"""Blender 内运行：FBX 减面到指定三角面数 + Smart UV 重展。
调用：blender -b --factory-startup --python bl_decimate.py -- <src.fbx> <out.fbx> <target_tris>
"""
import os
import sys

sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))

TOLERANCE = 0.03    # 面数相对误差容忍
MAX_RETRY = 2       # ratio 修正轮数上限


def decimate_ratio(target, cur):
    """Decimate collapse ratio；cur <= target 或非法时返回 1.0（不减面）。"""
    if cur <= 0 or cur <= target:
        return 1.0
    return target / float(cur)


def within_tolerance(target, actual, tol=TOLERANCE):
    """减面结果是否落在目标 ±tol 内。"""
    if target <= 0:
        return False
    return abs(actual - target) <= target * tol


# ---------------- 以下仅在 Blender 内执行 ----------------


def join_meshes(objs):
    """多 mesh join 成单对象，返回结果对象（bl_bake 复用）。"""
    import bpy
    bpy.ops.object.select_all(action='DESELECT')
    for o in objs:
        o.select_set(True)
    bpy.context.view_layer.objects.active = objs[0]
    if len(objs) > 1:
        bpy.ops.object.join()
    return bpy.context.view_layer.objects.active


def _apply_modifier(obj, mod):
    import bpy
    bpy.context.view_layer.objects.active = obj
    bpy.ops.object.modifier_apply(modifier=mod.name)


def _triangulate(obj):
    mod = obj.modifiers.new("mt_tri", 'TRIANGULATE')
    _apply_modifier(obj, mod)


def _decimate(obj, ratio):
    mod = obj.modifiers.new("mt_dec", 'DECIMATE')
    mod.decimate_type = 'COLLAPSE'
    mod.ratio = ratio
    mod.use_collapse_triangulate = True
    _apply_modifier(obj, mod)


def _smart_unwrap(obj):
    """删旧 UV 层后 Smart UV Project 重展。island_margin 0.002 ≈ 2048 图 4px。"""
    import bpy
    import math
    mesh = obj.data
    while mesh.uv_layers:
        mesh.uv_layers.remove(mesh.uv_layers[0])
    bpy.context.view_layer.objects.active = obj
    bpy.ops.object.mode_set(mode='EDIT')
    bpy.ops.mesh.select_all(action='SELECT')
    bpy.ops.uv.smart_project(angle_limit=math.radians(66.0), island_margin=0.002)
    bpy.ops.object.mode_set(mode='OBJECT')


def main():
    import bpy
    import json
    argv = sys.argv[sys.argv.index("--") + 1:]
    src, out_fbx, target = argv[0], argv[1], int(argv[2])
    warnings = []

    bpy.ops.wm.read_factory_settings(use_empty=True)
    bpy.ops.import_scene.fbx(filepath=src)

    meshes = [o for o in bpy.data.objects if o.type == 'MESH']
    skipped = [o.name for o in bpy.data.objects if o.type != 'MESH']
    if skipped:
        warnings.append("忽略非 mesh 对象：%s（本工具只处理静态网格）" % ", ".join(skipped))
    if not meshes:
        print("MT_SUMMARY " + json.dumps({"error": "FBX 中没有 mesh"}, ensure_ascii=False))
        return
    obj = join_meshes(meshes)

    _triangulate(obj)
    orig = len(obj.data.polygons)
    cur = orig
    if cur <= target:
        warnings.append("当前 %d 面 <= 目标 %d，跳过减面" % (cur, target))
    else:
        # collapse 结果是近似值；未达容差时按新面数修正 ratio 再来，最多 MAX_RETRY 轮
        for _ in range(1 + MAX_RETRY):
            _decimate(obj, decimate_ratio(target, cur))
            _triangulate(obj)  # collapse triangulate 后仍可能残留非三角面
            cur = len(obj.data.polygons)
            if within_tolerance(target, cur) or cur <= target:
                break
        # 重试用尽仍超差且偏多：记录警告，交由上层决定是否可接受
        if not within_tolerance(target, cur) and cur > target:
            warnings.append("修正 %d 轮后仍超差：%d 面（目标 %d ±3%%）" % (MAX_RETRY, cur, target))

    _smart_unwrap(obj)
    out_dir = os.path.dirname(os.path.abspath(out_fbx))
    os.makedirs(out_dir, exist_ok=True)
    # 仅导出合并后的对象；整场景导出会把 armature/empty 等非 mesh 带进 _low.fbx
    bpy.ops.export_scene.fbx(filepath=out_fbx, use_selection=True,
                             path_mode='STRIP', embed_textures=False)

    print("MT_SUMMARY " + json.dumps(
        {"src": os.path.basename(src), "fbx": os.path.basename(out_fbx),
         "tris_before": orig, "tris_after": cur, "target": target,
         "warnings": warnings}, ensure_ascii=False))


if __name__ == "__main__" and "--" in sys.argv:
    main()