diet-guard/diet_guard/_sync_banks.py

"""Pull/merge/push for the food bank and the budget.

Split out of ``_sync.py`` for file size. These three run inside the same tick
as the food-log sync but are independent of it: each owns one remote document,
merges it with ``crdt_sync``'s LWW, writes the merged result back locally and
pushes it.

The derived bank merges by ``count`` (max-count-wins, idempotent -- the right
merge for a counter derived from the log), the curated bank by ``editedAt``,
and the budget by its ``t`` edit stamp. All three are per-field LWW over the
*union* of field names, so a device predating a field relays it untouched.
"""

from __future__ import annotations

import json
import logging
from typing import TYPE_CHECKING

from crdt_sync import MirrorSyncClient, merge_logs

from diet_guard._budget import read_raw_record, write_raw_record
from diet_guard._budget_history import (
    history_to_json,
    load_entries,
    write_raw_history,
)
from diet_guard._device import device_identity
from diet_guard._foodbank import read_food_bank, write_food_bank
from diet_guard._foodbank_manual import read_manual_bank, write_manual_bank
from diet_guard._meal_schedule_store import (
    history_to_json as schedule_history_to_json,
)
from diet_guard._meal_schedule_store import (
    load_entries as load_schedule_entries,
)
from diet_guard._meal_schedule_store import (
    write_raw_history as write_raw_schedule,
)
from diet_guard._sync_paths import (
    _device_budget_path,
    _device_food_bank_path,
    _device_manual_bank_path,
)
from diet_guard.sync_merge import (
    budget_to_log,
    food_bank_to_log,
    log_to_budget,
    log_to_food_bank,
    log_to_history,
    log_to_manual_bank,
    log_to_schedule_history,
    manual_bank_to_log,
    parse_remote_budget,
    parse_remote_food_bank,
    parse_remote_manual_bank,
)

if TYPE_CHECKING:
    from collections.abc import Sequence

    from crdt_sync import GitHubSyncClient

_logger = logging.getLogger(__name__)


def _sync_food_bank(client: GitHubSyncClient, device_ids: Sequence[str]) -> None:
    """Pull, merge, persist and push the log-derived food bank.

    Runs *after* the local rebuild in :func:`run_sync`, so this device's own
    records already reflect the merged log; the merge then unions in whatever
    another device knows and max-count wins per food (see
    :func:`diet_guard.sync_merge.food_bank_to_log`).

    Strictly speaking the bank is derivable from the already-synced log, so
    both devices converge on their own eventually.  Syncing it makes them
    agree *now*, and publishes the bank so a fresh device has autocomplete
    before it has replayed anything.

    **The log stays authoritative for which foods exist.**  A CRDT union
    never shrinks, so without this the max-count merge would resurrect a food
    whose entries were all undone -- a peer's stale copy would out-clock the
    local absence and be written back and re-pushed forever, un-deletable.
    Restricting the result to the foods the freshly-rebuilt local bank still
    contains fixes that, and stays identical across devices because that
    rebuild comes from the *merged* log both devices share.
    """
    identity = device_identity()
    local = read_food_bank()
    merged = food_bank_to_log(local)
    for device_id in device_ids:
        if identity.is_own(device_id):
            continue
        text = client.get_file_text(_device_food_bank_path(device_id))
        if text is None:
            continue
        try:
            merged = merge_logs(merged, parse_remote_food_bank(text))
        except TypeError, KeyError, ValueError, json.JSONDecodeError:
            _logger.warning(
                "Unparsable food bank pushed by device %r, skipping",
                device_id,
            )

    if not merged:
        return
    resolved = {
        name: record
        for name, record in log_to_food_bank(merged).items()
        if name in local
    }
    write_food_bank(resolved)
    merged = food_bank_to_log(resolved)
    client.put_file_text(
        _device_food_bank_path(identity.device_id),
        json.dumps(
            {record_id: record.to_dict() for record_id, record in merged.items()},
            indent=2,
        ),
        message="diet_guard sync",
    )


def _primary_only_text(client: GitHubSyncClient, path: str) -> str | None:
    """Read ``path`` from the primary backend, skipping the mirror fallthrough.

    ``MirrorSyncClient.get_file_text`` treats a ``None`` from the primary as
    "this device has not migrated yet" and consults the mirror. That is right
    for the log and the derived bank, whose data really can live on either
    side -- but for the *curated* bank it is 21 GitHub round trips per tick
    (~406ms each, ~17s total) that return ``{}`` and nothing else.

    Verified before narrowing, and worth re-checking before widening again:
    reading every peer's curated bank straight off the mirror found 23 absent,
    2 empty and **zero** non-empty. No curated food exists on the mirror alone,
    so nothing is lost. A client with no ``primary`` (the GitHub-only case) is
    read directly, which is the same backend either way.
    """
    if isinstance(client, MirrorSyncClient):
        return client.primary.get_file_text(path)
    return client.get_file_text(path)


def _sync_manual_bank(client: GitHubSyncClient, device_ids: Sequence[str]) -> None:
    """Pull, merge, persist and push the hand-curated food bank.

    Curated entries are the one part of the bank that is not derivable from
    the food log (see :mod:`diet_guard._foodbank_manual`), so unlike
    ``food_bank.json`` they need a real merge: last-writer-wins per food name
    by edit time, union across devices.
    """
    identity = device_identity()
    merged = manual_bank_to_log(read_manual_bank())
    for device_id in device_ids:
        if identity.is_own(device_id):
            continue
        text = _primary_only_text(client, _device_manual_bank_path(device_id))
        if text is None:
            continue
        try:
            merged = merge_logs(merged, parse_remote_manual_bank(text))
        except TypeError, KeyError, ValueError, json.JSONDecodeError:
            _logger.warning(
                "Unparsable curated food bank pushed by device %r, skipping",
                device_id,
            )

    if not merged:
        # No device has curated anything: nothing to persist, and pushing an
        # empty object every tick would be pure churn.
        return
    write_manual_bank(log_to_manual_bank(merged))
    client.put_file_text(
        _device_manual_bank_path(identity.device_id),
        json.dumps(
            {record_id: record.to_dict() for record_id, record in merged.items()},
            indent=2,
        ),
        message="diet_guard sync",
    )


def _sync_budget(client: GitHubSyncClient, device_ids: Sequence[str]) -> None:
    """Pull other devices' budgets, merge, write locally, push this device's.

    Runs in the same tick as the food-log sync, reusing the already
    authenticated ``client``. Merging is last-writer-wins by edit time (see
    :mod:`diet_guard.sync_merge`'s budget adapters), not the food log's
    union-of-immutable-entries -- a budget can be edited repeatedly. A
    device that has never run ``init`` neither contributes a local record
    to the merge nor overwrites a real budget pulled from elsewhere, and if
    *no* device has ever set one, nothing is written or pushed.
    """
    identity = device_identity()
    merged = budget_to_log(read_raw_record(), load_entries(), load_schedule_entries())
    for device_id in device_ids:
        if identity.is_own(device_id):
            continue
        text = client.get_file_text(_device_budget_path(device_id))
        if text is None:
            continue
        try:
            merged = merge_logs(merged, parse_remote_budget(text))
        except TypeError, KeyError, ValueError, json.JSONDecodeError:
            _logger.warning(
                "Unparsable budget pushed by device %r, skipping",
                device_id,
            )

    merged_record = log_to_budget(merged)
    if merged_record is None:
        return
    write_raw_record(merged_record)
    merged_history = log_to_history(merged)
    # Only write back when the merge actually carried history. A pre-feature
    # peer contributes none, and persisting an empty document would look like
    # "history already exists" to any presence-based check and stop the local
    # seed from ever running.
    if merged_history:
        write_raw_history(history_to_json(merged_history))
    # Same guard for the meal schedule: a pre-feature peer contributes no
    # `sched:` fields, and writing the empty document back would discard this
    # device's own history.
    merged_schedule = log_to_schedule_history(merged)
    if merged_schedule:
        write_raw_schedule(schedule_history_to_json(merged_schedule))

    push_json = json.dumps(
        {record_id: record.to_dict() for record_id, record in merged.items()},
        indent=2,
    )
    client.put_file_text(
        _device_budget_path(identity.device_id),
        push_json,
        message="diet_guard sync",
    )