Expose TextBasedChannel#fetchMessage() (#602)

src/client/rest/RESTMethods.js

@@ -287,6 +287,18 @@ class RESTMethods {
     });
   }
 
+  getChannelMessage(channel, messageID) {
+    return new Promise((resolve, reject) => {
+      const msg = channel.messages.get(messageID);
+      if (msg) return resolve(msg);
+
+      const endpoint = Constants.Endpoints.channelMessage(channel.id, messageID);
+      return this.rest.makeRequest('get', endpoint, true)
+        .then(resolve)
+        .catch(reject);
+    });
+  }
+
   updateGuildMember(member, data) {
     return new Promise((resolve, reject) => {
       if (data.channel) data.channel_id = this.rest.client.resolver.resolveChannel(data.channel).id;

src/structures/DMChannel.js

@@ -59,6 +59,10 @@ class DMChannel extends Channel {
     return;
   }
 
+  fetchMessage() {
+    return;
+  }
+
   bulkDelete() {
     return;
   }

src/structures/GroupDMChannel.js

@@ -118,6 +118,10 @@ class GroupDMChannel extends Channel {
     return;
   }
 
+  fetchMessage() {
+    return;
+  }
+
   bulkDelete() {
     return;
   }

src/structures/TextChannel.js

@@ -43,6 +43,10 @@ class TextChannel extends GuildChannel {
     return;
   }
 
+  fetchMessage() {
+    return;
+  }
+
   bulkDelete() {
     return;
   }

src/structures/interface/TextBasedChannel.js

@@ -133,6 +133,28 @@ class TextBasedChannel {
     });
   }
 
+  /**
+   * Gets a single message from this channel, regardless of it being cached or not.
+   * @param {string} messageID The ID of the message to get
+   * @returns {Promise<Message>}
+   * @example
+   * // get message
+   * channel.fetchMessage('99539446449315840')
+   *   .then(message => console.log(message.content))
+   *   .catch(console.error);
+   */
+  fetchMessage(messageID) {
+    return new Promise((resolve, reject) => {
+      this.client.rest.methods.getChannelMessage(this, messageID).then(data => {
+        let msg = data;
+        if (!(msg instanceof Message)) msg = new Message(this, data, this.client);
+
+        this._cacheMessage(msg);
+        resolve(msg);
+      }).catch(reject);
+    });
+  }
+
   /**
    * Starts a typing indicator in the channel.
    * @param {number} [count] The number of times startTyping should be considered to have been called
@@ -394,6 +416,7 @@ exports.applyToClass = (structure, full = false) => {
   if (full) {
     props.push('_cacheMessage');
     props.push('fetchMessages');
+    props.push('fetchMessage');
     props.push('bulkDelete');
     props.push('startTyping');
     props.push('stopTyping');