<?php

// Send header
header("content-type: image/gif");

// Check for Magic Quotes
// Is magic quotes on? 
if (get_magic_quotes_gpc()) { 
	// Yes? Strip the added slashes 
	$_REQUEST = array_map('stripslashes', $_REQUEST); 
	$_GET = array_map('stripslashes', $_GET); 
	$_POST = array_map('stripslashes', $_POST); 
	$_COOKIE = array_map('stripslashes', $_COOKIE); 
}

// Declare global variables here.
$fu;

// do string processing here, and call the individual functions.
function calculate($input) {
	$$fu = makeJS($input);
	drawGraph($$fu,$xmin,$xmax,$ymin,$ymax);
	return;
}

// Finds the correct $location of the $x and y $axis.
function findAxis ($xmin,$xmax,$ymin,$ymax) {
	$axis = Array();
	array_push($axis, round((-1*$xmin)/($xmax - $xmin)*$size));
	array_push($axis, round($ymin/($ymax-$ymin)*$size+$size));
	return $axis;
}

// Change the numbering of the $axis according to the scale found above.
// This needs reworking.  Doesn't calculate the number correctly.
// Got the y in the correct direction at least.
function changeAxis ($xjump,$yjump,$xmin,$xmax,$ymin,$ymax) {

	return;
}

// Find the $size of the jump between each gridline
function findJump($vmin, $vmax) {
	return ($vmax-$vmin)/15;
}

// Takes $a position on the canvas and returns the value of the $x variable.
function xloc($location,$jump,$xmin) {
	return 	(($location*$jump/15)+$xmin);
}
// Takes $a position on the canvas and returns the value of the y variable.
function yloc($location,$jump,$ymin) {
	return 	(($location*$jump/15)+$ymin)*-1;
}
// Takes $a position on the canvas and returns the value of the canvas $x variable.
function ixloc($location,$xmin,$xmax) {
	return 	$size*($location-$xmax)/($xmax-$xmin);
}
// Takes $a position on the canvas and returns the value of the canvas y variable.
function iyloc($location,$ymin,$ymax, $size) {
	return $size*($ymax-$location)/($ymax-$ymin);
}

// turns a string into a polynomial

// Turns $a polynomial into the correct PHP syntax.
function polyJS($x)
{	
	while (preg_match('/\^/', $x)&&($m<10))
	{					
		$az = strpos($x,'^');	
		$a = substr($x, 0, $az);		
		$z = substr($x, $az+1);				
		$$p = 0; 
		$$ch;
		$lim = $az-1;
		while (true)
		{
			$ch = charAt($a, $lim);					
			if ($ch == ')') $p++;
			else if ($ch == '(') $p--;
			if ($p < 0 || !$p && (!($lim+1) || preg_match('/[\+\-\*\/\,]/', $ch))) break;
			$lim--;
		}		
		$a = substr($a, 0, $lim+1).'pow('.substr($a, $lim+1, $az);
		$lim = 0; $p = 0;
		while (true)
		{
			$ch = charAt($z, $lim);			
			if ($ch == '(') $p++;
			else if ($ch == ')') $p--;
			if ($p < 0 || !$p && ($lim == count($z) || $lim > 0 && preg_match('/[\+\-\*\/\^\,]/', $ch))) {
				 break;
			}
			$lim++;
		}
		$z = substr($z, 0, $lim).')'.substr($z, $lim);
		$x = $a.','.$z;
	}
	return $x;
}

// Converts the text by the user to the Javascript functions.
function makeJS($x)
{	
	$x = strtolower($x);
	$x = preg_replace('/ln\((.*?)\)/','log($1)',$x);
	$x = preg_replace('/rand(om)\((.*?)\)/','rand()',$x);
	$x = preg_replace('/acsc\((.*?)\)/','acos(1/($1))',$x);
	$x = preg_replace('/sech\((.*?)\)/','2/(exp($1)+exp(-1*($1)))',$x);
	$x = preg_replace('/acot\((.*?)\)/','atan(-1*($1))',$x);
	$x = preg_replace('/sec\((.*?)\)/','1/sin($1)',$x);
	$x = preg_replace('/cot\((.*?)\)/','1/tan($1)',$x);
	$x = preg_replace('/acoth\((.*?)\)/','log(($1+1)/($1-1))/2',$x);
	$x = preg_replace('/asech\((.*?)\)/','log(1/($1)+sqrt(1/(($1)*($1))-1))',$x);
	$x = preg_replace('/acsch\((.*?)\)/','log(1/($1)+sqrt(1/(($1)*($1))+1))',$x);	
	$reg = '/(x|e|pi|\)|\}|\])(e|\d)/';
	$x = polyJS($x);
		for ($l=0;$l<=strlen($x)-1;$l++) {
		$a = substr($x,$l,2);
		if (preg_match($reg,$a)) {
			$x = substr($x,0,$l+1)."*".substr($x,$l+1);
		}
	}			
	$reg = '/(\d|e|pi|x|\)|\}|\])(\(|\{|\[|x|a|c|f|l|m|p|r|s|tan|pi)/';
	for ($l=0;$l<=strlen($x)-1;$l++) {
		$a = substr($x,$l,2);
		if (preg_match($reg,$a)) {
			$x = substr($x,0,$l+1)."*".substr($x,$l+1);
		}
	}
	$x = preg_replace('/x(?!p)/', '$x', $x);
	return $x;
}

// The important actual calculations.  Hopefully this is secure.
function f($x, $fu) {
	eval("return \$return=" . $fu . ";");
	return $return;
}

function validate($input) {
	$input = preg_replace("/[^a-z0-9()\*\/\\\^\+-\s]+/", "", $input);
	$input = preg_replace("/[fd]/","", $input);
	// Just in case, strip BAD php commands
	$input = preg_replace("/(exec|shell|file|passthru|escapeshellcmd|popen|pcntl_exec)/", "", $input);
	$input = preg_replace("/'/","",$input);
	$input = preg_replace('/"/','',$input);
	return $input;
}

function charAt($str, $pos){
       return (substr($str, $pos, 1)) ? substr($str, $pos, 1) : -1;
}

// Get the user information and validate it.
$fu = strip_tags(preg_replace('/plus/','+',$_GET['f']));
$fu = preg_replace('/\{\}/', '', $fu);
$fuarray = split(';', $fu);

// Create a hash of the information the user has entered AFTER it's been validated, and
// check to see if this image has been done before.  If it has, return the image, otherwise, redraw
// the image and cache it.
$image_path = "cache/".md5(implode("",$fuarray));

if (file_exists($image_path)) {
	// Read the cached file.
	readfile($image_path);
} else {
		
	// Get User Defined Properties
	// Not sure yet if I want to do this by reading a config file (added security problems) or finding a way to output
	// an image when the parameters are called through $_POST
	
	$size = 270;
	$width = $size;
	$height = 270;	
	$xmin = -10;
	$xmax = 10;
	$ymin = -10;
	$ymax = 10;	
	
	// Start New Image creation
	$image = imagecreatetruecolor($width,$height);
	imageantialias($image, true);
	$white = imagecolorallocate($image, 255, 255, 255);
	$black = imagecolorallocate($image, 0, 0, 0);
	$red = imagecolorallocate($image, 255, 0, 0);
	$blue = imagecolorallocate($image, 0, 0, 255);
	$green = imagecolorallocate($image, 0, 255, 0);
	$grey = imagecolorallocate($image, 228, 226, 235);
	// White background
	imagefilledrectangle($image, 0, 0, $width, $height, $grey);
	
	// $axis
	imagefilledrectangle($image, 136, 15, 138, 255, $red);
	imagefilledrectangle($image, 17, 134, 257, 136, $red);
	
	// This section creates the labels for the $axis
	// Numbers on left side
	for ($i=0;$i<=16;$i++) {
		$num = -1*($i-8);
		if ($num<0) {
			$$x = 2;	
		} else {
			$$x = 8;
		}
		$y = 15*$i+7;
		ImageString($image, 3, $$x, $y, $num, $black);
	}
	
	// Numbers across bottom
	for ($i=0;$i<=16;$i++) {
		$num = $i-8;
		If ($num >= 0){
			$$x = 15*$i + 14;
		} else {
			$$x = 15*$i + 8;
		}
		$y = 255;
		ImageString($image, 3, $$x, $y, $num, $black);
	}

	// Gridlines
	// Vertical lines
	for ($i=15;$i<=$width-14;$i+=15) {
		imageline($image, $i+2, 15, $i+2, 255, $black);
	}
	// Horizontal lines
	for ($i=15;$i<=$width-14;$i+=15) {	
		imageline($image, 17, $i, 257, $i, $black);
	}
	
	$color = $blue;
	// Draw the actual functions themselves
	for ($j=0; $j<=count($fuarray)-1; $j++) {
		$fu = validate($fuarray[$j]);
		$fu = makeJS($fu);
		for ($i=15;$i<=$width-14;$i++) {
			$newx = round($i/15, 2) - 9;
			$y =  -f($newx,$fu);
			if (is_infinite($y)) {
				/*if ($y > 0) {
					$y = -1*$size;
				} else {
					$y = $size;
				}*/
				continue;
			}
			$newj = round(($y+9)*15, 0);
			$oldx = round(($i-1)/15, 2) - 9;	
			$y = -f($oldx,$fu);
			if (is_infinite($y)) {
				/*if ($y > 0) {
					$y = -1*($size-14);
				} else {
					$y = $size-14;
				}*/
				continue;
			}		
			$oldj = round(($y+9)*15, 0);	
			if (($newj>=15)&&($oldj>=15)) {		
				imageline($image, $i+1, $oldj, $i+3, $newj, $color);
			}
		}
	}

	imagegif($image);
	imagegif($image, $image_path);
	imagedestroy($image);
}
?>