/*
 * Copyright 2016 IoT.bzh
 * Author: José Bollo <jose.bollo@iot.bzh>
 *
 * Inspired by the work of 
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define _GNU_SOURCE
#include <microhttpd.h>
#include <assert.h>
#include <errno.h>
#include <sys/uio.h>

#include <openssl/sha.h>
#include <openssl/bio.h>
#include <openssl/evp.h>

#include "websock.h"

#include "../include/local-def.h"

#include "afb-method.h"
#include "afb-hreq.h"

static const char websocket_s[] = "websocket";
static const char sec_websocket_key_s[] = "Sec-WebSocket-Key";
static const char sec_websocket_version_s[] = "Sec-WebSocket-Version";
static const char sec_websocket_accept_s[] = "Sec-WebSocket-Accept";
static const char sec_websocket_protocol_s[] = "Sec-WebSocket-Protocol";
static const char websocket_guid[] = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";


struct afb_websock
{
	int fd;
	struct MHD_Connection *connection;
	struct websock *ws;
};

static ssize_t afb_websock_writev(struct afb_websock *ws, const struct iovec *iov, int iovcnt)
{
	ssize_t rc;
	do {
		rc = writev(ws->fd, iov, iovcnt);
	} while(rc == -1 && errno == EINTR);
	return rc;
}

static ssize_t afb_websock_readv(struct afb_websock *ws, const struct iovec *iov, int iovcnt)
{
	ssize_t rc;
	do {
		rc = readv(ws->fd, iov, iovcnt);
	} while(rc == -1 && errno == EINTR);
	return rc;
}

static void afb_websock_disconnect(struct afb_websock *ws)
{
}

static void afb_websock_on_close(struct afb_websock *ws, uint16_t code, size_t size)
{
}

static void afb_websock_on_content(struct afb_websock *ws, int last, size_t size)
{
}

static struct websock_itf afb_websock_itf = {
	.writev = (void*)afb_websock_writev,
	.readv = (void*)afb_websock_readv,
	.disconnect = (void*)afb_websock_disconnect,

	.on_ping = NULL,
	.on_pong = NULL,
	.on_close = (void*)afb_websock_on_close,
	.on_text = (void*)afb_websock_on_content,
	.on_binary = (void*)afb_websock_on_content,
	.on_continue = (void*)afb_websock_on_content
};

static void enc64(unsigned char *in, char *out)
{
	static const char tob64[] =
		"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
		"abcdefghijklmnopqrstuvwxyz"
		"0123456789+/";
	out[0] = tob64[in[0] >> 2];
	out[1] = tob64[((in[0] & 0x03) << 4) | ((in[1] & 0xf0) >> 4)];
	out[2] = tob64[((in[1] & 0x0f) << 2) | ((in[2] & 0xc0) >> 6)];
	out[3] = tob64[in[2] & 0x3f];
}

static void make_accept_value(const char *key, char result[29])
{
	unsigned char md[SHA_DIGEST_LENGTH+1];
	size_t len = strlen(key);
	char *buffer = alloca(len + sizeof websocket_guid - 1);
	memcpy(buffer, key, len);
	memcpy(buffer + len, websocket_guid, sizeof websocket_guid - 1);
	SHA1((const unsigned char *)buffer, (unsigned long)(len + sizeof websocket_guid - 1), md);
	assert(SHA_DIGEST_LENGTH == 20);
	md[20] = 0;
	enc64(&md[0], &result[0]);
	enc64(&md[3], &result[4]);
	enc64(&md[6], &result[8]);
	enc64(&md[9], &result[12]);
	enc64(&md[12], &result[16]);
	enc64(&md[15], &result[20]);
	enc64(&md[18], &result[24]);
	result[27] = '=';
	result[28] = 0;
}

static int headerhas(const char *header, const char *needle)
{
	static const char sep[] = " \t,";
	size_t len, n;

	n = strlen(needle);
	for(;;) {
		header += strspn(header, sep);
		if (!*header)
			return 0;
		len = strcspn(header, sep);
		if (n == len && 0 == strncasecmp(needle, header, n))
			return 1;
		header += len;
	}
}

int afb_websock_check(struct afb_hreq *hreq, int *later)
{
	const char *connection, *upgrade, *key, *version, *protocols;
	char acceptval[29];
	int vernum;
	struct MHD_Response *response;

	/* is an upgrade to websocket ? */
	upgrade = afb_hreq_get_header(hreq, MHD_HTTP_HEADER_UPGRADE);
	if (upgrade == NULL || strcasecmp(upgrade, websocket_s))
		return 0;

	/* is a connection for upgrade ? */
	connection = afb_hreq_get_header(hreq, MHD_HTTP_HEADER_CONNECTION);
	if (connection == NULL || !headerhas (connection, MHD_HTTP_HEADER_UPGRADE))
		return 0;

	/* is a get ? */
	if(hreq->method != afb_method_get || strcasecmp(hreq->version, MHD_HTTP_VERSION_1_1))
		return 0;

	/* has a key and a version ? */
	key = afb_hreq_get_header(hreq, sec_websocket_key_s);
	version = afb_hreq_get_header(hreq, sec_websocket_version_s);
	if (key == NULL || version == NULL)
		return 0;

	/* is a supported version ? */
	vernum = atoi(version);
	if (vernum != 13) {
		response = MHD_create_response_from_buffer(0, NULL, MHD_RESPMEM_PERSISTENT);
		MHD_add_response_header (response, sec_websocket_version_s, "13");
		MHD_queue_response (hreq->connection, MHD_HTTP_BAD_REQUEST, response);
		MHD_destroy_response (response);
		*later = 1;
		return 1;
	}

	/* is the protocol supported ? */
	protocols = afb_hreq_get_header(hreq, sec_websocket_protocol_s);

	/* send the accept connection */
	make_accept_value(key, acceptval);
	response = MHD_create_response_from_buffer(0, NULL, MHD_RESPMEM_PERSISTENT);
	MHD_add_response_header (response, sec_websocket_accept_s, acceptval);
	MHD_add_response_header (response, MHD_HTTP_HEADER_CONNECTION, MHD_HTTP_HEADER_UPGRADE);
	MHD_add_response_header (response, MHD_HTTP_HEADER_UPGRADE, websocket_s);
	MHD_queue_response (hreq->connection, MHD_HTTP_SWITCHING_PROTOCOLS, response);
	MHD_destroy_response (response);

	*later = 0;
	return 1;
}

struct afb_websock *afb_websock_create(struct MHD_Connection *connection)
{
	struct afb_websock *result;

	result = malloc(sizeof * result);
	if (result) {
		result->connection = connection;
		result->fd = MHD_get_connection_info(connection, MHD_CONNECTION_INFO_CONNECTION_FD)->connect_fd;
		result->ws = websock_create(&afb_websock_itf, result);
		if (result->ws == NULL) {
			free(result);
			result = NULL;
		}
	}
	return result;
}