import socket
import struct
import json


def pack_str(data: str):
    encoded = data.encode()
    return struct.pack('I', len(encoded)) + encoded


def pack_bytes(data: bytes):
    return struct.pack('I', len(data)) + data


def handle_request(data, connection):
    request = json.loads(data)

    # Хотя метод только один, но все равно лучше
    # сразу написать расширяемое приложение
    if request['method'] == 'get':
        path = request['path']

        try:
            with open(path, 'rb') as f:
                file_data = f.read()

        except FileNotFoundError:
            header = json.dumps({'status': 1, 'reason': 'Файл не найден'})
            connection.sendall(pack_str(header))

        except PermissionError:
            header = json.dumps({'status': 1, 'reason': 'Файл не доступен для чтения'})
            connection.sendall(pack_str(header))

        # Я знаю, что это плохо, но сервер не должен падать,
        # а других ошибок я не смог вспомнить
        except Exception as e:
            header = json.dumps({'status': 2, 'reason': str(e)})
            connection.sendall(pack_str(header))

        else:
            length = len(file_data)
            header = json.dumps({'status': 0, 'size': length, 'path': request['path']})
            connection.sendall(pack_str(header))
            i = 0
            while i < length:
                packet = pack_bytes(file_data[i: i + CHUNK_SIZE])
                connection.sendall(packet)
                i += CHUNK_SIZE


def get_data(connection):
    buffer = b''
    while len(buffer) < 4:
        data = connection.recv(4 - len(buffer))
        if not data:
            raise ConnectionError('Connection was closed')

        buffer += data

    size_packed, buffer = buffer[:4], buffer[4:]
    if not size_packed:
        raise ConnectionError('Connection was closed')

    (size,) = struct.unpack('I', size_packed)
    data = connection.recv(size - len(buffer))
    return buffer + data


def handle_connection(connection, address):
    while True:
        try:
            data = get_data(connection)

        except ConnectionResetError:
            print(f'Connection with {address[0]} was unexpectedly closed')
            break

        except ConnectionError:
            print(f'Connection with {address[0]} was ended')
            break

        except KeyboardInterrupt:
            raise KeyboardInterrupt()

        else:
            if not data:
                print(f'Connection with {address[0]} was ended')
                break
            handle_request(data.decode(), connection)


HOST, PORT = ADDR = '0.0.0.0', 6000
CHUNK_SIZE = 4096
sock = socket.socket()
sock.bind(ADDR)
sock.listen(5)

while True:
    print('Listening for new connections...')
    try:
        connection, address = sock.accept()
        print(f'Got a connection from {address[0]}')
        handle_connection(connection, address)

    except KeyboardInterrupt:
        print('Stopping server...')
        sock.close()
        print('Server stopped')
        break