const fs = require('fs');
const path = require('path');
const NodeStl = require('node-stl');
const AdmZip = require('adm-zip');

const THUMBNAIL_DIR = './thumbnails';

const MODEL_FORMATS = ['stl', '3mf', 'obj', 'step', 'stp', 'gcode', 'gco', 'zip'];

function ensureThumbnailDir() {
  if (!fs.existsSync(THUMBNAIL_DIR)) fs.mkdirSync(THUMBNAIL_DIR, { recursive: true });
}

function formatOf(filename) {
  return path.extname(filename).slice(1).toLowerCase();
}

function isAllowed(filename) {
  return MODEL_FORMATS.includes(formatOf(filename));
}

// Geometry metadata. Only STL is computed natively today; others return nulls
// (3MF/OBJ/STEP volume can be added later via a Python/trimesh sidecar).
function extractMetadata(filePath, format) {
  if (format !== 'stl') return { volume: null, bbox: null, facets: null };
  try {
    const stl = new NodeStl(filePath);
    const bb = stl.boundingBox; // [x, y, z]
    return {
      volume: Number.isFinite(stl.volume) ? stl.volume : null,
      bbox: Array.isArray(bb) ? { x: bb[0], y: bb[1], z: bb[2] } : null,
      facets: null, // node-stl does not expose facet count
    };
  } catch (err) {
    console.error('STL metadata extraction failed:', err.message);
    return { volume: null, bbox: null, facets: null };
  }
}

// A .3mf is a zip; slicers embed a PNG preview under /Metadata/. If present,
// pull it out as the model thumbnail. Returns a path under thumbnails/ or null.
function extract3mfThumbnail(filePath, baseName) {
  try {
    ensureThumbnailDir();
    const zip = new AdmZip(filePath);
    const entry = zip.getEntries().find((e) => {
      const n = e.entryName.toLowerCase();
      return n.endsWith('.png') && (n.includes('thumbnail') || n.includes('/metadata/'));
    });
    if (!entry) return null;
    const out = path.join(THUMBNAIL_DIR, `${baseName}.png`);
    fs.writeFileSync(out, entry.getData());
    return out;
  } catch (err) {
    console.error('3MF thumbnail extraction failed:', err.message);
    return null;
  }
}

module.exports = { MODEL_FORMATS, formatOf, isAllowed, extractMetadata, extract3mfThumbnail };