import type { NextRequest } from "next/server";
import { isLocale } from "@/translations/config";

export const dynamic = "force-dynamic";
export const runtime = "nodejs";

const PROXY_PATH_PARAM = "__proxyPath";

const REQUEST_HEADERS_TO_FORWARD = [
  "accept",
  "accept-language",
  "authorization",
  "cookie",
  "token",
  "content-type",
  "x-csrf-token",
  "x-csrftoken",
  "x-requested-with",
  "x-xsrf-token",
];

const RESPONSE_HEADERS_TO_DROP = [
  "connection",
  "content-encoding",
  "content-length",
  "keep-alive",
  "proxy-authenticate",
  "proxy-authorization",
  "te",
  "trailer",
  "transfer-encoding",
  "upgrade",
];

const MAX_LOG_BODY_LENGTH = 10_000;
const shouldLogProxy = process.env.LOG_API_PROXY === "true";
const shouldLogProxyTiming =
  process.env.LOG_API_PROXY_TIMING === "true" || shouldLogProxy;

class ProxyError extends Error {
  constructor(
    message: string,
    readonly status: number,
  ) {
    super(message);
  }
}

function getApiBaseUrl() {
  const apiBaseUrl =
    process.env.API_BASE_URL ?? process.env.NEXT_PUBLIC_API_BASE_URL;

  if (!apiBaseUrl) {
    throw new ProxyError(
      "API_BASE_URL or NEXT_PUBLIC_API_BASE_URL is required",
      500,
    );
  }

  try {
    return new URL(apiBaseUrl);
  } catch {
    throw new ProxyError("API base URL is invalid", 500);
  }
}

function getProxyPath(request: NextRequest) {
  const proxyPath = request.nextUrl.searchParams.get(PROXY_PATH_PARAM);

  if (!proxyPath) {
    throw new ProxyError("Proxy path is required", 400);
  }

  if (/^[a-z][a-z\d+\-.]*:/i.test(proxyPath) || proxyPath.startsWith("//")) {
    throw new ProxyError("Proxy path must be relative", 400);
  }

  return proxyPath.startsWith("/") ? proxyPath : `/${proxyPath}`;
}

function getTargetUrl(request: NextRequest) {
  const targetUrl = getApiBaseUrl();
  const proxyUrl = new URL(getProxyPath(request), targetUrl.origin);
  const basePath = targetUrl.pathname.replace(/\/$/, "");

  targetUrl.pathname = `${basePath}${proxyUrl.pathname}`;

  const searchParams = new URLSearchParams(proxyUrl.search);
  request.nextUrl.searchParams.forEach((value, key) => {
    if (key !== PROXY_PATH_PARAM) {
      searchParams.append(key, value);
    }
  });
  targetUrl.search = searchParams.toString();

  return targetUrl;
}

function getCookieValue(cookieHeader: string, name: string) {
  const escapedName = name.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
  const pattern = new RegExp(`(?:^|;\\s*)${escapedName}=([^;]*)`);
  const match = cookieHeader.match(pattern);

  return match ? decodeURIComponent(match[1]) : null;
}

function getRequestHeaders(request: NextRequest, targetUrl: URL) {
  const headers = new Headers();
  const authKey = process.env.NEXT_PUBLIC_AUTH_KEY;
  const cookieHeader = request.headers.get("cookie") ?? "";

  for (const header of REQUEST_HEADERS_TO_FORWARD) {
    const value = request.headers.get(header);

    if (value) {
      if (header === "token") {
        // Convert token header to Authorization
        headers.set("authorization", `Token ${value}`);
      } else {
        headers.set(header, value);
      }
    }
  }

  // Prefer a cookie-based token when the browser session is anonymous.
  if (!headers.has("authorization")) {
    const cookieToken =
      getCookieValue(cookieHeader, "HABIB_TOKEN") ??
      getCookieValue(cookieHeader, "habib_token") ??
      getCookieValue(cookieHeader, "token") ??
      getCookieValue(cookieHeader, "auth_token");

    if (
      cookieToken &&
      cookieToken !== "NO_TOKEN" &&
      cookieToken.trim() !== ""
    ) {
      headers.set("authorization", `Token ${cookieToken}`);
    }
  }

  // Override with authKey if set and no authorization header exists.
  if (authKey && !headers.has("authorization")) {
    headers.set("authorization", `Token ${authKey}`);
  }

  // Dynamically set language headers
  const requestedLanguages = [
    request.headers.get("x-user-language"),
    getCookieValue(cookieHeader, "HABIB_LANGUAGE"),
    getCookieValue(cookieHeader, "habib_language"),
    request.headers.get("accept-language")?.split(",")[0]?.split("-")[0],
  ];
  const lang =
    requestedLanguages.find(
      (candidate): candidate is string =>
        candidate !== null && isLocale(candidate),
    ) ?? "en";

  headers.set("accept-encoding", "gzip, br");
  headers.set("accept-language", lang);
  headers.set("x-user-language", lang);
  headers.set("http_x_user_language", lang);
  headers.set("origin", targetUrl.origin);
  const clientUserAgent = request.headers.get("user-agent");
  headers.set("user-agent", clientUserAgent || "dart:io");

  // Forward client IP headers so backend can determine actual user location
  const clientIp =
    request.headers.get("cf-connecting-ip") ||
    request.headers.get("x-real-ip") ||
    request.headers.get("x-forwarded-for")?.split(",")[0]?.trim();

  if (clientIp) {
    headers.set("x-forwarded-for", clientIp);
    headers.set("x-real-ip", clientIp);
    headers.set("x-client-ip", clientIp);
  }

  return headers;
}

function getResponseHeaders(upstreamHeaders: Headers) {
  const headers = new Headers(upstreamHeaders);

  for (const header of RESPONSE_HEADERS_TO_DROP) {
    headers.delete(header);
  }

  const setCookieHeaders =
    (
      upstreamHeaders as Headers & { getSetCookie?: () => string[] }
    ).getSetCookie?.() ?? [];

  if (setCookieHeaders.length > 0) {
    headers.delete("set-cookie");

    for (const cookie of setCookieHeaders) {
      headers.append("set-cookie", cookie);
    }
  }

  return headers;
}

function getBodyLogValue(body: ArrayBuffer | undefined, contentType?: string) {
  if (!body || body.byteLength === 0) {
    return null;
  }

  if (contentType && !isTextContentType(contentType)) {
    return `[${body.byteLength} bytes; ${contentType}]`;
  }

  const text = new TextDecoder().decode(body);

  if (text.length <= MAX_LOG_BODY_LENGTH) {
    return parseJsonForLog(text, text);
  }

  return `${text.slice(0, MAX_LOG_BODY_LENGTH)}... [truncated ${text.length - MAX_LOG_BODY_LENGTH} chars]`;
}

function isTextContentType(contentType: string) {
  return (
    contentType.includes("application/json") ||
    contentType.includes("application/problem+json") ||
    contentType.startsWith("text/") ||
    contentType.includes("+json") ||
    contentType.includes("+xml")
  );
}

function parseJsonForLog(text: string, fallback: string) {
  try {
    return JSON.parse(text);
  } catch {
    return fallback;
  }
}

function headersToObject(headers: Headers) {
  return Object.fromEntries(headers.entries());
}

function logProxyRequest(
  request: NextRequest,
  targetUrl: URL,
  requestHeaders: Headers,
  requestBody: ArrayBuffer | undefined,
) {
  if (!shouldLogProxy) {
    return;
  }

  writeProxyLog("request", {
    incomingRequest: {
      method: request.method,
      url: request.url,
      nextUrl: request.nextUrl.toString(),
      headers: headersToObject(request.headers),
      body: getBodyLogValue(
        requestBody,
        request.headers.get("content-type") ?? undefined,
      ),
    },
    upstreamRequest: {
      method: request.method,
      url: targetUrl.toString(),
      headers: headersToObject(requestHeaders),
      body: getBodyLogValue(
        requestBody,
        requestHeaders.get("content-type") ?? undefined,
      ),
    },
    payload: getBodyLogValue(
      requestBody,
      request.headers.get("content-type") ?? undefined,
    ),
  });
}

function logProxyResponse(
  upstreamResponse: Response,
  metrics: Record<string, number>,
) {
  if (!shouldLogProxyTiming) {
    return;
  }

  writeProxyLog("response", {
    status: upstreamResponse.status,
    statusText: upstreamResponse.statusText,
    headers: headersToObject(upstreamResponse.headers),
    metrics,
  });
}

function writeProxyLog(label: string, value: unknown) {
  console.log(`[api-proxy] ${label} ${JSON.stringify(value)}`);
}

async function proxyRequest(request: NextRequest) {
  try {
    const proxyStartedAt = performance.now();
    const targetUrl = getTargetUrl(request);
    const requestBody =
      request.method === "GET" || request.method === "HEAD"
        ? undefined
        : await request.arrayBuffer();
    const requestHeaders = getRequestHeaders(request, targetUrl);

    logProxyRequest(request, targetUrl, requestHeaders, requestBody);

    const upstreamStartedAt = performance.now();
    const upstreamResponse = await fetch(targetUrl, {
      method: request.method,
      headers: requestHeaders,
      body: requestBody,
      cache: "no-store",
    });
    const upstreamTtfb = performance.now() - upstreamStartedAt;

    const responseHeaders = getResponseHeaders(upstreamResponse.headers);

    // Force no caching on API proxy responses – always fetch fresh data
    responseHeaders.set(
      "Cache-Control",
      "no-store, no-cache, must-revalidate, proxy-revalidate, max-age=0",
    );
    responseHeaders.set("Pragma", "no-cache");
    responseHeaders.set("Expires", "0");
    responseHeaders.set(
      "Server-Timing",
      `upstream-ttfb;dur=${upstreamTtfb.toFixed(1)}`,
    );
    responseHeaders.set("X-Proxy-Upstream-TTFB-Ms", upstreamTtfb.toFixed(1));

    let responseBytes = 0;
    const responseBody =
      upstreamResponse.body?.pipeThrough(
        new TransformStream<Uint8Array, Uint8Array>({
          transform(chunk, controller) {
            responseBytes += chunk.byteLength;
            controller.enqueue(chunk);
          },
          flush() {
            const total = performance.now() - proxyStartedAt;
            logProxyResponse(upstreamResponse, {
              upstreamTtfb: Math.round(upstreamTtfb),
              upstreamBody: Math.round(total - upstreamTtfb),
              proxyTotal: Math.round(total),
              responseBytes,
            });
          },
        }),
      ) ?? null;

    return new Response(responseBody, {
      status: upstreamResponse.status,
      statusText: upstreamResponse.statusText,
      headers: responseHeaders,
    });
  } catch (error) {
    if (error instanceof ProxyError) {
      return Response.json({ error: error.message }, { status: error.status });
    }

    console.error("API proxy request failed", error);

    return Response.json(
      { error: "API proxy request failed" },
      { status: 502 },
    );
  }
}

export {
  proxyRequest as DELETE,
  proxyRequest as GET,
  proxyRequest as HEAD,
  proxyRequest as OPTIONS,
  proxyRequest as PATCH,
  proxyRequest as POST,
  proxyRequest as PUT,
};