import hashlib
import datetime
# 交易记录类
class DaDaMessage:

  def __init__(self, data):
    self.hash = None # 自身hash
    self.preHash = None # 上一个区块hash
    self.data = data # 交易信息
    self.timestamp = datetime.datetime.now() # 交易时间
    self.payloadHash = self.payload_hash() # 交易后的哈希，防止篡改

  #对交易信息进行hash
  def payload_hash(self):
    sha = hashlib.md5()
    datastr = (str(self.data) + str(self.timestamp)).encode("utf-8")
    sha.update(datastr)
    return sha.hexdigest()
  #密封，锁定交易信息
  def seal(self):
    self.hash = self.hash_message()
  #将交易信息和上一个区块密封
  def hash_message(self):
    sha = hashlib.md5()
    datastr = (str(self.preHash) + str(self.payloadHash)).encode("utf-8")
    sha.update(datastr)
    return sha.hexdigest()
  #校验区块信息
  def validate(self):
    if self.hash != self.hash_message():
      raise InvalidateMessage("交易哈希鏈接唄修改")
    if self.payloadHash != self.payload_hash():
      raise InvalidateMessage("交易時間與數據被修改")
  #鏈接區塊
  def link(self,Message):
    self.preHash = Message.hash
  def __repr__(self):
    return "hash:{},preHash:{},data:{}".format(self.hash,self.preHash,self.data)

class InvalidateMessage(Exception):
  def __init__(self,*args,**kwargs):
    super(Exception,self).__init__(*args,**kwargs)

if __name__=="__main__":
  m1 = DaDaMessage("I love coins 12")
  m2 = DaDaMessage("I love coins 13")
  m3 = DaDaMessage("I love coins 14")
  try:
    m1.seal()
    m2.link(m1)
    m2.seal()
    m3.link(m2)
    m3.seal()
    m1.hash = "0xaaaajjjjj"
    m1.data = "I　don't love "
    m1.validate()
    m2.validate()
    m3.validate()
    print(m1)
    print(m2)
    print(m3)
  except InvalidateMessage as e:
    print(e)