// PROCITY Lane C — draw-call batcher (round 6, decision #2: ≤350 draws/room is law).
//
// Interiors were 1 draw per stock item (a book barn = ~600 spine meshes; a multi-material box cost
// one draw PER face). Two-tier merge collapses hundreds of draws into dozens:
//
//   • STOCK (products: sleeves/spines/boxes/garments/snacks/treasures — tagged userData.isStock) is
//     merged at the ROOM level, grouped by material, across ALL fittings. World transforms are baked
//     so the merged meshes sit in the room group. A hall full of clothes racks → ~8 garment meshes
//     total, not ~8 per rack.
//   • FIXTURE frames (shelf uprights, cabinets, counters) are merged WITHIN each fitting group, so the
//     group + its userData survive (record bins stay raycast targets for ?dig=1) and the GLB upgrade
//     can still hide the fixture (isFrame) while the room-level stock rides on top of the GLB.
//
// Constraints honoured: determinism (merge follows deterministic child order), dig-compat (bins keep
// their frame as a hit target; the dig regenerates its own sleeves), leak-free (merged geometries are
// ctx-tracked, clones disposed immediately), keeper/stock/API contracts unchanged. Meshes whose
// material is unique in their scope are LEFT in place (nothing to merge).

import { mergeGeometries } from 'three/addons/utils/BufferGeometryUtils.js';

// A visual signature for a single-material mesh; same key ⇒ mergeable into one draw.
function matKey(m) {
  if (!m || Array.isArray(m)) return null;   // multi-material meshes are not merged (there are none post-fix)
  const c = m.color ? m.color.getHexString() : '------';
  const map = m.map ? m.map.uuid : '';
  return `${map}|${c}|${m.transparent ? 1 : 0}|${m.side}|${m.alphaTest || 0}|${m.emissive ? m.emissive.getHexString() : ''}`;
}

// Merge each material bucket of ≥2 meshes into one mesh appended to `target`; ≤1 stays put.
// `bake(mesh)` returns the geometry-space matrix for a mesh (room-local for stock, group-local for frames).
function flushBuckets(ctx, target, buckets, stockTag, bake) {
  const THREE = ctx.THREE;
  let saved = 0;
  for (const b of buckets.values()) {
    if (b.meshes.length < 2) continue;                       // unique material — leave the mesh in place
    const geos = b.meshes.map(m => { const g = m.geometry.clone(); g.applyMatrix4(bake(m)); return g; });
    let merged;
    try { merged = mergeGeometries(geos, false); } catch (e) { merged = null; }
    geos.forEach(g => g.dispose());
    if (!merged) continue;
    ctx._geometries.add(merged);
    for (const m of b.meshes) m.parent && m.parent.remove(m);
    const mm = new THREE.Mesh(merged, b.material);
    mm.userData = stockTag ? { isStock: true, batched: true } : { isFrame: true, batched: true };
    target.add(mm);
    saved += b.meshes.length - 1;
  }
  return saved;
}

function bucketPush(map, key, mesh) {
  let b = map.get(key); if (!b) { b = { material: mesh.material, meshes: [] }; map.set(key, b); }
  b.meshes.push(mesh);
}

export function batchRoom(ctx, roomGroup) {
  const THREE = ctx.THREE;
  roomGroup.updateMatrixWorld(true);
  const roomInv = roomGroup.matrixWorld.clone().invert();
  const stock = new Map();                 // room-level stock, keyed by material
  const frames = [];                       // [{group, buckets}] per fitting

  for (const fit of roomGroup.children) {
    if (!fit.isGroup) continue;            // shell meshes + wall decor stay as-is
    fit.updateMatrixWorld(true);
    const frame = new Map();
    for (const mesh of fit.children) {
      if (!mesh.isMesh) continue;
      const key = matKey(mesh.material);
      if (key == null || (mesh.userData && mesh.userData.noBatch)) continue;
      if (mesh.userData && mesh.userData.isStock) bucketPush(stock, key, mesh);
      else bucketPush(frame, key, mesh);
    }
    frames.push({ group: fit, buckets: frame });
  }

  const tmp = new THREE.Matrix4();
  const stockBake = (m) => { m.updateMatrixWorld(true); return tmp.multiplyMatrices(roomInv, m.matrixWorld); };
  const frameBake = (m) => { m.updateMatrix(); return m.matrix; };

  let saved = flushBuckets(ctx, roomGroup, stock, true, stockBake);        // room-level stock
  for (const f of frames) saved += flushBuckets(ctx, f.group, f.buckets, false, frameBake);  // per-fitting frames
  return saved;
}