#!/usr/bin/env python3
"""Cut a grid-based sprite sheet (rows x cols of equal-size frames in one
PNG) into the assets/sprites/<state>/frame_NN.png convention this project's
sprite loader expects.

Usage:
    python scripts/slice_spritesheet.py idle_sheet.png assets/sprites/idle --cols 6 --rows 1
"""

from __future__ import annotations

import argparse
from pathlib import Path

from PIL import Image


def slice_sheet(sheet_path: Path, out_dir: Path, cols: int, rows: int) -> int:
    sheet = Image.open(sheet_path).convert("RGBA")
    frame_w = sheet.width // cols
    frame_h = sheet.height // rows
    if frame_w == 0 or frame_h == 0:
        raise ValueError(f"sheet is {sheet.width}x{sheet.height}, too small for {cols}x{rows} frames")

    out_dir.mkdir(parents=True, exist_ok=True)
    count = 0
    for row in range(rows):
        for col in range(cols):
            box = (col * frame_w, row * frame_h, (col + 1) * frame_w, (row + 1) * frame_h)
            frame = sheet.crop(box)
            frame.save(out_dir / f"frame_{count:02d}.png")
            count += 1
    return count


def main() -> int:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("sheet", type=Path, help="path to the grid sprite sheet PNG")
    parser.add_argument("out_dir", type=Path, help="e.g. assets/sprites/idle")
    parser.add_argument("--cols", type=int, required=True)
    parser.add_argument("--rows", type=int, default=1)
    args = parser.parse_args()

    count = slice_sheet(args.sheet, args.out_dir, args.cols, args.rows)
    print(f"Wrote {count} frames to {args.out_dir}")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())