/*
 * Copyright (c) 1989 - 1994, Julianne Frances Haugh
 * Copyright (c) 1996 - 2000, Marek Michałkiewicz
 * Copyright (c) 2000 - 2006, Tomasz Kłoczko
 * Copyright (c) 2007 - 2011, Nicolas François
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the copyright holders or contributors may not be used to
 *    endorse or promote products derived from this software without
 *    specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT
 * HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <assert.h>
#include <getopt.h>
#include <lastlog.h>
#include <pwd.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <time.h>
#include <stdbool.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <err.h>
#include <math.h>
#include <sys/param.h>

/*
 * Needed for MkLinux DR1/2/2.1 - J.
 */
#ifndef LASTLOG_FILE
#define LASTLOG_FILE "/var/log/lastlog"
#endif

/*
 * Global variables
 */
const char *Prog;		/* Program name */
static FILE *lastlogfile;	/* lastlog file stream */
static struct stat statbuf;	/* fstat buffer for file size */

// TODO just put that in a variable...
#define	NOW	(time ((time_t *) 0))

/* https://gist.github.com/ciembor/1494530
 * under the "do what you want :)" license */
float hue2rgb(float p, float q, float t) {
	if (t < 0)
		t += 1;
	if (t > 1)
		t -= 1;
	if (t < 1./6)
		return p + (q - p) * 6 * t;
	if (t < 1./2)
		return q;
	if (t < 2./3)
		return p + (q - p) * (2./3 - t) * 6;
	return p;
}
int byteclamp(int n) {
	if (n < 0) return 0;
	if (n > 0xFF) return 0xFF;
	return n;
}
int hsl2rgb(float h, float s, float l) {
	float r, g, b;

	if (0 == s) {
		r = g = b = l; // achromatic
	} else {
		float q = l < 0.5 ? l * (1 + s) : l + s - l * s;
		float p = 2 * l - q;
		r = hue2rgb(p, q, h + 1./3) * 255;
		g = hue2rgb(p, q, h) * 255;
		b = hue2rgb(p, q, h - 1./3) * 255;
	}

	return (byteclamp(r) << 16) + (byteclamp(g) << 8) + byteclamp(b);
}

static void print_one(const struct passwd *pw)
{
	char *cp;
	struct tm *tm;
	time_t ll_time;
	off_t offset;
	struct lastlog ll;
	char ptime[80];

	if (NULL == pw) {
		return;
	}

	if (pw->pw_uid < 1000 || pw->pw_uid == 65534) {
		return;
	}

	offset = (off_t) pw->pw_uid * sizeof(ll);
	if (offset + sizeof(ll) <= statbuf.st_size) {
		/* fseeko errors are not really relevant for us. */
		int err = fseeko(lastlogfile, offset, SEEK_SET);
		assert(0 == err);
		/* lastlog is a sparse file. Even if no entries were
		 * entered for this user, which should be able to get the
		 * empty entry in this case.
		 */
		if (fread((char *) &ll, sizeof(ll), 1, lastlogfile) != 1) {
			return;
		}
	} else {
		/* Outsize of the lastlog file.
		 * Behave as if there were a missing entry (same behavior
		 * as if we were reading an non existing entry in the
		 * sparse lastlog file).
		 */
		memset(&ll, 0, sizeof(ll));
	}


	ll_time = ll.ll_time;
	tm = localtime(&ll_time);
	strftime(ptime, sizeof(ptime), "%a %b %e %H:%M:%S %z %Y", tm);
	cp = ptime;

	if (ll.ll_time == (time_t) 0) {
		cp = "**Never logged in**\0";
	}
	int ago = NOW-ll.ll_time;
	float f = 1.0 - ((float)ago) / ((float)(60*60*24*365*5));
	if (f < 0.0) f = 0.0;
	f = pow(f, 3.0);
	float a = 80.0;
	float b = 2.5;
	f = MAX(f * f / b, f * a - a + 1.0);
	float hue = f * 90.0 + 260.;
	printf("<a href=\"/~%s\" style=\"background: #%06x\"></a>\n", pw->pw_name, hsl2rgb(hue / 360., .2 + f*.7, .1 + f*.9));
}

int main(void)
{
	const struct passwd *pwent;

	lastlogfile = fopen(LASTLOG_FILE, "r");
	if (NULL == lastlogfile) {
		perror(LASTLOG_FILE);
		exit(EXIT_FAILURE);
	}

	/* Get the lastlog size */
	if (fstat(fileno(lastlogfile), &statbuf) != 0) {
		err(1, "can't get lastlog size");
	}

	setpwent();
	while ( (pwent = getpwent()) != NULL ) {
		print_one(pwent);
	}
	endpwent();

	(void) fclose(lastlogfile);

	return EXIT_SUCCESS;
}