"""IMP-43 (#72) u4 — focused tests for the --reuse-from entry helpers.

u4 scope (per the Stage 2 Exit Report):

- Pure path resolution, file copy, snapshot load+validate, MdxSection +
  CompositionUnit rehydration, and reuse-marker writing.
- Helpers RAISE on missing artifacts / corrupt snapshot / mdx_sha256
  mismatch — u4b adds the stderr + sys.exit(2) translation and the
  prev_run_dir == new_run_dir accidental-write guard around them.
- The kwarg threading + the in-``run_phase_z2_mvp1`` branch that
  invokes these helpers land in u5.

Tested helpers (``src/phase_z2_pipeline.py``):
  * ``_resolve_reuse_from_prev_run_dir``
  * ``_copy_reuse_artifacts_from_prev_run``
  * ``_load_and_validate_reuse_snapshot``
  * ``_rehydrate_mdx_sections_from_snapshot``
  * ``_rehydrate_composition_units_from_snapshot``
  * ``_write_reuse_marker``
  * ``_RehydratedV4Candidate`` (V4Match-shape duck type)
  * ``_REUSE_STEP_ARTIFACTS`` / ``REUSE_MARKER_FILENAME`` /
    ``REUSE_MARKER_SCHEMA_VERSION``
"""
from __future__ import annotations

import hashlib
import json
from dataclasses import dataclass, field
from pathlib import Path
from typing import Any, Optional

import pytest

import src.phase_z2_pipeline as _pz2
from src.phase_z2_composition import CompositionUnit
from src.phase_z2_reuse_snapshot import (
    SNAPSHOT_FILENAME,
    SNAPSHOT_VERSION,
    SnapshotValidationError,
    build_snapshot,
)


# -- synthetic duck-typed inputs (mirror u3 test fixture) -----------------


@dataclass
class _Section:
    section_id: str
    section_num: int
    title: str
    raw_content: str
    heading_number: Optional[str] = None
    v4_alias_keys: list = field(default_factory=list)
    sub_sections: list = field(default_factory=list)


@dataclass
class _V4Candidate:
    template_id: str
    frame_id: str
    frame_number: int
    confidence: float
    label: str


@dataclass
class _Unit:
    source_section_ids: list
    merge_type: str
    frame_template_id: str
    frame_id: str
    frame_number: int
    confidence: float
    label: str
    phase_z_status: str
    raw_content: str
    title: str
    score: float
    v4_rank: Optional[int] = 1
    selection_path: str = "rank_1"
    fallback_reason: Optional[str] = None
    rationale: dict = field(default_factory=dict)
    auto_selectable: bool = True
    filter_reasons: list = field(default_factory=list)
    notes: list = field(default_factory=list)
    v4_candidates: list = field(default_factory=list)
    provisional: bool = False


def _mdx_text() -> str:
    return "# Slide\n\n## 03-1 DX status\n\n- bullet one\n- bullet two\n"


def _build_canonical_snapshot(
    *,
    mdx_source_text: Optional[str] = None,
    layout_preset: str = "single",
) -> dict:
    text = mdx_source_text if mdx_source_text is not None else _mdx_text()
    cand = _V4Candidate(
        template_id="tpl_a",
        frame_id="fid_a",
        frame_number=13,
        confidence=0.91,
        label="use_as_is",
    )
    section = _Section(
        section_id="03-1",
        section_num=1,
        title="DX status",
        raw_content="- bullet one\n- bullet two",
        heading_number="3.1",
        v4_alias_keys=["03-1.1"],
        sub_sections=[],
    )
    unit = _Unit(
        source_section_ids=["03-1"],
        merge_type="single",
        frame_template_id="tpl_a",
        frame_id="fid_a",
        frame_number=13,
        confidence=0.91,
        label="use_as_is",
        phase_z_status="auto_renderable",
        raw_content="- bullet one\n- bullet two",
        title="DX status",
        score=0.91,
        v4_candidates=[cand],
        provisional=False,
        auto_selectable=True,
        filter_reasons=[],
        notes=["a note"],
        rationale={"weight": 1.0},
    )
    return build_snapshot(
        mdx_sha256=hashlib.sha256(text.encode("utf-8")).hexdigest(),
        slide_title="Slide",
        slide_footer=None,
        sections=[section],
        stage0_adapter_diagnostics={"used": True, "fallback_reason": None},
        stage0_normalized_assets={"popups": [], "images": [], "tables": []},
        v4_evidence=[
            {
                "section_id": "03-1",
                "v4_candidates": [
                    {
                        "template_id": "tpl_a",
                        "frame_id": "fid_a",
                        "frame_number": 13,
                        "confidence": 0.91,
                        "label": "use_as_is",
                    }
                ],
                "candidate_status": "ok",
            }
        ],
        layout_preset_pre_override=layout_preset,
        units=[unit],
        comp_debug={"v4_fallback_summary": {"fallback_used_count": 0}},
        v4_fallback_traces={"03-1": {"selection_path": "rank_1"}},
        ai_preflight={"enabled": False, "skipped": True},
    )


def _seed_prev_run_dir(prev_run_dir: Path, *, snapshot: dict) -> None:
    """Populate ``prev_run_dir`` with the Step 0/1/2/5/6 artifacts plus
    the reuse snapshot — minimal but valid surface for u4 helpers."""
    (prev_run_dir / "steps").mkdir(parents=True, exist_ok=True)
    for fname in _pz2._REUSE_STEP_ARTIFACTS:
        # JSON-shaped surface — exact shape doesn't matter for u4 (the
        # copy helper doesn't introspect contents); just must exist.
        (prev_run_dir / "steps" / fname).write_text(
            f'{{"name": "{fname}"}}'
            if fname.endswith(".json")
            else "raw mdx body bytes",
            encoding="utf-8",
        )
    (prev_run_dir / SNAPSHOT_FILENAME).write_text(
        json.dumps(snapshot, ensure_ascii=False, indent=2),
        encoding="utf-8",
    )


# -- _REUSE_STEP_ARTIFACTS constant ---------------------------------------


def test_reuse_step_artifacts_locks_stage2_boundary():
    """Stage 2 boundary lock — Step 0/1/2/5/6 artifacts only.
    Step 3/4 deliberately absent: step03 / step04 ARE written after
    Step 6 (around src/phase_z2_pipeline.py:5931 / 5964) before the
    Step 7 artifact (~6294), but both are emitted with
    step_status='trace-only' / pipeline_path_connected=False — they
    are diagnostic projections of the Step 6 debug_zones, not
    pipeline-path-connected inputs that Step 7+ rehydrate from."""
    assert _pz2._REUSE_STEP_ARTIFACTS == (
        "step00_preconditions.json",
        "step01_mdx_upload.json",
        "step01_mdx_source.md",
        "step02_normalized.json",
        "step05_v4_evidence.json",
        "step06_composition_plan.json",
    )


def test_reuse_marker_filename_is_dotfile_at_run_dir_root():
    assert _pz2.REUSE_MARKER_FILENAME == "_reuse_marker.json"


# -- _resolve_reuse_from_prev_run_dir -------------------------------------


def test_resolve_prev_run_dir_returns_runs_dir_phase_z2_path():
    rv = _pz2._resolve_reuse_from_prev_run_dir("20260524_120000_phase_z2")
    expected = _pz2.RUNS_DIR / "20260524_120000_phase_z2" / "phase_z2"
    assert rv == expected


def test_resolve_prev_run_dir_does_not_check_existence(tmp_path: Path):
    """Pure path computation — must NOT touch the filesystem (u4b
    handles the missing-prev-run case)."""
    rv = _pz2._resolve_reuse_from_prev_run_dir("never_existed_run_id")
    assert isinstance(rv, Path)
    # The path does not actually exist; helper still returned cleanly.
    assert not rv.exists()


# -- _copy_reuse_artifacts_from_prev_run ----------------------------------


def test_copy_reuse_artifacts_copies_all_step_files(tmp_path: Path):
    prev = tmp_path / "prev" / "phase_z2"
    new = tmp_path / "new" / "phase_z2"
    snap = _build_canonical_snapshot()
    _seed_prev_run_dir(prev, snapshot=snap)

    copied = _pz2._copy_reuse_artifacts_from_prev_run(prev, new)

    for fname in _pz2._REUSE_STEP_ARTIFACTS:
        assert (new / "steps" / fname).exists(), f"missing copy: {fname}"
        assert copied[fname] == f"steps/{fname}"


def test_copy_reuse_artifacts_copies_snapshot_to_run_dir_root(tmp_path: Path):
    prev = tmp_path / "prev" / "phase_z2"
    new = tmp_path / "new" / "phase_z2"
    snap = _build_canonical_snapshot()
    _seed_prev_run_dir(prev, snapshot=snap)

    copied = _pz2._copy_reuse_artifacts_from_prev_run(prev, new)

    # Snapshot lives at run_dir root (NOT under steps/) per u3 contract.
    assert (new / SNAPSHOT_FILENAME).exists()
    assert copied[SNAPSHOT_FILENAME] == SNAPSHOT_FILENAME


def test_copy_reuse_artifacts_creates_steps_subdir_if_absent(tmp_path: Path):
    prev = tmp_path / "prev" / "phase_z2"
    new = tmp_path / "new" / "phase_z2"
    snap = _build_canonical_snapshot()
    _seed_prev_run_dir(prev, snapshot=snap)

    # new_run_dir / steps does not yet exist
    assert not (new / "steps").exists()
    _pz2._copy_reuse_artifacts_from_prev_run(prev, new)
    assert (new / "steps").is_dir()


def test_copy_reuse_artifacts_missing_step_raises_filenotfound(
    tmp_path: Path,
):
    prev = tmp_path / "prev" / "phase_z2"
    new = tmp_path / "new" / "phase_z2"
    snap = _build_canonical_snapshot()
    _seed_prev_run_dir(prev, snapshot=snap)
    # Delete one of the required step artifacts.
    (prev / "steps" / "step05_v4_evidence.json").unlink()

    with pytest.raises(FileNotFoundError) as ei:
        _pz2._copy_reuse_artifacts_from_prev_run(prev, new)
    msg = str(ei.value)
    assert "step05_v4_evidence.json" in msg
    assert "prev_run_dir" in msg


def test_copy_reuse_artifacts_missing_snapshot_raises_filenotfound(
    tmp_path: Path,
):
    prev = tmp_path / "prev" / "phase_z2"
    new = tmp_path / "new" / "phase_z2"
    snap = _build_canonical_snapshot()
    _seed_prev_run_dir(prev, snapshot=snap)
    (prev / SNAPSHOT_FILENAME).unlink()

    with pytest.raises(FileNotFoundError) as ei:
        _pz2._copy_reuse_artifacts_from_prev_run(prev, new)
    assert SNAPSHOT_FILENAME in str(ei.value)


def test_copy_reuse_artifacts_byte_identical_copy(tmp_path: Path):
    """Bytes must match exactly — copy, not transform."""
    prev = tmp_path / "prev" / "phase_z2"
    new = tmp_path / "new" / "phase_z2"
    snap = _build_canonical_snapshot()
    _seed_prev_run_dir(prev, snapshot=snap)

    _pz2._copy_reuse_artifacts_from_prev_run(prev, new)

    for fname in _pz2._REUSE_STEP_ARTIFACTS:
        assert (
            (prev / "steps" / fname).read_bytes()
            == (new / "steps" / fname).read_bytes()
        )
    assert (
        (prev / SNAPSHOT_FILENAME).read_bytes()
        == (new / SNAPSHOT_FILENAME).read_bytes()
    )


# -- _load_and_validate_reuse_snapshot ------------------------------------


def test_load_and_validate_returns_snapshot_dict(tmp_path: Path):
    text = _mdx_text()
    snap = _build_canonical_snapshot(mdx_source_text=text)
    (tmp_path / SNAPSHOT_FILENAME).write_text(
        json.dumps(snap, ensure_ascii=False, indent=2), encoding="utf-8"
    )

    loaded = _pz2._load_and_validate_reuse_snapshot(
        tmp_path, mdx_source_text=text
    )
    assert loaded["schema_version"] == SNAPSHOT_VERSION
    assert loaded["slide_title"]["value"] == "Slide"


def test_load_and_validate_mdx_sha256_mismatch_raises(tmp_path: Path):
    """Snapshot was built for ``text_a`` but caller passes ``text_b``;
    u2 validator raises ``SnapshotValidationError`` (subclass of
    ``ValueError``). u4b translates to exit 2 — here we only assert the
    raise."""
    text_a = "# Slide A\n"
    text_b = "# Slide B (different bytes)\n"
    snap = _build_canonical_snapshot(mdx_source_text=text_a)
    (tmp_path / SNAPSHOT_FILENAME).write_text(
        json.dumps(snap, ensure_ascii=False, indent=2), encoding="utf-8"
    )

    with pytest.raises(SnapshotValidationError) as ei:
        _pz2._load_and_validate_reuse_snapshot(
            tmp_path, mdx_source_text=text_b
        )
    assert "mdx_sha256 mismatch" in str(ei.value)


def test_load_and_validate_corrupt_json_raises(tmp_path: Path):
    (tmp_path / SNAPSHOT_FILENAME).write_text(
        "{ not valid json", encoding="utf-8"
    )
    with pytest.raises(json.JSONDecodeError):
        _pz2._load_and_validate_reuse_snapshot(
            tmp_path, mdx_source_text=_mdx_text()
        )


def test_load_and_validate_missing_snapshot_file_raises(tmp_path: Path):
    """No snapshot at all — bare ``read_text`` raises FileNotFoundError.
    u4b translates this to exit 2 with a provenance message."""
    with pytest.raises(FileNotFoundError):
        _pz2._load_and_validate_reuse_snapshot(
            tmp_path, mdx_source_text=_mdx_text()
        )


def test_load_and_validate_schema_version_mismatch_raises(tmp_path: Path):
    text = _mdx_text()
    snap = _build_canonical_snapshot(mdx_source_text=text)
    snap["schema_version"] = SNAPSHOT_VERSION + 1  # force mismatch
    (tmp_path / SNAPSHOT_FILENAME).write_text(
        json.dumps(snap, ensure_ascii=False, indent=2), encoding="utf-8"
    )
    with pytest.raises(SnapshotValidationError) as ei:
        _pz2._load_and_validate_reuse_snapshot(
            tmp_path, mdx_source_text=text
        )
    assert "schema_version" in str(ei.value)


# -- _rehydrate_mdx_sections_from_snapshot --------------------------------


def test_rehydrate_sections_returns_mdxsection_instances():
    snap = _build_canonical_snapshot()
    sections = _pz2._rehydrate_mdx_sections_from_snapshot(snap)
    assert len(sections) == 1
    assert isinstance(sections[0], _pz2.MdxSection)
    assert sections[0].section_id == "03-1"
    assert sections[0].title == "DX status"
    assert sections[0].raw_content == "- bullet one\n- bullet two"


def test_rehydrate_sections_preserves_heading_number_and_aliases():
    snap = _build_canonical_snapshot()
    sections = _pz2._rehydrate_mdx_sections_from_snapshot(snap)
    assert sections[0].heading_number == "3.1"
    assert sections[0].v4_alias_keys == ["03-1.1"]
    assert sections[0].sub_sections == []


# -- _rehydrate_composition_units_from_snapshot ---------------------------


def test_rehydrate_units_returns_composition_unit_instances():
    snap = _build_canonical_snapshot()
    units = _pz2._rehydrate_composition_units_from_snapshot(snap)
    assert len(units) == 1
    assert isinstance(units[0], CompositionUnit)


def test_rehydrate_units_preserves_core_fields():
    snap = _build_canonical_snapshot()
    units = _pz2._rehydrate_composition_units_from_snapshot(snap)
    u = units[0]
    assert u.source_section_ids == ["03-1"]
    assert u.merge_type == "single"
    assert u.frame_template_id == "tpl_a"
    assert u.frame_id == "fid_a"
    assert u.frame_number == 13
    assert u.confidence == pytest.approx(0.91)
    assert u.label == "use_as_is"
    assert u.phase_z_status == "auto_renderable"
    assert u.title == "DX status"
    assert u.score == pytest.approx(0.91)


def test_rehydrate_units_preserves_provisional_and_auto_selectable():
    snap = _build_canonical_snapshot()
    units = _pz2._rehydrate_composition_units_from_snapshot(snap)
    assert units[0].provisional is False
    assert units[0].auto_selectable is True
    assert units[0].filter_reasons == []
    assert units[0].notes == ["a note"]
    assert units[0].rationale == {"weight": 1.0}


def test_rehydrate_units_v4_candidates_expose_attribute_access():
    """``_apply_frame_override_to_unit`` reads
    ``cand.template_id`` / ``cand.frame_id`` / etc. off
    ``unit.v4_candidates`` — restored entries MUST expose attribute
    access, not raw dict access."""
    snap = _build_canonical_snapshot()
    units = _pz2._rehydrate_composition_units_from_snapshot(snap)
    cands = units[0].v4_candidates
    assert len(cands) == 1
    c = cands[0]
    assert isinstance(c, _pz2._RehydratedV4Candidate)
    assert c.template_id == "tpl_a"
    assert c.frame_id == "fid_a"
    assert c.frame_number == 13
    assert c.confidence == pytest.approx(0.91)
    assert c.label == "use_as_is"


def test_rehydrate_units_empty_v4_candidates_yields_empty_list():
    snap = _build_canonical_snapshot()
    snap["units"]["value"][0]["v4_candidates"] = []
    units = _pz2._rehydrate_composition_units_from_snapshot(snap)
    assert units[0].v4_candidates == []


# -- _write_reuse_marker --------------------------------------------------


def test_write_reuse_marker_writes_json_with_prev_run_id(tmp_path: Path):
    copied = {
        "step00_preconditions.json": "steps/step00_preconditions.json",
        SNAPSHOT_FILENAME: SNAPSHOT_FILENAME,
    }
    rv = _pz2._write_reuse_marker(
        tmp_path,
        prev_run_id="20260524_010101_phase_z2",
        copied_artifacts=copied,
    )
    assert rv == tmp_path / _pz2.REUSE_MARKER_FILENAME
    marker = json.loads(rv.read_text(encoding="utf-8"))
    assert marker["schema_version"] == _pz2.REUSE_MARKER_SCHEMA_VERSION
    assert marker["reuse_from_prev_run_id"] == "20260524_010101_phase_z2"
    assert marker["snapshot_filename"] == SNAPSHOT_FILENAME


def test_write_reuse_marker_records_copied_artifacts_and_boundary(
    tmp_path: Path,
):
    copied = {
        fname: f"steps/{fname}" for fname in _pz2._REUSE_STEP_ARTIFACTS
    }
    copied[SNAPSHOT_FILENAME] = SNAPSHOT_FILENAME
    _pz2._write_reuse_marker(
        tmp_path,
        prev_run_id="20260524_010101_phase_z2",
        copied_artifacts=copied,
    )
    marker = json.loads(
        (tmp_path / _pz2.REUSE_MARKER_FILENAME).read_text(encoding="utf-8")
    )
    assert marker["copied_artifacts"] == copied
    assert marker["boundary_steps"] == list(_pz2._REUSE_STEP_ARTIFACTS)
    assert marker["resume_at_step"] == 7


# -- module surface anchors -----------------------------------------------


def test_pipeline_exposes_all_u4_helpers():
    """u5 wires these into ``run_phase_z2_mvp1`` — they must remain
    module-level callable surface on ``phase_z2_pipeline``."""
    for name in (
        "_resolve_reuse_from_prev_run_dir",
        "_copy_reuse_artifacts_from_prev_run",
        "_load_and_validate_reuse_snapshot",
        "_rehydrate_mdx_sections_from_snapshot",
        "_rehydrate_composition_units_from_snapshot",
        "_write_reuse_marker",
        "_RehydratedV4Candidate",
        "_REUSE_STEP_ARTIFACTS",
        "REUSE_MARKER_FILENAME",
        "REUSE_MARKER_SCHEMA_VERSION",
    ):
        assert hasattr(_pz2, name), f"u4 surface missing: {name}"


def test_pipeline_run_signature_reuse_from_is_kw_only_optional_none():
    """u5 — ``reuse_from`` is now part of ``run_phase_z2_mvp1``'s public
    signature. The kwarg MUST be keyword-only (after the ``*`` barrier),
    default to ``None`` (so absent flag preserves the pre-u5 behaviour),
    and sit alongside the existing override kwargs. The locked
    ``until_u5`` regression has flipped — keep this assertion as the
    forward-direction lock so future signature drift (e.g. a positional
    promotion or a default change) trips loudly."""
    import inspect

    sig = inspect.signature(_pz2.run_phase_z2_mvp1)
    assert "reuse_from" in sig.parameters, (
        "u5 must thread reuse_from into run_phase_z2_mvp1 — kwarg missing. "
        f"current params: {list(sig.parameters)}"
    )
    param = sig.parameters["reuse_from"]
    assert param.kind is inspect.Parameter.KEYWORD_ONLY, (
        f"reuse_from must be keyword-only (after the ``*`` barrier); "
        f"got kind={param.kind}"
    )
    assert param.default is None, (
        f"reuse_from must default to None to preserve pre-u5 behaviour; "
        f"got default={param.default!r}"
    )