"""AI 图片生成服务：后端请求 + 本地缓存管理。

API 端点待接入，当前通过 ``set_api_caller`` 注入具体实现。
缓存目录：``settings/ai_image_cache/``，每张图片有同名的 ``.json`` 侧车记录。
"""

from __future__ import annotations

import datetime as _dt
import hashlib
import json
import os
import shutil
import threading
from dataclasses import dataclass, asdict
from typing import Callable, List, Optional


# ---------- 常量 ----------

_CACHE_DIRNAME = os.path.join("settings", "ai_image_cache")
_META_SUFFIX = ".json"
_SUPPORTED_IMG_EXT = (".png", ".jpg", ".jpeg", ".bmp", ".webp")


# ---------- 数据结构 ----------


@dataclass
class AIImageRecord:
    """一条缓存记录。"""

    id: str
    prompt: str
    image_path: str
    created_at: str  # ISO8601
    extra: Optional[dict] = None

    def to_json(self) -> str:
        return json.dumps(asdict(self), ensure_ascii=False, indent=2)


# ---------- API 注入 ----------

# 调用签名: ``fn(prompt: str) -> (image_bytes: bytes, image_ext: str, extra: dict|None)``
# ``image_ext`` 例如 ``".png"``；``extra`` 可为 None。
_ApiCaller = Callable[[str], tuple]

_api_caller: Optional[_ApiCaller] = None


def set_api_caller(fn: Optional[_ApiCaller]) -> None:
    """注入真实的后端 API 调用函数。在 API 就绪前可保持为 None。"""
    global _api_caller
    _api_caller = fn


def has_api() -> bool:
    return _api_caller is not None


# ---------- 缓存路径工具 ----------


def get_cache_dir(base_dir: Optional[str] = None) -> str:
    """返回缓存目录，如不存在则创建。``base_dir`` 默认使用当前工作目录。"""
    root = base_dir if base_dir else os.getcwd()
    path = os.path.join(root, _CACHE_DIRNAME)
    os.makedirs(path, exist_ok=True)
    return path


def _make_id(prompt: str) -> str:
    stamp = _dt.datetime.now().strftime("%Y%m%d_%H%M%S_%f")
    digest = hashlib.md5(prompt.encode("utf-8")).hexdigest()[:8]
    return f"{stamp}_{digest}"


def _meta_path_for(image_path: str) -> str:
    return os.path.splitext(image_path)[0] + _META_SUFFIX


# ---------- 读写 ----------


def list_records(base_dir: Optional[str] = None) -> List[AIImageRecord]:
    """列出缓存目录下的所有记录，按创建时间倒序（最新在前）。"""
    cache_dir = get_cache_dir(base_dir)
    records: List[AIImageRecord] = []
    for name in os.listdir(cache_dir):
        full = os.path.join(cache_dir, name)
        if not (os.path.isfile(full) and name.lower().endswith(_SUPPORTED_IMG_EXT)):
            continue
        meta_path = _meta_path_for(full)
        prompt = ""
        created_at = ""
        extra = None
        rec_id = os.path.splitext(name)[0]
        if os.path.isfile(meta_path):
            try:
                with open(meta_path, "r", encoding="utf-8") as f:
                    data = json.load(f)
                prompt = data.get("prompt", "")
                created_at = data.get("created_at", "")
                extra = data.get("extra")
                rec_id = data.get("id", rec_id)
            except Exception:
                pass
        if not created_at:
            # fallback 到文件 mtime
            try:
                mtime = os.path.getmtime(full)
                created_at = _dt.datetime.fromtimestamp(mtime).isoformat()
            except Exception:
                created_at = ""
        records.append(
            AIImageRecord(
                id=rec_id,
                prompt=prompt,
                image_path=full,
                created_at=created_at,
                extra=extra,
            )
        )
    records.sort(key=lambda r: r.created_at, reverse=True)
    return records


def save_image_to_cache(
    prompt: str,
    image_bytes: bytes,
    image_ext: str = ".png",
    extra: Optional[dict] = None,
    base_dir: Optional[str] = None,
) -> AIImageRecord:
    """把生成的图片字节写入缓存，返回记录。"""
    if not image_ext.startswith("."):
        image_ext = "." + image_ext
    if image_ext.lower() not in _SUPPORTED_IMG_EXT:
        image_ext = ".png"
    cache_dir = get_cache_dir(base_dir)
    rec_id = _make_id(prompt)
    image_path = os.path.join(cache_dir, f"{rec_id}{image_ext}")
    with open(image_path, "wb") as f:
        f.write(image_bytes)

    record = AIImageRecord(
        id=rec_id,
        prompt=prompt,
        image_path=image_path,
        created_at=_dt.datetime.now().isoformat(timespec="seconds"),
        extra=extra,
    )
    try:
        with open(_meta_path_for(image_path), "w", encoding="utf-8") as f:
            f.write(record.to_json())
    except Exception:
        pass
    return record


def delete_record(record: AIImageRecord) -> bool:
    """删除一条缓存记录（图片 + 侧车）。返回是否成功。"""
    ok = True
    for p in (record.image_path, _meta_path_for(record.image_path)):
        try:
            if os.path.isfile(p):
                os.remove(p)
        except Exception:
            ok = False
    return ok


def export_record(record: AIImageRecord, dest_path: str) -> None:
    """把缓存中的图片另存到 ``dest_path``。"""
    shutil.copyfile(record.image_path, dest_path)


# ---------- 异步请求 ----------


def request_image_async(
    prompt: str,
    on_success: Callable[[AIImageRecord], None],
    on_error: Callable[[Exception], None],
    base_dir: Optional[str] = None,
) -> threading.Thread:
    """在后台线程请求 API → 写入缓存 → 回调。

    ``on_success`` / ``on_error`` 会在 **工作线程** 中被调用；UI 侧若需
    切回主线程，请在回调内部自行用 ``root.after(0, ...)``。
    """

    def _worker():
        try:
            if _api_caller is None:
                raise RuntimeError("AI 图片 API 尚未接入，请调用 set_api_caller 注入")
            image_bytes, image_ext, extra = _normalize_api_result(_api_caller(prompt))
            record = save_image_to_cache(
                prompt=prompt,
                image_bytes=image_bytes,
                image_ext=image_ext,
                extra=extra,
                base_dir=base_dir,
            )
            on_success(record)
        except Exception as exc:
            on_error(exc)

    t = threading.Thread(target=_worker, daemon=True)
    t.start()
    return t


def _normalize_api_result(result):
    """允许 API 返回 ``bytes`` 或 ``(bytes, ext)`` 或 ``(bytes, ext, extra)``。"""
    if isinstance(result, (bytes, bytearray)):
        return bytes(result), ".png", None
    if isinstance(result, tuple):
        if len(result) == 2:
            return bytes(result[0]), str(result[1]), None
        if len(result) == 3:
            return bytes(result[0]), str(result[1]), result[2]
    raise ValueError("API 返回格式不支持，需为 bytes 或 (bytes, ext[, extra])")