chore: refactor main code into smaller parts

lib/offlineCommand.js

@@ -0,0 +1,27 @@
+'use strict'
+
+const Errors = require('redis-errors')
+const utils = require('./utils')
+const debug = require('./debug')
+
+function offlineCommand (client, command) {
+  const commandName = command.command.toUpperCase()
+  if (client.closing || !client.enableOfflineQueue) {
+    const msg = client.closing === true
+      ? 'The connection is already closed.'
+      : client._stream.writable === true
+      ? 'The connection is not yet established and the offline queue is deactivated.'
+      : 'Stream not writeable.'
+    const err = new Errors.AbortError(`${commandName} can't be processed. ${msg}`)
+    err.code = 'NR_CLOSED'
+    err.command = commandName
+    err.args = command.args
+    utils.replyInOrder(client, command.callback, err)
+  } else {
+    debug('Queueing %s for next server connection.', commandName)
+    client.offlineQueue.push(command)
+  }
+  client.shouldBuffer = true
+}
+
+module.exports = offlineCommand