Add !version command

src/main.js

@@ -17,6 +17,7 @@ const suspend = require('./modules/suspend');
 const webserver = require('./modules/webserver');
 const greeting = require('./modules/greeting');
 const typingProxy = require('./modules/typingProxy');
+const version = require('./modules/version');
 const attachments = require("./data/attachments");
 const {ACCIDENTAL_THREAD_MESSAGES} = require('./data/constants');
 
@@ -167,6 +168,7 @@ module.exports = {
     await greeting(bot);
     await webserver(bot);
     await typingProxy(bot);
+    await version(bot);
 
     // Connect to Discord
     console.log('Connecting to Discord...');

src/modules/version.js

@@ -0,0 +1,47 @@
+const path = require('path');
+const fs = require('fs');
+const {promisify} = require('util');
+const utils = require("../utils");
+const threadUtils = require("../threadUtils");
+
+const access = promisify(fs.access);
+const readFile = promisify(fs.readFile);
+
+const GIT_DIR = path.join(__dirname, '..', '..', '.git');
+
+module.exports = bot => {
+  const addInboxServerCommand = (...args) => threadUtils.addInboxServerCommand(bot, ...args);
+
+  addInboxServerCommand('version', async (msg, args, thread) => {
+    const packageJson = require('../../package.json');
+    const packageVersion = packageJson.version;
+
+    let response = `Modmail v${packageVersion}`;
+
+    let isGit;
+    try {
+      await access(GIT_DIR);
+      isGit = true;
+    } catch (e) {
+      isGit = false;
+    }
+
+    if (isGit) {
+      let commitHash;
+      const HEAD = await readFile(path.join(GIT_DIR, 'HEAD'), {encoding: 'utf8'});
+
+      if (HEAD.startsWith('ref:')) {
+        // Branch
+        const ref = HEAD.match(/^ref: (.*)$/m)[1];
+        commitHash = (await readFile(path.join(GIT_DIR, ref), {encoding: 'utf8'})).trim();
+      } else {
+        // Detached head
+        commitHash = HEAD.trim();
+      }
+
+      response += ` (${commitHash.slice(0, 7)})`;
+    }
+
+    utils.postSystemMessageWithFallback(msg.channel, thread, response);
+  });
+};