import { Router, Request, Response } from "express";
import { renderPdf, renderUrlPdf } from "../services/browser.js";
import { markdownToHtml, wrapHtml } from "../services/markdown.js";
import dns from "node:dns/promises";
import logger from "../services/logger.js";
import net from "node:net";

function isPrivateIP(ip: string): boolean {
  // IPv6 loopback/unspecified
  if (ip === "::1" || ip === "::") return true;
  
  // IPv6 link-local (fe80::/10)
  if (ip.toLowerCase().startsWith("fe8") || ip.toLowerCase().startsWith("fe9") ||
      ip.toLowerCase().startsWith("fea") || ip.toLowerCase().startsWith("feb")) return true;
  
  // IPv6 unique local (fc00::/7)
  const lower = ip.toLowerCase();
  if (lower.startsWith("fc") || lower.startsWith("fd")) return true;
  
  // IPv4-mapped IPv6
  if (ip.startsWith("::ffff:")) ip = ip.slice(7);
  if (!net.isIPv4(ip)) return false;
  
  const parts = ip.split(".").map(Number);
  if (parts[0] === 0) return true;                           // 0.0.0.0/8
  if (parts[0] === 10) return true;                           // 10.0.0.0/8
  if (parts[0] === 127) return true;                          // 127.0.0.0/8
  if (parts[0] === 169 && parts[1] === 254) return true;     // 169.254.0.0/16
  if (parts[0] === 172 && parts[1] >= 16 && parts[1] <= 31) return true; // 172.16.0.0/12
  if (parts[0] === 192 && parts[1] === 168) return true;     // 192.168.0.0/16
  return false;
}

function sanitizeFilename(name: string): string {
  // Strip characters dangerous in Content-Disposition headers
  return name.replace(/[\x00-\x1f"\\\r\n]/g, "").trim() || "document.pdf";
}

export const convertRouter = Router();

interface ConvertBody {
  html?: string;
  markdown?: string;
  css?: string;
  format?: string;
  landscape?: boolean;
  margin?: { top?: string; right?: string; bottom?: string; left?: string };
  printBackground?: boolean;
  filename?: string;
}

// POST /v1/convert/html
convertRouter.post("/html", async (req: Request & { acquirePdfSlot?: () => Promise<void>; releasePdfSlot?: () => void }, res: Response) => {
  let slotAcquired = false;
  try {
    // Reject non-JSON content types
    const ct = req.headers["content-type"] || "";
    if (!ct.includes("application/json")) {
      res.status(415).json({ error: "Unsupported Content-Type. Use application/json." });
      return;
    }
    const body: ConvertBody =
      typeof req.body === "string" ? { html: req.body } : req.body;

    if (!body.html) {
      res.status(400).json({ error: "Missing 'html' field" });
      return;
    }

    // Acquire concurrency slot
    if (req.acquirePdfSlot) {
      await req.acquirePdfSlot();
      slotAcquired = true;
    }

    // Wrap bare HTML fragments
    const fullHtml = body.html.includes("<html")
      ? body.html
      : wrapHtml(body.html, body.css);

    const pdf = await renderPdf(fullHtml, {
      format: body.format,
      landscape: body.landscape,
      margin: body.margin,
      printBackground: body.printBackground,
    });

    const filename = sanitizeFilename(body.filename || "document.pdf");
    res.setHeader("Content-Type", "application/pdf");
    res.setHeader("Content-Disposition", `inline; filename="${filename}"`);
    res.send(pdf);
  } catch (err: any) {
    logger.error({ err }, "Convert HTML error");
    if (err.message === "QUEUE_FULL") {
      res.status(429).json({ error: "Server busy - too many concurrent PDF generations. Please try again in a few seconds." });
      return;
    }
    res.status(500).json({ error: `PDF generation failed: ${err.message}` });
  } finally {
    if (slotAcquired && req.releasePdfSlot) {
      req.releasePdfSlot();
    }
  }
});

// POST /v1/convert/markdown
convertRouter.post("/markdown", async (req: Request & { acquirePdfSlot?: () => Promise<void>; releasePdfSlot?: () => void }, res: Response) => {
  let slotAcquired = false;
  try {
    // Reject non-JSON content types
    const ct = req.headers["content-type"] || "";
    if (!ct.includes("application/json")) {
      res.status(415).json({ error: "Unsupported Content-Type. Use application/json." });
      return;
    }
    const body: ConvertBody =
      typeof req.body === "string" ? { markdown: req.body } : req.body;

    if (!body.markdown) {
      res.status(400).json({ error: "Missing 'markdown' field" });
      return;
    }

    // Acquire concurrency slot
    if (req.acquirePdfSlot) {
      await req.acquirePdfSlot();
      slotAcquired = true;
    }

    const html = markdownToHtml(body.markdown, body.css);
    const pdf = await renderPdf(html, {
      format: body.format,
      landscape: body.landscape,
      margin: body.margin,
      printBackground: body.printBackground,
    });

    const filename = sanitizeFilename(body.filename || "document.pdf");
    res.setHeader("Content-Type", "application/pdf");
    res.setHeader("Content-Disposition", `inline; filename="${filename}"`);
    res.send(pdf);
  } catch (err: any) {
    logger.error({ err }, "Convert MD error");
    if (err.message === "QUEUE_FULL") {
      res.status(429).json({ error: "Server busy - too many concurrent PDF generations. Please try again in a few seconds." });
      return;
    }
    res.status(500).json({ error: `PDF generation failed: ${err.message}` });
  } finally {
    if (slotAcquired && req.releasePdfSlot) {
      req.releasePdfSlot();
    }
  }
});

// POST /v1/convert/url
convertRouter.post("/url", async (req: Request & { acquirePdfSlot?: () => Promise<void>; releasePdfSlot?: () => void }, res: Response) => {
  let slotAcquired = false;
  try {
    // Reject non-JSON content types
    const ct = req.headers["content-type"] || "";
    if (!ct.includes("application/json")) {
      res.status(415).json({ error: "Unsupported Content-Type. Use application/json." });
      return;
    }
    const body = req.body as { url?: string; format?: string; landscape?: boolean; margin?: any; printBackground?: boolean; waitUntil?: string; filename?: string };

    if (!body.url) {
      res.status(400).json({ error: "Missing 'url' field" });
      return;
    }

    // URL validation + SSRF protection
    let parsed: URL;
    try {
      parsed = new URL(body.url);
      if (!["http:", "https:"].includes(parsed.protocol)) {
        res.status(400).json({ error: "Only http/https URLs are supported" });
        return;
      }
    } catch {
      res.status(400).json({ error: "Invalid URL" });
      return;
    }

    // DNS lookup to block private/reserved IPs + pin resolution to prevent DNS rebinding
    let resolvedAddress: string;
    try {
      const { address } = await dns.lookup(parsed.hostname);
      if (isPrivateIP(address)) {
        res.status(400).json({ error: "URL resolves to a private/internal IP address" });
        return;
      }
      resolvedAddress = address;
    } catch {
      res.status(400).json({ error: "DNS lookup failed for URL hostname" });
      return;
    }

    // Acquire concurrency slot
    if (req.acquirePdfSlot) {
      await req.acquirePdfSlot();
      slotAcquired = true;
    }

    const pdf = await renderUrlPdf(body.url, {
      format: body.format,
      landscape: body.landscape,
      margin: body.margin,
      printBackground: body.printBackground,
      waitUntil: body.waitUntil,
      hostResolverRules: `MAP ${parsed.hostname} ${resolvedAddress}`,
    });

    const filename = sanitizeFilename(body.filename || "page.pdf");
    res.setHeader("Content-Type", "application/pdf");
    res.setHeader("Content-Disposition", `inline; filename="${filename}"`);
    res.send(pdf);
  } catch (err: any) {
    logger.error({ err }, "Convert URL error");
    if (err.message === "QUEUE_FULL") {
      res.status(429).json({ error: "Server busy - too many concurrent PDF generations. Please try again in a few seconds." });
      return;
    }
    res.status(500).json({ error: `PDF generation failed: ${err.message}` });
  } finally {
    if (slotAcquired && req.releasePdfSlot) {
      req.releasePdfSlot();
    }
  }
});
