"""集中序列化工具（用于将执行结果中的复杂对象转换为 JSON 友好的预览格式）。

设计原则：
- 将 DataFrame/大对象的序列化集中到一个位置，便于维护与优化。
- 在同一次进程内尽量避免对相同对象重复序列化（基于 id 缓存），以减少 CPU/内存开销。
"""
from typing import Any, Dict

# 简单的按对象 id 缓存，避免在同一次执行中重复序列化同一对象。
# 这是一个进程级缓存，生命周期与进程相同；适用于短期请求场景。
_OBJ_SERIALIZE_CACHE: Dict[int, Any] = {}


def smart_serialize(value: Any, preview_limit: int = 20) -> Any:
    """Serialize outputs into JSON-friendly, preview-first representation.

    - Polars DataFrame -> {"__type":"DataFrame", "columns":..., "preview": [...], "rows": n}
    - list/tuple/dict -> recursively serialize
    - primitives -> pass through

    Caches serialization results per-object-id to avoid duplicate work within
    the same process/request.
    """
    cache_key = id(value)
    # Fast path: return cached serialization when available and object identity matches
    cached = _OBJ_SERIALIZE_CACHE.get(cache_key)
    if cached is not None and cached[0] is value:
        return cached[1]

    # Local import to avoid hard dependency at module import time
    try:
        import polars as pl
    except Exception:
        pl = None

    def _ser(v: Any) -> Any:
        # DataFrame
        if pl is not None and isinstance(v, pl.DataFrame):
            try:
                cols = list(v.columns)
                preview = v.head(preview_limit).to_dicts()
                return {
                    "__type": "DataFrame",
                    "columns": cols,
                    "preview": preview,
                    "rows": v.height,
                }
            except Exception:
                return {"__type": "DataFrame", "columns": [], "preview": [], "rows": 0}

        # list/tuple
        if isinstance(v, (list, tuple)):
            return [_ser(x) for x in v]

        # dict
        if isinstance(v, dict):
            return {k: _ser(val) for k, val in v.items()}

        # primitives
        try:
            if isinstance(v, (str, int, float, bool)) or v is None:
                return v
            import numpy as _np
            if isinstance(v, (_np.generic,)):
                return v.item()
        except Exception:
            pass

        # fallback to string
        try:
            return str(v)
        except Exception:
            return None

    result = _ser(value)
    try:
        _OBJ_SERIALIZE_CACHE[cache_key] = (value, result)
    except Exception:
        # ignore cache failures
        pass

    return result