from __future__ import annotations

import os
import pty
import select
import signal
import sys
from collections.abc import Callable, Sequence

from .broker import InputBroker


class PtyTap:
    """Full-duplex PTY proxy. Input is observed, never rewritten."""

    def __init__(self, command: Sequence[str], broker: InputBroker, *, on_line: Callable[[str], None] | None = None):
        self.command = list(command)
        self.broker = broker
        self.on_line = on_line

    def run(self) -> int:
        pid, master = pty.fork()
        if pid == 0:
            os.execvp(self.command[0], self.command)
        input_buffer = bytearray()
        try:
            while True:
                readable, _, _ = select.select([master, sys.stdin], [], [])
                if master in readable:
                    try:
                        data = os.read(master, 65536)
                    except OSError:
                        break
                    if not data:
                        break
                    os.write(sys.stdout.fileno(), data)
                if sys.stdin in readable:
                    data = os.read(sys.stdin.fileno(), 65536)
                    if not data:
                        break
                    os.write(master, data)
                    input_buffer.extend(data)
                    while b"\n" in input_buffer:
                        raw, _, rest = input_buffer.partition(b"\n")
                        input_buffer = bytearray(rest)
                        line = raw.decode("utf-8", errors="replace")
                        routed = self.broker.inspect_line(line)
                        if routed and self.on_line:
                            self.on_line(line)
        finally:
            try:
                _, status = os.waitpid(pid, 0)
                return os.waitstatus_to_exitcode(status)
            except ChildProcessError:
                return 0