"""SSR tests for the commit diff page.

The diff page must render all file diffs server-side — no "Loading diff…"
spinner in the initial HTML response. This file drives the implementation of
SSR diff rendering in ui_commits.py::diff_page.

Test matrix
-----------
test_diff_page_renders_without_loading_spinner
    The response must NOT contain the loading-state text ("Loading diff…").

test_diff_page_renders_stats_bar
    The response must contain the stats bar element (.df3-stats-bar).

test_diff_page_added_file_shows_plus_lines
    An added file's diff lines have "+" signs rendered in the HTML.

test_diff_page_removed_file_shows_minus_lines
    A removed file's diff lines have "−" signs rendered in the HTML.

test_diff_page_modified_file_shows_cohen_hunk_header
    A modified file's hunk header includes a Cohen action label
    (e.g. "[change: inserted]" or "[change: modified]").

test_diff_page_modified_file_shows_add_and_del_lines
    A modified file has both "+" and "-" diff lines in the HTML.

test_diff_page_root_commit_no_parent_shows_added_file
    A root commit (no parent) still renders the diff for the added file.

test_diff_page_no_changes_shows_empty_state
    A commit with no snapshot diffs renders the empty-state element.

test_diff_page_returns_200_for_unknown_commit
    An unknown commit_id returns 200 (page shell) without 500.
"""
from __future__ import annotations

import secrets
from datetime import datetime, timezone
from unittest.mock import AsyncMock, MagicMock, patch

import pytest
from httpx import AsyncClient
from sqlalchemy.ext.asyncio import AsyncSession

from musehub.core.genesis import compute_branch_id, compute_identity_id, compute_repo_id
from musehub.db.musehub_repo_models import MusehubBranch, MusehubCommit, MusehubCommitRef, MusehubRepo
from musehub.types.json_types import StrDict

# ── Constants ─────────────────────────────────────────────────────────────────

_OWNER = "diffssrowner"
_SLUG  = "diff-ssr-repo"

_SHA_PARENT = "pp" + "0" * 62
_SHA_COMMIT = "cc" + "0" * 62

_SNAP_PARENT = "sp" + "0" * 62
_SNAP_COMMIT = "sc" + "0" * 62

# object IDs stored in fake manifests
_OID_OLD = "sha256:" + "a" * 64
_OID_NEW = "sha256:" + "b" * 64

_OLD_CONTENT = b"line one\nline two\nline three\n"
_NEW_CONTENT = b"line one\nline two modified\nline three\nline four inserted\n"


# ── Seed helpers ──────────────────────────────────────────────────────────────


async def _seed_repo(db: AsyncSession) -> str:
    owner_id = compute_identity_id(_OWNER.encode())
    created_at = datetime.now(tz=timezone.utc)
    repo = MusehubRepo(
        repo_id=compute_repo_id(owner_id, _SLUG, "code", created_at.isoformat()),
        name=_SLUG,
        owner=_OWNER,
        slug=_SLUG,
        visibility="public",
        owner_user_id=owner_id,
        created_at=created_at,
        updated_at=created_at,
    )
    db.add(repo)
    await db.flush()
    return str(repo.repo_id)


async def _seed_commit_pair(db: AsyncSession, repo_id: str) -> None:
    """Seed a parent commit and a child commit, both with snapshot IDs."""
    db.add(MusehubCommit(
        commit_id=_SHA_PARENT,
        branch="main",
        parent_ids=[],
        message="initial",
        author="gabriel",
        timestamp=datetime.now(tz=timezone.utc),
        snapshot_id=_SNAP_PARENT,
    ))
    db.add(MusehubCommitRef(repo_id=repo_id, commit_id=_SHA_PARENT))
    db.add(MusehubCommit(
        commit_id=_SHA_COMMIT,
        branch="main",
        parent_ids=[_SHA_PARENT],
        message="feat: add feature",
        author="gabriel",
        timestamp=datetime.now(tz=timezone.utc),
        snapshot_id=_SNAP_COMMIT,
    ))
    db.add(MusehubCommitRef(repo_id=repo_id, commit_id=_SHA_COMMIT))
    db.add(MusehubBranch(
        branch_id=compute_branch_id(repo_id, "main"),
        repo_id=repo_id,
        name="main",
        head_commit_id=_SHA_COMMIT,
    ))
    await db.flush()


async def _seed_root_commit(db: AsyncSession, repo_id: str) -> str:
    """Seed a single root commit (no parent) with a snapshot."""
    sha = "rr" + "0" * 62
    db.add(MusehubCommit(
        commit_id=sha,
        branch="main",
        parent_ids=[],
        message="root commit",
        author="gabriel",
        timestamp=datetime.now(tz=timezone.utc),
        snapshot_id=_SNAP_COMMIT,
    ))
    db.add(MusehubCommitRef(repo_id=repo_id, commit_id=sha))
    db.add(MusehubBranch(
        branch_id=compute_branch_id(repo_id, "main"),
        repo_id=repo_id,
        name="main",
        head_commit_id=sha,
    ))
    await db.flush()
    return sha


# ── Manifest + storage mock helpers ───────────────────────────────────────────


def _make_manifests(
    *,
    added: bool = False,
    removed: bool = False,
    modified: bool = False,
) -> tuple[StrDict, StrDict]:
    """Return (old_manifest, new_manifest) for the requested scenario."""
    old: dict[str, str] = {}
    new: dict[str, str] = {}

    if added:
        new["src/added.py"] = _OID_NEW
    if removed:
        old["src/removed.py"] = _OID_OLD
    if modified:
        old["src/changed.py"] = _OID_OLD
        new["src/changed.py"] = _OID_NEW

    return old, new


def _storage_backend(*, old_bytes: bytes = _OLD_CONTENT, new_bytes: bytes = _NEW_CONTENT) -> None:
    """Return a mock storage backend whose get_batch returns the two objects."""
    backend = MagicMock()
    backend.get_batch = AsyncMock(return_value={
        _OID_OLD: old_bytes,
        _OID_NEW: new_bytes,
    })
    return backend


# ── Patch context manager helper ──────────────────────────────────────────────


def _patch_manifests(old: StrDict, new: StrDict) -> None:
    """Patch get_snapshot_manifest keyed on snap_id constants."""
    async def _fake_manifest(_session: AsyncSession, snap_id: str) -> StrDict:
        # _SNAP_COMMIT → new manifest; _SNAP_PARENT → old manifest
        return new if snap_id == _SNAP_COMMIT else old

    return patch(
        "musehub.services.musehub_snapshot.get_snapshot_manifest",
        side_effect=_fake_manifest,
    )


# ── Tests ──────────────────────────────────────────────────────────────────────


@pytest.mark.asyncio
async def test_diff_page_renders_without_loading_spinner(
    client: AsyncClient,
    db_session: AsyncSession,
) -> None:
    """The initial HTML must not contain the loading spinner text."""
    repo_id = await _seed_repo(db_session)
    await _seed_commit_pair(db_session, repo_id)
    await db_session.commit()

    old_m, new_m = _make_manifests(modified=True)

    with _patch_manifests(old_m, new_m), \
         patch("musehub.storage.backends.get_backend", return_value=_storage_backend()):
        resp = await client.get(f"/{_OWNER}/{_SLUG}/commits/{_SHA_COMMIT}/diff")

    assert resp.status_code == 200
    assert "Loading diff" not in resp.text


@pytest.mark.asyncio
async def test_diff_page_renders_stats_bar(
    client: AsyncClient,
    db_session: AsyncSession,
) -> None:
    """The stats bar element must be present in the server-rendered HTML."""
    repo_id = await _seed_repo(db_session)
    await _seed_commit_pair(db_session, repo_id)
    await db_session.commit()

    old_m, new_m = _make_manifests(modified=True)

    with _patch_manifests(old_m, new_m), \
         patch("musehub.storage.backends.get_backend", return_value=_storage_backend()):
        resp = await client.get(f"/{_OWNER}/{_SLUG}/commits/{_SHA_COMMIT}/diff")

    assert resp.status_code == 200
    assert "df3-stats-bar" in resp.text


@pytest.mark.asyncio
async def test_diff_page_added_file_shows_plus_lines(
    client: AsyncClient,
    db_session: AsyncSession,
) -> None:
    """An added file's content is rendered with '+' lines in the diff."""
    repo_id = await _seed_repo(db_session)
    await _seed_commit_pair(db_session, repo_id)
    await db_session.commit()

    old_m, new_m = _make_manifests(added=True)

    with _patch_manifests(old_m, new_m), \
         patch("musehub.storage.backends.get_backend", return_value=_storage_backend(
             old_bytes=b"", new_bytes=_NEW_CONTENT
         )):
        resp = await client.get(f"/{_OWNER}/{_SLUG}/commits/{_SHA_COMMIT}/diff")

    assert resp.status_code == 200
    # File path present
    assert "src/added.py" in resp.text
    # At least one '+' diff line
    assert "df3-dl-add" in resp.text


@pytest.mark.asyncio
async def test_diff_page_removed_file_shows_minus_lines(
    client: AsyncClient,
    db_session: AsyncSession,
) -> None:
    """A removed file is rendered with '−' lines in the diff."""
    repo_id = await _seed_repo(db_session)
    await _seed_commit_pair(db_session, repo_id)
    await db_session.commit()

    old_m, new_m = _make_manifests(removed=True)

    with _patch_manifests(old_m, new_m), \
         patch("musehub.storage.backends.get_backend", return_value=_storage_backend(
             old_bytes=_OLD_CONTENT, new_bytes=b""
         )):
        resp = await client.get(f"/{_OWNER}/{_SLUG}/commits/{_SHA_COMMIT}/diff")

    assert resp.status_code == 200
    assert "src/removed.py" in resp.text
    assert "df3-dl-del" in resp.text


@pytest.mark.asyncio
async def test_diff_page_modified_file_shows_cohen_hunk_header(
    client: AsyncClient,
    db_session: AsyncSession,
) -> None:
    """A modified file's hunk header carries a Cohen action label."""
    repo_id = await _seed_repo(db_session)
    await _seed_commit_pair(db_session, repo_id)
    await db_session.commit()

    old_m, new_m = _make_manifests(modified=True)

    with _patch_manifests(old_m, new_m), \
         patch("musehub.storage.backends.get_backend", return_value=_storage_backend()):
        resp = await client.get(f"/{_OWNER}/{_SLUG}/commits/{_SHA_COMMIT}/diff")

    assert resp.status_code == 200
    # Cohen label: [change: inserted], [change: modified], or [change: deleted]
    assert "[change:" in resp.text


@pytest.mark.asyncio
async def test_diff_page_modified_file_shows_add_and_del_lines(
    client: AsyncClient,
    db_session: AsyncSession,
) -> None:
    """A modified file produces both addition and deletion diff rows."""
    repo_id = await _seed_repo(db_session)
    await _seed_commit_pair(db_session, repo_id)
    await db_session.commit()

    old_m, new_m = _make_manifests(modified=True)

    with _patch_manifests(old_m, new_m), \
         patch("musehub.storage.backends.get_backend", return_value=_storage_backend()):
        resp = await client.get(f"/{_OWNER}/{_SLUG}/commits/{_SHA_COMMIT}/diff")

    assert resp.status_code == 200
    assert "df3-dl-add" in resp.text
    assert "df3-dl-del" in resp.text


@pytest.mark.asyncio
async def test_diff_page_root_commit_no_parent_shows_added_file(
    client: AsyncClient,
    db_session: AsyncSession,
) -> None:
    """Root commit (no parent snapshot) renders all files as added."""
    repo_id = await _seed_repo(db_session)
    sha = await _seed_root_commit(db_session, repo_id)
    await db_session.commit()

    new_m = {"src/new_file.py": _OID_NEW}

    async def _fake_manifest(_session: AsyncSession, snap_id: str) -> StrDict:
        return new_m

    with patch("musehub.services.musehub_snapshot.get_snapshot_manifest",
               side_effect=_fake_manifest), \
         patch("musehub.storage.backends.get_backend",
               return_value=_storage_backend(old_bytes=b"", new_bytes=_NEW_CONTENT)):
        resp = await client.get(f"/{_OWNER}/{_SLUG}/commits/{sha}/diff")

    assert resp.status_code == 200
    assert "src/new_file.py" in resp.text
    assert "df3-dl-add" in resp.text


@pytest.mark.asyncio
async def test_diff_page_no_changes_shows_empty_state(
    client: AsyncClient,
    db_session: AsyncSession,
) -> None:
    """A commit with identical snapshots renders the empty-state element."""
    repo_id = await _seed_repo(db_session)
    await _seed_commit_pair(db_session, repo_id)
    await db_session.commit()

    # Both manifests identical → no added/modified/removed
    same_m = {"src/stable.py": _OID_OLD}

    async def _fake_manifest(_session: AsyncSession, snap_id: str) -> StrDict:
        return same_m

    with patch("musehub.services.musehub_snapshot.get_snapshot_manifest",
               side_effect=_fake_manifest):
        resp = await client.get(f"/{_OWNER}/{_SLUG}/commits/{_SHA_COMMIT}/diff")

    assert resp.status_code == 200
    assert "df3-empty" in resp.text


@pytest.mark.asyncio
async def test_diff_page_returns_200_for_unknown_commit(
    client: AsyncClient,
    db_session: AsyncSession,
) -> None:
    """An unknown commit ID returns a 200 page shell — never a 500."""
    repo_id = await _seed_repo(db_session)
    # No commit seeded — repo exists but commit does not
    await db_session.commit()

    unknown_sha = "ee" + "0" * 62
    resp = await client.get(f"/{_OWNER}/{_SLUG}/commits/{unknown_sha}/diff")

    assert resp.status_code == 200