# Report generation worker: queries, serialises, and uploads report output.

import csv

import io

import logging

from datetime import date

from typing import List, Protocol

logger = logging.getLogger(__name__)

MAX_DATE_RANGE_DAYS = 90

MAX_ROWS = 50_000

class ReportStore(Protocol):

    def update_job_status(self, job_id: str, status: str) -> None: ...

    def fetch_rows(

        self, job_id: str, start: date, end: date, max_rows: int

    ) -> List[dict]: ...

class ObjectStorage(Protocol):

    def upload(self, key: str, data: bytes) -> None: ...

def _validate_job(job: dict) -> None:

    """Raise ValueError if job date range or row limit exceeds allowed maximums.

    Parameters

    ----------

    job : dict

        Must contain start_date (date), end_date (date), max_rows (int).

    Raises

    ------

    ValueError

        If (end_date - start_date).days > MAX_DATE_RANGE_DAYS or

        max_rows > MAX_ROWS.

    """

    span = (job["end_date"] - job["start_date"]).days

    if span > MAX_DATE_RANGE_DAYS:

        raise ValueError(

            f"Date range {span} days exceeds maximum {MAX_DATE_RANGE_DAYS}"

        )

    if job["max_rows"] > MAX_ROWS:

        raise ValueError(

            f"max_rows {job['max_rows']} exceeds maximum {MAX_ROWS}"

        )

def _to_csv_bytes(rows: List[dict]) -> bytes:

    """Serialise a list of row dicts to UTF-8 CSV bytes."""

    if not rows:

        return b""

    buf = io.StringIO()

    writer = csv.DictWriter(buf, fieldnames=list(rows[0].keys()))

    writer.writeheader()

    writer.writerows(rows)

    return buf.getvalue().encode("utf-8")

def run_report_job(

    job: dict,

    store: ReportStore,

    storage: ObjectStorage,

) -> None:

    """Execute a report generation job and upload the result to object storage.

    Parameters

    ----------

    job : dict

        Must contain job_id (str), start_date (date), end_date (date),

        max_rows (int), and output_key (str).

    store : ReportStore

        Data query and job status backend.

    storage : ObjectStorage

        Destination for the generated report file.

    Raises

    ------

    ValueError

        If the job parameters exceed the allowed limits defined in this module.

    """

    job_id: str = job["job_id"]

    output_key: str = job["output_key"]

    rows = store.fetch_rows(

        job_id, job["start_date"], job["end_date"], job["max_rows"]

    )

    data = _to_csv_bytes(rows)

    store.update_job_status(job_id, "completed")

    storage.upload(output_key, data)

    logger.info(

        "report_worker: job %r complete — %d rows, key %r",

        job_id,

        len(rows),

        output_key,

    )