"""Download ECMWF SEAS5.1 data for the configured Asia-Pacific PCA domain.

One initial month is one CDS request and one NetCDF file.  This makes the
1981-2020 baseline restartable: a completed file is never requested again
unless ``--overwrite`` is supplied.
"""
from __future__ import annotations

import argparse
import json
from pathlib import Path

from .config import PROJECT_ROOT
from .download_ecmwf import DATASET, lead_hours_through_lt7_boundary


def load_domain(path: str | Path = "config/ecmwf_domain.json") -> dict:
    source = Path(path)
    if not source.is_absolute():
        source = PROJECT_ROOT / source
    with source.open(encoding="utf-8") as handle:
        return json.load(handle)


def request_for(init: str, domain: dict, predictands_only: bool = False) -> dict:
    year, month = map(int, init.split("-"))
    groups = domain["variables"]
    variables = groups["predictands"] if predictands_only else groups["predictands"] + groups["predictors"]
    return {
        "originating_centre": domain["originating_centre"],
        "system": domain["system"],
        "variable": variables,
        "year": str(year),
        "month": f"{month:02d}",
        "day": "01",
        "leadtime_hour": lead_hours_through_lt7_boundary(year, month),
        "area": domain["area"],
        "data_format": "netcdf",
    }


def retrieve(init: str, output: Path, domain: dict, predictands_only: bool, overwrite: bool) -> Path:
    if output.exists() and not overwrite:
        print(f"Already exists; skipped: {output}")
        return output
    try:
        import cdsapi
    except ImportError as exc:
        raise SystemExit("cdsapi is required in the active Python environment.") from exc
    output.parent.mkdir(parents=True, exist_ok=True)
    cdsapi.Client().retrieve(DATASET, request_for(init, domain, predictands_only), str(output))
    return output


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--init", required=True, help="Initial month, formatted YYYY-MM")
    parser.add_argument("--predictands-only", action="store_true")
    parser.add_argument("--overwrite", action="store_true")
    parser.add_argument("--domain-config", default="config/ecmwf_domain.json")
    args = parser.parse_args()
    domain = load_domain(args.domain_config)
    suffix = "predictands" if args.predictands_only else "all"
    target = PROJECT_ROOT / "data/ecmwf/raw" / f"ecmwf_seas51_{args.init}_{suffix}.nc"
    print(retrieve(args.init, target, domain, args.predictands_only, args.overwrite))


if __name__ == "__main__":
    main()