#!/usr/bin/env python3
"""Split rgb/seg/depth into train/val/test splits.

Default split: 400 / 80 / 20  (80% / 16% / 4% of 500)
All modalities share exactly the same random stems.

Usage:
    python split_train_val.py                        # default 400/80/20, copy
    python split_train_val.py --n-train 400 --n-val 80 --n-test 20
    python split_train_val.py --move --force         # move files, overwrite existing
    python split_train_val.py --dry-run              # print counts only
"""
import argparse
import random
import shutil
from pathlib import Path

MODALITIES = ("rgb", "depth", "seg")
SPLITS = ("train", "val", "test")
IMAGE_SUFFIXES = {".tif", ".tiff", ".png", ".jpg", ".jpeg", ".bmp", ".webp", ".jp2", ".gif"}


def list_images(folder: Path):
    return [p for p in folder.iterdir() if p.is_file() and p.suffix.lower() in IMAGE_SUFFIXES]


def build_stem_map(folder: Path):
    mapping = {}
    for p in list_images(folder):
        if p.stem in mapping:
            raise RuntimeError(f"Duplicate stem in {folder}: {p.stem}")
        mapping[p.stem] = p
    return mapping


def ensure_dirs(root: Path):
    for split in SPLITS:
        for m in MODALITIES:
            (root / split / m).mkdir(parents=True, exist_ok=True)


def clear_split_dirs(root: Path):
    for split in SPLITS:
        d = root / split
        if d.exists():
            shutil.rmtree(d)


def copy_or_move(src: Path, dst: Path, do_move: bool):
    if do_move:
        shutil.move(str(src), str(dst))
    else:
        shutil.copy2(src, dst)


def main():
    parser = argparse.ArgumentParser(
        description="Split rgb/depth/seg into train/val/test splits."
    )
    parser.add_argument("--root", type=Path, default=Path(__file__).resolve().parent,
                        help="Dataset root containing rgb/depth/seg. Default: script dir.")
    parser.add_argument("--n-train", type=int, default=400,
                        help="Number of train samples. Default: 400")
    parser.add_argument("--n-val", type=int, default=80,
                        help="Number of val samples. Default: 80")
    parser.add_argument("--n-test", type=int, default=20,
                        help="Number of test samples. Default: 20")
    parser.add_argument("--seed", type=int, default=42,
                        help="Random seed for reproducibility. Default: 42")
    parser.add_argument("--move", action="store_true",
                        help="Move files instead of copying.")
    parser.add_argument("--force", action="store_true",
                        help="Remove existing train/val/test folders before split.")
    parser.add_argument("--dry-run", action="store_true",
                        help="Only print split summary without writing files.")
    args = parser.parse_args()

    root = args.root.resolve()

    # Build stem maps for each modality
    source_maps = {}
    for m in MODALITIES:
        folder = root / m
        if not folder.exists() or not folder.is_dir():
            raise FileNotFoundError(f"Missing folder: {folder}")
        source_maps[m] = build_stem_map(folder)

    # Intersection of stems across all modalities
    common_stems = set(source_maps[MODALITIES[0]].keys())
    for m in MODALITIES[1:]:
        common_stems &= set(source_maps[m].keys())

    if not common_stems:
        raise RuntimeError("No common stems across rgb/depth/seg")

    for m in MODALITIES:
        missing = set(source_maps[m].keys()) - common_stems
        if missing:
            print(f"[WARN] {m}: {len(missing)} files excluded (no match in other modalities)")

    n_total = len(common_stems)
    n_train = args.n_train
    n_val = args.n_val
    n_test = args.n_test
    n_requested = n_train + n_val + n_test

    if n_requested > n_total:
        raise ValueError(
            f"Requested {n_train}+{n_val}+{n_test}={n_requested} samples "
            f"but only {n_total} common stems available."
        )
    if n_requested < n_total:
        print(f"[WARN] {n_total - n_requested} samples will be left unassigned "
              f"(total={n_total}, requested={n_requested}). They will be ignored.")

    # Shuffle deterministically then slice
    stems = sorted(common_stems)
    rnd = random.Random(args.seed)
    rnd.shuffle(stems)

    train_stems = set(stems[:n_train])
    val_stems   = set(stems[n_train:n_train + n_val])
    test_stems  = set(stems[n_train + n_val:n_train + n_val + n_test])

    print(f"[INFO] root    : {root}")
    print(f"[INFO] total   : {n_total} common stems")
    print(f"[INFO] split   : train={n_train}, val={n_val}, test={n_test}")
    print(f"[INFO] mode    : {'move' if args.move else 'copy'}")
    print(f"[INFO] seed    : {args.seed}")

    if args.dry_run:
        print("[INFO] dry-run only — no files written")
        return

    if args.force:
        clear_split_dirs(root)
    else:
        for split in SPLITS:
            split_dir = root / split
            if split_dir.exists() and any(split_dir.rglob("*")):
                raise RuntimeError(
                    f"{split_dir} already exists and is non-empty. Use --force to overwrite."
                )

    ensure_dirs(root)

    stem_to_split = {}
    for s in train_stems:
        stem_to_split[s] = "train"
    for s in val_stems:
        stem_to_split[s] = "val"
    for s in test_stems:
        stem_to_split[s] = "test"

    written = {"train": 0, "val": 0, "test": 0}
    for m in MODALITIES:
        for stem, src in source_maps[m].items():
            split = stem_to_split.get(stem)
            if split is None:
                continue  # unassigned surplus
            dst = root / split / m / src.name
            copy_or_move(src, dst, args.move)
            written[split] += 1

    total_written = sum(written.values())
    print(f"[OK]  written  : {total_written} files total  "
          f"(train={written['train']}, val={written['val']}, test={written['test']})")
    print("[OK]  done.")


if __name__ == "__main__":
    main()