import argparse
import csv
import os
import shutil
from pathlib import Path


def parse_args() -> argparse.Namespace:
    parser = argparse.ArgumentParser(
        description="Split a flat image folder by source-video prefixes from CSV."
    )
    parser.add_argument(
        "--flat-root",
        type=Path,
        required=True,
        help="Flat folder with extracted images.",
    )
    parser.add_argument(
        "--split-csv",
        type=Path,
        required=True,
        help="CSV with recommended_split and flat_prefix columns.",
    )
    parser.add_argument(
        "--output-root",
        type=Path,
        required=True,
        help="Output folder that will contain train/valid/test.",
    )
    parser.add_argument(
        "--image-ext",
        default="jpg",
        help="Image extension in the flat folder, default: jpg.",
    )
    parser.add_argument(
        "--mode",
        choices=("hardlink", "copy"),
        default="hardlink",
        help="Write mode for split files. hardlink avoids doubling disk usage.",
    )
    parser.add_argument(
        "--overwrite",
        action="store_true",
        help="Remove existing output_root before writing.",
    )
    return parser.parse_args()


def load_split_rows(csv_path: Path) -> list[dict]:
    with csv_path.open("r", encoding="utf-8-sig", newline="") as f:
        rows = list(csv.DictReader(f))
    required = {"recommended_split", "flat_prefix"}
    if not rows:
        raise ValueError(f"No rows found in {csv_path}")
    missing = required - set(rows[0].keys())
    if missing:
        raise ValueError(f"Missing required CSV columns: {sorted(missing)}")
    return rows


def ensure_clean_dir(path: Path, overwrite: bool) -> None:
    if path.exists():
        if not overwrite:
            raise FileExistsError(
                f"Output path already exists: {path}. Use --overwrite to replace it."
            )
        shutil.rmtree(path)
    path.mkdir(parents=True, exist_ok=True)


def link_or_copy(src: Path, dst: Path, mode: str) -> str:
    if mode == "hardlink":
        try:
            os.link(src, dst)
            return "hardlink"
        except OSError:
            shutil.copy2(src, dst)
            return "copy_fallback"
    shutil.copy2(src, dst)
    return "copy"


def main() -> None:
    args = parse_args()
    rows = load_split_rows(args.split_csv)
    ext = args.image_ext.lower().lstrip(".")

    ensure_clean_dir(args.output_root, args.overwrite)
    manifest_path = args.output_root / "_split_manifest.csv"

    split_name_map = {
        "train": "train",
        "val": "valid",
        "valid": "valid",
        "test": "test",
    }

    total_written = 0
    total_missing = 0

    with manifest_path.open("w", encoding="utf-8-sig", newline="") as mf:
        writer = csv.DictWriter(
            mf,
            fieldnames=[
                "recommended_split",
                "output_split",
                "group_name",
                "file_name",
                "flat_prefix",
                "written_count",
                "missing",
                "write_mode",
            ],
        )
        writer.writeheader()

        for row in rows:
            split_raw = row["recommended_split"].strip().lower()
            output_split = split_name_map.get(split_raw)
            if output_split is None:
                raise ValueError(f"Unsupported split value: {row['recommended_split']}")

            prefix = row["flat_prefix"].strip()
            pattern = f"{prefix}__f*.{ext}"
            matches = sorted(args.flat_root.glob(pattern))

            out_dir = args.output_root / output_split
            out_dir.mkdir(parents=True, exist_ok=True)

            write_mode = ""
            for src in matches:
                dst = out_dir / src.name
                write_mode = link_or_copy(src, dst, args.mode)

            missing = 0 if matches else 1
            total_missing += missing
            total_written += len(matches)

            writer.writerow(
                {
                    "recommended_split": row["recommended_split"],
                    "output_split": output_split,
                    "group_name": row.get("group_name", ""),
                    "file_name": row.get("file_name", ""),
                    "flat_prefix": prefix,
                    "written_count": len(matches),
                    "missing": missing,
                    "write_mode": write_mode,
                }
            )

    print(f"output_root={args.output_root}")
    print(f"manifest={manifest_path}")
    print(f"total_written={total_written}")
    print(f"missing_prefixes={total_missing}")


if __name__ == "__main__":
    main()