"""Tests for apply-under-drift (SHARD-WP-0008 T4)."""

from shard_wiki.adapters import FolderAdapter
from shard_wiki.coordination import ApplyStatus, DecisionLog, OverlayEngine
from shard_wiki.model import Identity


def _writable(tmp_path, files):
    for rel, text in files.items():
        (tmp_path / rel).write_text(text, encoding="utf-8")
    return FolderAdapter("w", tmp_path, writable=True)


def test_fast_forward_apply_writes_through(tmp_path):
    shard = _writable(tmp_path, {"Home.md": "old"})
    eng = OverlayEngine("space", DecisionLog())
    base = shard.current_rev("Home")
    ov = eng.draft(Identity("w", "Home"), "new", base_rev=base)

    result = eng.apply(ov.overlay_id, shard)
    assert result.status is ApplyStatus.APPLIED
    assert shard.read("Home").body == "new"  # written through
    assert eng.get(ov.overlay_id) is None  # overlay closed in the fold


def test_drift_refuses_without_clobber(tmp_path):
    shard = _writable(tmp_path, {"Home.md": "old"})
    eng = OverlayEngine("space", DecisionLog())
    ov = eng.draft(Identity("w", "Home"), "mine", base_rev="STALE-REV")

    result = eng.apply(ov.overlay_id, shard)
    assert result.status is ApplyStatus.REFUSED_DRIFT
    assert shard.read("Home").body == "old"  # not clobbered (I-5)
    assert eng.get(ov.overlay_id) is not None  # overlay still open


def test_read_only_target_keeps_draft(tmp_path):
    (tmp_path / "Home.md").write_text("canon", encoding="utf-8")
    ro = FolderAdapter("ro", tmp_path)  # not writable
    eng = OverlayEngine("space", DecisionLog())
    ov = eng.draft(Identity("ro", "Home"), "my edit", base_rev=ro.current_rev("Home"))

    result = eng.apply(ov.overlay_id, ro)
    assert result.status is ApplyStatus.KEPT_DRAFT
    assert ro.read("Home").body == "canon"  # source untouched
    assert eng.get(ov.overlay_id) is not None  # local truth retained


def test_new_page_fast_forwards(tmp_path):
    shard = _writable(tmp_path, {})
    eng = OverlayEngine("space", DecisionLog())
    ov = eng.draft(Identity("w", "Fresh"), "brand new", base_rev=None)  # didn't exist
    result = eng.apply(ov.overlay_id, shard)
    assert result.status is ApplyStatus.APPLIED
    assert shard.read("Fresh").body == "brand new"


def test_wrong_adapter_is_rejected(tmp_path):
    shard = _writable(tmp_path, {"Home.md": "x"})
    eng = OverlayEngine("space", DecisionLog())
    ov = eng.draft(Identity("other", "Home"), "y", base_rev=None)
    try:
        eng.apply(ov.overlay_id, shard)
        raise AssertionError("expected ValueError")
    except ValueError:
        pass