Add sendFile function (#562)

* sendFile

* Add default value to filename

* eslint

* (╯°□°）╯︵ ┻━┻

src/structures/DMChannel.js

@@ -47,6 +47,10 @@ class DMChannel extends Channel {
     return;
   }
 
+  sendFile() {
+    return;
+  }
+
   _cacheMessage() {
     return;
   }

src/structures/GroupDMChannel.js

@@ -124,6 +124,10 @@ class GroupDMChannel extends Channel {
     return;
   }
 
+  sendFile() {
+    return;
+  }
+
   _cacheMessage() {
     return;
   }

src/structures/GuildMember.js

@@ -222,6 +222,10 @@ class GuildMember {
   sendTTSMessage() {
     return;
   }
+
+  sendFile() {
+    return;
+  }
 }
 
 TextBasedChannel.applyToClass(GuildMember);

src/structures/TextChannel.js

@@ -32,6 +32,10 @@ class TextChannel extends GuildChannel {
     return;
   }
 
+  sendFile() {
+    return;
+  }
+
   _cacheMessage() {
     return;
   }

src/structures/User.js

@@ -122,6 +122,10 @@ class User {
   sendTTSMessage() {
     return;
   }
+
+  sendFile() {
+    return;
+  }
 }
 
 TextBasedChannel.applyToClass(User);

src/structures/interface/TextBasedChannel.js

@@ -68,7 +68,24 @@ class TextBasedChannel {
   sendTTSMessage(content, options = {}) {
     return this.client.rest.methods.sendMessage(this, content, true, options.nonce);
   }
-
+  /**
+   * Send a file to this channel
+   * @param {FileResolvable} attachment The file to send
+   * @param {String} [fileName="file.jpg"] The name and extension of the file
+   * @returns {Promise<Message>}
+   */
+  sendFile(attachment, fileName = 'file.jpg') {
+    return new Promise((resolve, reject) => {
+      this.client.resolver.resolveFile(attachment)
+      .then(file => {
+        this.client.rest.methods.sendMessage(this, undefined, false, undefined, {
+          file,
+          name: fileName,
+        }).then(resolve).catch(reject);
+      })
+      .catch(reject);
+    });
+  }
   /**
    * The parameters to pass in when requesting previous messages from a channel. `around`, `before` and
    * `after` are mutually exclusive. All the parameters are optional.
@@ -173,7 +190,7 @@ function applyProp(structure, prop) {
 }
 
 exports.applyToClass = (structure, full = false) => {
-  const props = ['sendMessage', 'sendTTSMessage'];
+  const props = ['sendMessage', 'sendTTSMessage', 'sendFile'];
   if (full) {
     props.push('_cacheMessage');
     props.push('getMessages');