"""
layout/page/loader.py
---------------------
JSON 資料載入與結構解析。
無任何 Dash / DMC 依賴，可獨立單元測試。

公開 API：
    load_json(source)               → {"blocks", "sections", "toc"}
    norm_id_or_none(raw)            → str | None
    build_toc_titles(blocks, toc)   → [{"id", "label", "level"}, ...]
"""

from __future__ import annotations
import os
import json
from typing import Any

# ---------------------------------------------------------------------------
# 檔案快取（process 層級，同一 JSON 只讀一次）
# ---------------------------------------------------------------------------
_cache: dict[str, dict] = {}

def _load_file_cached(path: str) -> dict:
    """讀取並快取 JSON 檔案，檔案未更動時直接回傳快取。"""
    try:
        mtime = os.path.getmtime(path)
    except OSError:
        return {}

    cached = _cache.get(path)
    if cached and cached.get("_mtime") == mtime:
        return cached["_data"]

    try:
        with open(path, "r", encoding="utf-8") as f:
            data = json.load(f)
    except Exception:
        data = {}

    _cache[path] = {"_mtime": mtime, "_data": data}
    return data


# ---------------------------------------------------------------------------
# 錯誤佔位文件
# ---------------------------------------------------------------------------

def _err_doc(msg: str) -> dict[str, Any]:
    return {"blocks": [{"type": "paragraph", "content": f"⚠ {msg}"}], "toc": []}


# ---------------------------------------------------------------------------
# 主要載入函式
# ---------------------------------------------------------------------------

def load_json(source: Any) -> dict[str, Any]:
    """
    接受多種來源，統一回傳 {"blocks": [...], "sections": [...], "toc": [...]}。

    source 可以是：
        - list / dict：直接使用
        - str / Path：當作檔案路徑讀取
    """
    if isinstance(source, (list, dict)):
        obj = source
    else:
        p = str(source or "").strip()
        if not p:
            return _err_doc("未提供 JSON 路徑")
        if not os.path.exists(p):
            return _err_doc(f"找不到 JSON：{p}")
        try:
            obj = _load_file_cached(p)
            if not obj:
                return _err_doc(f"讀取 JSON 失敗或為空：{p}")
        except Exception as e:
            return _err_doc(f"讀取 JSON 失敗：{e}")

    if isinstance(obj, list):
        return {"blocks": obj, "sections": [], "toc": []}

    if isinstance(obj, dict):
        blocks   = obj.get("blocks") or obj.get("doc") or obj.get("content") or []
        sections = obj.get("sections") or []
        toc      = obj.get("toc") or obj.get("TOC") or []

        if sections and isinstance(sections, list):
            return {"blocks": blocks, "sections": sections, "toc": toc}

        return {"blocks": blocks, "sections": [], "toc": toc}

    return _err_doc(f"不支援的 JSON 型別：{type(obj).__name__}")


# ---------------------------------------------------------------------------
# ID 正規化
# ---------------------------------------------------------------------------

def norm_id_or_none(raw: str | None) -> str | None:
    """
    把 URL fragment 或帶前綴的 id 字串還原成純 id。

    範例：
        '頁面#h-CH4-P2_id2' → 'CH4-P2_id2'
        '#h-foo'            → 'foo'
        'h-bar'             → 'bar'
        ''  / None          → None
    """
    if not raw:
        return None
    s = str(raw).strip()
    if not s:
        return None
    if "#" in s:
        s = s.split("#", 1)[1].strip()
    if s.startswith("h-"):
        s = s[2:]
    return s or None


# ---------------------------------------------------------------------------
# TOC 標題清單建立
# ---------------------------------------------------------------------------

def build_toc_titles(
    blocks: list[dict[str, Any]],
    raw_toc: list[Any],
) -> list[dict[str, Any]]:
    """
    回傳給 make_toc() 使用的 titles 清單：
        [{"id": str, "label": str, "level": int}, ...]

    優先使用 JSON 內嵌的 toc；若無，則從 blocks 的 heading 自動產生。
    """
    titles: list[dict[str, Any]] = []

    # 優先：JSON 內嵌 toc
    if isinstance(raw_toc, list) and raw_toc:
        for it in raw_toc:
            if not isinstance(it, dict):
                continue
            label = (
                it.get("title") or it.get("text") or it.get("label") or ""
            ).strip()
            nid   = norm_id_or_none(
                it.get("id") or it.get("href") or it.get("slug")
            )
            level = int(it.get("level") or 1)
            if not label or not nid:
                continue
            titles.append({"id": nid, "label": label, "level": max(1, min(level, 6))})
        return titles

    # 退回：從 blocks heading 產生
    for b in blocks or []:
        if (b.get("type") or "").lower() != "heading":
            continue
        nid = norm_id_or_none(b.get("id"))
        if not nid:
            continue
        label = (b.get("content") or "").strip()
        level = int(b.get("level") or 3)
        titles.append({
            "id": nid,
            "label": label or "(空白標題)",
            "level": max(1, min(level, 6)),
        })

    return titles