#!/usr/bin/env python3
"""Render a preview PNG for an OpenSCAD project folder.

Prefers OpenSCAD's native PNG export (needs a display or xvfb-run). Falls back
to PyVista offscreen rendering from an exported STL (no display required).

Usage:
    python3 scripts/render-preview.py ring-solar-siding-adapter
    python3 scripts/render-preview.py ring-solar-siding-adapter --output custom.png

Dependencies (fallback path only):
    pip install pyvista
    sudo apt install xvfb   # optional, enables native OpenSCAD PNG export
"""

from __future__ import annotations

import argparse
import shutil
import subprocess
import sys
import tempfile
from pathlib import Path

REPO_ROOT = Path(__file__).resolve().parents[1]


def find_scad(project_dir: Path) -> Path:
    matches = sorted(project_dir.glob("*.scad"))
    matches = [p for p in matches if not p.name.endswith(".backup.scad")]
    if len(matches) != 1:
        names = ", ".join(p.name for p in matches) or "(none)"
        raise SystemExit(f"Expected exactly one .scad in {project_dir}, found: {names}")
    return matches[0]


def export_stl(scad: Path, stl: Path) -> None:
    cmd = ["openscad", "--export-format=binstl", "-o", str(stl), str(scad)]
    result = subprocess.run(cmd, capture_output=True, text=True)
    if result.returncode != 0:
        sys.stderr.write(result.stderr or result.stdout)
        raise SystemExit(f"openscad STL export failed ({result.returncode})")


def render_openscad_png(scad: Path, png: Path, width: int, height: int) -> bool:
    """Return True if OpenSCAD wrote a PNG (requires display or xvfb-run)."""
    openscad = ["openscad", "--render", "--viewall", f"--imgsize={width},{height}"]
    xvfb = shutil.which("xvfb-run")
    cmd = ([xvfb, "-a"] if xvfb else []) + openscad + ["-o", str(png), str(scad)]
    result = subprocess.run(cmd, capture_output=True, text=True)
    if result.returncode == 0 and png.is_file() and png.stat().st_size > 0:
        return True
    if result.stderr:
        sys.stderr.write(result.stderr)
    return False


def render_pyvista_png(stl: Path, png: Path, width: int, height: int) -> None:
    try:
        import pyvista as pv
    except ImportError as exc:
        raise SystemExit(
            "No display for OpenSCAD PNG export and PyVista is not installed.\n"
            "Install one of:\n"
            "  sudo apt install xvfb          # native OpenSCAD previews\n"
            "  pip install pyvista            # headless fallback"
        ) from exc

    pv.OFF_SCREEN = True
    mesh = pv.read(stl)
    plotter = pv.Plotter(off_screen=True, window_size=(width, height))
    plotter.set_background("#1a2332")
    plotter.add_mesh(mesh, color="#6bb3dc", smooth_shading=True, show_edges=False)
    plotter.camera_position = "iso"
    png.parent.mkdir(parents=True, exist_ok=True)
    plotter.show(screenshot=str(png), auto_close=True)


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument(
        "project",
        type=Path,
        help="Project folder name or path (e.g. ring-solar-siding-adapter)",
    )
    parser.add_argument(
        "--output",
        type=Path,
        help="Output PNG path (default: <project>/preview.png)",
    )
    parser.add_argument("--width", type=int, default=1200)
    parser.add_argument("--height", type=int, default=900)
    parser.add_argument(
        "--force-fallback",
        action="store_true",
        help="Skip OpenSCAD PNG and use PyVista STL render",
    )
    args = parser.parse_args()

    project_dir = args.project
    if not project_dir.is_absolute():
        project_dir = REPO_ROOT / project_dir
    project_dir = project_dir.resolve()
    if not project_dir.is_dir():
        raise SystemExit(f"Project directory not found: {project_dir}")

    scad = find_scad(project_dir)
    png = args.output or (project_dir / "preview.png")
    if not png.is_absolute():
        png = project_dir / png

    if not args.force_fallback and render_openscad_png(scad, png, args.width, args.height):
        print(f"Wrote {png} (OpenSCAD)")
        return

    with tempfile.TemporaryDirectory() as tmp:
        stl = Path(tmp) / "preview.stl"
        export_stl(scad, stl)
        render_pyvista_png(stl, png, args.width, args.height)

    print(f"Wrote {png} (PyVista fallback)")


if __name__ == "__main__":
    main()