"""Archive journal state machine and evidence table (US06-02).

The evidence table decides whether an original may be deleted, so every
combination of journal state and disk reality is asserted here as a pure function —
no database, no files. A wrong cell in this table is data loss.
"""

import pytest

from photo_pipeline.services.archive_journal import (
    ALLOWED_TRANSITIONS,
    FORWARD,
    MANUAL,
    RESUMABLE,
    TERMINAL_STATES,
    UNSAFE_STATES,
    ArchiveState,
    _classify,
    can_transition,
)

pytestmark = pytest.mark.phase_f


# ── state machine ────────────────────────────────────────────────────────────


def test_the_happy_path_is_the_only_way_forward():
    assert can_transition(ArchiveState.PLANNED, ArchiveState.TRANSFERRING)
    assert can_transition(ArchiveState.TRANSFERRING, ArchiveState.VERIFIED)
    assert can_transition(ArchiveState.VERIFIED, ArchiveState.REMOVING)
    assert can_transition(ArchiveState.REMOVING, ArchiveState.COMPLETE)
    # No shortcut may skip verification before a source is removed.
    assert not can_transition(ArchiveState.TRANSFERRING, ArchiveState.REMOVING)
    assert not can_transition(ArchiveState.PLANNED, ArchiveState.VERIFIED)
    assert not can_transition(ArchiveState.VERIFIED, ArchiveState.COMPLETE)


def test_removal_never_goes_backwards():
    """Once the source may be gone, retrying the transfer would archive nothing and
    could overwrite the copy that is now the only one."""
    assert ALLOWED_TRANSITIONS[ArchiveState.REMOVING] == {
        ArchiveState.COMPLETE,
        ArchiveState.FAILED,
    }
    assert not can_transition(ArchiveState.REMOVING, ArchiveState.TRANSFERRING)
    assert not can_transition(ArchiveState.REMOVING, ArchiveState.PLANNED)


def test_complete_is_terminal_and_failed_can_be_retried():
    assert ALLOWED_TRANSITIONS[ArchiveState.COMPLETE] == set()
    assert TERMINAL_STATES == {ArchiveState.COMPLETE}
    assert can_transition(ArchiveState.FAILED, ArchiveState.TRANSFERRING)
    assert can_transition(ArchiveState.FAILED, ArchiveState.PLANNED)


def test_every_state_that_can_touch_the_disk_is_marked_unsafe():
    assert UNSAFE_STATES == {
        ArchiveState.TRANSFERRING,
        ArchiveState.VERIFIED,
        ArchiveState.REMOVING,
    }
    assert ArchiveState.PLANNED not in UNSAFE_STATES


# ── evidence table ───────────────────────────────────────────────────────────


@pytest.mark.parametrize(
    "state,source,destination,matches,expected",
    [
        # Nothing published yet: the source is still the only copy.
        (ArchiveState.TRANSFERRING, True, False, False, RESUMABLE),
        (ArchiveState.FAILED, True, False, False, RESUMABLE),
        # The archive copy is durable and correct: finish the remaining steps.
        (ArchiveState.TRANSFERRING, True, True, True, FORWARD),
        (ArchiveState.TRANSFERRING, False, True, True, FORWARD),
        (ArchiveState.VERIFIED, True, True, True, FORWARD),
        (ArchiveState.REMOVING, False, True, True, FORWARD),
        (ArchiveState.FAILED, True, True, True, FORWARD),
        # Wrong bytes at the destination: never overwrite, never remove.
        (ArchiveState.TRANSFERRING, True, True, False, MANUAL),
        (ArchiveState.VERIFIED, True, True, False, MANUAL),
        (ArchiveState.REMOVING, False, True, False, MANUAL),
        # The journal claims an archived copy that is not there.
        (ArchiveState.VERIFIED, True, False, False, MANUAL),
        (ArchiveState.REMOVING, False, False, False, MANUAL),
        # Neither copy exists — never silently accepted as success.
        (ArchiveState.TRANSFERRING, False, False, False, MANUAL),
        (ArchiveState.FAILED, False, False, False, MANUAL),
    ],
)
def test_classification_of_every_evidence_combination(
    state, source, destination, matches, expected
):
    classification, reason = _classify(state, source, destination, matches)

    assert classification == expected, reason


def test_a_source_that_is_gone_without_an_archive_copy_is_never_called_recoverable():
    """The one combination that must always stop: the original left active storage
    and nothing verifiable took its place."""
    for state in (ArchiveState.TRANSFERRING, ArchiveState.VERIFIED, ArchiveState.REMOVING):
        assert _classify(state, False, False, False)[0] == MANUAL