"""Symlink prepared S2 into a temp dir, omitting gap-window acquisitions (REFL/GCC + DIST)."""

from __future__ import annotations

import re
from datetime import date, datetime
from pathlib import Path

# Acquisition calendar day in prepared S2 names (BtI REFL/DIST; ItB GCC/DIST).
S2_PREP_DATE_RE = re.compile(r"_(\d{8})_(?:REFL|GCC|DIST_CLOUD)\.tif$", re.IGNORECASE)


def yyyymmdd_in_name(name: str) -> str | None:
    m = S2_PREP_DATE_RE.search(name)
    return m.group(1) if m else None


def yyyymmdd_from_iso(iso_d: str) -> str:
    return datetime.strptime(iso_d[:10], "%Y-%m-%d").strftime("%Y%m%d")


def acquisition_yyyymmdd_in_window(
    prepared_s2: Path, window_start: date, window_end: date
) -> set[str]:
    """All S2 acquisition days (from REFL filenames) inside [window_start, window_end]."""
    out: set[str] = set()
    if not prepared_s2.is_dir():
        return out
    for p in prepared_s2.glob("*REFL.tif"):
        m = re.search(r"S2A_MSIL2A_(\d{8})_REFL\.tif$", p.name)
        if not m:
            continue
        d = datetime.strptime(m.group(1), "%Y%m%d").date()
        if window_start <= d <= window_end:
            out.add(m.group(1))
    return out


def build_masked_s2_dir(
    prepared_s2: Path,
    excluded_yyyymmdd: set[str],
    dest: Path,
    patterns: tuple[str, ...],
) -> int:
    """Symlink all files matching ``patterns`` except excluded acquisition days."""
    dest.mkdir(parents=True, exist_ok=True)
    n = 0
    for pattern in patterns:
        for src in sorted(prepared_s2.glob(pattern)):
            if not src.is_file() and not src.is_symlink():
                continue
            y = yyyymmdd_in_name(src.name)
            if y and y in excluded_yyyymmdd:
                continue
            link = dest / src.name
            if link.exists() or link.is_symlink():
                link.unlink()
            link.symlink_to(src.resolve())
            n += 1
    return n


def assert_no_leakage(withheld_yyyymmdd: str, masked_s2_dir: Path) -> None:
    """Fail if the withheld validation acquisition is present in the fusion input dir."""
    for p in masked_s2_dir.iterdir():
        y = yyyymmdd_in_name(p.name)
        if y == withheld_yyyymmdd:
            raise RuntimeError(
                f"Data leakage: withheld acquisition {withheld_yyyymmdd} "
                f"found in masked S2 dir {masked_s2_dir}"
            )


def build_masked_s2_dir_bti(
    prepared_s2: Path,
    excluded_yyyymmdd: set[str],
    dest: Path,
) -> int:
    return build_masked_s2_dir(
        prepared_s2, excluded_yyyymmdd, dest, ("*REFL.tif", "*DIST_CLOUD.tif")
    )


def build_masked_s2_dir_itb(
    prepared_s2: Path,
    excluded_yyyymmdd: set[str],
    dest: Path,
) -> int:
    return build_masked_s2_dir(
        prepared_s2, excluded_yyyymmdd, dest, ("*GCC.tif", "*DIST_CLOUD.tif")
    )