nex_docus/backend/app/services/pdf_service.py

"""
PDF 生成服务 - 基于 WeasyPrint + 系统字体
"""
import io
import os
import platform
from pathlib import Path


class PDFService:
    def __init__(self):
        self.markdown = None
        self.html_class = None
        self.css_class = None
        self.font_config = None

    def _configure_macos_library_path(self):
        """为 macOS 上的 Homebrew 动态库补充兜底搜索路径。"""
        if platform.system() != "Darwin":
            return

        candidate_paths = [
            Path("/opt/homebrew/lib"),
            Path("/usr/local/lib"),
        ]
        existing_paths = [
            path for path in os.environ.get("DYLD_FALLBACK_LIBRARY_PATH", "").split(":") if path
        ]

        for candidate in candidate_paths:
            candidate_str = str(candidate)
            if candidate.exists() and candidate_str not in existing_paths:
                existing_paths.append(candidate_str)

        if existing_paths:
            os.environ["DYLD_FALLBACK_LIBRARY_PATH"] = ":".join(existing_paths)

    def _ensure_dependencies(self):
        """按需加载 PDF 依赖，避免系统库缺失时影响整个服务启动。"""
        if self.markdown and self.html_class and self.css_class and self.font_config:
            return

        try:
            self._configure_macos_library_path()
            import markdown
            from weasyprint import HTML, CSS
            from weasyprint.text.fonts import FontConfiguration
        except Exception as exc:
            raise RuntimeError(
                "PDF 导出依赖不可用，请先安装 backend/requirements.txt 中的 Python 依赖，"
                "并为 WeasyPrint 安装系统库（如 glib、pango、cairo）。"
            ) from exc

        self.markdown = markdown
        self.html_class = HTML
        self.css_class = CSS
        self.font_config = FontConfiguration()

    def get_css(self):
        return """
            @page {
                margin: 2cm;
                @bottom-right {
                    content: counter(page);
                    font-size: 9pt;
                }
            }
            /* 全局：macOS 用 Hiragino Sans GB / Heiti SC，Docker 用 WenQuanYi Micro Hei */
            * {
                font-family: "Hiragino Sans GB", "Heiti SC", "WenQuanYi Micro Hei",
                             "Arial Unicode MS", sans-serif !important;
            }
            body {
                font-size: 11pt;
                line-height: 1.6;
                color: #333;
                background-color: #fff;
            }
            h1, h2, h3, h4, h5, h6 {
                border-bottom: 1px solid #eee;
                padding-bottom: 0.3em;
                margin-top: 1.5em;
                margin-bottom: 1em;
                font-weight: bold;
            }
            /* 代码块：等宽字体优先，中文回退到对应平台的 CJK 字体 */
            pre, code, pre *, code * {
                font-family: "Menlo", "DejaVu Sans Mono", "Courier New",
                             "Hiragino Sans GB", "Heiti SC", "WenQuanYi Micro Hei", monospace !important;
                background-color: transparent;
            }
            pre {
                background-color: #f6f8fa !important;
                padding: 16px;
                border-radius: 6px;
                white-space: pre-wrap;
                word-break: break-all;
                display: block;
            }
            code {
                background-color: rgba(175, 184, 193, 0.2);
                padding: 0.2em 0.4em;
                border-radius: 6px;
            }
            table {
                border-collapse: collapse;
                width: 100%;
                margin-bottom: 1em;
            }
            th, td {
                border: 1px solid #dfe2e5;
                padding: 6px 13px;
            }
            tr:nth-child(2n) {
                background-color: #f6f8fa;
            }
            img {
                max-width: 100%;
            }
            blockquote {
                border-left: 0.25em solid #dfe2e5;
                color: #6a737d;
                padding: 0 1em;
                margin-left: 0;
            }
        """

    async def md_to_pdf(self, md_content: str, title: str = "Document", base_url: str = None) -> io.BytesIO:
        """将 Markdown 转换为 PDF 字节流"""
        self._ensure_dependencies()

        html_content = self.markdown.markdown(
            md_content,
            extensions=['extra', 'codehilite', 'toc', 'tables']
        )

        full_html = f"""
        <!DOCTYPE html>
        <html>
        <head>
            <meta charset="UTF-8">
            <title>{title}</title>
        </head>
        <body class="markdown-body">
            {html_content}
        </body>
        </html>
        """

        pdf_buffer = io.BytesIO()
        css = self.css_class(string=self.get_css(), font_config=self.font_config)
        self.html_class(string=full_html, base_url=base_url).write_pdf(
            pdf_buffer,
            stylesheets=[css],
            font_config=self.font_config
        )
        pdf_buffer.seek(0)
        return pdf_buffer

pdf_service = PDFService()