import pytest

"""Tests for reclaiming the virtiofs mount's file handles.
These guard a mechanism that exists only because of an environment defect: the
mount's daemon holds a host descriptor per inode the guest looks up, and runs out.
The properties that matter are that reclaim is *actually verified* rather than
assumed, and that the expensive fallback is used only when it must be.
"""


from suvi import vfs


def test_drop_caches_reports_failure_without_root(monkeypatch):
    """Must return False rather than raise, so the fallback can run."""
    def refuse(*args, **kwargs):
        raise PermissionError(13, "Permission denied")

    monkeypatch.setattr("builtins.open", refuse)
    assert vfs.drop_caches() is False


def test_reclaimable_kb_reads_the_slab():
    assert vfs.reclaimable_kb() > 0  # real /proc/meminfo


def test_reclaimable_kb_survives_a_broken_meminfo(monkeypatch):
    monkeypatch.setattr("builtins.open", lambda *a, **k: (_ for _ in ()).throw(OSError()))
    assert vfs.reclaimable_kb() == 0


def test_release_prefers_drop_caches(monkeypatch):
    """The fallback allocates tens of GiB; it must not run when drop_caches works."""
    monkeypatch.setattr(vfs, "drop_caches", lambda: True)

    def explode(*args, **kwargs):
        raise AssertionError("allocated memory despite drop_caches succeeding")

    monkeypatch.setattr(vfs, "bytearray", explode, raising=False)
    assert vfs.release_handles() is True


def test_fallback_reports_failure_when_nothing_is_reclaimed(monkeypatch):
    monkeypatch.setattr(vfs, "drop_caches", lambda: False)
    monkeypatch.setattr(vfs, "reclaimable_kb", lambda: 1000)
    assert vfs.release_handles(budget_gib=1, floor_kb=0) is False


def test_release_gives_up_when_the_slab_cannot_be_read(monkeypatch):
    monkeypatch.setattr(vfs, "drop_caches", lambda: False)
    monkeypatch.setattr(vfs, "reclaimable_kb", lambda: 0)
    assert vfs.release_handles() is False


# --------------------------------------------------------------- memory bounding


def test_available_gib_reads_meminfo():
    assert vfs.available_gib() > 0


def test_pressure_stops_at_the_reserve_not_a_fraction(monkeypatch):
    """Capping at a fraction of available memory reclaims nothing.

    The kernel only frees slab under genuine pressure, so leaving 40% headroom
    means it never triggers: an earlier version allocated 14 GiB of a 23 GiB
    allowance and freed zero, costing the machine the memory for no benefit.
    Pressure must run down to a fixed reserve instead.
    """
    monkeypatch.setattr(vfs, "drop_caches", lambda: False)
    monkeypatch.setattr(vfs, "reclaimable_kb", lambda: 1000)  # never yields
    available = [20.0]
    monkeypatch.setattr(vfs, "available_gib", lambda: available[0])
    allocated = []
    real = bytearray

    def fake(n):
        allocated.append(n)
        available[0] -= 1.0  # each GiB claimed reduces what is available
        return real(1)

    monkeypatch.setattr(vfs, "bytearray", fake, raising=False)
    assert vfs.release_handles(reserve_gib=2.0, floor_kb=0) is False
    # Pushed from 20 GiB down to the 2 GiB reserve, not stopped at 60%.
    assert 17 <= len(allocated) <= 19, f"allocated {len(allocated)} GiB"


def test_pressure_stops_as_soon_as_the_slab_yields(monkeypatch):
    monkeypatch.setattr(vfs, "drop_caches", lambda: False)
    readings = iter([1000, 1000, 1000, 400])
    monkeypatch.setattr(vfs, "reclaimable_kb", lambda: next(readings))
    monkeypatch.setattr(vfs, "available_gib", lambda: 20.0)
    allocated = []
    real = bytearray
    monkeypatch.setattr(
        vfs, "bytearray", lambda n: allocated.append(n) or real(1), raising=False
    )
    assert vfs.release_handles(floor_kb=0) is True
    assert len(allocated) == 2, "kept allocating after the kernel gave ground"


# ------------------------------------------------------------------- Reliever


def test_reliever_fires_on_the_interval(monkeypatch):
    calls = []
    monkeypatch.setattr(vfs, "release_handles", lambda *a, **k: calls.append(1) or True)
    reliever = vfs.Reliever(interval=10)
    for _ in range(9):
        reliever.tick()
    assert calls == []
    reliever.tick()
    assert len(calls) == 1


def test_reliever_keeps_firing_across_a_long_run(monkeypatch):
    calls = []
    monkeypatch.setattr(vfs, "release_handles", lambda *a, **k: calls.append(1) or True)
    reliever = vfs.Reliever(interval=10)
    for _ in range(100):
        reliever.tick()
    assert len(calls) == 10, "stopped reclaiming partway through a long traversal"
    assert reliever.releases == 10


def test_reliever_counts_batched_items(monkeypatch):
    """Callers processing six bands per timestamp tick by six, not one."""
    calls = []
    monkeypatch.setattr(vfs, "release_handles", lambda *a, **k: calls.append(1) or True)
    reliever = vfs.Reliever(interval=10)
    reliever.tick(6)
    reliever.tick(6)
    assert len(calls) == 1
    assert reliever.seen == 12


def test_reliever_can_be_disabled(monkeypatch):
    def explode(*a, **k):
        raise AssertionError("reclaimed while disabled")

    monkeypatch.setattr(vfs, "release_handles", explode)
    reliever = vfs.Reliever(interval=1, enabled=False)
    for _ in range(50):
        reliever.tick()
    assert reliever.releases == 0


def test_reliever_reclaims_when_the_run_ends(monkeypatch):
    """Reclaiming only during a run leaves the machine loaded once it finishes.

    The inodes a traversal cached stay pinned -- and with them the host's file
    handles -- until something else forces reclaim.  That is why the system was
    still saturated with nothing of ours running.
    """
    calls = []
    monkeypatch.setattr(vfs, "release_handles", lambda *a, **k: calls.append(1) or True)
    reliever = vfs.Reliever(interval=1000, on_exit=False)
    reliever.tick(5)
    assert calls == [], "should not have reclaimed mid-run yet"
    reliever.finish()
    assert len(calls) == 1


def test_finish_is_idempotent(monkeypatch):
    calls = []
    monkeypatch.setattr(vfs, "release_handles", lambda *a, **k: calls.append(1) or True)
    reliever = vfs.Reliever(interval=1000, on_exit=False)
    reliever.tick()
    reliever.finish()
    reliever.finish()
    reliever.finish()
    assert len(calls) == 1


def test_finish_does_nothing_if_no_work_happened(monkeypatch):
    def explode(*a, **k):
        raise AssertionError("reclaimed despite processing nothing")

    monkeypatch.setattr(vfs, "release_handles", explode)
    vfs.Reliever(on_exit=False).finish()


def test_reliever_works_as_a_context_manager(monkeypatch):
    calls = []
    monkeypatch.setattr(vfs, "release_handles", lambda *a, **k: calls.append(1) or True)
    with vfs.Reliever(interval=1000, on_exit=False) as reliever:
        reliever.tick(3)
        assert calls == []
    assert len(calls) == 1


def test_context_manager_reclaims_even_when_the_body_raises(monkeypatch):
    calls = []
    monkeypatch.setattr(vfs, "release_handles", lambda *a, **k: calls.append(1) or True)
    with pytest.raises(ValueError):
        with vfs.Reliever(interval=1000, on_exit=False) as reliever:
            reliever.tick()
            raise ValueError("boom")
    assert len(calls) == 1, "a failed job must still hand its handles back"


def test_no_pressure_is_applied_when_the_slab_is_already_small(monkeypatch):
    """Below the floor the slab is live processes' working set, not archive inodes.

    Squeezing the machine to shave a few hundred megabytes off it costs far more
    than it gains -- and during a long job this runs every RELIEF_INTERVAL items.
    """
    monkeypatch.setattr(vfs, "drop_caches", lambda: False)
    monkeypatch.setattr(vfs, "reclaimable_kb", lambda: 500 * 1024)  # 0.5 GiB

    def explode(*a, **k):
        raise AssertionError("applied memory pressure below the floor")

    monkeypatch.setattr(vfs, "bytearray", explode, raising=False)
    assert vfs.release_handles() is True