"""Tests for un-merge (#2165) — reversing one source out of a merged survivor.

The design question this task said to settle first was how to subtract without
stripping call sites the survivor legitimately owns. The answer is per-source
attribution recorded AT MERGE TIME: each `merged_from` entry holds only what
that source actually added. These tests pin that rule, and the refusal that
guards the case where the attribution isn't there.
"""
from types import SimpleNamespace
from unittest.mock import AsyncMock, MagicMock, patch

import pytest

from scribe.services import snippets as s


def _loc(path, repo="r", symbol=""):
    return {"repo": repo, "path": path, "symbol": symbol}


def _survivor(locations, merged_from, tags=None, owner=7):
    """A survivor note whose `data` carries locations + merge provenance."""
    return SimpleNamespace(
        id=1, user_id=owner, note_type="snippet", deleted_at=None,
        title="f — does a thing", tags=tags or ["python", "snippet"],
        body=s.compose_body(code="x = 1", language="python", locations=locations,
                            merged_from=merged_from),
        data=s.compose_data(name="f", when_to_use="does a thing", language="python",
                            code="x = 1", locations=locations,
                            merged_from=merged_from),
    )


async def _run_unmerge(survivor, *, source_alive=None, restore=1):
    """Drive unmerge_snippet with the DB stubbed; return update_note's kwargs."""
    async def fake_get(_uid, sid):
        if sid == survivor.id:
            return survivor
        return source_alive

    with (
        patch.object(s, "get_snippet", AsyncMock(side_effect=fake_get)),
        patch("scribe.services.access.can_write_note", AsyncMock(return_value=True)),
        patch("scribe.services.trash.restore_entity", AsyncMock(return_value=restore)),
        patch.object(s.notes_svc, "update_note",
                     AsyncMock(return_value=survivor)) as upd,
        patch.object(s, "_embed_snippet", MagicMock()),
    ):
        await s.unmerge_snippet(7, 1, 2)
    return upd.await_args.kwargs


# --- the subtraction ------------------------------------------------------


async def test_unmerge_strips_only_what_the_source_contributed():
    """The survivor's own location survives; the source's is removed."""
    mine, theirs = _loc("mine.py"), _loc("theirs.py")
    survivor = _survivor(
        [mine, theirs],
        [{"id": 2, "locations": [theirs], "tags": ["helper"]}],
        tags=["python", "snippet", "helper", "core"],
    )
    kwargs = await _run_unmerge(survivor)
    assert kwargs["data"]["locations"] == [mine]
    assert "helper" not in kwargs["tags"]
    assert "core" in kwargs["tags"]


async def test_a_location_the_survivor_also_owned_is_never_stripped():
    """The central hazard the task named. If a source brought a location the
    survivor ALREADY had, merge attributes nothing to it — so reversing must
    leave that call site in place."""
    shared = _loc("shared.py")
    survivor = _survivor([shared], [{"id": 2, "locations": [], "tags": ["t"]}])
    kwargs = await _run_unmerge(survivor)
    assert kwargs["data"]["locations"] == [shared]


async def test_the_reversed_entry_leaves_the_provenance_list():
    survivor = _survivor(
        [_loc("a.py"), _loc("b.py")],
        [{"id": 2, "locations": [_loc("b.py")]}, {"id": 3, "locations": []}],
    )
    kwargs = await _run_unmerge(survivor)
    assert s.merged_from_ids(kwargs["data"]["merged_from"]) == [3]
    assert "#2" not in kwargs["body"]
    # The other source's history is untouched — un-merge reverses one thing.
    assert "**Merged from:** #3" in kwargs["body"]


async def test_unmerging_the_last_source_clears_the_provenance_line():
    survivor = _survivor([_loc("a.py")], [{"id": 2, "locations": [], "tags": ["t"]}])
    kwargs = await _run_unmerge(survivor)
    assert "Merged from" not in kwargs["body"]


# --- restoring the source -------------------------------------------------


async def test_an_already_restored_source_is_repaired_not_refused():
    """The scenario that motivated the feature: the operator restored the source
    from the trash by hand, so both records claim its call sites and nothing ever
    stripped the survivor's copy. Un-merge must fix that, not reject it."""
    theirs = _loc("theirs.py")
    survivor = _survivor([_loc("mine.py"), theirs],
                         [{"id": 2, "locations": [theirs]}])
    alive = SimpleNamespace(id=2, user_id=7, note_type="snippet", deleted_at=None,
                            title="g — x", tags=["snippet"], body="", data=None)
    with patch("scribe.services.trash.restore_entity", AsyncMock()) as revive:
        kwargs = await _run_unmerge(survivor, source_alive=alive)
    # Nothing to revive — it's already alive — but the subtraction still happens.
    revive.assert_not_called()
    assert kwargs["data"]["locations"] == [_loc("mine.py")]


async def test_a_purged_source_is_refused_and_the_survivor_is_untouched():
    """If the source can't come back, stripping the survivor would lose the
    locations entirely — no record would claim them."""
    survivor = _survivor([_loc("a.py")], [{"id": 2, "locations": [_loc("a.py")]}])

    async def fake_get(_uid, sid):
        return survivor if sid == 1 else None

    with (
        patch.object(s, "get_snippet", AsyncMock(side_effect=fake_get)),
        patch("scribe.services.access.can_write_note", AsyncMock(return_value=True)),
        patch("scribe.services.trash.restore_entity", AsyncMock(return_value=None)),
        patch.object(s.notes_svc, "update_note", AsyncMock()) as upd,
        patch.object(s, "_embed_snippet", MagicMock()),
    ):
        with pytest.raises(s.UnmergeError, match="purged"):
            await s.unmerge_snippet(7, 1, 2)
    upd.assert_not_called()


# --- refusals -------------------------------------------------------------


async def test_an_entry_without_attribution_is_refused_not_guessed():
    """Bare-id provenance comes from parsing the body, which can only hold ids.
    Subtracting a guess could strip call sites the survivor owns — so refuse and
    say what to do instead."""
    survivor = _survivor([_loc("a.py")], [2])

    async def fake_get(_uid, sid):
        return survivor if sid == 1 else None

    with (
        patch.object(s, "get_snippet", AsyncMock(side_effect=fake_get)),
        patch("scribe.services.access.can_write_note", AsyncMock(return_value=True)),
        patch.object(s.notes_svc, "update_note", AsyncMock()) as upd,
        patch.object(s, "_embed_snippet", MagicMock()),
    ):
        with pytest.raises(s.UnmergeError, match="provenance"):
            await s.unmerge_snippet(7, 1, 2)
    upd.assert_not_called()


async def test_unmerging_something_never_absorbed_is_refused():
    survivor = _survivor([_loc("a.py")], [{"id": 99, "locations": []}])
    with (
        patch.object(s, "get_snippet", AsyncMock(return_value=survivor)),
        patch("scribe.services.access.can_write_note", AsyncMock(return_value=True)),
    ):
        with pytest.raises(s.UnmergeError, match="no record of absorbing"):
            await s.unmerge_snippet(7, 1, 2)


async def test_unmerge_requires_write_access():
    """Same rule as merge: a read-only share can see the record, not rearrange it."""
    survivor = _survivor([_loc("a.py")], [{"id": 2, "locations": []}])
    with (
        patch.object(s, "get_snippet", AsyncMock(return_value=survivor)),
        patch("scribe.services.access.can_write_note", AsyncMock(return_value=False)),
    ):
        with pytest.raises(PermissionError):
            await s.unmerge_snippet(7, 1, 2)


async def test_unmerge_on_a_missing_survivor_returns_none():
    with patch.object(s, "get_snippet", AsyncMock(return_value=None)):
        assert await s.unmerge_snippet(7, 1, 2) is None