import socket
import random

class NetworkLayer:
    def __init__(self, host:str, port:int) -> None:
        self.socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.socket.connect((host, port))
        print("下层的不可靠传输连接成功，等待发送方传输。")

    def udt_send(self, data:str):
        self.socket.send(data.encode())

    def udt_rcv(self) -> str:
        message = self.socket.recv(12).decode("utf-8")
        return message
    
    def close(self):
        self.socket.close()
                

class ApplicationLayer:
    def __init__(self) -> None:
        self.data = list()


class Receiver:
    def __init__(self, networkLayer:NetworkLayer, applicationLayer:ApplicationLayer):
        self.expected_seq_num = 1
        self.networkLayer = networkLayer
        self.applicationLayer = applicationLayer
        
    def deliver_data(self, data, seq_num):
        if seq_num == self.expected_seq_num:
            print(f'成功收到seq_num={seq_num}, data=\"{data}\"的包。')
            self.applicationLayer.data.append(data)
            self.udt_send(seq_num)
            self.expected_seq_num += 1
        else:
            print(f'收到seq_num={seq_num}, 与预期seq_num={self.expected_seq_num}不符。')
            self.udt_send(self.expected_seq_num - 1)

    def udt_send(self, ack_num):
        print(f"发送ACK={ack_num}", end="")
        if random.random() > 0.25:
            self.networkLayer.socket.send("{:0>4d}".format(ack_num).encode())
        else:
            print("，此包丢失。", end="")
        print()

    def extract(self, message:str):
        seq_num = int(message[:3])
        data = message[4:]
        return seq_num, data

if __name__ == "__main__":
    max_seq_num = 20
    networkLayer = NetworkLayer(host="192.168.31.197", port=23666)
    applicationLayer = ApplicationLayer()
    receiver = Receiver(networkLayer, applicationLayer)
    while True:
        message = networkLayer.udt_rcv()
        if message:
            seq_num, data = receiver.extract(message)
            receiver.deliver_data(data, seq_num)
            if receiver.expected_seq_num > max_seq_num:
                break
    print("序列传输完成。")
    networkLayer.close()