refactor: rewrite message creation (#2774)

* Rework createMessage
- MessageAttachment is now structurally similar to FileOptions
- No longer mutates the object passed as options
- Supports more permutations of arguments

* Ignore complexity warning

* Refactor name finding

* Fix typo

* Update typings

* Default name to null for MessageAttachment

* Make Message#reply use transformOptions

* Move transformOptions

* Fix Message#reply

* Fix mutation

* Update tests

* Fix options passing

* Refactor into APIMessage

* Fix webhook send

* Expose APIMessage

* Add documentation

* Add types

* Fix type doc

* Fix another type doc

* Fix another another type doc (is this one even right!?)

* Remove trailing comma

* Properly clone split options

* Add support for sending file as stream

* Missed a doc

* Resolve files only once when splitting messages

* This looks nicer

* Assign directly

* Don't cache data and files

* Missing return type

* Use object spread instead Object.assign

* Document constructors

* Crawl is a little dot

* comp pls

* tests: sanitize local file path, disable no-await-in-loop

src/structures/Webhook.js

@@ -1,6 +1,6 @@
 const DataResolver = require('../util/DataResolver');
 const Channel = require('./Channel');
-const { createMessage } = require('./shared');
+const APIMessage = require('./APIMessage');
 
 /**
  * Represents a webhook.
@@ -82,11 +82,10 @@ class Webhook {
    * it exceeds the character limit. If an object is provided, these are the options for splitting the message.
    */
 
-  /* eslint-disable max-len */
   /**
    * Sends a message with this webhook.
-   * @param {StringResolvable} [content] The content to send
-   * @param {WebhookMessageOptions|MessageEmbed|MessageAttachment|MessageAttachment[]} [options={}] The options to provide
+   * @param {StringResolvable} [content=''] The content to send
+   * @param {WebhookMessageOptions|MessageAdditions} [options={}] The options to provide
    * @returns {Promise<Message|Object>}
    * @example
    * // Send a basic message
@@ -127,20 +126,18 @@ class Webhook {
    *   .catch(console.error);
    */
   async send(content, options) {
-    if (!options && typeof content === 'object' && !(content instanceof Array)) {
-      options = content;
-      content = null;
-    } else if (!options) {
-      options = {};
-    }
-    if (!options.content) options.content = content;
-
-    const { data, files } = await createMessage(this, options);
-
+    const apiMessage = APIMessage.create(this, content, options);
+    const data = apiMessage.resolveData();
     if (data.content instanceof Array) {
       const messages = [];
       for (let i = 0; i < data.content.length; i++) {
-        const opt = i === data.content.length - 1 ? { embeds: data.embeds, files } : {};
+        let opt;
+        if (i === data.content.length - 1) {
+          opt = { embeds: data.embeds, files: apiMessage.options.files };
+        } else {
+          opt = {};
+        }
+
         Object.assign(opt, { avatarURL: data.avatar_url, content: data.content[i], username: data.username });
         // eslint-disable-next-line no-await-in-loop
         const message = await this.send(data.content[i], opt);
@@ -149,7 +146,7 @@ class Webhook {
       return messages;
     }
 
-
+    const files = await apiMessage.resolveFiles();
     return this.client.api.webhooks(this.id, this.token).post({
       data, files,
       query: { wait: true },