Add RobloxAPIError class (#841)

* Create extremely basic error class

* Make most of class

* Fix typo

lib/util/apiError.js

@@ -0,0 +1,41 @@
+// The data should be a response object
+
+class RobloxAPIError extends Error {
+  constructor (data) {
+    super(getResponseBody(data))
+
+    this.name = 'RobloxAPIError'
+    this.httpStatusCode = data.statusCode
+    this.responseBody = getResponseBody(data)
+  }
+
+  get error () {
+    let obj
+
+    try {
+      obj = JSON.parse(this.responseBody)
+    } catch {
+      return { code: 0, message: this.responseBody.toString() }
+    }
+
+    if (Object.hasOwn(obj, 'error')) return obj.error // V1 open cloud and some very old BEDEV1 endpoints + some global errors
+
+    else if (Object.hasOwn(obj, 'errors')) { // Most BEDEV1 endpoints
+      return obj.errors.at(0) // In spite of BEDEV1 endpoint errors being nested in an array, they are never seen in groups.
+    } else if (Object.hasOwn(obj, 'code') && Object.hasOwn(obj, 'message')) { // V2 open cloud
+      return obj
+    } else return { code: 0, message: this.responseBody } // Roblox did a funny (i.e. the platform is down)
+  }
+}
+
+function getResponseBody (data) {
+  if (typeof data.body === 'string') return data.body
+
+  try {
+    return JSON.stringify(data.body)
+  } catch {
+    throw Error('The passed response body is not a valid object')
+  }
+}
+
+export default RobloxAPIError