"""Per-session preview images for the dataset README.

For each session, composites the GelSight stitched panorama (left) and the
D555 overhead with crop-grid overlay (right) into a single side-by-side PNG
at modest height so the README renders fast on the Hub.

Run after 01_crop_d555.py (which writes rgb_grid_debug.png):
    uv run python scripts/v1/03_make_previews.py

Outputs previews/v1/<session>.png.
"""

from __future__ import annotations

from pathlib import Path

import cv2
import numpy as np

REPO_ROOT = Path(__file__).resolve().parents[2]
SOURCE_DIR = REPO_ROOT / "source" / "v1"
PREVIEWS_DIR = REPO_ROOT / "previews" / "v1"

PREVIEW_HEIGHT = 400
GAP_PX = 16
BG = (255, 255, 255)


def _resize_to_height(img: np.ndarray, h: int) -> np.ndarray:
    w = int(round(img.shape[1] * h / img.shape[0]))
    return cv2.resize(img, (w, h), interpolation=cv2.INTER_AREA)


def make_preview(session_dir: Path) -> None:
    gel = cv2.imread(str(session_dir / "gelsight_stitched.png"))
    rgb = cv2.imread(str(session_dir / "rgb_grid_debug.png"))
    if gel is None or rgb is None:
        raise FileNotFoundError(f"missing preview source in {session_dir}")

    gel_r = _resize_to_height(gel, PREVIEW_HEIGHT)
    rgb_r = _resize_to_height(rgb, PREVIEW_HEIGHT)
    total_w = gel_r.shape[1] + GAP_PX + rgb_r.shape[1]
    canvas = np.full((PREVIEW_HEIGHT, total_w, 3), BG, dtype=np.uint8)
    canvas[:, : gel_r.shape[1]] = gel_r
    canvas[:, gel_r.shape[1] + GAP_PX :] = rgb_r

    out_path = PREVIEWS_DIR / f"{session_dir.name}.png"
    cv2.imwrite(str(out_path), canvas)
    print(f"  {out_path.name}: {canvas.shape[1]}x{canvas.shape[0]}")


def main() -> None:
    sessions = sorted(p for p in SOURCE_DIR.iterdir() if p.is_dir())
    if not sessions:
        raise SystemExit(f"no sessions found in {SOURCE_DIR}")
    PREVIEWS_DIR.mkdir(parents=True, exist_ok=True)
    print(f"writing previews for {len(sessions)} sessions -> {PREVIEWS_DIR}")
    for sess in sessions:
        make_preview(sess)


if __name__ == "__main__":
    main()