/*
SPDX-License-Identifier: AGPL-3.0-or-later
Copyright (C) 2026 mrkubax10 <mrkubax10@onet.pl>
*/

#include <apr_base64.h>
#include <httpd.h>
#include <http_core.h>
#include <http_protocol.h>
#include <http_log.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <util_cookies.h>
#include <util_md5.h>

static const char* const TOKEN_COOKIE_NAME = "webgate_token";

// Returns true if user agent of client which performed the request looks like Git
static bool check_user_agent_exception(request_rec* r) {
	static const char GIT_USER_AGENT_PREFIX[] = "git/";
	const char* const user_agent = apr_table_get(r->headers_in, "User-Agent");
	if(!user_agent || strncmp(user_agent, GIT_USER_AGENT_PREFIX, sizeof(GIT_USER_AGENT_PREFIX))!=0)
		return false;
	return apr_table_get(r->headers_in, "Git-Protocol");
}

static char* generate_token(apr_pool_t* pool) {
	char rnd[32];
	apr_generate_random_bytes(rnd, sizeof(rnd));
	char rnd_md5[APR_MD5_DIGESTSIZE];
	apr_md5(rnd_md5, rnd, sizeof(rnd));

	const apr_size_t encoded_size = apr_base64_encode_len(sizeof(rnd_md5));
	char* output = apr_palloc(pool, encoded_size);
	apr_base64_encode(output, rnd_md5, sizeof(rnd_md5));
	return output;
}

// Generates new token and sets HTTP cookie containing it then presents client with challenge
static void handle_challenge(request_rec* r) {
	char* generated = generate_token(r->pool);
	ap_cookie_write(r, TOKEN_COOKIE_NAME, generated, NULL, 0, r->headers_out, NULL);
	ap_rprintf(r, "Token: %s\n", generated);
}

static int request_check_handler(request_rec* r) {
	// Provide exception for requests performed by Git
	if(check_user_agent_exception(r))
		return DECLINED;
	// Check if client already has the token
	const char* token;
	if(ap_cookie_read(r, TOKEN_COOKIE_NAME, &token, 0)!=APR_SUCCESS || !token) {
		handle_challenge(r);
		return OK;
	}

	return OK;
}

static void register_hooks(apr_pool_t* pool) {
	ap_hook_handler(request_check_handler, NULL, NULL, APR_HOOK_FIRST);
}

module AP_MODULE_DECLARE_DATA webgate_module = {
	STANDARD20_MODULE_STUFF,
	NULL,
	NULL,
	NULL,
	NULL,
	NULL,
	register_hooks
};