"""TDD — _walk_commit_delta scale regression (issue #60).

L-tier bench (1000 commits) fails: wire_fetch_mpack returns mpack_id='' because
_walk_commit_delta returns {} for a 1000-commit chain. M-tier (100 commits) passes.

These tests confirm _walk_commit_delta returns the full delta at any scale:

  WD-1  Single commit, have=[] → returns 1 commit.
  WD-2  100-commit linear chain, have=[] → returns 100 commits.
  WD-3  1000-commit linear chain, have=[] → returns 1000 commits.  ← RED at L-tier
  WD-4  have cuts the chain — only commits above have are returned.
"""
from __future__ import annotations

import pytest
import msgpack
from datetime import datetime, timezone
from muse.core.types import fake_id
from musehub.db import musehub_repo_models as db
from musehub.db.musehub_repo_models import MusehubCommitGraph
from sqlalchemy.ext.asyncio import AsyncSession


def _now() -> datetime:
    return datetime.now(tz=timezone.utc)


async def _build_chain(session: AsyncSession, n: int) -> list[str]:
    """Insert a linear chain of N commits. Returns commit_ids tip→root order."""
    commit_ids: list[str] = []
    parent: list[str] = []
    for i in range(n):
        snap_id = fake_id(f"snap-wdscale-{i}")
        snap = db.MusehubSnapshot(
            snapshot_id=snap_id,
            manifest_blob=msgpack.packb({f"file{i}.txt": fake_id(f"obj-{i}")}, use_bin_type=True),
            directories=[],
            entry_count=1,
            created_at=_now(),
        )
        session.add(snap)
        cid = fake_id(f"commit-wdscale-{i}")
        commit = db.MusehubCommit(
            commit_id=cid,
            branch="main",
            parent_ids=parent,
            message=f"commit {i}",
            author="gabriel",
            timestamp=_now(),
            snapshot_id=snap_id,
        )
        session.add(commit)
        session.add(MusehubCommitGraph(
            commit_id=cid,
            parent_ids=parent,
            generation=i,
            snapshot_id=snap_id,
        ))
        commit_ids.append(cid)
        parent = [cid]
    await session.commit()
    return commit_ids  # [root, ..., tip]


# ── WD-1 ──────────────────────────────────────────────────────────────────────

@pytest.mark.asyncio
async def test_wd1_single_commit(db_session: AsyncSession) -> None:
    """Single commit, have=[] → _walk_commit_delta returns exactly that commit."""
    from musehub.services.musehub_wire import _walk_commit_delta

    ids = await _build_chain(db_session, 1)
    result = await _walk_commit_delta(db_session, want=[ids[-1]], have=[])

    assert len(result) == 1
    assert ids[-1] in result


# ── WD-2 ──────────────────────────────────────────────────────────────────────

@pytest.mark.asyncio
async def test_wd2_hundred_commit_chain(db_session: AsyncSession) -> None:
    """100-commit linear chain, have=[] → _walk_commit_delta returns all 100 commits."""
    from musehub.services.musehub_wire import _walk_commit_delta

    ids = await _build_chain(db_session, 100)
    result = await _walk_commit_delta(db_session, want=[ids[-1]], have=[])

    assert len(result) == 100, f"expected 100 commits, got {len(result)}"


# ── WD-3 ──────────────────────────────────────────────────────────────────────

@pytest.mark.asyncio
async def test_wd3_thousand_commit_chain(db_session: AsyncSession) -> None:
    """1000-commit linear chain, have=[] → _walk_commit_delta returns all 1000 commits.

    This is the L-tier regression: the bench push succeeds (commits exist in DB)
    but clone/fetch/pull return mpack_id='' because _walk_commit_delta returns {}.
    """
    from musehub.services.musehub_wire import _walk_commit_delta

    ids = await _build_chain(db_session, 1_000)
    result = await _walk_commit_delta(db_session, want=[ids[-1]], have=[])

    assert len(result) == 1_000, f"expected 1000 commits, got {len(result)}"


# ── WD-4 ──────────────────────────────────────────────────────────────────────

@pytest.mark.asyncio
async def test_wd4_have_cuts_delta(db_session: AsyncSession) -> None:
    """have=[root] → only commits above root are returned."""
    from musehub.services.musehub_wire import _walk_commit_delta

    ids = await _build_chain(db_session, 10)
    # ids[0] = root, ids[9] = tip; have=[ids[4]] means commits 5–9 are needed
    result = await _walk_commit_delta(db_session, want=[ids[-1]], have=[ids[4]])

    assert len(result) == 5, f"expected 5 commits above have, got {len(result)}"
    for cid in ids[5:]:
        assert cid in result
    for cid in ids[:5]:
        assert cid not in result