"""BigQuery driver stub: contract reference + implementation roadmap.

ships as part of ``datasource-task-12`` to prove the :class:`Driver`
ABC fits a stateless-HTTPS backend (no pool, no connection objects)
without requiring the backend library to be installed. paired with
:mod:`threetears.datasources.drivers.snowflake_driver` -- the
contrast between the two stubs proves the ABC handles two very
different driver shapes (stateful-pooled vs stateless-HTTPS) so
future drivers (Athena, Trino, DuckDB, ...) will slot in cleanly.

contract reference -- DO NOT REINVENT these helpers in the future
implementation:

Backend library
    `google-cloud-bigquery <https://pypi.org/project/google-cloud-bigquery/>`_
    (Apache-2.0, Google-maintained). minimum version 3.0. installed
    via the ``[bigquery]`` extras key on this package; the factory
    lazy-imports this module only when a
    :class:`BigQueryConnectionConfig` actually dispatches.

Connection lifecycle
    stateless. one :class:`google.cloud.bigquery.Client` instance
    handles every call -- each call is an HTTPS request to the
    BigQuery REST API; the Client is thread-safe; NO pool needed.
    construct the Client in ``__init__`` (lazy or eager -- the
    Client construction is cheap) and reuse it for every method.

    AUTH: the Client takes
    :class:`google.oauth2.service_account.Credentials` built from
    the JSON blob held by
    :attr:`BigQueryConnectionConfig.credentials_json_ref`. resolve
    the reference via :meth:`BigQueryConnectionConfig.resolve_credentials_json`
    (returns :class:`SecretStr`), unwrap via ``.get_secret_value()``
    at the LAST moment when handing to
    ``service_account.Credentials.from_service_account_info(
    json.loads(blob))``. NEVER an intermediate ``str`` variable
    holding the JSON blob.

Placeholder style
    BigQuery uses ``@p1``-style named query parameters via
    :class:`google.cloud.bigquery.ScalarQueryParameter` /
    :class:`ArrayQueryParameter` attached to a
    :class:`QueryJobConfig`. callers pass ``$N``-style placeholders
    per the ABC contract; the driver translates via
    :func:`threetears.datasources.drivers._util._translate_placeholders`
    with target ``"named-at"`` -- ``$1`` -> ``@p1``. then walks the
    ``params`` positional tuple and builds the matching
    :class:`ScalarQueryParameter("p1", type_str, value)` list to
    attach to the :class:`QueryJobConfig`. DO NOT reimplement the
    regex dance -- the shared helper already handles ``$10`` vs
    ``$1`` correctly.

Cancellation mechanism
    :meth:`QueryJob.cancel` on the job handle. BigQuery jobs are
    first-class entities -- the Client returns a
    :class:`QueryJob` from ``client.query(sql, ...)``; the cancel
    hook is bound to that specific job. capture the
    :class:`QueryJob` reference BEFORE entering the
    :meth:`Driver._with_cancellation` wrapper so the cancel
    callback closes over it.

Sync-to-async bridge
    ``google-cloud-bigquery`` is blocking (HTTPS calls are
    synchronous); route every call through
    :class:`threetears.datasources.drivers._sync_bridge.AsyncSyncBridge`
    (the SAME bridge :class:`RedshiftDriver` already uses). size
    from :attr:`BigQueryConnectionConfig.executor_max_workers`.
    NEVER instantiate :class:`concurrent.futures.ThreadPoolExecutor`
    directly -- the enforcement test catches it at compile time.

Row-shape pinning
    :meth:`list_tables` returns :class:`threetears.datasources.drivers.base.TableRow`;
    :meth:`list_columns` returns
    :class:`threetears.datasources.drivers.base.ColumnRow`. BigQuery
    does NOT have an ``information_schema`` you can SELECT from
    over the REST API; instead query the metadata via
    :meth:`Client.list_tables(dataset_ref)` +
    :meth:`Client.get_table(table_ref).schema`. each
    :class:`SchemaField` carries ``name``, ``field_type``, and
    ``mode``: build the :class:`ColumnRow` dict with
    ``is_nullable`` derived from ``mode``:

    - ``mode == "NULLABLE"`` -> ``is_nullable = "YES"``
    - ``mode == "REQUIRED"`` -> ``is_nullable = "NO"``
    - ``mode == "REPEATED"`` -> ``is_nullable = "NO"`` (repeated
      array fields are NOT nullable; the array can be empty but the
      field itself is required)

    document the mapping prominently in the implementation -- the
    Tier-2 hash equivalence depends on these strings being stable
    across BigQuery API versions.

Tier-2 column hash
    BigQuery has NO ``MD5(LISTAGG(...))`` equivalent that you can
    run server-side over the metadata catalog -- the metadata lives
    in the REST API, not in queryable tables. compute the hash
    PYTHON-SIDE using the same payload formula as
    :class:`AsyncpgDriver` /
    :class:`RedshiftDriver`'s warehouse-side SQL:

    .. code-block:: python

        payload = ",".join(
            f"{c['column_name']}:{c['data_type']}:{c['is_nullable']}"
            for c in sorted(cols, key=lambda c: c['ordinal_position'])
        )
        return hashlib.md5(payload.encode()).hexdigest()

    same byte-equivalence contract; just no server-side aggregation
    available. lift the python helper to
    :mod:`threetears.datasources.introspection` per shard 13's
    DS-13-14 note when this implementation lands -- BigQuery will
    be the first consumer.

Pool / executor / timeout knobs
    every knob reads from :class:`BigQueryConnectionConfig`. the
    enforcement test
    ``tests/enforcement/test_no_hardcoded_pool_params.py`` walks
    every concrete driver module on every test run and fails the
    build on banned-kwarg literals. add a new field if a knob needs
    more documentation than a default value provides. note that
    BigQuery's per-query timeout is
    ``QueryJobConfig.job_timeout_ms`` (milliseconds; the driver
    converts ``query_timeout_seconds * 1000``).

Secret handling
    :meth:`BigQueryConnectionConfig.resolve_credentials_json`
    returns :class:`pydantic.SecretStr` wrapping the SA-JSON blob;
    unwrap via ``.get_secret_value()`` only inside the
    ``service_account.Credentials.from_service_account_info(
    json.loads(blob))`` call. wrap auth/transport errors in
    :class:`DriverConnectError` with ``from None`` to break the
    cause chain. mirror the asyncpg / redshift patterns.

Observability
    decorate query-emitting methods with
    :func:`threetears.datasources.drivers.base._observed`
    (``driver_type="bigquery"``). cancellation.fired / .failed,
    executor.saturation are manual emissions mirroring the
    :class:`RedshiftDriver` pattern. cache.hit/miss does NOT apply
    (no pool to cache); document the absence in the implementation.

Anything that does NOT transfer from postgres/redshift/snowflake
    - no ``test_connection`` :sql:`SELECT 1` -- the cheapest BigQuery
      health-check is a metadata REST call like
      :meth:`Client.list_datasets()` capped at one item. document
      the rationale; the contract from the ABC (``test_connection``
      is the cheapest round-trip) is satisfied.
    - no in-flight job tracking inside ``fetch_iter`` -- BigQuery
      paginates via :meth:`QueryJob.result()` which returns a
      :class:`RowIterator`. iterate it on the bridge's worker; yield
      one row per chunk so the asyncio caller never blocks on a
      multi-page network round-trip.
    - no concept of "connection cache" -- delete the
      :meth:`cache.hit` / :meth:`cache.miss` counter emissions from
      your manual metric path; only fired/failed/saturation apply.

CI-required live test
    when the implementation lands, mirror the
    ``tests/integration/test_redshift_driver_live.py`` shape: env-
    gated on a ``GOOGLE_APPLICATION_CREDENTIALS`` (or analogous)
    pointing at a service-account JSON; in CI when the env var is
    missing AND ``CI=1`` is set, fail rather than skip silently.
    the live test is the smoking-gun proof the driver actually
    works against a real BigQuery project.
"""

from __future__ import annotations

from typing import Any

from threetears.datasources.config import BigQueryConnectionConfig
from threetears.datasources.drivers.base import ColumnRow, Driver, TableRow
from threetears.observe import get_logger

__all__ = ["BigQueryDriver"]

log = get_logger(__name__)


_NOT_IMPLEMENTED_HINT = (
    "See docs/datasource-task-12-snowflake-bigquery-stubs.md + the module docstring for the implementation roadmap."
)


class BigQueryDriver(Driver):
    """BigQuery :class:`Driver` -- STUB. raises :class:`NotImplementedError` on every call.

    constructor validates the config so the
    :func:`threetears.datasources.drivers.create_driver` dispatch
    path is exercised end-to-end today; method bodies land when the
    implementation does. read this module's top-of-file docstring
    before writing the implementation -- the helpers to reuse
    (:class:`AsyncSyncBridge`, :meth:`Driver._with_cancellation`,
    :func:`_translate_placeholders` with ``"named-at"`` target, the
    :func:`_observed` decorator) and the BigQuery-specific
    deviations (no information_schema, ``QueryJob.cancel``,
    REST-paginated row iteration, python-side Tier-2 hash) are all
    documented there.

    :param config: bigquery connection config validated at
        construction; carries project_id, credentials_json_ref,
        executor_max_workers, query_timeout_seconds
    :ptype config: BigQueryConnectionConfig
    :param datasource_name: human-readable datasource name surfaced
        as the ``datasource_name`` attribute on every OTel metric
        emitted by :func:`_observed` (when the impl lands). defaults
        to ``"unknown"`` so callers that don't have the name in scope
        still produce valid metric streams
    :ptype datasource_name: str
    """

    def __init__(
        self,
        config: BigQueryConnectionConfig,
        *,
        datasource_name: str = "unknown",
    ) -> None:
        """validate the config + capture the datasource_name. no I/O.

        :param config: bigquery connection config
        :ptype config: BigQueryConnectionConfig
        :param datasource_name: name surfaced on OTel metric attributes
        :ptype datasource_name: str
        :return: nothing
        :rtype: None
        """
        self._config = config
        self._datasource_name = datasource_name

    async def fetch(self, sql: str, *params: Any) -> list[dict[str, Any]]:
        """run a SELECT statement -- NOT YET IMPLEMENTED.

        :raises NotImplementedError: stub method; see module docstring
        """
        raise NotImplementedError(f"BigQueryDriver.fetch is not yet implemented. {_NOT_IMPLEMENTED_HINT}")

    async def execute(self, sql: str, *params: Any) -> None:
        """run a DML / DDL statement -- NOT YET IMPLEMENTED.

        :raises NotImplementedError: stub method; see module docstring
        """
        raise NotImplementedError(f"BigQueryDriver.execute is not yet implemented. {_NOT_IMPLEMENTED_HINT}")

    async def list_tables(self, schemas: list[str]) -> list[TableRow]:
        """list tables in the schema (dataset) allow-list -- NOT YET IMPLEMENTED.

        :raises NotImplementedError: stub method; see module docstring
        """
        raise NotImplementedError(f"BigQueryDriver.list_tables is not yet implemented. {_NOT_IMPLEMENTED_HINT}")

    async def list_columns(self, schemas: list[str]) -> list[ColumnRow]:
        """list columns via the BigQuery REST API -- NOT YET IMPLEMENTED.

        :raises NotImplementedError: stub method; see module docstring
        """
        raise NotImplementedError(f"BigQueryDriver.list_columns is not yet implemented. {_NOT_IMPLEMENTED_HINT}")

    async def table_hashes(self, schemas: list[str]) -> dict[tuple[str, str], str]:
        """per-table MD5 over column shape (computed python-side) -- NOT YET IMPLEMENTED.

        :raises NotImplementedError: stub method; see module docstring
        """
        raise NotImplementedError(f"BigQueryDriver.table_hashes is not yet implemented. {_NOT_IMPLEMENTED_HINT}")

    async def test_connection(self) -> None:
        """cheapest round-trip via metadata REST -- NOT YET IMPLEMENTED.

        :raises NotImplementedError: stub method; see module docstring
        """
        raise NotImplementedError(f"BigQueryDriver.test_connection is not yet implemented. {_NOT_IMPLEMENTED_HINT}")

    async def close(self) -> None:
        """release driver resources -- NOT YET IMPLEMENTED.

        :raises NotImplementedError: stub method; see module docstring
        """
        raise NotImplementedError(f"BigQueryDriver.close is not yet implemented. {_NOT_IMPLEMENTED_HINT}")
