import selectors
import socket

sel = selectors.DefaultSelector()
total_blocks = 0
data = b""


def on_disconnect(conn):
    print("disconnected %s" % conn)
    sel.unregister(conn)
    conn.close()


def accept(sock, mask):
    conn, addr = sock.accept()
    conn.setblocking(False)
    sel.register(conn, selectors.EVENT_READ, read)


def write(conn, mask):
    global total_blocks, data
    # emulates a case where the first call to send() will always block
    sel.modify(conn, selectors.EVENT_WRITE, write)
    try:
        conn.send(data)
    except (ConnectionResetError, BrokenPipeError):
        on_disconnect(conn)
    except BlockingIOError as err:
        total_blocks += 1
        sel.modify(conn, selectors.EVENT_WRITE, write)
        # print("err write %s %s" % (err, total_blocks))
    data = b""
    read(conn, mask)


def read(conn, mask):
    global total_blocks, data
    # emulates a case where the first call to recv() will always block
    try:
        data += conn.recv(819200)  # Should be ready
        if data:
            if b"\r\n" not in data:
                read(conn, mask)
            else:
                write(conn, mask)
        else:
            on_disconnect(conn)
    except (ConnectionResetError, BrokenPipeError):
        on_disconnect(conn)
    except BlockingIOError as err:
        total_blocks += 1
        sel.modify(conn, selectors.EVENT_READ, read)
        # print("err read %s %s" % (err, total_blocks))


sock = socket.socket()
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.bind(('localhost', 1234))
sock.listen(100)
sock.setblocking(False)
sel.register(sock, selectors.EVENT_READ, accept)

try:
    while True:
        events = sel.select()
        for key, mask in events:
            callback = key.data
            callback(key.fileobj, mask)
finally:
    print("total_blocks would blocks = %s" % total_blocks)