// id.c, version 0.1.1
// OMKOV coreutils implementation of POSIX id
// Copyright (C) 2020, Jakob Wakeling
// MIT Licence

/*
	TODO Fix memory leak when listing supplementary groups (may be unfixable)
*/

#include "util/error.h"
#include "util/optget.h"

#include <grp.h>
#include <pwd.h>
#include <sys/types.h>
#include <unistd.h>

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define VERSION "0.1.1"

typedef struct passwd pwd_t;
typedef struct group  grp_t;

static struct lop lops[] = {
	{ "help",    ARG_NUL, 256 },
	{ "version", ARG_NUL, 257 },
	{ NULL, 0, 0 }
};

static char mode;
static bool nflag;
static bool rflag;

static inline void id(uid_t uid, uid_t euid, gid_t gid, gid_t egid);
static inline void groups(const char *user, gid_t gid, gid_t egid);

static void hlp(void);
static void ver(void);

int main(int ac, char *av[]) { A0 = av[0];
	struct opt opt = OPTGET_INIT; opt.str = "Ggnru"; opt.lops = lops;
	for (int o; (o = optget(&opt, av, 1)) != -1;) switch (o) {
	case 'G': case 'g': case 'u': {
		if (mode) { error(1, "invalid option combination"); }
		else { mode = (char)o; } break;
	}
	case 'n': { nflag = true; break; }
	case 'r': { rflag = true; break; }
	case 256: { hlp(); return 0; }
	case 257: { ver(); return 0; }
	default: { return 1; }
	}
	
	if (!mode && (nflag || rflag)) {
		error(1, "options 'n' and 'r' require 'G', 'g', or 'u'");
	}
	
	uid_t uid, euid; gid_t gid, egid;
	
	if (opt.ind == ac) {
		uid = getuid(); euid = geteuid();
		gid = getgid(); egid = getegid();
		id (uid, euid, gid, egid);
	}
	else for (char **p = &av[opt.ind]; *p; ++p) {
		pwd_t *pwd;
		
		if (!(pwd = getpwnam(*p))) { error(1, "%s: invalid user", *p); }
		
		uid = euid = pwd->pw_uid;
		gid = egid = pwd->pw_gid;
		id (uid, euid, gid, egid);
	}
	
	return 0;
}

static inline void id(uid_t uid, uid_t euid, gid_t gid, gid_t egid) {
	pwd_t *pwd; grp_t *grp;
	
	if (mode == 'G') {
		pwd = getpwuid(uid);
		groups(pwd->pw_name, gid, egid);
	}
	else if (mode == 'g') {
		grp = getgrgid(rflag ? gid : egid);
		nflag ? fputs(grp->gr_name, stdout) : printf("%u", grp->gr_gid);
	}
	else if (mode == 'u') {
		pwd = getpwuid(rflag ? uid : euid);
		nflag ? fputs(pwd->pw_name, stdout) : printf("%u", pwd->pw_uid);
	}
	else {
		pwd = getpwuid(uid); grp = getgrgid(gid);
		printf("uid=%u(%s) gid=%u(%s) ", uid, pwd->pw_name, gid, grp->gr_name);
		if (uid != euid) {
			pwd = getpwuid(euid);
			printf("euid=%u(%s) ", euid, pwd->pw_name);
			pwd = getpwuid(uid);
		}
		if (gid != egid) {
			grp = getgrgid(egid);
			printf("egid=%u(%s) ", egid, grp->gr_name);
		}
		fputs("groups=", stdout);
		groups(pwd->pw_name, gid, egid);
	}
	fputc('\n', stdout);
	
	return;
}

static inline void groups(const char *user, gid_t gid, gid_t egid) {
	grp_t *grp = getgrgid(gid);
	if (mode) { nflag ? fputs(grp->gr_name, stdout) : printf("%u", gid); }
	else { printf("%u(%s)", gid, grp->gr_name); }
	
	if (gid != egid) {
		grp = getgrgid(egid);
		if (mode) { nflag ? printf(" %s", grp->gr_name) : printf(" %u", egid); }
		else { printf(",%u(%s)", egid, grp->gr_name); }
	}
	
	setgrent();
	while ((grp = getgrent()) != NULL) {
		if (grp->gr_gid == gid || grp->gr_gid == egid) { continue; }
		for (int i = 0; grp->gr_mem[i]; ++i) {
			if (strcmp(grp->gr_mem[i], user) == 0) {
				if (mode) { nflag ? printf(" %s", grp->gr_name) :
					printf(" %u", grp->gr_gid); }
				else { printf(",%u(%s)", grp->gr_gid, grp->gr_name); }
			}
		}
	}
	endgrent();
	
	return;
}

static void hlp(void) {
	puts("id - return user identity\n");
	puts("usage: id [-G|-g|-u] [-nr] [user...]\n");
	puts("options:");
	puts("  -G         Output all group IDs");
	puts("  -g         Output only the effective group ID");
	puts("  -n         Output names of groups and users instead of their IDs");
	puts("  -r         Output the real ID instead of the effective ID");
	puts("  -u         Output only the effective user ID");
	puts("  --help     Display help information");
	puts("  --version  Display version information");
}

static void ver(void) {
	puts("OMKOV coreutils id, version " VERSION);
	puts("Copyright (C) 2020, Jakob Wakeling");
	puts("MIT Licence (https://opensource.org/licenses/MIT)");
}