import { resolve, join, sep, extname } from "node:path";
import { promises as fsp } from "node:fs";
import {
    decodePath,
    withLeadingSlash,
    withoutTrailingSlash,
    parseURL,
} from "ufo";
import type { H3Event } from "h3";
import mime from "mime";

const METHODS = new Set(["HEAD", "GET"]);
const SAFE_BASE_DIR = resolve("public");

// 缓存配置
const CACHE_CONTROL = "public, max-age=31536000, immutable";
const NOT_MODIFIED = 304;
const FORBIDDEN = 403;
const NOT_FOUND = 404;
const SERVER_ERROR = 500;

export default eventHandler(async (event: H3Event) => {
    if (!event.path.startsWith("/public")) return;

    const { req, res } = event.node;
    const method = req.method;

    if (method && !METHODS.has(method)) return;

    try {
        // 安全解析路径
        const url = event.path.replace(/^\/public/, "");
        const pathname = decodePath(
            withLeadingSlash(withoutTrailingSlash(parseURL(url).pathname))
        );

        const targetPath = join(SAFE_BASE_DIR, pathname);
        const resolvedPath = resolve(targetPath);

        // 安全校验
        if (!resolvedPath.startsWith(SAFE_BASE_DIR + sep)) {
            res.statusCode = FORBIDDEN;
            return "Forbidden";
        }

        const stat = await fsp.stat(resolvedPath);
        if (!stat.isFile()) {
            res.statusCode = NOT_FOUND;
            return "Not Found";
        }

        // ====================== 缓存逻辑 ======================
        const mtime = stat.mtime.toUTCString();
        const etag = `"${stat.mtime.getTime().toString(16)}-${stat.size.toString(16)}"`;

        const contentType = mime.getType(resolvedPath) || "application/octet-stream";

        // 设置缓存头
        res.setHeader("Cache-Control", CACHE_CONTROL);
        res.setHeader("ETag", etag);
        res.setHeader("Last-Modified", mtime);
        res.setHeader("Content-Type", contentType);
        res.setHeader("Content-Length", stat.size);
        
        // 禁用 keep-alive
        res.setHeader("Connection", "close");

        // 304 协商缓存
        const ifNoneMatch = req.headers["if-none-match"];
        const ifModifiedSince = req.headers["if-modified-since"];
        if (ifNoneMatch === etag || (ifModifiedSince && ifModifiedSince === mtime)) {
            res.statusCode = NOT_MODIFIED;
            return "";
        }
        // ======================================================

        if (method === "HEAD") return "";
        return fsp.readFile(resolvedPath);

    } catch (err: any) {
        if (err.code === "ENOENT") {
            res.statusCode = NOT_FOUND;
            return "Not Found";
        }
        res.statusCode = SERVER_ERROR;
        return "Server Error";
    }
});