"""角色头像文件服务。

职责：
- 上传头像文件到本地文件系统
- 提供头像文件流
- 清理头像文件
"""

from __future__ import annotations

from pathlib import Path

from fastapi.responses import FileResponse

from app.core.config import settings
from app.core.errors import AppError
from app.services.characters import get_owned_character

_ALLOWED_EXTENSIONS = frozenset({".jpg", ".jpeg", ".png", ".webp"})
_MAX_FILE_SIZE = 5 * 1024 * 1024  # 5MB


def _avatar_path(character_id: str) -> Path:
    """获取角色头像文件路径（无扩展名，需遍历查找实际文件）。"""
    return settings.resolved_avatar_dir / character_id


def _find_avatar_file(character_id: str) -> Path | None:
    """查找角色已有的头像文件（任一格式）。"""
    base = _avatar_path(character_id)
    for ext in _ALLOWED_EXTENSIONS:
        f = base.with_suffix(ext)
        if f.exists():
            return f
    return None


def _allowed(content_type: str) -> bool:
    return content_type in {
        "image/jpeg",
        "image/png",
        "image/webp",
    }


async def upload_avatar(
    character_id: str,
    content: bytes,
    content_type: str,
    owner_scope: str = settings.default_owner_scope,
) -> str:
    """上传角色头像。

    Args:
        character_id: 角色 ID
        content: 图片文件二进制内容
        content_type: MIME 类型
        owner_scope: 归属范围

    Returns:
        头像访问的相对 URL 路径

    Raises:
        AppError: 文件类型不允许、大小超限、角色不存在
    """
    from app.db.session import AsyncSessionLocal

    # 校验角色存在性
    async with AsyncSessionLocal() as session:
        await get_owned_character(session, character_id, owner_scope=owner_scope)

    if not _allowed(content_type):
        raise AppError(
            "invalid_input",
            f"不支持的文件类型 '{content_type}'，仅支持 JPG/PNG/WebP。",
        )
    if len(content) > _MAX_FILE_SIZE:
        raise AppError(
            "invalid_input",
            "头像文件过大，最大允许 5MB。",
        )

    # 扩展名映射
    ext_map = {
        "image/jpeg": ".jpg",
        "image/png": ".png",
        "image/webp": ".webp",
    }
    ext = ext_map[content_type]

    # 删除旧头像
    old = _find_avatar_file(character_id)
    if old:
        old.unlink(missing_ok=True)

    # 写入新文件
    dest = _avatar_path(character_id).with_suffix(ext)
    dest.parent.mkdir(parents=True, exist_ok=True)
    dest.write_bytes(content)

    return f"/api/v1/characters/{character_id}/avatar"


async def get_avatar_response(character_id: str) -> FileResponse:
    """获取角色头像文件响应。

    Args:
        character_id: 角色 ID

    Returns:
        FileResponse 或 None（无头像时抛出 not_found）
    """
    avatar_file = _find_avatar_file(character_id)
    if avatar_file is None:
        raise AppError("not_found", "该角色未设置头像。")
    # 推测 media_type
    ext = avatar_file.suffix.lower()
    media_type = {
        ".jpg": "image/jpeg",
        ".jpeg": "image/jpeg",
        ".png": "image/png",
        ".webp": "image/webp",
    }.get(ext, "application/octet-stream")
    return FileResponse(str(avatar_file), media_type=media_type)


async def delete_avatar(character_id: str) -> None:
    """删除角色头像文件。"""
    avatar_file = _find_avatar_file(character_id)
    if avatar_file:
        avatar_file.unlink(missing_ok=True)