/* 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 <tls.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;
	struct tls_config *tls;
	char *trust;
	char *account;
	char *nick;
	char *pronouns;
} info;

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

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:\n"
		"%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:\n"
			"%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 int connectSock(void) {
	log("Connecting to %s:%s", info.host, info.port);
	for (struct addrinfo *ai = info.addr; ai; ai = ai->ai_next) {
		int sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
		if (sock < 0) err(EX_OSERR, "socket");

		int error = connect(sock, ai->ai_addr, ai->ai_addrlen);
		if (!error) return sock;

		close(sock);
	}
	printf(
		"Could not connect to %s:%s: %s.\n",
		info.host, info.port, strerror(errno)
	);
	return -1;
}

static struct tls *connectTLS(int sock) {
	struct tls *client = tls_client();
	if (!client) errx(EX_SOFTWARE, "tls_client");

	int error = tls_configure(client, info.tls);
	if (error) errx(EX_SOFTWARE, "tls_configure: %s", tls_error(client));

	error = tls_connect_socket(client, sock, info.host)
		|| tls_handshake(client);
	if (!error) return client;

	printf(
		"Could not establish TLS with %s:%s:\n"
		"%s\n",
		info.host, info.port, tls_error(client)
	);
	tls_close(client);
	tls_free(client);
	close(sock);
	return NULL;
}

static int getTLS(const char *configHome) {
	info.tls = tls_config_new();
	if (!info.tls) errx(EX_SOFTWARE, "tls_config_new");

	struct tls *client = tls_client();
	if (!client) errx(EX_SOFTWARE, "tls_client");

	int error = tls_configure(client, info.tls);
	if (error) errx(EX_SOFTWARE, "tls_configure: %s", tls_error(client));

	int sock = connectSock();
	if (sock < 0) goto fail;

	log("Performing TLS handshake");
	error = tls_connect_socket(client, sock, info.host)
		|| tls_handshake(client);
	if (!error) {
		log("TLS established");
		tls_close(client);
		tls_free(client);
		close(sock);
		return 0;
	}
	printf(
		"Could not establish TLS with %s:%s:\n"
		"%s\n",
		info.host, info.port, tls_error(client)
	);

	// XXX: Comparing error strings, don't have a better way.
	bool selfSigned = !strcmp(
		tls_error(client),
		"certificate verification failed: self-signed certificate"
	);
	tls_close(client);
	tls_free(client);
	close(sock);
	if (!selfSigned) goto fail;

	int n = asprintf(&info.trust, "%s/catgirl/%s.pem", configHome, info.host);
	if (n < 0) err(EX_OSERR, "asprintf");

	char *suffix = info.trust;
	const char *home = getenv("HOME");
	size_t homeLen = strlen(home);
	if (!strncmp(suffix, home, homeLen)) {
		suffix += homeLen;
	}

	bool trustIt;
	int pop = yesno(
		&trustIt, true,
		"Trust the server's self-signed certificate?\n"
		"If you are sure you are connecting to the right place, answer yes.\n"
		"The current certificate will be saved and explicitly trusted for\n"
		"future connections to this network.\n"
		"The certificate will be written to:\n"
		"%s%s\n",
		(suffix != info.trust ? "~" : ""), suffix
	);
	if (pop || !trustIt) goto fail;

	tls_config_insecure_noverifycert(info.tls);
	tls_config_insecure_noverifyname(info.tls);
	sock = connectSock();
	if (sock < 0) goto fail;
	client = connectTLS(sock);
	if (!client) goto fail;

	size_t pemLen;
	const uint8_t *pem = tls_peer_cert_chain_pem(client, &pemLen);
	if (!pem) {
		printf(
			"Could not obtain TLS certificate from %s:%s.\n",
			info.host, info.port
		);
		goto fail;
	}

	log("Writing certificate to %s", info.trust);
	FILE *file = fopen(info.trust, "w");
	if (!file) err(EX_CANTCREAT, "%s", info.trust);
	fprintf(file, "subject= %s\n", tls_peer_cert_subject(client));
	fwrite(pem, pemLen, 1, file);
	error = fclose(file);
	if (error) err(EX_IOERR, "%s", info.trust);

	tls_close(client);
	tls_free(client);
	close(sock);

	tls_config_verify(info.tls);
	tls_config_insecure_noverifyname(info.tls);
	error = tls_config_set_ca_file(info.tls, info.trust);
	if (error) {
		errx(EX_SOFTWARE, "%s: %s", info.trust, tls_config_error(info.tls));
	}

	return 0;

fail:
	unset(&info.trust);
	tls_config_free(info.tls);
	info.tls = NULL;
	return -1;
}

static int getAccount(void) {
	int pop = prompt(
		&info.account, "",
		"If you already have an account on %s, what is its name?\n"
		"If you have a NickServ account already, enter the name of the\n"
		"account. If you aren't sure, leave this blank.\n",
		info.network
	);
	if (pop) return pop;
	if (!info.account[0]) return 0;

	info.nick = strdup(info.account);
	if (!info.nick) err(EX_OSERR, "strdup");

	// TODO: Prompt for account password.
	return 0;
}

static int getNick(void) {
	return prompt(
		&info.nick, getenv("USER"),
		"What name would you like to use on %s?\n"
		"This is the name others will see on IRC, called a nick. It must be\n"
		"unique, and can usually contain letters, digits, underscores and\n"
		"hyphens, but cannot start with a digit.\n",
		info.network
	);
}

static int getPronouns(void) {
	return prompt(
		&info.pronouns, NULL,
		"What are your pronouns?\n"
		"This will be added to your \"real name\" so that other IRC users can\n"
		"find out how to refer to you with /whois.\n"
		"Examples: they/them, she/her, he/him\n"
	);
}

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 if (!info.tls) {
			pop = getTLS(configHome);
			if (pop) {
				freeaddrinfo(info.addr);
				info.addr = NULL;
				unset(&info.host);
				unset(&info.port);
			}
		} else if (!info.account) {
			pop = getAccount();
			if (pop) {
				unset(&info.trust);
				freeaddrinfo(info.addr);
				info.addr = NULL;
				unset(&info.host);
				unset(&info.port);
			}
		} else if (!info.nick) {
			pop = getNick();
			if (pop) unset(&info.account);
		} else if (!info.pronouns) {
			pop = getPronouns();
			if (pop) unset(&info.nick);
		} 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);
	}
	if (info.trust) {
		fprintf(file, "trust = %s.pem\n", info.host);
	}
	fprintf(file, "nick = %s\n", info.nick);
	if (strlen(info.pronouns) > 1) {
		fprintf(file, "real = %s [%s]\n", info.nick, info.pronouns);
	}

	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");
}