PHP - generate a date range progress bar chart as an image

chart-image.php

<?php 

// some defaults 
$start = new DateTime('2013-04-11');
$end = new DateTime('2013-05-09');
$current = new DateTime('2013-04-19');


if (isset($_REQUEST['s']))
  $start = new DateTime($_REQUEST['s']);

if (isset($_REQUEST['e']))
	$end = new DateTime($_REQUEST['e']);

if (isset($_REQUEST['c']))
	$current = new DateTime($_REQUEST['c']);



$dateChart = new GGADateProgressChart();
$dateChart->init(); 


// vertical grey line to the left of the blue bar 
$dateChart->draw_line($dateChart->bar_start-1, 1, $dateChart->bar_start-1, $dateChart->bottom_line_y);

// horizontal grey line to the bottom of the blue bar 
$dateChart->draw_line($dateChart->bar_start-1, $dateChart->bottom_line_y, $dateChart->bar_end, $dateChart->bottom_line_y);

// start date tick
$dateChart->draw_line($dateChart->bar_start-1, $dateChart->bottom_line_y, $dateChart->bar_start-1, $dateChart->bottom_line_y + $dateChart->tick_height);


// end date tick
$dateChart->draw_line($dateChart->bar_end, $dateChart->bottom_line_y, $dateChart->bar_end, $dateChart->bottom_line_y + $dateChart->tick_height);


// draw start date
$dateChart->draw_date($start, $dateChart->bar_start-1);

// draw end date
$dateChart->draw_date($end, $dateChart->bar_end);

// figure out how far into the date range we are and draw a progress bar accordingly
$total_days = date_diff($start, $end)->days;
$days_into_range = date_diff($start, $current)->days;
$percent_into_range = $days_into_range / $total_days;


// draw ticks at 25%, 50%, 75%
$percent_ticks_x = [];
for ($i = .25; $i <= .75 ; $i += .25)
	$percent_ticks_x[] = $dateChart->bar_start + floor($dateChart->bar_max_width * $i);



foreach ($percent_ticks_x as $p)
	$dateChart->draw_line($p, $dateChart->bottom_line_y, $p, $dateChart->bottom_line_y + $dateChart->tick_height);


// create dates for 25%, 50% and 75%
$percent_date = [];
for ($i = .25; $i <= .75 ; $i += .25) 
	$percent_date[] = date_add(clone $start, new DateInterval('P' . floor($total_days * $i) . 'D'));


// draw dates at 25%, 50%, 75%
for ($i=0; $i < 3; $i++)
	$dateChart->draw_date($percent_date[$i], $percent_ticks_x[$i]);



$dateChart->draw_progress_bar($percent_into_range);





header('Content-type: image/png');
imagepng($dateChart->im);
imagedestroy($dateChart->im);

die();





class GGADateProgressChart {

	var $month_year = 'n/d';
	var $font = 'arial.ttf';
	var $font_size = 9;
	var $bottom_line_y = 26;
	var $tick_height = 3;
	var $text_top_padding = 3;
	var $bar_max_width;
	var $bar_width;
	var $bar_height = 22;
	var $bar_top_x = 2;
	var $bar_start = 18;
	var $bar_end = 244;
	var $im;
	var $textcolor;
	var $bluebar;
	var $greyline;
	var $width = 260;
	var $height = 45;

	function init() {
		$this->bar_max_width = $this->bar_end - $this->bar_start;

		// create image resource
		$this->im = imagecreate($this->width, $this->height);
		
		//background 
		$bg = imagecolorallocate($this->im, 246, 246, 247);
		
		// grey text
		$this->textcolor = imagecolorallocate($this->im, 103, 103, 103);

		// blue progress bar
		$this->bluebar = imagecolorallocate($this->im, 26, 117, 187);
		
		// lines and ticks
		$this->greyline = imagecolorallocate($this->im, 175, 175, 175);
		
	}


	function draw_date($date, $text_center) {
		$date_string = date($this->month_year, date_timestamp_get( $date));
		$box = imagettfbbox($this->font_size, 0, $this->font, $date_string);
		$text_width = abs($box[4] - $box[0]);
		$text_height = abs($box[5] - $box[1]);
		$text_start = $text_center - ($text_width / 2);
		imagettftext($this->im, $this->font_size, 0, $text_start, $this->bottom_line_y + $text_height + $this->tick_height + $this->text_top_padding, $this->textcolor, $this->font, $date_string);	
	}

	function draw_line($from_x, $from_y, $to_x, $to_y) {
		imageline($this->im, $from_x, $from_y, $to_x, $to_y, $this->greyline);
	}

	function draw_progress_bar($percent_progress) {
		$bar_width = ceil($this->bar_max_width * $percent_progress);
		imagefilledrectangle($this->im, $this->bar_start, $this->bar_top_x, $this->bar_start +	 $bar_width, $this->bar_top_x + $this->bar_height, $this->bluebar);
	}


}