          item.resolve(data);
+          finish();
+        }
+      });
+    });
+  }
+
+  reset() {
+    this.globallyLimited = false;
+    this.remaining = 1;
+  }
+}
+
+module.exports = RequestHandler;