package com.nimbusds.oauth2.sdk.http;


import java.io.BufferedReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Enumeration;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import net.jcip.annotations.ThreadSafe;

import com.nimbusds.oauth2.sdk.ParseException;


/**
 * HTTP servlet utilities.
 */
@ThreadSafe
public class ServletUtils {


        /**
         * Reconstructs the request URL string for the specified servlet
         * request. The host part is always the local IP address. The query
         * string and fragment is always omitted.
         *
         * @param request The servlet request. Must not be {@code null}.
         *
         * @return The reconstructed request URL string.
         */
        private static String reconstructRequestURLString(final HttpServletRequest request) {

                StringBuilder sb = new StringBuilder("http");

                if (request.isSecure())
                        sb.append('s');

                sb.append("://");

                String localAddress = request.getLocalAddr();

                if (localAddress.contains(".")) {
                        // IPv3 address
                        sb.append(localAddress);
                } else if (localAddress.contains(":")) {
                        // IPv6 address, see RFC 2732
                        sb.append('[');
                        sb.append(localAddress);
                        sb.append(']');
                } else {
                        // Don't know what to do
                }

                if (! request.isSecure() && request.getLocalPort() != 80) {
                        // HTTP plain at port other than 80
                        sb.append(':');
                        sb.append(request.getLocalPort());
                }

                if (request.isSecure() && request.getLocalPort() != 443) {
                        // HTTPS at port other than 443 (default TLS)
                        sb.append(':');
                        sb.append(request.getLocalPort());
                }

                String path = request.getRequestURI();

                if (path != null)
                        sb.append(path);

                return sb.toString();
        }


        /**
         * Creates a new HTTP request from the specified HTTP servlet request.
         *
         * @param sr The servlet request. Must not be {@code null}.
         *
         * @return The HTTP request.
         *
         * @throws IllegalArgumentException The the servlet request method is
         *                                  not GET, POST, PUT or DELETE or the
         *                                  content type header value couldn't
         *                                  be parsed.
         * @throws IOException              For a POST or PUT body that
         *                                  couldn't be read due to an I/O
         *                                  exception.
         */
        public static HTTPRequest createHTTPRequest(final HttpServletRequest sr)
                throws IOException {

                return createHTTPRequest(sr, -1);
        }


        /**
         * Creates a new HTTP request from the specified HTTP servlet request.
         *
         * @param sr              The servlet request. Must not be
         *                        {@code null}.
         * @param maxEntityLength The maximum entity length to accept, -1 for
         *                        no limit.
         *
         * @return The HTTP request.
         *
         * @throws IllegalArgumentException The the servlet request method is
         *                                  not GET, POST, PUT or DELETE or the
         *                                  content type header value couldn't
         *                                  be parsed.
         * @throws IOException              For a POST or PUT body that
         *                                  couldn't be read due to an I/O
         *                                  exception.
         */
        public static HTTPRequest createHTTPRequest(final HttpServletRequest sr, final long maxEntityLength)
                throws IOException {

                HTTPRequest.Method method = HTTPRequest.Method.valueOf(sr.getMethod().toUpperCase());

                String urlString = reconstructRequestURLString(sr);

                URL url;

                try {
                        url = new URL(urlString);

                } catch (MalformedURLException e) {

                        throw new IllegalArgumentException("Invalid request URL: " + e.getMessage() + ": " + urlString, e);
                }

                HTTPRequest request = new HTTPRequest(method, url);

                try {
                        request.setContentType(sr.getContentType());

                } catch (ParseException e) {

                        throw new IllegalArgumentException("Invalid Content-Type header value: " + e.getMessage(), e);
                }

                Enumeration<String> headerNames = sr.getHeaderNames();

                while (headerNames.hasMoreElements()) {
                        final String headerName = headerNames.nextElement();
                        request.setHeader(headerName, sr.getHeader(headerName));
                }

                if (method.equals(HTTPRequest.Method.GET) || method.equals(HTTPRequest.Method.DELETE)) {

                        request.setQuery(sr.getQueryString());

                } else if (method.equals(HTTPRequest.Method.POST) || method.equals(HTTPRequest.Method.PUT)) {

                        // read body
                        StringBuilder body = new StringBuilder(256);

                        BufferedReader reader = sr.getReader();

                        char[] cbuf = new char[256];

                        int readChars;

                        while ((readChars = reader.read(cbuf)) != -1) {

                                body.append(cbuf, 0, readChars);

                                if (maxEntityLength > 0 && body.length() > maxEntityLength) {
                                        throw new IOException("Request entity body is too large, limit is " + maxEntityLength + " chars");
                                }
                        }

                        reader.close();

                        request.setQuery(body.toString());
                }

                return request;
        }


        /**
         * Applies the status code, headers and content of the specified HTTP
         * response to a HTTP servlet response.
         *
         * @param httpResponse    The HTTP response. Must not be {@code null}.
         * @param servletResponse The HTTP servlet response. Must not be
         *                        {@code null}.
         *
         * @throws IOException If the response content couldn't be written.
         */
        public static void applyHTTPResponse(final HTTPResponse httpResponse,
                                             final HttpServletResponse servletResponse)
                throws IOException {

                // Set the status code
                servletResponse.setStatus(httpResponse.getStatusCode());


                // Set the headers, but only if explicitly specified
                for (Map.Entry<String,String> header : httpResponse.getHeaders().entrySet()) {
                        servletResponse.setHeader(header.getKey(), header.getValue());
                }

                if (httpResponse.getContentType() != null)
                        servletResponse.setContentType(httpResponse.getContentType().toString());


                // Write out the content

                if (httpResponse.getContent() != null) {

                        PrintWriter writer = servletResponse.getWriter();
                        writer.print(httpResponse.getContent());
                        writer.close();
                }
        }


        /**
         * Prevents public instantiation.
         */
        private ServletUtils() {

        }
}