dy/backend/link_cards.py

"""链接卡片落地页：带 SEO meta 与自动跳转。"""
from __future__ import annotations

import html
import json
import os
import re
import secrets
from io import BytesIO
from typing import Optional, TYPE_CHECKING

if TYPE_CHECKING:
    from fastapi import Request

_SLUG_RE = re.compile(r"^[a-zA-Z0-9_-]{6,64}$")

FAVICON_SIZE = 32
COVER_SIZE = 256
FAVICON_MIME = "image/png"


def generate_slug() -> str:
    return secrets.token_urlsafe(9).replace("-", "_").replace(".", "_")[:12]


def is_valid_slug(slug: str) -> bool:
    return bool(_SLUG_RE.match(slug or ""))


def public_base_url(request: Optional["Request"] = None) -> str:
    env = os.getenv("KEFU_PUBLIC_BASE_URL", "").strip().rstrip("/")
    if env:
        return env
    if request is not None:
        return str(request.base_url).rstrip("/")
    return ""


def absolute_media_url(path: str, request: Optional["Request"] = None) -> str:
    path = (path or "").strip()
    if not path:
        return ""
    if path.startswith("http://") or path.startswith("https://"):
        return path
    base = public_base_url(request)
    if not base:
        return path
    if not path.startswith("/"):
        path = f"/{path}"
    return f"{base}{path}"


def favicon_mime(image_path: str) -> str:
    ext = (image_path or "").rsplit(".", 1)[-1].lower()
    return {
        "svg": "image/svg+xml",
        "png": "image/png",
        "gif": "image/gif",
        "webp": "image/webp",
        "jpg": "image/jpeg",
        "jpeg": "image/jpeg",
        "ico": "image/x-icon",
    }.get(ext, FAVICON_MIME)


def favicon_path_for_cover(cover_path: str) -> str:
    """由封面路径推导同名 favicon 文件路径。"""
    path = (cover_path or "").strip()
    if not path:
        return ""
    if path.endswith(".favicon.png"):
        return path
    if path.endswith(".png"):
        return f"{path[:-4]}.favicon.png"
    base, _ = os.path.splitext(path)
    return f"{base}.favicon.png"


def media_path_to_disk(upload_dir: str, media_path: str) -> str:
    prefix = "/api/media/link-cards/"
    path = (media_path or "").strip()
    if not path.startswith(prefix):
        return ""
    rel = path[len(prefix) :].replace("/", os.sep)
    return os.path.join(upload_dir, rel)


def process_card_upload(raw: bytes) -> tuple[bytes, bytes]:
    """将任意位图转为封面 PNG (256x256) 与 favicon PNG (32x32)。"""
    if not raw:
        raise ValueError("图片为空")
    try:
        from PIL import Image
    except ImportError as exc:
        raise RuntimeError("服务器未安装 Pillow，无法转换 favicon") from exc

    try:
        with Image.open(BytesIO(raw)) as img:
            if getattr(img, "is_animated", False):
                img.seek(0)
            if img.mode not in ("RGB", "RGBA"):
                img = img.convert("RGBA")
            else:
                img = img.copy()

            width, height = img.size
            if width < 1 or height < 1:
                raise ValueError("图片尺寸无效")

            side = min(width, height)
            left = (width - side) // 2
            top = (height - side) // 2
            square = img.crop((left, top, left + side, top + side))

            resample = Image.Resampling.LANCZOS
            cover = square.resize((COVER_SIZE, COVER_SIZE), resample)
            favicon = square.resize((FAVICON_SIZE, FAVICON_SIZE), resample)

            cover_buf = BytesIO()
            cover.save(cover_buf, format="PNG", optimize=True)
            favicon_buf = BytesIO()
            favicon.save(favicon_buf, format="PNG", optimize=True)
            return cover_buf.getvalue(), favicon_buf.getvalue()
    except ValueError:
        raise
    except Exception as exc:
        raise ValueError("无法识别图片格式，请上传 JPG、PNG、GIF 或 WebP") from exc


def normalize_target_url(url: str) -> str:
    url = (url or "").strip()
    if not url:
        return ""
    if not url.startswith("http://") and not url.startswith("https://"):
        url = f"https://{url}"
    return url


def build_keywords(title: str, content: str) -> str:
    parts = [p.strip() for p in (title, content) if p and p.strip()]
    return ", ".join(dict.fromkeys(parts))


def render_link_card_page(
    *,
    title: str,
    content: str,
    keywords: str,
    cover_url: str,
    favicon_url: str,
    target_url: str,
) -> str:
    safe_title = html.escape(title or "跳转中")
    safe_desc = html.escape(content or title or "")
    safe_keywords = html.escape(keywords or build_keywords(title, content))
    safe_cover = html.escape(cover_url or "")
    safe_favicon = html.escape(favicon_url or cover_url or "")
    redirect_url = normalize_target_url(target_url)
    safe_target = html.escape(redirect_url)
    js_target = json.dumps(redirect_url, ensure_ascii=False)

    favicon_tag = ""
    og_image_tag = ""
    if safe_favicon:
        favicon_tag = f'  <link rel="icon" type="{FAVICON_MIME}" href="{safe_favicon}" />\n'
    if safe_cover:
        og_image_tag = f'  <meta property="og:image" content="{safe_cover}" />\n'

    return f"""<!DOCTYPE html>
<html lang="zh-CN">
<head>
  <meta charset="utf-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1" />
  <title>{safe_title}</title>
  <meta name="description" content="{safe_desc}" />
  <meta name="keywords" content="{safe_keywords}" />
  <meta property="og:title" content="{safe_title}" />
  <meta property="og:description" content="{safe_desc}" />
{og_image_tag}{favicon_tag}  <meta http-equiv="refresh" content="0;url={safe_target}" />
  <script>location.replace({js_target});</script>
</head>
<body>
  <p>正在跳转到目标页面…</p>
  <p><a href="{safe_target}">若未自动跳转，请点击这里</a></p>
</body>
</html>"""