"""find_blender / run_blender_script：model_decimate 与 model_bake 共享的
headless Blender 运行器（与 model_translator.py 同模式，脚本名与参数泛化）。"""
import collections
import json
import os
import shutil
import subprocess
import sys

DEFAULT_BLENDER = r"D:\tools\blender-5.0.0-windows-x64\blender.exe"
HERE = os.path.dirname(os.path.abspath(__file__))


def find_blender(cli_arg):
    for cand in (cli_arg, os.environ.get("BLENDER_EXE"), DEFAULT_BLENDER,
                 shutil.which("blender")):
        if cand and os.path.isfile(cand):
            return cand
    sys.exit("找不到 blender.exe，请用 --blender 指定或设置环境变量 BLENDER_EXE")


def run_blender_script(blender, script, script_args, blender_args=()):
    """跑 HERE 下的 bl_*.py，返回 MT_SUMMARY JSON；失败或 summary 带 error 则退出。
    流式读子进程输出：`MT_PROGRESS ` 行实时转发到本进程 stdout（供上层 UI 显示阶段进度），
    `MT_SUMMARY ` 行解析为结果，其余行仅缓存尾部用于出错诊断。stderr 并入 stdout 防管道死锁。"""
    cmd = [blender, "-b", *blender_args, "--factory-startup",
           "--python", os.path.join(HERE, script), "--"] + list(script_args)
    proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
                            text=True, encoding="utf-8", errors="replace", bufsize=1)
    summary = None
    tail = collections.deque(maxlen=400)
    for line in proc.stdout:
        line = line.rstrip("\r\n")
        if line.startswith("MT_SUMMARY "):
            summary = json.loads(line[len("MT_SUMMARY "):])
        elif line.startswith("MT_PROGRESS "):
            print(line[len("MT_PROGRESS "):], flush=True)  # 实时透传给上层
        else:
            tail.append(line)
    proc.wait()
    if proc.returncode != 0 or summary is None or "error" in summary:
        sys.stderr.write("\n".join(tail)[-2000:] + "\n")
        err = summary["error"] if summary and "error" in summary else script
        sys.exit("Blender 执行失败：%s" % err)
    return summary