export default function buildTree(messages) {
  let messageMap = {};
  let rootMessages = [];

  // Traverse the messages array and store each element in messageMap.
  messages.forEach(message => {
    messageMap[message.messageId] = {...message, children: []};

    const parentMessage = messageMap[message.parentMessageId];
    if (parentMessage)
      parentMessage.children.push(messageMap[message.messageId]);
    else 
      rootMessages.push(messageMap[message.messageId]);
  });

  return rootMessages;
}