def RECEIVE_MESSAGE(op):
    '''
        This is sample for implement BOT in LINE group
        Invite your BOT to group, then BOT will auto accept your invitation
        Command availabe :
        > hi
        > /author
    '''
    msg = op.message
    
    text = msg.text
    msg_id = msg.id
    receiver = msg.to
    sender = msg._from
    
    try:
        # Check content only text message
        if msg.contentType == 0:
            # Check only group chat
            if msg.toType == 2:
                # Chat checked request
                line.sendChatChecked(receiver, msg_id)
                # Get sender contact
                contact = line.getContact(sender)
                # Command list
                if text.lower() == 'hi':
                    line.log('[%s] %s' % (contact.displayName, text))
                    line.sendMessage(receiver, 'Hi too! How are you?')
                elif text.lower() == '/author':
                    line.log('[%s] %s' % (contact.displayName, text))
                    line.sendMessage(receiver, 'My author is linepy')
    except Exception as e:
        line.log("[RECEIVE_MESSAGE] ERROR : " + str(e))