from __future__ import annotations

import asyncio
import socket
from collections.abc import Iterable


def pick_free_port(host: str = "127.0.0.1", candidates: Iterable[int] | None = None) -> int:
    """Choose an available TCP port without binding a privileged/system port."""

    ports = list(candidates or range(49152, 65536))
    for port in ports:
        with socket.socket(
            socket.AF_INET6 if ":" in host else socket.AF_INET, socket.SOCK_STREAM
        ) as sock:
            try:
                sock.bind((host, port))
            except OSError:
                continue
            return port
    raise OSError("no free high TCP port")


async def drain_process_output(process: asyncio.subprocess.Process) -> list[str]:
    """Read both streams until a process exits, returning sanitized text lines."""

    lines: list[str] = []

    async def read(stream: asyncio.StreamReader | None) -> None:
        if stream is None:
            return
        while line := await stream.readline():
            lines.append(line.decode("utf-8", errors="replace").rstrip())

    await asyncio.gather(read(process.stdout), read(process.stderr))
    return lines