"""Fetch path — wire_fetch_presign, wire_fetch_mpack, wire_fetch, process_mpack_gc_job."""

import asyncio
import hashlib
import logging
import msgpack as _msgpack
import time as _time_module
from datetime import datetime, timezone
from typing import TypedDict

from sqlalchemy import func, select, text as _sa_text
from sqlalchemy.dialects.postgresql import insert as _pg_insert
from sqlalchemy.ext.asyncio import AsyncSession

from musehub.db.musehub_repo_models import (
    MusehubBranch,
    MusehubCommit,
    MusehubCommitGraph,
    MusehubFetchMPackCache,
    MusehubMPackIndex,
    MusehubObject,
    MusehubObjectRef,
    MusehubRepo,
    MusehubSnapshot,
)
from musehub.models.wire import WireFetchRequest
from muse.core.types import blob_id
from musehub.storage import get_backend

from musehub.services.musehub_wire_shared import (
    FetchMPackResult,
    FetchNotIndexedError,
    FetchPresignResult,
    MPackValidationError,
    _reconstruct_manifest,
    _snap_row_to_wire_s3,
    _commit_to_wire_s3,
    _to_wire_commit,
    _utc_now,
    logger,
)


type _CommitDeltaMap = dict[str, MusehubCommitGraph | MusehubCommit]


async def _walk_commit_delta(
    session: AsyncSession,
    want: list[str] | set[str],
    have: list[str] | set[str],
) -> _CommitDeltaMap:
    _wcd_t0 = _time_module.perf_counter()
    _want_list = list(want)
    _have_list = list(have)
    logger.info("[_walk_commit_delta] START want=%d have=%d want_ids=%s",
                len(_want_list), len(_have_list),
                [cid[:16] for cid in _want_list[:5]])

    have_set: frozenset[str] = frozenset(_have_list)
    starts = [cid for cid in _want_list if cid not in have_set]
    if not starts:
        logger.info("[_walk_commit_delta] SKIP — all want in have, 0ms")
        return {}

    if True:  # fast path always active — commit graph is global (no repo_id)
        from sqlalchemy import func as _func

        want_gen_q = await session.execute(
            select(_func.max(MusehubCommitGraph.generation))
            .where(MusehubCommitGraph.commit_id.in_(starts))
        )
        _want_gen_raw = want_gen_q.scalar()
        max_want_gen: int = _want_gen_raw or 0

        _missing_from_graph: list[str] = []
        _found_in_graph: list[tuple[str, int]] = []
        for _scid in starts[:10]:
            _sg = await session.execute(
                select(MusehubCommitGraph.generation)
                .where(MusehubCommitGraph.commit_id == _scid)
            )
            _sg_val = _sg.scalar_one_or_none()
            if _sg_val is None:
                _missing_from_graph.append(_scid[:16])
            else:
                _found_in_graph.append((_scid[:16], _sg_val))
        logger.info(
            "[_walk_commit_delta] want_gen_raw=%s max_want_gen=%d "
            "starts_in_graph=%s starts_missing_from_graph=%s",
            _want_gen_raw, max_want_gen, _found_in_graph, _missing_from_graph,
        )

        min_have_gen: int = -1
        if have_set:
            have_gen_q = await session.execute(
                select(_func.max(MusehubCommitGraph.generation))
                .where(MusehubCommitGraph.commit_id.in_(list(have_set)))
            )
            min_have_gen = have_gen_q.scalar() or -1

        range_q = await session.execute(
            select(
                MusehubCommitGraph.commit_id,
                MusehubCommitGraph.parent_ids,
                MusehubCommitGraph.snapshot_id,
            )
            .where(MusehubCommitGraph.generation > min_have_gen)
            .where(MusehubCommitGraph.generation <= max_want_gen)
        )
        graph_map: dict[str, tuple[list[str], str | None]] = {
            cid: (pids or [], sid) for cid, pids, sid in range_q
        }
        logger.info(
            "[_walk_commit_delta] range_scan gen=(%d,%d] returned %d rows "
            "starts_in_map=%s",
            min_have_gen, max_want_gen, len(graph_map),
            [cid[:16] for cid in starts if cid in graph_map],
        )

        visited_mem: set[str] = set(have_set)
        frontier_mem = [cid for cid in starts if cid not in visited_mem]
        reachable_cids: set[str] = set()
        while frontier_mem:
            next_mem: list[str] = []
            for cid in frontier_mem:
                if cid in visited_mem:
                    continue
                visited_mem.add(cid)
                reachable_cids.add(cid)
                pids_for_cid, _ = graph_map.get(cid, ([], None))
                for p in pids_for_cid:
                    if p not in visited_mem and p not in have_set:
                        next_mem.append(p)
            frontier_mem = next_mem

        from types import SimpleNamespace as _SN
        needed_graph: dict[str, _SN] = {}
        for cid in reachable_cids:
            pids_ns, sid_ns = graph_map.get(cid, ([], None))
            needed_graph[cid] = _SN(commit_id=cid, snapshot_id=sid_ns, parent_ids=pids_ns)

        _wcd_elapsed = (_time_module.perf_counter() - _wcd_t0) * 1000
        logger.info(
            "[_walk_commit_delta] DONE (graph) commits=%d elapsed=%.1fms (%.3fms/commit) "
            "gen_range=(%d,%d] graph_rows=%d reachable=%d",
            len(needed_graph), _wcd_elapsed, _wcd_elapsed / max(len(needed_graph), 1),
            min_have_gen, max_want_gen, len(graph_map), len(reachable_cids),
        )
        return needed_graph  # type: ignore[return-value]

    # Legacy fallback
    from musehub.graph.walk import walk_dag_async

    _row_cache: dict[str, MusehubCommit] = {}
    _db_calls = 0

    async def _adj(cid: str) -> list[str]:
        nonlocal _db_calls
        _db_calls += 1
        row = await session.get(MusehubCommit, cid)
        if row is not None:
            _row_cache[cid] = row
        return row.parent_ids or [] if row else []

    needed_legacy: dict[str, MusehubCommit] = {}
    async for cid in walk_dag_async(starts, _adj, exclude=have_set):
        if cid in _row_cache:
            needed_legacy[cid] = _row_cache[cid]

    _wcd_elapsed = (_time_module.perf_counter() - _wcd_t0) * 1000
    logger.info(
        "[_walk_commit_delta] DONE (legacy) commits=%d db_calls=%d elapsed=%.1fms (%.2fms/commit)",
        len(needed_legacy), _db_calls, _wcd_elapsed,
        _wcd_elapsed / max(len(needed_legacy), 1),
    )
    return needed_legacy


async def wire_fetch_presign(
    session: AsyncSession,
    repo_id: str,
    req: WireFetchRequest,
    ttl_seconds: int = 3600,
) -> FetchPresignResult:
    import asyncio
    from datetime import timedelta

    _empty: FetchPresignResult = {
        "presign": False,
        "blob_urls": {},
        "commits": [],
        "snapshots": [],
        "branch_heads": {},
        "repo_id": repo_id,
        "domain": "",
        "default_branch": "main",
        "expires_at": None,
        "commit_count": 0,
        "blob_count": 0,
    }

    if not req.want:
        return _empty

    repo_row = await session.get(MusehubRepo, repo_id)
    if repo_row is None:
        return _empty
    _domain: str = repo_row.domain_id or ""
    _default_branch: str = repo_row.default_branch if repo_row.default_branch else "main"
    _empty["domain"] = _domain
    _empty["default_branch"] = _default_branch
    _empty["repo_id"] = repo_id

    have_set = set(req.have)
    needed_rows = await _walk_commit_delta(session, req.want, have_set)

    if not needed_rows:
        return {**_empty, "domain": _domain, "default_branch": _default_branch}

    _presign_commit_rows: dict[str, MusehubCommit] = {}
    _presign_any = next(iter(needed_rows.values()))
    if not isinstance(_presign_any, MusehubCommit):
        _PRESIGN_WIRE_BATCH = 2000
        _presign_cids = list(needed_rows.keys())
        for _pi in range(0, len(_presign_cids), _PRESIGN_WIRE_BATCH):
            _pq = await session.execute(
                select(MusehubCommit).where(MusehubCommit.commit_id.in_(_presign_cids[_pi : _pi + _PRESIGN_WIRE_BATCH]))
            )
            for _pr in _pq.scalars():
                _presign_commit_rows[_pr.commit_id] = _pr
    else:
        _presign_commit_rows = needed_rows  # type: ignore[assignment]

    snap_ids = [r.snapshot_id for r in needed_rows.values() if r.snapshot_id]
    all_oids: set[str] = set()
    if snap_ids:
        snaps_q = await session.execute(
            select(MusehubSnapshot).where(MusehubSnapshot.snapshot_id.in_(snap_ids))
        )
        for snap in snaps_q.scalars().all():
            manifest = (
                _msgpack.unpackb(snap.manifest_blob, raw=False)
                if snap.manifest_blob
                else await _reconstruct_manifest(session, snap.snapshot_id)
            )
            all_oids.update(v for v in manifest.values() if v)

    have_snap_ids: list[str] = []
    if have_set:
        have_commits_q = await session.execute(
            select(MusehubCommit).where(MusehubCommit.commit_id.in_(have_set))
        )
        have_snap_ids = [r.snapshot_id for r in have_commits_q.scalars().all() if r.snapshot_id]
    have_oids: set[str] = set()
    if have_snap_ids:
        have_snaps_q = await session.execute(
            select(MusehubSnapshot).where(MusehubSnapshot.snapshot_id.in_(have_snap_ids))
        )
        for snap in have_snaps_q.scalars().all():
            manifest = (
                _msgpack.unpackb(snap.manifest_blob, raw=False)
                if snap.manifest_blob
                else await _reconstruct_manifest(session, snap.snapshot_id)
            )
            have_oids.update(v for v in manifest.values() if v)

    new_oids = all_oids - have_oids
    n_objects = len(new_oids)
    n_commits = len(needed_rows)

    total_size = 0
    if new_oids:
        size_q = await session.execute(
            select(func.coalesce(func.sum(MusehubObject.size_bytes), 0)).where(
                MusehubObject.object_id.in_(list(new_oids))
            )
        )
        total_size = int(size_q.scalar() or 0)

    backend = get_backend()

    wire_commits = [
        (await _commit_to_wire_s3(row, backend)).model_dump()
        for row in _presign_commit_rows.values()
    ]

    snap_rows_q = await session.execute(
        select(MusehubSnapshot).where(MusehubSnapshot.snapshot_id.in_(snap_ids))
    )
    wire_snaps = [
        await _snap_row_to_wire_s3(snap, backend, session=session)
        for snap in snap_rows_q.scalars().all()
    ]

    branch_rows_q = await session.execute(
        select(MusehubBranch).where(MusehubBranch.repo_id == repo_id)
    )
    branch_heads = {
        b.name: b.head_commit_id
        for b in branch_rows_q.scalars().all()
        if b.head_commit_id
    }

    sem = asyncio.Semaphore(50)

    logger.info(
        "fetch/presign: generating %d presigned GET URLs repo=%s/%s",
        len(new_oids), repo_row.owner, repo_row.slug,
    )

    async def _presign_one(oid: str) -> tuple[str, str]:
        async with sem:
            url = await backend.presign_get(oid, ttl_seconds)
            logger.debug("fetch/presign: presigned oid=%s", oid)
            return oid, url

    pairs = await asyncio.gather(*(_presign_one(oid) for oid in new_oids))
    blob_urls = {oid: url for oid, url in pairs}
    expires_at = (_utc_now() + timedelta(seconds=ttl_seconds)).isoformat()

    return {
        "presign": True,
        "blob_urls": blob_urls,
        "commits": wire_commits,
        "snapshots": wire_snaps,
        "branch_heads": branch_heads,
        "repo_id": repo_id,
        "domain": _domain,
        "default_branch": _default_branch,
        "expires_at": expires_at,
        "commit_count": n_commits,
        "blob_count": n_objects,
    }

async def wire_fetch_mpack(
    session: AsyncSession,
    repo_id: str,
    want: list[str],
    have: list[str],
    ttl_seconds: int = 3600,
) -> FetchMPackResult:
    import msgpack as _msgpack_local

    _t0 = _time_module.perf_counter()
    def _ms() -> float:
        return (_time_module.perf_counter() - _t0) * 1000

    logger.info("[wire_fetch_mpack] START repo_id=%s want=%d have=%d want_ids=%s",
                repo_id, len(want), len(have), [cid[:16] for cid in want[:5]])

    _up_to_date: FetchMPackResult = {
        "mpack_url": None,
        "mpack_id": None,
        "commit_count": 0,
        "blob_count": 0,
    }

    if not want:
        logger.info("[wire_fetch_mpack] SKIP — want is empty")
        return _up_to_date

    backend = get_backend()
    have_set = set(have)
    logger.info("[wire_fetch_mpack] step=1 DAG walk starting t=%.1fms", _ms())
    needed_rows = await _walk_commit_delta(session, want, have_set)
    logger.info("[wire_fetch_mpack] step=1 DAG walk done commits=%d t=%.1fms", len(needed_rows), _ms())

    if not needed_rows:
        logger.info("[wire_fetch_mpack] SKIP — client already up-to-date (needed_rows empty)")
        return _up_to_date

    commit_rows: dict[str, MusehubCommit] = {}
    _any = next(iter(needed_rows.values()))
    _is_proxy = not isinstance(_any, MusehubCommit)
    logger.info("[wire_fetch_mpack] step=1b needed_rows=%d is_proxy=%s t=%.1fms",
                len(needed_rows), _is_proxy, _ms())
    if _is_proxy:
        _cids = list(needed_rows.keys())
        _q = await session.execute(
            select(MusehubCommit).where(
                _sa_text("commit_id = ANY(:ids)").bindparams(ids=_cids)
            )
        )
        for _row in _q.scalars():
            commit_rows[_row.commit_id] = _row
        _missing_from_db = set(_cids) - set(commit_rows.keys())
        logger.info(
            "[wire_fetch_mpack] step=1b bulk fetch done commits_in_db=%d missing_from_db=%d "
            "missing_ids=%s t=%.1fms",
            len(commit_rows), len(_missing_from_db),
            [cid[:16] for cid in list(_missing_from_db)[:5]], _ms(),
        )
    else:
        commit_rows = needed_rows  # type: ignore[assignment]
        logger.info("[wire_fetch_mpack] step=1b using MusehubCommit rows directly commits=%d t=%.1fms",
                    len(commit_rows), _ms())

    _proxy_snap_ids_raw = [r.snapshot_id for r in needed_rows.values()]
    _graph_snap_ids = [sid for sid in _proxy_snap_ids_raw if sid]
    _proxy_snap_none_count = sum(1 for s in _proxy_snap_ids_raw if not s)
    _commit_row_snap_ids = [r.snapshot_id for r in commit_rows.values() if r.snapshot_id]
    # Defensive fallback: CommitGraph rows from server-side merges may have snapshot_id=None
    # (pre-fix state). The MusehubCommit row always has the correct snapshot_id — merge both.
    snap_ids = list({*_graph_snap_ids, *_commit_row_snap_ids})
    logger.info(
        "[wire_fetch_mpack] step=2 snap_ids_from_graph=%d snap_ids_none_in_graph=%d "
        "snap_ids_from_commit_rows=%d snap_ids_total=%d t=%.1fms",
        len(_graph_snap_ids), _proxy_snap_none_count, len(_commit_row_snap_ids), len(snap_ids), _ms(),
    )

    snap_map: dict[str, dict] = {}
    if snap_ids:
        snaps_q = await session.execute(
            select(MusehubSnapshot).where(
                _sa_text("snapshot_id = ANY(:ids)").bindparams(ids=snap_ids)
            )
        )
        for snap in snaps_q.scalars().all():
            snap_map[snap.snapshot_id] = await _snap_row_to_wire_s3(snap, backend, session=session)
    logger.info("[wire_fetch_mpack] step=2 snap_map loaded=%d t=%.1fms", len(snap_map), _ms())

    all_oids: set[str] = set()
    _needed_cids = list(needed_rows.keys())
    logger.warning("[GRAPH-DEBUG] wire_fetch_mpack: needed_rows=%d needed_cids_sample=%s",
                   len(_needed_cids), [c[:16] for c in _needed_cids[:3]])
    _debug_graph_q = await session.execute(
        select(MusehubCommitGraph.commit_id, MusehubCommitGraph.generation, MusehubCommitGraph.snapshot_id)
        .where(MusehubCommitGraph.commit_id.in_(_needed_cids))
        .order_by(MusehubCommitGraph.generation.desc())
        .limit(5)
    )
    _debug_graph_rows = _debug_graph_q.all()
    logger.warning("[GRAPH-DEBUG] wire_fetch_mpack: CommitGraph has %d rows for needed_cids (top 5 by gen): %s",
                   len(_debug_graph_rows),
                   [(r[1], r[0][:16]) for r in _debug_graph_rows])
    want_tip_snap_q = await session.execute(
        select(MusehubCommitGraph.snapshot_id)
        .where(MusehubCommitGraph.commit_id.in_(_needed_cids))
        .order_by(MusehubCommitGraph.generation.desc())
        .limit(1)
    )
    want_tip_snap_id = want_tip_snap_q.scalar_one_or_none()
    logger.warning("[GRAPH-DEBUG] wire_fetch_mpack: want_tip_snap_id=%s",
                   want_tip_snap_id[:20] if want_tip_snap_id else "NONE")
    logger.info("[wire_fetch_mpack] step=2 want_tip_snap_id=%s (from CommitGraph) t=%.1fms",
                want_tip_snap_id[:16] if want_tip_snap_id else None, _ms())
    if want_tip_snap_id:
        wt_blob_q = await session.execute(
            select(MusehubSnapshot.manifest_blob)
            .where(MusehubSnapshot.snapshot_id == want_tip_snap_id)
        )
        wt_blob = wt_blob_q.scalar_one_or_none()
        if wt_blob:
            all_oids.update(v for v in _msgpack_local.unpackb(wt_blob, raw=False).values() if v)
        logger.warning("[GRAPH-DEBUG] wire_fetch_mpack: want_tip manifest all_oids=%d wt_blob_present=%s",
                       len(all_oids), wt_blob is not None)
        logger.info("[wire_fetch_mpack] step=2 want_tip manifest all_oids=%d wt_blob_present=%s t=%.1fms",
                    len(all_oids), wt_blob is not None, _ms())
    else:
        logger.warning(
            "[wire_fetch_mpack] step=2 WARN want_tip_snap_id=None — CommitGraph missing tip "
            "needed_cids=%s commit_rows_snap_ids=%s",
            [cid[:16] for cid in list(needed_rows.keys())[:5]],
            [sid[:16] for sid in _commit_row_snap_ids[:5]],
        )

    have_oids: set[str] = set()
    if have_set:
        ht_snap_q = await session.execute(
            select(MusehubCommitGraph.snapshot_id)
            .where(MusehubCommitGraph.commit_id.in_(list(have_set)))
            .order_by(MusehubCommitGraph.generation.desc())
            .limit(1)
        )
        have_tip_snap_id = ht_snap_q.scalar_one_or_none()
        if have_tip_snap_id:
            ht_blob_q = await session.execute(
                select(MusehubSnapshot.manifest_blob)
                .where(MusehubSnapshot.snapshot_id == have_tip_snap_id)
            )
            ht_blob = ht_blob_q.scalar_one_or_none()
            if ht_blob:
                have_oids.update(v for v in _msgpack_local.unpackb(ht_blob, raw=False).values() if v)

    new_oids = all_oids - have_oids
    logger.info(
        "[wire_fetch_mpack] step=2 done snap_map=%d all_oids=%d have_oids=%d new_oids=%d t=%.1fms",
        len(snap_map), len(all_oids), len(have_oids), len(new_oids), _ms(),
    )

    if new_oids:
        indexed_q = await session.execute(
            select(MusehubMPackIndex.entity_id)
            .where(MusehubMPackIndex.entity_id.in_(list(new_oids)))
            .where(MusehubMPackIndex.entity_type == "object")
        )
        indexed_oids = {row[0] for row in indexed_q}
        missing = new_oids - indexed_oids
        if missing:
            logger.warning(
                "[wire_fetch_mpack] step=3 NOT INDEXED %d/%d objects — raising FetchNotIndexedError t=%.1fms",
                len(missing), len(new_oids), _ms(),
            )
            raise FetchNotIndexedError(len(missing))
        logger.info("[wire_fetch_mpack] step=3 index coverage OK oids=%d t=%.1fms", len(new_oids), _ms())

    cache_hits: dict[str, bytes] = {}
    if new_oids:
        _CACHE_CHUNK = 10000
        _new_oid_list = list(new_oids)
        for _ci in range(0, len(_new_oid_list), _CACHE_CHUNK):
            _chunk = _new_oid_list[_ci : _ci + _CACHE_CHUNK]
            _cache_q = await session.execute(
                select(MusehubObject.object_id, MusehubObject.content_cache)
                .where(MusehubObject.object_id.in_(_chunk))
                .where(MusehubObject.content_cache.isnot(None))
            )
            for _oid, _cached in _cache_q:
                if _cached:
                    cache_hits[_oid] = bytes(_cached)

    cache_miss_oids = [oid for oid in new_oids if oid not in cache_hits]

    oid_to_mpack: dict[str, str] = {}
    if cache_miss_oids:
        _MIDX_CHUNK = 10000
        for _ci in range(0, len(cache_miss_oids), _MIDX_CHUNK):
            _chunk = cache_miss_oids[_ci : _ci + _MIDX_CHUNK]
            _midx_q = await session.execute(
                select(MusehubMPackIndex.entity_id, MusehubMPackIndex.mpack_id)
                .where(MusehubMPackIndex.entity_id.in_(_chunk))
                .where(MusehubMPackIndex.entity_type == "object")
            )
            for _oid, _mid in _midx_q:
                oid_to_mpack[_oid] = _mid

    mpack_to_oids: dict[str, list[str]] = {}
    no_mpack_oids: list[str] = []
    for oid in cache_miss_oids:
        mid = oid_to_mpack.get(oid)
        if mid:
            mpack_to_oids.setdefault(mid, []).append(oid)
        else:
            no_mpack_oids.append(oid)

    mpack_hits: dict[str, bytes] = {}
    mpack_miss_oids: list[str] = []
    _sem_mpack = asyncio.Semaphore(8)

    async def _extract_from_mpack(mpack_id: str, oids: list[str]) -> None:
        async with _sem_mpack:
            raw = await backend.get_mpack(mpack_id)
            if raw is None:
                mpack_miss_oids.extend(oids)
                return
            import zstandard as _zstd_phase1
            _dctx_phase1 = _zstd_phase1.ZstdDecompressor()
            try:
                if raw[:4] == b"MUSE":
                    from muse.core.mpack import parse_wire_mpack as _parse_wire_fetch
                    payload = _parse_wire_fetch(raw)
                else:
                    payload = _msgpack_local.unpackb(raw, raw=False)
            except Exception as _parse_err:
                logger.warning(
                    "[_extract_from_mpack] failed to parse mpack=%s: %s",
                    mpack_id[:20], _parse_err,
                )
                mpack_miss_oids.extend(oids)
                return
            obj_index: dict[str, bytes] = {}
            for o in payload.get("blobs", []):
                oid_entry = o.get("object_id", "")
                content = o.get("content") or b""
                if not isinstance(content, bytes):
                    content = bytes(content)
                _ZSTD_MAGIC = b"\x28\xb5\x2f\xfd"
                if (o.get("encoding") == "zstd" or content[:4] == _ZSTD_MAGIC) and content:
                    try:
                        content = _dctx_phase1.decompress(content)
                    except Exception as _decomp_err:
                        logger.warning(
                            "[_extract_from_mpack] zstd decompress failed oid=%s: %s",
                            oid_entry[:20], _decomp_err,
                        )
                        continue
                obj_index[oid_entry] = content
            for oid in oids:
                content = obj_index.get(oid)
                if content is not None:
                    mpack_hits[oid] = content
                else:
                    mpack_miss_oids.append(oid)

    if mpack_to_oids:
        await asyncio.gather(
            *(_extract_from_mpack(mid, oids) for mid, oids in mpack_to_oids.items())
        )

    legacy_hits: dict[str, bytes] = {}
    _fallback_oids = no_mpack_oids + mpack_miss_oids
    if _fallback_oids:
        _sem_legacy = asyncio.Semaphore(50)

        async def _get_legacy(oid: str) -> None:
            async with _sem_legacy:
                data = await backend.get(oid)
                if data:
                    legacy_hits[oid] = data

        await asyncio.gather(*(_get_legacy(oid) for oid in _fallback_oids))

    _all_blob_bytes: dict[str, bytes] = {**legacy_hits, **mpack_hits, **cache_hits}
    blob_pairs = [(oid, _all_blob_bytes[oid]) for oid in new_oids if oid in _all_blob_bytes]
    logger.info(
        "[wire_fetch_mpack] step=4 fetched %d blobs (cache=%d mpack=%d legacy=%d) t=%.1fms",
        len(blob_pairs), len(cache_hits), len(mpack_hits), len(legacy_hits), _ms(),
    )

    wire_commits = [
        (await _commit_to_wire_s3(row, backend)).model_dump()
        for row in commit_rows.values()
    ]
    wire_snaps = [snap_map[sid] for sid in snap_ids if sid in snap_map]
    wire_blobs = [
        {"object_id": oid, "content": data}
        for oid, data in blob_pairs
        if data
    ]
    logger.info(
        "[wire_fetch_mpack] step=5 assembly: wire_commits=%d wire_snaps=%d wire_blobs=%d "
        "snap_ids_total=%d snap_ids_in_map=%d commit_rows=%d t=%.1fms",
        len(wire_commits), len(wire_snaps), len(wire_blobs),
        len(snap_ids), sum(1 for sid in snap_ids if sid in snap_map),
        len(commit_rows), _ms(),
    )

    from muse.core.mpack import build_wire_mpack as _build_wire_mpack
    _head_commit_id = want[0] if want else ""
    mpack_bytes = _build_wire_mpack(
        {
            "commits":   wire_commits,
            "snapshots": wire_snaps,
            "blobs":     wire_blobs,
            "tags":      [],
        },
        meta={"repo_id": repo_id, "head_commit_id": _head_commit_id},
    )
    mpack_id = blob_id(mpack_bytes)

    n_commits = len(wire_commits)
    n_blobs = len(wire_blobs)
    logger.info(
        "[wire_fetch_mpack] step=5 assembled commits=%d snapshots=%d blobs=%d bytes=%d t=%.1fms",
        n_commits, len(wire_snaps), n_blobs, len(mpack_bytes), _ms(),
    )

    await backend.put_mpack(mpack_id, mpack_bytes)
    mpack_url = await backend.presign_mpack_get(mpack_id, ttl_seconds)
    logger.info(
        "[wire_fetch_mpack] step=6 mpack_id=%s mpack_url=%s t=%.1fms",
        mpack_id[:20], mpack_url[:80] if mpack_url else None, _ms(),
    )
    logger.info("[wire_fetch_mpack] RETURN commits=%d blobs=%d TOTAL=%.1fms", n_commits, n_blobs, _ms())

    async def _cleanup() -> None:
        await asyncio.sleep(ttl_seconds)
        try:
            await backend.delete(mpack_id)
        except Exception:
            pass

    asyncio.ensure_future(_cleanup())

    return {
        "mpack_url":    mpack_url,
        "mpack_id":     mpack_id,
        "commit_count": n_commits,
        "blob_count":   n_blobs,
    }

async def _check_missing_objects(
    session: AsyncSession,
    needs_check: set[str],
) -> set[str]:
    if not needs_check:
        return set()
    from musehub.db.musehub_repo_models import MusehubObject
    registered: set[str] = set(
        (await session.execute(
            select(MusehubObject.object_id).where(
                MusehubObject.object_id.in_(list(needs_check)),
                MusehubObject.deleted_at.is_(None),
            )
        )).scalars().all()
    )
    return needs_check - registered


class MPackGCResult(TypedDict):
    skipped: bool
    packs_before: int
    packs_after: int
    consolidated_key: str


async def process_mpack_gc_job(session: AsyncSession, repo_id: str) -> MPackGCResult:
    import msgpack as _mp

    _skipped: MPackGCResult = {
        "skipped": True,
        "packs_before": 0,
        "packs_after": 0,
        "consolidated_key": "",
    }

    repo_oids_q = await session.execute(
        select(MusehubObjectRef.object_id)
        .where(MusehubObjectRef.repo_id == repo_id)
    )
    repo_oid_set = {row[0] for row in repo_oids_q}
    mpack_q = await session.execute(
        select(MusehubMPackIndex.mpack_id)
        .where(MusehubMPackIndex.entity_id.in_(list(repo_oid_set)))
        .where(MusehubMPackIndex.entity_type == "object")
        .distinct()
    )
    mpack_ids = [row[0] for row in mpack_q]
    packs_before = len(mpack_ids)

    if packs_before <= 1:
        _skipped["packs_before"] = packs_before
        if mpack_ids:
            _skipped["consolidated_key"] = mpack_ids[0]
        return _skipped

    import musehub.storage.backends as _backends_mod
    backend = _backends_mod.get_backend()

    merged_objects: dict[str, bytes] = {}

    async def _download(pid: str) -> None:
        raw = await backend.get_mpack(pid)
        if not raw:
            logger.warning("[mpack_gc] mpack not found in storage: %s", pid)
            return
        if raw[:4] == b"MUSE":
            from muse.core.mpack import parse_wire_mpack as _parse_gc
            _parsed = _parse_gc(raw)
        else:
            _parsed = _mp.unpackb(raw, raw=False)
        for obj in _parsed.get("blobs", []):
            oid = obj.get("object_id", "")
            content = obj.get("content", b"")
            if oid and oid not in merged_objects:
                merged_objects[oid] = content

    await asyncio.gather(*(_download(pid) for pid in mpack_ids))

    from muse.core.mpack import build_wire_mpack as _build_gc_mpack
    consolidated_bytes = _build_gc_mpack({
        "commits": [],
        "snapshots": [],
        "blobs": [
            {"object_id": oid, "content": merged_objects[oid]}
            for oid in sorted(merged_objects)
        ],
        "tags": [],
    })
    consolidated_key = "sha256:" + hashlib.sha256(consolidated_bytes).hexdigest()

    await backend.put_mpack(consolidated_key, consolidated_bytes)

    old_mpack_ids = [p for p in mpack_ids if p != consolidated_key]
    if old_mpack_ids:
        from sqlalchemy import delete as sa_delete
        await session.execute(
            sa_delete(MusehubMPackIndex)
            .where(MusehubMPackIndex.mpack_id.in_(old_mpack_ids))
            .where(MusehubMPackIndex.entity_type == "object")
        )
    _gc_now = datetime.now(timezone.utc)
    new_rows = [
        {
            "entity_id": oid,
            "mpack_id": consolidated_key,
            "entity_type": "object",
            "created_at": _gc_now,
        }
        for oid in merged_objects
    ]
    if new_rows:
        _GC_MIDX_CHUNK = 5000
        for _gmi in range(0, len(new_rows), _GC_MIDX_CHUNK):
            await session.execute(
                _pg_insert(MusehubMPackIndex)
                .values(new_rows[_gmi : _gmi + _GC_MIDX_CHUNK])
                .on_conflict_do_nothing(index_elements=["entity_id", "mpack_id"])
            )

    logger.info(
        "[mpack_gc] repo=%s consolidated %d mpacks → 1 (objects=%d key=%s)",
        repo_id, packs_before, len(merged_objects), consolidated_key,
    )

    return {
        "skipped": False,
        "packs_before": packs_before,
        "packs_after": 1,
        "consolidated_key": consolidated_key,
    }


class FetchResult(TypedDict):
    mpack_id:     str
    mpack_url:    str | None
    commit_count: int
    blob_count: int


class FetchMPackPrebuildResult(TypedDict):
    tips_requested: int
    tips_built: int
    tips_skipped: int
    elapsed_ms: float


async def process_fetch_mpack_prebuild_job(
    session: AsyncSession,
    job_id: str,
) -> FetchMPackPrebuildResult:
    """Build and cache a fetch mpack for every branch tip in the job payload.

    Called by the background worker after every push.  For each tip commit ID
    in ``payload["tip_commit_ids"]``, checks whether a fresh cache entry
    already exists in ``musehub_fetch_mpack_cache``; skips tips that are
    cached and builds the rest by calling ``wire_fetch_mpack``.

    The mpack_id returned by ``wire_fetch_mpack`` is written (or upserted) into
    ``musehub_fetch_mpack_cache`` so that subsequent fetch requests hit the
    cache and return a presigned URL in under a second.
    """
    from datetime import timedelta

    from musehub.db.musehub_jobs_models import MusehubBackgroundJob
    from sqlalchemy.dialects.postgresql import insert as _upsert

    _t0 = _time_module.monotonic()

    def _ms() -> float:
        return (_time_module.monotonic() - _t0) * 1000

    job_row = (await session.execute(
        select(MusehubBackgroundJob).where(MusehubBackgroundJob.job_id == job_id)
    )).scalar_one_or_none()
    if job_row is None:
        raise ValueError(f"fetch.mpack.prebuild job not found: {job_id}")

    repo_id: str = job_row.repo_id
    payload = job_row.payload or {}
    tip_commit_ids: list[str] = [str(t) for t in (payload.get("tip_commit_ids") or [])]

    if not tip_commit_ids:
        logger.warning("[fetch.mpack.prebuild] job=%s repo=%s no tip_commit_ids in payload", job_id[:16], repo_id)
        return {"tips_requested": 0, "tips_built": 0, "tips_skipped": 0, "elapsed_ms": 0.0}

    # Find which tips already have a fresh (non-expired) cache entry.
    now = _utc_now()
    cached_q = await session.execute(
        select(MusehubFetchMPackCache.tip_commit_id)
        .where(MusehubFetchMPackCache.repo_id == repo_id)
        .where(MusehubFetchMPackCache.tip_commit_id.in_(tip_commit_ids))
        .where(MusehubFetchMPackCache.expires_at > now)
    )
    already_cached: set[str] = {row[0] for row in cached_q}

    tips_to_build = [t for t in tip_commit_ids if t not in already_cached]
    tips_skipped = len(already_cached)

    logger.warning(
        "[fetch.mpack.prebuild] job=%s repo=%s tips=%d cached=%d to_build=%d t=%.1fms",
        job_id[:16], repo_id, len(tip_commit_ids), tips_skipped, len(tips_to_build), _ms(),
    )

    tips_built = 0
    for tip in tips_to_build:
        _tip_t0 = _time_module.monotonic()
        try:
            result = await wire_fetch_mpack(session, repo_id, want=[tip], have=[])
            mpack_id = result.get("mpack_id") or ""
            if not mpack_id:
                logger.warning(
                    "[fetch.mpack.prebuild] tip=%s produced no mpack_id — skipping cache write",
                    tip[:20],
                )
                continue

            cache_id = blob_id((repo_id + tip).encode()).replace("sha256:", "")
            expires_at = now + timedelta(days=7)
            await session.execute(
                _upsert(MusehubFetchMPackCache)
                .values(
                    cache_id=cache_id,
                    repo_id=repo_id,
                    tip_commit_id=tip,
                    mpack_id=mpack_id,
                    created_at=now,
                    expires_at=expires_at,
                )
                .on_conflict_do_update(
                    index_elements=["repo_id", "tip_commit_id"],
                    set_={"mpack_id": mpack_id, "expires_at": expires_at},
                )
            )
            tips_built += 1
            _tip_ms = (_time_module.monotonic() - _tip_t0) * 1000
            logger.warning(
                "[fetch.mpack.prebuild] built tip=%s mpack_id=%s t=%.1fms",
                tip[:20], mpack_id[:20], _tip_ms,
            )
        except Exception as exc:
            logger.error(
                "[fetch.mpack.prebuild] tip=%s FAILED: %s", tip[:20], exc, exc_info=True,
            )

    total_ms = _ms()
    logger.warning(
        "[fetch.mpack.prebuild] DONE job=%s repo=%s tips=%d built=%d skipped=%d TOTAL=%.1fms",
        job_id[:16], repo_id, len(tip_commit_ids), tips_built, tips_skipped, total_ms,
    )
    return {
        "tips_requested": len(tip_commit_ids),
        "tips_built": tips_built,
        "tips_skipped": tips_skipped,
        "elapsed_ms": total_ms,
    }


class FetchCommitNotFound(Exception):
    """A want commit_id does not exist in musehub_commits."""


class FetchNotReady(Exception):
    """Needed objects are absent from musehub_mpack_index — client must retry."""


async def wire_fetch(
    session: AsyncSession,
    repo_id: str,
    want: list[str],
    have: list[str],
    ttl_seconds: int = 3600,
) -> FetchResult:
    import msgpack as _mp

    _empty: FetchResult = {"mpack_id": "", "mpack_url": None, "commit_count": 0, "blob_count": 0}

    for entry in want:
        if not (isinstance(entry, str) and entry.startswith("sha256:")):
            raise MPackValidationError(f"want entry is not a sha256: id: {entry!r}")

    for entry in have:
        if not (isinstance(entry, str) and entry.startswith("sha256:")):
            raise MPackValidationError(f"have entry is not a sha256: id: {entry!r}")

    if want:
        existing_q = await session.execute(
            select(MusehubCommit.commit_id).where(MusehubCommit.commit_id.in_(want))
        )
        found = {row[0] for row in existing_q}
        missing_want = [cid for cid in want if cid not in found]
        if missing_want:
            raise FetchCommitNotFound(missing_want[0])

    have_set = set(have)
    needed = await _walk_commit_delta(session, want, have_set)
    if not needed:
        return _empty

    cids = list(needed.keys())
    commit_rows: dict[str, MusehubCommit] = {}
    for i in range(0, len(cids), 2000):
        q = await session.execute(
            select(MusehubCommit).where(MusehubCommit.commit_id.in_(cids[i:i + 2000]))
        )
        for row in q.scalars():
            commit_rows[row.commit_id] = row

    want_snap_ids = {r.snapshot_id for r in needed.values() if r.snapshot_id}
    have_snap_ids: set[str] = set()
    if have_set:
        have_commits_q = await session.execute(
            select(MusehubCommit.snapshot_id).where(MusehubCommit.commit_id.in_(list(have_set)))
        )
        have_snap_ids = {row[0] for row in have_commits_q if row[0]}

    new_snap_ids = want_snap_ids - have_snap_ids
    snap_map: dict[str, dict] = {}
    new_oids: set[str] = set()
    backend = get_backend()
    if new_snap_ids:
        snaps_q = await session.execute(
            select(MusehubSnapshot).where(MusehubSnapshot.snapshot_id.in_(list(new_snap_ids)))
        )
        for snap in snaps_q.scalars():
            manifest = (
                _mp.unpackb(snap.manifest_blob, raw=False)
                if snap.manifest_blob
                else await _reconstruct_manifest(session, snap.snapshot_id)
            )
            new_oids.update(v for v in manifest.values() if v)
            snap_map[snap.snapshot_id] = await _snap_row_to_wire_s3(snap, backend, session=session)

    if have_snap_ids:
        have_snaps_q = await session.execute(
            select(MusehubSnapshot).where(MusehubSnapshot.snapshot_id.in_(list(have_snap_ids)))
        )
        for snap in have_snaps_q.scalars():
            m = (
                _mp.unpackb(snap.manifest_blob, raw=False)
                if snap.manifest_blob
                else await _reconstruct_manifest(session, snap.snapshot_id)
            )
            new_oids -= {v for v in m.values() if v}

    if new_oids:
        idx_q = await session.execute(
            select(MusehubMPackIndex.entity_id).where(
                MusehubMPackIndex.entity_id.in_(list(new_oids)),
                MusehubMPackIndex.entity_type == "object",
            )
        )
        indexed = {row[0] for row in idx_q}
        unindexed = new_oids - indexed
        if unindexed:
            raise FetchNotReady(f"{len(unindexed)} object(s) not yet in mpack_index")

    objects: list[dict] = []
    if new_oids:
        obj_q = await session.execute(
            select(MusehubObject).where(MusehubObject.object_id.in_(list(new_oids)))
        )
        for obj_row in obj_q.scalars():
            if obj_row.content_cache is not None:
                content = obj_row.content_cache
            else:
                content = await backend.get(obj_row.object_id) or b""
            objects.append({"object_id": obj_row.object_id, "content": content})

    wire_commits = [_to_wire_commit(r).model_dump() for r in commit_rows.values()]
    from muse.core.mpack import build_wire_mpack as _build_fetch_mpack
    wire_bytes = _build_fetch_mpack({
        "commits":   wire_commits,
        "snapshots": list(snap_map.values()),
        "blobs":     objects,
        "tags":      [],
    })
    mpack_id = blob_id(wire_bytes)

    await backend.put_mpack(mpack_id, wire_bytes)
    mpack_url = await backend.presign_mpack_get(mpack_id, ttl_seconds)

    return {
        "mpack_id":     mpack_id,
        "mpack_url":    mpack_url,
        "commit_count": len(commit_rows),
        "blob_count": len(objects),
    }