#!/usr/bin/perl

use Time::HiRes qw(usleep);
use POSIX;

$0 = "fan_t420s";

my $fan_min = 1;
my $fan_max = 7;
my $temp_max = 65;
my $setpoint = 48;
my $interval = 1;
my $integral = 0;
my $kc = 2;
#my $ti = 8;
my $td = 1;
my $kp = $kc;
#my $ki = 1 / $ti;
my $kd = 1 / $td; 
my $i = 0;
my $output_max = $kc * ($temp_max - $setpoint) + ($kd * 2) / $interval;
        
my $last_error = $setpoint - &getTemp; 

while (1) {
        my $temp = &getTemp;
        my $e = $setpoint - $temp; 
	#$i = $i + $e * $interval;
	my $d = ($e - $last_error)/$interval;
	#my $out = $kp * $e + $ki * $i + $kd * $d;
	my $out = $kp * $e + $kd * $d;
	$last_error = $e;
	$level = &getLevel($out);
	if ($e < 0) {       
		&setFanSpeed($level);
	} else {
		&setFanSpeed($fan_min);
	}
	#print "e:".$e."-->";
	#print "i:".$i."\(".($ki*$i)."\)-->";
	#print "d:".$d."\(".($kd*$d)."\)-->";
	#print "o:".$out."-->";
	#print $level."\n";
	sleep $interval; 
}

sub getLevel {
	my $result = $fan_min;
	my $output = shift;
	if ($output < 0) {
		$result = floor(abs($fan_max * $output / $output_max));
		if ($fan_max < $result) {
			$result = "full-speed";
		} elsif ($result < $fan_min) {
			$result = $fan_min;
		} 
	}
	return $result;
}

sub getTemp {
	my $sensor = `sensors | grep °C`;
	my ($temp) = ($sensor =~ m/temp\d:\s+\+(\d+)\.\d°C.*/);
	return $temp;
}

sub setFanSpeed {
	my $level = shift;
	`echo level $level > /proc/acpi/ibm/fan`;
}