"""Regression: the Windows Desktop update hand-off must not meter its step pipes.

``scripts/desktop-update/windows.ps1`` runs each update step through
``Invoke-HermesStep``, which starts the step with ``RedirectStandardOutput`` /
``RedirectStandardError``. Reading those pipes back has two failure modes, and
this fixture covers both because they pull in opposite directions.

**Waiting for EOF (#90455).** The drain used to collect output with
``ReadToEndAsync().Result``. That task does not return when the *step* exits --
it returns when the *pipe* reaches EOF. On Windows the write end of a redirected
pipe is handed to the child as an inheritable handle, so every descendant
spawned without its own redirection holds a duplicate, and EOF waits for the
last of them to close it. ``hermes update`` deliberately runs build steps with
stdout inherited (the tee-stderr runner in ``hermes_cli/main.py``), so the
process tree under a step is arbitrarily deep and not something the hand-off can
enumerate. When one of those descendants is a resident gateway, the pipe never
closes and ``Invoke-HermesStep`` blocks for the life of the gateway.

Everything the hand-off owes the Desktop is downstream of that call:
``.hermes-update-result.json`` is never written, ``.hermes-update-in-progress``
is never cleared, and the Desktop is never relaunched -- so the app sits on
"Updating Hermes" until the user kills the gateway by hand, and the stale marker
then refuses the next update too.

**Trickling toward EOF.** The fix reads in chunks so an abandoned pipe still
yields what arrived. But a chunked drain that idles after every chunk it reads
is metered at one buffer per tick (16 KiB / 150ms ~ 107 KB/s), and because the
pipe then backs up that is backpressure on the *running* step, not just a slow
read -- a chatty step blocks on ``write()`` waiting for the reader. Measured on
this fixture's own flood arm: 4 MiB took 39.1s metered vs 0.09s unmetered, and a
step writing to both pipes took 18.3s vs 0.29s. ``hermes update`` is exactly this
shape; the Electron/vite build alone is megabytes.

So the contract is: bounded when a descendant holds the pipe open, and never
slower than the step can write. Both arms live in the script's own
``-SelfTestPipeDrain`` fixture, which is ``windows_only`` because Linux CI
cannot execute the PowerShell hand-off.
"""

from __future__ import annotations

import os
import subprocess
from pathlib import Path

import pytest


REPO_ROOT = Path(__file__).resolve().parent.parent
WINDOWS_PS1 = REPO_ROOT / "scripts" / "desktop-update" / "windows.ps1"


@pytest.mark.windows_only
def test_pipe_drain_survives_a_leak_without_metering_a_chatty_step(
    tmp_path: Path,
) -> None:
    """Execute the real drain against both shapes of step.

    ``-SelfTestPipeDrain`` runs two steps through the real
    ``Invoke-HermesStep``:

    *leak* -- a step that spawns a grandchild with ``UseShellExecute = $false``
    and no redirection (the shape that makes the grandchild inherit the step's
    stdout/stderr), then exits 7 while the grandchild sleeps on. The fixture
    asserts the grandchild was **still alive** when ``Invoke-HermesStep``
    returned, so a pass cannot be a timing coincidence, and that the exit code
    and the step's output both survived the abandonment.

    *flood* -- a step that writes megabytes and holds nothing, exiting 5. It
    must complete in wall-clock far under what a sleep-per-chunk drain would
    take, and every byte must arrive.

    Measured on Windows 11 / PowerShell 5.1: leak 4.3s (vs 47.4s waiting out the
    grandchild), flood 8 MiB in ~1s (vs ~76s metered).
    """
    system_root = Path(os.environ.get("SystemRoot", r"C:\Windows"))
    powershell = (
        system_root / "System32" / "WindowsPowerShell" / "v1.0" / "powershell.exe"
    )
    if not powershell.is_file():
        pytest.skip(f"Windows PowerShell not found at {powershell}")

    env = {
        **os.environ,
        # The fixture writes its child scripts, pid file and hand-off log under
        # TEMP; point that at tmp_path so the test leaves nothing behind.
        "TEMP": str(tmp_path),
        "TMP": str(tmp_path),
        # Keep the test quick. The grace is what the fix bounds; the hold is
        # how long the leaking grandchild lives. hold >> grace is what makes a
        # regression measurable rather than lucky.
        "HERMES_UPDATE_PIPE_DRAIN_SECONDS": "3",
        "HERMES_SELFTEST_HOLD_SECONDS": "45",
    }

    result = subprocess.run(
        [
            str(powershell),
            "-NoProfile",
            "-ExecutionPolicy",
            "Bypass",
            "-File",
            str(WINDOWS_PS1),
            "-SelfTestPipeDrain",
        ],
        capture_output=True,
        text=True,
        # Comfortably past both arms' worst cases (the 45s hold, and a metered
        # flood) so a regression fails with the fixture's own diagnosis instead
        # of an opaque timeout.
        timeout=300,
        env=env,
        cwd=str(REPO_ROOT),
    )

    assert "PIPE-DRAIN SELF-TEST: PASS" in result.stdout, (
        "The Windows update hand-off's step drain regressed: it either waited "
        "on a descendant holding the pipe open (the Desktop parks on 'Updating "
        "Hermes' forever) or metered a chatty step (backpressure on the running "
        f"update). Fixture diagnosis follows.\n--- stdout ---\n{result.stdout}\n"
        f"--- stderr ---\n{result.stderr}"
    )
    assert result.returncode == 0, (
        f"-SelfTestPipeDrain exited {result.returncode}.\n"
        f"--- stdout ---\n{result.stdout}\n--- stderr ---\n{result.stderr}"
    )