/* Copyright (C) 2022  June McEnroe <june@causal.agency>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 * Additional permission under GNU GPL version 3 section 7:
 *
 * If you modify this Program, or any covered work, by linking or
 * combining it with OpenSSL (or a modified version of that library),
 * containing parts covered by the terms of the OpenSSL License and the
 * original SSLeay license, the licensors of this Program grant you
 * additional permission to convey the resulting work. Corresponding
 * Source for a non-source form of such a combination shall include the
 * source code for the parts of OpenSSL used as well as that of the
 * covered work.
 */

#include <err.h>
#include <errno.h>
#include <limits.h>
#include <netdb.h>
#include <netinet/in.h>
#include <resolv.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sysexits.h>
#include <unistd.h>

char *readpassphrase(const char *prompt, char *buf, size_t bufsiz, int flags);

static bool verbose;
static void log(const char *format, ...) __attribute__((format(printf, 1, 2)));
static void log(const char *format, ...) {
	va_list ap;
	if (!verbose) return;
	va_start(ap, format);
	fprintf(stderr, "# ");
	vfprintf(stderr, format, ap);
	fprintf(stderr, "\n");
	va_end(ap);
}

static int prompt1(char **resp, const char *def, const char *desc) {
	static char *buf;
	static size_t cap;

	size_t head = strcspn(desc, "\n");
	for (*resp = NULL; !*resp;) {
		printf("%.*s [%s] ", (int)head, desc, (def ?: ""));
		ssize_t len = getline(&buf, &cap, stdin);
		if (len < 0 && feof(stdin)) {
			printf("\n");
			clearerr(stdin);
			return -1;
		} else if (len < 0) {
			err(EX_IOERR, "getline");
		}
		if (len && buf[len-1] == '\n') buf[len-1] = '\0';

		if (buf[0] == '?') {
			printf("\n%s\n", &desc[head+1]);
		} else if (buf[0]) {
			*resp = strdup(buf);
			if (!*resp) err(EX_OSERR, "strdup");
		} else if (def) {
			*resp = strdup(def);
			if (!*resp) err(EX_OSERR, "strdup");
		}
	}
	return 0;
}

static int prompt(char **resp, const char *def, const char *format, ...)
__attribute__((format(printf, 3, 4)));
static int prompt(char **resp, const char *def, const char *format, ...) {
	va_list ap;
	char desc[1024];
	va_start(ap, format);
	vsnprintf(desc, sizeof(desc), format, ap);
	va_end(ap);
	return prompt1(resp, def, desc);
}

static int yesno(bool *resp, bool def, const char *format, ...)
__attribute__((format(printf, 3, 4)));
static int yesno(bool *resp, bool def, const char *format, ...) {
	va_list ap;
	char desc[1024];
	va_start(ap, format);
	vsnprintf(desc, sizeof(desc), format, ap);
	va_end(ap);
	char *str;
	for (;;) {
		int pop = prompt1(&str, (def ? "yes" : "no"), desc);
		if (pop) return pop;
		char yn = str[0];
		free(str);
		if (yn == 'Y' || yn == 'y') {
			*resp = true;
			return 0;
		} else if (yn == 'N' || yn == 'n') {
			*resp = false;
			return 0;
		}
	}
}

static struct {
	char *network;
	char *config;
	char *host;
	char *port;
	struct addrinfo *addr;
} info;

static int getNetwork(const char *def) {
	return prompt(
		&info.network, def,
		"Which network would you like to connect to?\n"
		"Enter the domain name of the IRC network you wish to connect to.\n"
		"Examples: tilde.chat, libera.chat\n"
	);
}

static int getConfig(const char *configHome) {
	char *name = strdup(info.network);
	if (!name) err(EX_OSERR, "strdup");
	char *prev = NULL, *next = NULL;
	while (name) {
		prev = next;
		next = strsep(&name, ".");
	}

	const char *home = getenv("HOME");
	const char *suffix = configHome;
	size_t homeLen = strlen(home);
	if (!strncmp(configHome, home, homeLen)) {
		suffix += homeLen;
	}
	int pop = prompt(
		&info.config, prev,
		"What would you like to name this configuration?\n"
		"This is the name you will pass to catgirl to connect to %s.\n"
		"Example: $ catgirl %s\n"
		"The configuration will be written to: %s%s/catgirl\n",
		info.network, prev, (suffix != configHome ? "~" : ""), suffix
	);
	free(name);
	if (pop) return pop;

	char path[PATH_MAX];
	snprintf(path, sizeof(path), "%s/catgirl/%s", configHome, info.config);
	if (!access(path, F_OK)) {
		printf(
			"There is already a configuration named %s.\n"
			"Please remove or rename the file: %s%s/catgirl/%s\n"
			"Otherwise, enter a different name.\n",
			info.config, (suffix != configHome ? "~" : ""), suffix, info.config
		);
		free(info.config);
		info.config = NULL;
	}
	return 0;
}

static int srvLookup(char **host, char **port, const char *name) {
	char dname[256];
	snprintf(dname, sizeof(dname), "_ircs._tcp.%s", name);
	log("Looking up SRV record for %s", dname);

	uint8_t msg[512];
	int len = res_query(dname, 1 /* IN */, 33 /* SRV */, msg, sizeof(msg));
	if (len < 12) return -1;

	uint8_t *ptr = &msg[12];
#define NAME_SKIP \
	for (uint8_t n; ptr < &msg[len] && (n = *ptr++); ptr += n) { \
		if (n & 0xC0) { ptr++; break; } \
	}

	uint16_t qdcount = msg[4] << 8 | msg[5];
	for (uint16_t q = 0; ptr < &msg[len] && q < qdcount; ++q) {
		NAME_SKIP; // QNAME
		ptr += 4; // QTYPE, QCLASS
	}

	NAME_SKIP; // NAME
	ptr += 14; // TYPE, CLASS, TTL, RDLENGTH, Priority, Weight
	if (&msg[len] < ptr + 3) return -1;
#undef NAME_SKIP

	int n = asprintf(port, "%d", ptr[0] << 8 | ptr[1]);
	if (n < 0) err(EX_OSERR, "asprintf");
	ptr += 2;

	// Name compression is not used for Target.
	if (!ptr[0]) return -1;
	char *host0 = (char *)&ptr[1];
	for (uint8_t n; ptr < &msg[len] && (n = *ptr); ptr += n) {
		*ptr++ = '.';
	}
	*host = strdup(host0);
	if (!*host) err(EX_OSERR, "strdup");
	return 0;
}

static int getHostPort(void) {
	int error = srvLookup(&info.host, &info.port, info.network);
	if (!error) {
		log("Found SRV record %s:%s", info.host, info.port);
		return 0;
	}

	char *ircdot = info.network;
	if (strncmp(ircdot, "irc.", 4)) {
		int n = asprintf(&ircdot, "irc.%s", ircdot);
		if (n < 0) err(EX_OSERR, "asprintf");
	}

	int pop = prompt(
		&info.host, ircdot,
		"Which host should catgirl connect to?\n"
		"Enter the hostname of the IRC server to connect to. Usually this\n"
		"starts with \"irc.\".\n"
	);
	free(ircdot);
	if (pop) return pop;

	return prompt(
		&info.port, "6697",
		"Which port should catgirl connect to?\n"
		"Enter the port number of the IRC server. This must be the port for\n"
		"TLS, also called SSL.\n"
	);
}

static int getAddr(void) {
	log("Looking up %s:%s", info.host, info.port);
	struct addrinfo hints = {
		.ai_family = AF_UNSPEC,
		.ai_socktype = SOCK_STREAM,
		.ai_protocol = IPPROTO_TCP,
	};
	int error = getaddrinfo(info.host, info.port, &hints, &info.addr);
	if (error) {
		log("%s", gai_strerror(error));
		printf("Could not find %s.\n", info.host);
		return -1;
	}
	return 0;
}

static void unset(char **resp) {
	free(*resp);
	*resp = NULL;
}

int main(int argc, char *argv[]) {
	for (int opt; 0 < (opt = getopt(argc, argv, "v"));) {
		switch (opt) {
			break; case 'v': verbose = true;
			break; default: return EX_USAGE;
		}
	}

	char configHome[PATH_MAX];
	if (getenv("XDG_CONFIG_HOME")) {
		snprintf(
			configHome, sizeof(configHome), "%s", getenv("XDG_CONFIG_HOME")
		);
	} else if (getenv("HOME")) {
		snprintf(configHome, sizeof(configHome), "%s/.config", getenv("HOME"));
	} else {
		errx(EX_USAGE, "HOME unset");
	}

	char path[PATH_MAX];
	snprintf(path, sizeof(path), "%s/catgirl", configHome);
	int error = mkdir(path, S_IRWXU);
	if (error && errno != EEXIST) err(EX_CANTCREAT, "%s", path);
	umask(S_IRWXG | S_IRWXO);

	printf(
		"Welcome to catgirl enrollment! This tool should get you connected to\n"
		"IRC using catgirl :3\n"
		"\n"
		"Type ? at a prompt for a more detailed explanation.\n"
		"The default response is shown in [brackets].\n"
		"Press enter at a prompt to select the default response.\n"
		"Press control-D at a prompt to return to the previous one.\n"
		"\n"
	);

	int pop;
	for (;;) {
		if (!info.network) {
			// TODO: Parse ircs: URL in args.
			pop = getNetwork((optind < argc ? argv[optind] : NULL));
			if (pop) return EX_USAGE;
		} else if (!info.config) {
			pop = getConfig(configHome);
			if (pop) unset(&info.network);
		} else if (!info.host || !info.port) {
			pop = getHostPort();
			if (pop) unset(&info.config);
		} else if (!info.addr) {
			pop = getAddr();
			if (pop) {
				unset(&info.host);
				unset(&info.port);
			}
		} else {
			break;
		}
	}

	snprintf(path, sizeof(path), "%s/catgirl/%s", configHome, info.config);
	log("Writing configuration to %s", path);
	FILE *file = fopen(path, "w");
	if (!file) err(EX_CANTCREAT, "%s", path);

	fprintf(file, "host = %s\n", info.host);
	if (strcmp(info.port, "6697")) {
		fprintf(file, "port = %s\n", info.port);
	}

	error = fclose(file);
	if (error) err(EX_IOERR, "%s", path);

	printf(
		"\n"
		"You're all set! You can connect to %s using:\n"
		"$ catgirl %s\n"
		"\n",
		info.network, info.config
	);
	bool run;
	pop = yesno(
		&run, true,
		"Connect now?\n"
		"There's nothing left to do. This will start catgirl.\n"
	);
	if (pop || !run) return EX_OK;

	execlp("catgirl", "catgirl", info.config, NULL);
	err(EX_UNAVAILABLE, "catgirl");
}