"""Bounded child output in memory; never spool inventory to temporary files."""
import subprocess
import threading
import time


class CollectionCancelled(Exception):
    pass


class ProcessFailure(RuntimeError):
    def __init__(self, code, returncode=None):
        self.code = code
        self.returncode = returncode
        super().__init__('Inventory subprocess failed (' + code + '); diagnostics omitted.')


def capture(arguments, *, env, timeout, cancelled=lambda: False, limit=10*1024*1024, creationflags=0):
    if cancelled():
        raise CollectionCancelled()
    try:
        child = subprocess.Popen(arguments, stdin=subprocess.DEVNULL, stdout=subprocess.PIPE,
            stderr=subprocess.DEVNULL, shell=False, env=env, creationflags=creationflags)
    except OSError:
        raise ProcessFailure('command_unavailable') from None
    buffer = bytearray()
    exceeded = threading.Event()
    read_failed = threading.Event()
    def drain():
        try:
            while chunk := child.stdout.read(65536):
                if len(buffer)+len(chunk)>limit:
                    exceeded.set()
                    break
                buffer.extend(chunk)
        except (OSError, ValueError):
            read_failed.set()
    reader = threading.Thread(target=drain, daemon=True)
    reader.start()
    deadline = time.monotonic()+timeout
    try:
        while child.poll() is None:
            if cancelled(): raise CollectionCancelled()
            if exceeded.is_set(): raise ProcessFailure('output_limit')
            if time.monotonic()>=deadline: raise ProcessFailure('timeout')
            time.sleep(.02)
        reader.join(timeout=1)
        if reader.is_alive(): raise ProcessFailure('cleanup_failed')
        if cancelled(): raise CollectionCancelled()
        if exceeded.is_set(): raise ProcessFailure('output_limit')
        if read_failed.is_set() or child.returncode: raise ProcessFailure('collection_failed', child.returncode)
        return bytes(buffer)
    finally:
        if child.poll() is None: child.kill()
        try:
            child.wait(timeout=3)
        except subprocess.TimeoutExpired:
            raise ProcessFailure('cleanup_failed') from None
        # Fixed collectors must not spawn descendants holding stdout open.
        # Do not block on closing a buffered stream owned by a stalled reader.
        reader.join(timeout=.2)
        if not reader.is_alive(): child.stdout.close()