"""OEM 品牌图：落盘至项目根目录 images/，库内仅存相对路径。"""

from __future__ import annotations

import base64
import re
import uuid
from pathlib import Path

PROJECT_ROOT = Path(__file__).resolve().parents[2]
IMAGES_DIR = PROJECT_ROOT / "images"

DATA_URL_PATTERN = re.compile(r"^data:image/([\w+.-]+);base64,(.+)$", re.DOTALL)
MAX_IMAGE_BYTES = 5 * 1024 * 1024

EXT_ALIASES = {"jpeg": "jpg", "svg+xml": "svg"}


class BrandingImageError(Exception):
    def __init__(self, message: str) -> None:
        self.message = message
        super().__init__(message)


def ensure_images_dir() -> None:
    IMAGES_DIR.mkdir(parents=True, exist_ok=True)


def is_data_url(value: str) -> bool:
    return value.strip().startswith("data:image/")


def normalize_relative_path(value: str | None) -> str | None:
    """从完整 URL 或相对路径得到 images/xxx 形式。"""
    if not value:
        return None
    text = value.strip()
    if not text or is_data_url(text):
        return None
    marker = "/images/"
    if marker in text:
        suffix = text.split(marker, 1)[1].split("?")[0]
        return f"images/{suffix}"
    normalized = text.replace("\\", "/").lstrip("/")
    if normalized.startswith("images/"):
        return normalized
    return None


def absolute_path(relative_path: str | None) -> Path | None:
    rel = normalize_relative_path(relative_path)
    if not rel:
        return None
    name = rel.removeprefix("images/").lstrip("/")
    if not name or ".." in Path(name).parts:
        return None
    return IMAGES_DIR / name


def delete_local_image(relative_path: str | None) -> None:
    path = absolute_path(relative_path)
    if path is not None and path.is_file():
        path.unlink()


def save_data_url(data_url: str, *, file_prefix: str) -> str:
    match = DATA_URL_PATTERN.match(data_url.strip())
    if not match:
        raise BrandingImageError("无效的图片数据")

    ext = match.group(1).lower()
    ext = EXT_ALIASES.get(ext, ext)
    if ext not in {"png", "jpg", "gif", "webp", "svg"}:
        raise BrandingImageError(f"不支持的图片格式: {ext}")

    try:
        raw = base64.b64decode(match.group(2), validate=True)
    except Exception as exc:
        raise BrandingImageError("图片 Base64 解码失败") from exc

    if len(raw) > MAX_IMAGE_BYTES:
        raise BrandingImageError("单张图片不能超过 5MB")

    ensure_images_dir()
    filename = f"oem_{file_prefix}_{uuid.uuid4().hex[:12]}.{ext}"
    target = IMAGES_DIR / filename
    target.write_bytes(raw)
    return f"images/{filename}"


def resolve_image_field(
    new_value: str | None,
    old_path: str | None,
    *,
    file_prefix: str,
) -> str | None:
    """
    - 空：删除旧文件，返回 None
    - data URL：写入新文件，删除旧文件
    - 已是 images/ 路径（或与旧路径相同）：原样保留
    """
    if new_value is None or not str(new_value).strip():
        delete_local_image(old_path)
        return None

    text = str(new_value).strip()
    if is_data_url(text):
        delete_local_image(old_path)
        return save_data_url(text, file_prefix=file_prefix)

    rel = normalize_relative_path(text)
    if rel is None:
        raise BrandingImageError("图片须为上传数据或 images/ 下的路径")

    old_rel = normalize_relative_path(old_path)
    if rel == old_rel:
        return rel

    return rel