"""
Blender Python script for rendering a GLB file to PNG.
Targets Blender 5.0+ (EEVEE / Cycles).

Called by Blender:
  blender --background --python blender_render.py -- \
      <glb_path> <output_path> <width> <height> [engine] [samples]

engine: "cycles" (default) | "eevee"

Features:
- OCC-generated GLB: one mesh per STEP part, already in metres.
- Bounding-box-aware camera: object fills ~85 % of the frame.
- Isometric-style angle (elevation 28°, azimuth 40°).
- Dynamic clip planes.
- Standard (non-Filmic) colour management → no grey tint.
"""
import sys
import os
import math

# Force unbuffered stdout so render log lines appear immediately
os.environ["PYTHONUNBUFFERED"] = "1"
if hasattr(sys.stdout, "reconfigure"):
    sys.stdout.reconfigure(line_buffering=True)

import bpy
from mathutils import Vector, Matrix

# ── Colour palette (matches Three.js renderer) ───────────────────────────────

PALETTE_HEX = [
    "#4C9BE8", "#E85B4C", "#4CBE72", "#E8A84C", "#A04CE8",
    "#4CD4E8", "#E84CA8", "#7EC850", "#E86B30", "#5088C8",
]

def _srgb_to_linear(c: int) -> float:
    """Convert 0-255 sRGB integer to linear float."""
    v = c / 255.0
    return v / 12.92 if v <= 0.04045 else ((v + 0.055) / 1.055) ** 2.4

def _hex_to_linear(hex_color: str) -> tuple:
    """Return (r, g, b, 1.0) in Blender linear colour space."""
    h = hex_color.lstrip('#')
    return (
        _srgb_to_linear(int(h[0:2], 16)),
        _srgb_to_linear(int(h[2:4], 16)),
        _srgb_to_linear(int(h[4:6], 16)),
        1.0,
    )

PALETTE_LINEAR = [_hex_to_linear(h) for h in PALETTE_HEX]

# ── Parse arguments ───────────────────────────────────────────────────────────

argv = sys.argv
if "--" in argv:
    argv = argv[argv.index("--") + 1:]
else:
    argv = []

if len(argv) < 4:
    print("Usage: blender --background --python blender_render.py -- "
          "<glb_path> <output_path> <width> <height> [engine] [samples] [smooth_angle] [cycles_device] [transparent_bg]")
    sys.exit(1)

import json as _json

glb_path    = argv[0]
output_path = argv[1]
width       = int(argv[2])
height      = int(argv[3])
engine        = argv[4].lower() if len(argv) > 4 else "cycles"
samples       = int(argv[5])    if len(argv) > 5 else (64 if engine == "eevee" else 256)
smooth_angle  = int(argv[6])    if len(argv) > 6 else 30   # degrees; 0 = flat shading
cycles_device = argv[7].lower() if len(argv) > 7 else "auto"  # "auto", "gpu", "cpu"
transparent_bg = argv[8] == "1" if len(argv) > 8 else False
template_path  = argv[9]  if len(argv) > 9  and argv[9]  else ""
target_collection = argv[10] if len(argv) > 10 else "Product"
material_library_path = argv[11] if len(argv) > 11 and argv[11] else ""
material_map_raw = argv[12] if len(argv) > 12 else "{}"
try:
    material_map = _json.loads(material_map_raw) if material_map_raw else {}
except _json.JSONDecodeError:
    material_map = {}

part_names_ordered_raw = argv[13] if len(argv) > 13 else "[]"
try:
    part_names_ordered = _json.loads(part_names_ordered_raw) if part_names_ordered_raw else []
except _json.JSONDecodeError:
    part_names_ordered = []

lighting_only = argv[14] == "1" if len(argv) > 14 else False
shadow_catcher = argv[15] == "1" if len(argv) > 15 else False
rotation_x = float(argv[16]) if len(argv) > 16 else 0.0
rotation_y = float(argv[17]) if len(argv) > 17 else 0.0
rotation_z = float(argv[18]) if len(argv) > 18 else 0.0
noise_threshold_arg = argv[19] if len(argv) > 19 else ""
denoiser_arg = argv[20] if len(argv) > 20 else ""
denoising_input_passes_arg = argv[21] if len(argv) > 21 else ""
denoising_prefilter_arg = argv[22] if len(argv) > 22 else ""
denoising_quality_arg = argv[23] if len(argv) > 23 else ""
denoising_use_gpu_arg = argv[24] if len(argv) > 24 else ""

# Named argument: --mesh-attributes <json>
_mesh_attrs: dict = {}
_sys_argv = sys.argv
if "--mesh-attributes" in _sys_argv:
    _idx = _sys_argv.index("--mesh-attributes")
    try:
        _mesh_attrs = _json.loads(_sys_argv[_idx + 1])
    except Exception:
        pass

# Validate template path: if provided it MUST exist on disk.
# Fail loudly rather than silently rendering with factory settings.
if template_path and not os.path.isfile(template_path):
    print(f"[blender_render] ERROR: template_path was provided but file not found: {template_path}")
    print("[blender_render] Check that the blend-templates directory is on the shared volume.")
    sys.exit(1)

use_template = bool(template_path)

print(f"[blender_render] engine={engine}, samples={samples}, size={width}x{height}, smooth_angle={smooth_angle}°, device={cycles_device}, transparent={transparent_bg}")
print(f"[blender_render] part_names_ordered: {len(part_names_ordered)} entries")
if use_template:
    print(f"[blender_render] template={template_path}, collection={target_collection}, lighting_only={lighting_only}")
else:
    print("[blender_render] no template — using factory settings (Mode A)")
if material_library_path:
    print(f"[blender_render] material_library={material_library_path}, material_map keys={list(material_map.keys())}")

# ── Helper: find or create collection by name ────────────────────────────────

def _ensure_collection(name: str):
    """Return a collection by name, creating it if needed."""
    if name in bpy.data.collections:
        return bpy.data.collections[name]
    col = bpy.data.collections.new(name)
    bpy.context.scene.collection.children.link(col)
    return col


def _apply_smooth(part_obj, angle_deg):
    """Apply smooth or flat shading to a mesh object."""
    bpy.context.view_layer.objects.active = part_obj
    part_obj.select_set(True)
    if angle_deg > 0:
        try:
            bpy.ops.object.shade_smooth_by_angle(angle=math.radians(angle_deg))
        except AttributeError:
            bpy.ops.object.shade_smooth()
            part_obj.data.use_auto_smooth = True
            part_obj.data.auto_smooth_angle = math.radians(angle_deg)
    else:
        bpy.ops.object.shade_flat()


def _assign_palette_material(part_obj, index):
    """Assign a palette colour material to a mesh part."""
    color = PALETTE_LINEAR[index % len(PALETTE_LINEAR)]
    mat = bpy.data.materials.new(name=f"Part_{index}")
    mat.use_nodes = True
    bsdf = mat.node_tree.nodes.get("Principled BSDF")
    if bsdf:
        bsdf.inputs["Base Color"].default_value = color
        bsdf.inputs["Metallic"].default_value   = 0.35
        bsdf.inputs["Roughness"].default_value  = 0.40
        try:
            bsdf.inputs["Specular IOR Level"].default_value = 0.5
        except KeyError:
            pass
    part_obj.data.materials.clear()
    part_obj.data.materials.append(mat)


import re as _re


# _scale_mm_to_m removed: OCC GLB export produces coordinates in metres already.


def _apply_rotation(parts, rx, ry, rz):
    """Apply Euler rotation (degrees, XYZ order) to all parts around world origin.

    After _import_glb the combined bbox center is at world origin,
    so rotating around origin is equivalent to rotating around the assembly center.
    """
    if not parts or (rx == 0.0 and ry == 0.0 and rz == 0.0):
        return
    from mathutils import Euler
    rot_mat = Euler((math.radians(rx), math.radians(ry), math.radians(rz)), 'XYZ').to_matrix().to_4x4()
    for p in parts:
        p.matrix_world = rot_mat @ p.matrix_world
    # Bake rotation into mesh data so camera bbox calculations see the rotated geometry
    bpy.ops.object.select_all(action='DESELECT')
    for p in parts:
        p.select_set(True)
    bpy.context.view_layer.objects.active = parts[0]
    bpy.ops.object.transform_apply(location=False, rotation=True, scale=False)
    print(f"[blender_render] applied rotation ({rx}°, {ry}°, {rz}°) to {len(parts)} parts")


def _mark_sharp_and_seams(obj, smooth_angle_deg: float, sharp_edge_midpoints=None):
    """Mark sharp edges and UV seams based on angle threshold and optional midpoints."""
    import math
    import bpy

    # Ensure we're working with the right object
    bpy.context.view_layer.objects.active = obj
    obj.select_set(True)

    # Set auto-smooth angle
    if hasattr(obj.data, 'auto_smooth_angle'):
        obj.data.auto_smooth_angle = math.radians(smooth_angle_deg)

    # Enter edit mode to mark edges
    bpy.ops.object.mode_set(mode='EDIT')
    bpy.ops.mesh.select_all(action='DESELECT')

    # Select edges above threshold angle and mark sharp
    bpy.ops.mesh.edges_select_sharp(sharpness=math.radians(smooth_angle_deg))
    bpy.ops.mesh.mark_sharp()

    # Mark same edges as UV seams
    bpy.ops.mesh.mark_seam(clear=False)

    # If we have OCC-derived midpoints, try to mark additional edges
    if sharp_edge_midpoints and len(sharp_edge_midpoints) > 0:
        try:
            import bmesh
            bpy.ops.object.mode_set(mode='OBJECT')
            bm = bmesh.new()
            bm.from_mesh(obj.data)
            bm.edges.ensure_lookup_table()
            bm.verts.ensure_lookup_table()

            # Build KD-tree for edge midpoints
            import mathutils
            kd = mathutils.kdtree.KDTree(len(bm.edges))
            for i, edge in enumerate(bm.edges):
                midpt = (edge.verts[0].co + edge.verts[1].co) / 2
                kd.insert(midpt, i)
            kd.balance()

            # For each OCC sharp midpoint, find nearest Blender edge
            tol = 0.5  # 0.5 mm tolerance (coordinates in mm before scale)
            for mp in sharp_edge_midpoints[:200]:
                vec = mathutils.Vector(mp)
                co, idx, dist = kd.find(vec)
                if dist < tol:
                    bm.edges[idx].seam = True
                    try:
                        bm.edges[idx].smooth = False
                    except Exception:
                        pass

            bm.to_mesh(obj.data)
            bm.free()
        except Exception:
            pass  # Non-fatal

    # Return to object mode
    bpy.ops.object.mode_set(mode='OBJECT')


def _import_glb(glb_file):
    """Import OCC-generated GLB into Blender.

    OCC exports one mesh object per STEP part, already in metres.
    Blender's native GLTF importer preserves part names.

    Returns list of Blender mesh objects, centred at world origin.
    """
    bpy.ops.object.select_all(action='DESELECT')
    bpy.ops.import_scene.gltf(filepath=glb_file)
    parts = [o for o in bpy.context.selected_objects if o.type == 'MESH']

    if not parts:
        print(f"ERROR: No mesh objects imported from {glb_file}")
        sys.exit(1)

    print(f"[blender_render] imported {len(parts)} part(s) from GLB: "
          f"{[p.name for p in parts[:5]]}")

    # Centre combined bbox at world origin
    all_corners = []
    for p in parts:
        all_corners.extend(p.matrix_world @ Vector(c) for c in p.bound_box)

    if all_corners:
        mins = Vector((min(v.x for v in all_corners),
                       min(v.y for v in all_corners),
                       min(v.z for v in all_corners)))
        maxs = Vector((max(v.x for v in all_corners),
                       max(v.y for v in all_corners),
                       max(v.z for v in all_corners)))
        center = (mins + maxs) * 0.5
        for p in parts:
            p.location -= center

    return parts


def _resolve_part_name(index, part_obj):
    """Get the STEP part name for a Blender part by index.

    With GLB import, part_obj.name IS the STEP name (possibly with
    Blender .NNN suffix for duplicates). Strip that suffix for lookup.
    Falls back to part_names_ordered index mapping.
    """
    # Strip Blender auto-suffix (.001, .002, etc.)
    base_name = _re.sub(r'\.\d{3}$', '', part_obj.name)
    # If the base name looks like a real STEP part name (not generic "Cube" etc.),
    # use it directly
    if part_names_ordered and index < len(part_names_ordered):
        return part_names_ordered[index]
    return base_name


def _apply_material_library(parts, mat_lib_path, mat_map):
    """Append materials from library .blend and assign to parts via material_map.

    GLB-imported objects are named after STEP parts, so matching is by name
    (stripping Blender .NNN suffix for duplicates). Falls back to
    part_names_ordered index-based matching.

    mat_map: {part_name_lower: material_name}
    Parts without a match keep their current material.
    """
    if not mat_lib_path or not os.path.isfile(mat_lib_path):
        print(f"[blender_render] material library not found: {mat_lib_path}")
        return

    # Collect unique material names needed
    needed = set(mat_map.values())
    if not needed:
        return

    # Append materials from library
    appended = {}
    for mat_name in needed:
        inner_path = f"{mat_lib_path}/Material/{mat_name}"
        try:
            bpy.ops.wm.append(
                filepath=inner_path,
                directory=f"{mat_lib_path}/Material/",
                filename=mat_name,
                link=False,
            )
            if mat_name in bpy.data.materials:
                appended[mat_name] = bpy.data.materials[mat_name]
                print(f"[blender_render] appended material: {mat_name}")
            else:
                print(f"[blender_render] WARNING: material '{mat_name}' not found after append")
        except Exception as exc:
            print(f"[blender_render] WARNING: failed to append material '{mat_name}': {exc}")

    if not appended:
        return

    # Assign materials to parts — primary: name-based (GLB object names),
    # secondary: index-based via part_names_ordered
    assigned_count = 0
    unmatched_names = []
    for i, part in enumerate(parts):
        # Try name-based matching first (strip Blender .NNN suffix)
        base_name = _re.sub(r'\.\d{3}$', '', part.name)
        # Strip OCC assembly-instance suffix (_AF0, _AF1, …) — GLB object
        # names may or may not have them while mat_map keys might.
        _prev = None
        while _prev != base_name:
            _prev = base_name
            base_name = _re.sub(r'_AF\d+$', '', base_name, flags=_re.IGNORECASE)
        part_key = base_name.lower().strip()
        mat_name = mat_map.get(part_key)

        # Prefix fallback: if a mat_map key starts with our base name or
        # vice-versa, use the longest matching key (most-specific wins).
        if not mat_name:
            for key, val in sorted(mat_map.items(), key=lambda x: len(x[0]), reverse=True):
                if len(key) >= 5 and len(part_key) >= 5 and (
                    part_key.startswith(key) or key.startswith(part_key)
                ):
                    mat_name = val
                    break

        # Fall back to index-based matching via part_names_ordered
        if not mat_name and part_names_ordered and i < len(part_names_ordered):
            step_name = part_names_ordered[i]
            step_key = step_name.lower().strip()
            mat_name = mat_map.get(step_key)
            # Also try stripping AF from part_names_ordered entry
            if not mat_name:
                _p2 = None
                while _p2 != step_key:
                    _p2 = step_key
                    step_key = _re.sub(r'_af\d+$', '', step_key)
                mat_name = mat_map.get(step_key)

        if mat_name and mat_name in appended:
            part.data.materials.clear()
            part.data.materials.append(appended[mat_name])
            assigned_count += 1
            print(f"[blender_render] assigned '{mat_name}' to part '{part.name}'", flush=True)
        else:
            unmatched_names.append(part.name)

    print(f"[blender_render] material assignment: {assigned_count}/{len(parts)} parts matched", flush=True)
    if unmatched_names:
        print(f"[blender_render] unmatched parts (palette fallback): {unmatched_names[:10]}", flush=True)


# ── Early GPU activation (must happen BEFORE open_mainfile / Cycles init) ────
# Blender compiles Cycles kernels when the engine first initializes.  If the
# compute_device_type is NONE at that point, Cycles locks to CPU for the rest
# of the session.  We therefore probe + enable GPU devices NOW, before any
# .blend template (which may trigger Cycles init) is loaded.
def _activate_gpu():
    """Probe for GPU compute devices and activate them.  Returns device type or None."""
    if cycles_device == "cpu":
        return None
    try:
        cprefs = bpy.context.preferences.addons['cycles'].preferences
        for dt in ('OPTIX', 'CUDA', 'HIP', 'ONEAPI'):
            try:
                cprefs.compute_device_type = dt
                cprefs.get_devices()
                gpu = [d for d in cprefs.devices if d.type != 'CPU']
                if gpu:
                    for d in cprefs.devices:
                        d.use = (d.type != 'CPU')
                    print(f"[blender_render] early GPU activation: {dt}, "
                          f"devices={[(d.name, d.type) for d in gpu]}", flush=True)
                    return dt
            except Exception as e:
                print(f"[blender_render] {dt} not available: {e}", flush=True)
    except Exception as e:
        print(f"[blender_render] early GPU probe failed: {e}", flush=True)
    return None

_early_gpu_type = _activate_gpu()

# ── SCENE SETUP ──────────────────────────────────────────────────────────────

if use_template:
    # ── MODE B: Template-based render ────────────────────────────────────────
    print(f"[blender_render] Opening template: {template_path}")
    bpy.ops.wm.open_mainfile(filepath=template_path)

    # Find or create target collection
    target_col = _ensure_collection(target_collection)

    # Import OCC GLB (already in metres, one object per STEP part)
    parts = _import_glb(glb_path)
    # Apply render position rotation (before camera/bbox calculations)
    _apply_rotation(parts, rotation_x, rotation_y, rotation_z)

    # Move imported parts into target collection
    for part in parts:
        # Remove from all existing collections
        for col in list(part.users_collection):
            col.objects.unlink(part)
        target_col.objects.link(part)

    # Apply smooth shading (Blender 5.0+ shade_smooth_by_angle adds a geometry
    # node modifier that handles both smooth shading AND sharp edge marking
    # automatically — no need for the old _mark_sharp_and_seams edit-mode loop)
    import time as _time
    _t_smooth = _time.time()
    for _si, part in enumerate(parts):
        _apply_smooth(part, smooth_angle)
    print(f"[blender_render] smooth shading: {len(parts)} parts ({_time.time()-_t_smooth:.1f}s)", flush=True)

    # Material assignment: library materials if available, otherwise palette
    if material_library_path and material_map:
        # Build lowercased material_map for matching.
        # Include BOTH the original key AND the key with _AF\d+ stripped,
        # so GLB names (which may lack AF suffixes) can match.
        mat_map_lower = {}
        for k, v in material_map.items():
            kl = k.lower().strip()
            mat_map_lower[kl] = v
            # Also add AF-stripped version
            _stripped = kl
            _p = None
            while _p != _stripped:
                _p = _stripped
                _stripped = _re.sub(r'_af\d+$', '', _stripped)
            if _stripped != kl:
                mat_map_lower.setdefault(_stripped, v)
        _apply_material_library(parts, material_library_path, mat_map_lower)
        # Parts not matched by library get palette fallback
        for i, part in enumerate(parts):
            if not part.data.materials or len(part.data.materials) == 0:
                _assign_palette_material(part, i)
    else:
        for i, part in enumerate(parts):
            _assign_palette_material(part, i)

    # ── Shadow catcher (Cycles only, template mode only) ─────────────────────
    if shadow_catcher:
        sc_col_name = "Shadowcatcher"
        sc_obj_name = "Shadowcatcher"
        # Enable the Shadowcatcher collection in all view layers
        for vl in bpy.context.scene.view_layers:
            def _enable_col_recursive(layer_col):
                if layer_col.collection.name == sc_col_name:
                    layer_col.exclude = False
                    layer_col.collection.hide_render = False
                    layer_col.collection.hide_viewport = False
                    return True
                for child in layer_col.children:
                    if _enable_col_recursive(child):
                        return True
                return False
            _enable_col_recursive(vl.layer_collection)

        sc_obj = bpy.data.objects.get(sc_obj_name)
        if sc_obj:
            # Calculate product bbox min Z (world space)
            all_world_corners = []
            for part in parts:
                for corner in part.bound_box:
                    all_world_corners.append((part.matrix_world @ Vector(corner)).z)
            if all_world_corners:
                sc_obj.location.z = min(all_world_corners)
            print(f"[blender_render] shadow catcher enabled, plane Z={sc_obj.location.z:.4f}")
        else:
            print(f"[blender_render] WARNING: shadow catcher object '{sc_obj_name}' not found in template")

    # lighting_only: use template World/HDRI but force auto-camera UNLESS the shadow
    # catcher is enabled — in that case the template camera is already positioned to
    # show both the product and its shadow on the ground plane.
    needs_auto_camera = (lighting_only and not shadow_catcher) or not bpy.context.scene.camera
    if lighting_only and not shadow_catcher:
        print("[blender_render] lighting_only mode: using template World/HDRI, forcing auto-camera")
    elif needs_auto_camera:
        print("[blender_render] WARNING: template has no camera — will create auto-camera")

    # Set very close near clip on template camera for mm-scale parts (now in metres)
    if not needs_auto_camera and bpy.context.scene.camera:
        bpy.context.scene.camera.data.clip_start = 0.001

    print(f"[blender_render] template mode: {len(parts)} parts imported into collection '{target_collection}'")

else:
    # ── MODE A: Factory settings (original behavior) ─────────────────────────
    needs_auto_camera = True
    bpy.ops.wm.read_factory_settings(use_empty=True)
    # Import OCC GLB (already in metres, one object per STEP part)
    parts = _import_glb(glb_path)
    # Apply render position rotation (before camera/bbox calculations)
    _apply_rotation(parts, rotation_x, rotation_y, rotation_z)

    import time as _time
    _t_smooth_a = _time.time()
    for i, part in enumerate(parts):
        _apply_smooth(part, smooth_angle)
        _assign_palette_material(part, i)
    print(f"[blender_render] smooth+palette: {len(parts)} parts ({_time.time()-_t_smooth_a:.1f}s)", flush=True)

    # Apply material library on top of palette colours (same logic as Mode B).
    # material_library_path / material_map are parsed from argv even in Mode A
    # but were previously never used here — that was the bug.
    if material_library_path and material_map:
        mat_map_lower = {}
        for k, v in material_map.items():
            kl = k.lower().strip()
            mat_map_lower[kl] = v
            _stripped = kl
            _p = None
            while _p != _stripped:
                _p = _stripped
                _stripped = _re.sub(r'_af\d+$', '', _stripped)
            if _stripped != kl:
                mat_map_lower.setdefault(_stripped, v)
        _apply_material_library(parts, material_library_path, mat_map_lower)
        # Parts not matched by the library keep their palette material (already set above)

if needs_auto_camera:
    # ── Combined bounding box / bounding sphere ──────────────────────────────
    all_corners = []
    for part in parts:
        all_corners.extend(part.matrix_world @ Vector(c) for c in part.bound_box)

    bbox_min = Vector((
        min(v.x for v in all_corners),
        min(v.y for v in all_corners),
        min(v.z for v in all_corners),
    ))
    bbox_max = Vector((
        max(v.x for v in all_corners),
        max(v.y for v in all_corners),
        max(v.z for v in all_corners),
    ))

    bbox_center    = (bbox_min + bbox_max) * 0.5
    bbox_dims      = bbox_max - bbox_min
    bsphere_radius = max(bbox_dims.length * 0.5, 0.001)

    print(f"[blender_render] bbox_dims={tuple(round(d,4) for d in bbox_dims)}, "
          f"bsphere_radius={bsphere_radius:.4f}, center={tuple(round(c,4) for c in bbox_center)}")

    # ── Lighting — only in Mode A (factory settings) ─────────────────────────
    # In template mode the .blend file provides its own World/HDRI lighting.
    # Adding auto-lights would overpower the template's intended look.
    if not use_template:
        light_dist = bsphere_radius * 6.0

        bpy.ops.object.light_add(type='SUN', location=(
            bbox_center.x + light_dist * 0.5,
            bbox_center.y - light_dist * 0.35,
            bbox_center.z + light_dist,
        ))
        sun = bpy.context.active_object
        sun.data.energy = 4.0
        sun.rotation_euler = (math.radians(45), 0, math.radians(30))

        bpy.ops.object.light_add(type='AREA', location=(
            bbox_center.x - light_dist * 0.4,
            bbox_center.y + light_dist * 0.4,
            bbox_center.z + light_dist * 0.7,
        ))
        fill = bpy.context.active_object
        fill.data.energy = max(800.0, bsphere_radius ** 2 * 2000.0)
        fill.data.size   = max(4.0,   bsphere_radius * 4.0)

    # ── Camera ───────────────────────────────────────────────────────────────
    ELEVATION_DEG   = 28.0
    AZIMUTH_DEG     = 40.0
    LENS_MM         = 50.0
    SENSOR_WIDTH_MM = 36.0
    FILL_FACTOR     = 0.85

    elevation_rad = math.radians(ELEVATION_DEG)
    azimuth_rad   = math.radians(AZIMUTH_DEG)

    cam_dir = Vector((
        math.cos(elevation_rad) * math.cos(azimuth_rad),
        math.cos(elevation_rad) * math.sin(azimuth_rad),
        math.sin(elevation_rad),
    )).normalized()

    fov_h = math.atan(SENSOR_WIDTH_MM / (2.0 * LENS_MM))
    fov_v = math.atan(SENSOR_WIDTH_MM * (height / width) / (2.0 * LENS_MM))
    fov_used = min(fov_h, fov_v)

    dist = (bsphere_radius / math.tan(fov_used)) / FILL_FACTOR
    dist = max(dist, bsphere_radius * 1.5)
    print(f"[blender_render] camera dist={dist:.4f}, fov={math.degrees(fov_used):.2f}°")

    cam_location = bbox_center + cam_dir * dist
    bpy.ops.object.camera_add(location=cam_location)
    cam_obj = bpy.context.active_object
    cam_obj.data.lens = LENS_MM
    bpy.context.scene.camera = cam_obj

    look_dir = (bbox_center - cam_location).normalized()
    up_world = Vector((0.0, 0.0, 1.0))
    right    = look_dir.cross(up_world)
    if right.length < 1e-6:
        right = Vector((1.0, 0.0, 0.0))
    right.normalize()
    cam_up = right.cross(look_dir).normalized()

    rot_mat = Matrix((
        ( right.x,     right.y,     right.z),
        ( cam_up.x,    cam_up.y,    cam_up.z),
        (-look_dir.x, -look_dir.y, -look_dir.z),
    )).transposed()
    cam_obj.rotation_euler = rot_mat.to_euler('XYZ')

    cam_obj.data.clip_start = max(dist * 0.001, 0.0001)
    cam_obj.data.clip_end   = dist + bsphere_radius * 3.0
    print(f"[blender_render] clip {cam_obj.data.clip_start:.6f} … {cam_obj.data.clip_end:.4f}")

    # ── World background — only in Mode A ────────────────────────────────────
    # In template mode the .blend file owns its World (HDRI, sky texture, studio
    # lighting).  Overwriting it would destroy the HDR look the template was
    # designed to use (e.g. Alpha-HDR output types with Filmic tonemapping).
    if not use_template:
        world = bpy.data.worlds.new("World")
        bpy.context.scene.world = world
        world.use_nodes = True
        bg = world.node_tree.nodes["Background"]
        bg.inputs["Color"].default_value    = (0.96, 0.96, 0.97, 1.0)
        bg.inputs["Strength"].default_value = 0.15

# ── Render engine ─────────────────────────────────────────────────────────────
scene = bpy.context.scene

if engine == "eevee":
    # Blender 4.x used 'BLENDER_EEVEE_NEXT'; Blender 5.x reverted to 'BLENDER_EEVEE'.
    # Try both names so the script works across versions.
    set_ok = False
    for eevee_id in ('BLENDER_EEVEE', 'BLENDER_EEVEE_NEXT'):
        try:
            scene.render.engine = eevee_id
            set_ok = True
            print(f"[blender_render] EEVEE engine id: {eevee_id}")
            break
        except TypeError:
            continue

    if not set_ok:
        print("[blender_render] WARNING: could not set EEVEE engine – falling back to Cycles")
        engine = "cycles"

    if engine == "eevee":
        # Sample attribute name changed across minor versions
        for attr in ('taa_render_samples', 'samples'):
            try:
                setattr(scene.eevee, attr, samples)
                print(f"[blender_render] EEVEE samples: scene.eevee.{attr}={samples}")
                break
            except AttributeError:
                continue

if engine != "eevee":   # covers both explicit Cycles and EEVEE-fallback
    # ── GPU preferences (before engine activation) ───────────────────────
    # Set compute_device_type in preferences so Cycles can find GPU kernels.
    gpu_type_found = _activate_gpu() or _early_gpu_type

    # ── Activate Cycles engine ───────────────────────────────────────────
    scene.render.engine = 'CYCLES'

    # ── Device selection AFTER engine activation ─────────────────────────
    # IMPORTANT: scene.cycles.device must be set AFTER scene.render.engine
    # = 'CYCLES'.  Setting it before can be overwritten when Cycles inits
    # and reads the scene's saved properties (template may have device=CPU).
    if gpu_type_found:
        scene.cycles.device = 'GPU'
        # Re-ensure preferences are set (engine activation may have reset them)
        _activate_gpu()
        print(f"[blender_render] Cycles GPU ({gpu_type_found}), samples={samples}", flush=True)
    else:
        scene.cycles.device = 'CPU'
        print(f"[blender_render] WARNING: GPU not found — falling back to CPU, samples={samples}", flush=True)

    scene.cycles.samples       = samples
    scene.cycles.use_denoising = True
    scene.cycles.denoiser = denoiser_arg if denoiser_arg else 'OPENIMAGEDENOISE'
    if denoising_input_passes_arg:
        try: scene.cycles.denoising_input_passes = denoising_input_passes_arg
        except Exception: pass
    if denoising_prefilter_arg:
        try: scene.cycles.denoising_prefilter = denoising_prefilter_arg
        except Exception: pass
    if denoising_quality_arg:
        try: scene.cycles.denoising_quality = denoising_quality_arg
        except Exception: pass
    if denoising_use_gpu_arg:
        try: scene.cycles.denoising_use_gpu = (denoising_use_gpu_arg == "1")
        except AttributeError: pass
    if noise_threshold_arg:
        scene.cycles.use_adaptive_sampling = True
        scene.cycles.adaptive_threshold = float(noise_threshold_arg)

# ── Colour management ─────────────────────────────────────────────────────────
# In template mode the .blend file owns its colour management (e.g. Filmic/
# AgX for HDR, custom exposure for Alpha-HDR output types). Overwriting it
# would destroy the look the template was designed for.
# In factory-settings mode (Mode A) force Standard to avoid the grey Filmic
# tint that Blender applies by default.
if not use_template:
    scene.view_settings.view_transform = 'Standard'
    scene.view_settings.exposure        = 0.0
    scene.view_settings.gamma           = 1.0
    try:
        scene.view_settings.look = 'None'
    except Exception:
        pass

# ── Render settings ───────────────────────────────────────────────────────────
scene.render.resolution_x               = width
scene.render.resolution_y               = height
scene.render.resolution_percentage      = 100
scene.render.image_settings.file_format = 'PNG'
scene.render.filepath                   = output_path
scene.render.film_transparent           = transparent_bg

# ── Render ────────────────────────────────────────────────────────────────────
# Final verification of render device settings
if scene.render.engine == 'CYCLES':
    cprefs = bpy.context.preferences.addons['cycles'].preferences
    print(f"[blender_render] VERIFY: engine={scene.render.engine}, "
          f"cycles.device={scene.cycles.device}, "
          f"compute_device_type={cprefs.compute_device_type}, "
          f"gpu_devices={[(d.name, d.type, d.use) for d in cprefs.devices if d.type != 'CPU']}",
          flush=True)
print(f"[blender_render] Rendering → {output_path}  (Blender {bpy.app.version_string})", flush=True)
sys.stdout.flush()
bpy.ops.render.render(write_still=True)
print("[blender_render] render done.", flush=True)

print("[blender_render] Done.")