<?php
   // base URL for Google Charts API
   define('CHART_BASE_URL', 'http://chart.apis.google.com/chart');
   
   // config for configuration files
   define('CHART_CONFIG_PATH', 'config/');
   define('CHART_CONFIG_SUPPORT_PHP', true);
   define('CHART_CONFIG_EXT', 'php');
   
   // location to cache chart images
   define('CHART_CACHE_PATH', 'cache/');
   // default cache settings, these can be overriden in each config file
   define('CHART_CACHE_ENABLED', 'yes'); // possible values - "yes" or "no"
   define('CHART_CACHE_EXPIRY', 300);
   
   // http request details
   define('CHART_HTTP_TIMEOUT', 3);
   define('CHART_HTTP_REQUEST_TIME', 5);
   define('CHART_HTTP_USERAGENT', 'Chart Proxy');
   
   // nothing will work without CURL support, check for this
   if (function_exists('curl_init')) {
      // is the config name specified valid
      if (!empty($_GET['config']) && preg_match("/^[a-z0-9_-]+$/i", $_GET['config'])) {
         // create config and cache directories if they don't already exist
         if (!is_dir(CHART_CONFIG_PATH)) {
            @mkdir(CHART_CONFIG_PATH);
         }

         if (!is_dir(CHART_CACHE_PATH)) {
            @mkdir(CHART_CACHE_PATH);
         }
      
         // create full config path
         $sConfig = CHART_CONFIG_PATH.$_GET['config'].'.'.CHART_CONFIG_EXT;
      
         $aSettings = array(
            'cache' => CHART_CACHE_ENABLED,
            'expiry' => CHART_CACHE_EXPIRY
         );
      
         // does the specified config file actually exist
         if (file_exists($sConfig)) {
            // grab config file contents
            if (CHART_CONFIG_SUPPORT_PHP) {
               // parse any PHP and store lines in array
               ob_start();
               require($sConfig);
               $aConfig = explode("\n", ob_get_clean());
            } else {
               $aConfig = file($sConfig);
            }
         
            // set up variable to store generated chart URL
            $sChartUrl = CHART_BASE_URL.'?';
      
            // create URL to request chart
            foreach ($aConfig as $sParameter) {
               // pass config format, strip comments
               if (preg_match("/^\s*([0-9a-z\._-]+)\s*=\s*((\\\\#|[^#])*).*$/iu", $sParameter, $aMatches)) {
                  $aMatches[2] = trim(str_replace('\#', '#', $aMatches[2]));
                  // check for script configuration property (not sent to Google)
                  if (array_key_exists($aMatches[1], $aSettings)) {
                     $aSettings[$aMatches[1]] = $aMatches[2];
                  } else {
                     $sChartUrl .= $aMatches[1]."={$aMatches[2]}&";
                  }
               }
            }
         
            // clean up chart URL and create MD5 equivalent for cache filename
            $sChartUrl = rtrim($sChartUrl, '&');
            $sChartUrlMD5 = CHART_CACHE_PATH.md5($sConfig.filemtime($sConfig)).'.png';
         
            // convert cached property to boolean
            $aSettings['cache'] = ($aSettings['cache'] == 'yes');
         
            // set image type
            header('Content-type: image/png');
         
            // check if a valid cache file already exists
            if (!$aSettings['cache'] || !file_exists($sChartUrlMD5) || filemtime($sChartUrlMD5) < time() - $aSettings['expiry']) {
            
               $oCurl = curl_init($sChartUrl);
            
               curl_setopt($oCurl, CURLOPT_CONNECTTIMEOUT, CHART_HTTP_TIMEOUT);
               curl_setopt($oCurl, CURLOPT_TIMEOUT, CHART_HTTP_REQUEST_TIME);
               curl_setopt($oCurl, CURLOPT_USERAGENT, CHART_HTTP_USERAGENT);
               curl_setopt($oCurl, CURLOPT_HEADER, false);
               curl_setopt($oCurl, CURLOPT_RETURNTRANSFER, true);
            
               // request chart, if curl fails for any reason just redirect directly to Google to retrieve chart
               if ($oChart = curl_exec($oCurl)) {
                  if ($aSettings['cache']) {
                     file_put_contents($sChartUrlMD5, $oChart);
                  } else {
                     echo $oChart;
                  }
               } else {
                  header("Location: $sChartUrl");
                  exit;
               }
            }
         
            // write cached chart to browser if cache enabled
            if ($aSettings['cache']) {
               readfile($sChartUrlMD5);
            }
         } else {
            echo 'Error: Specified configuration file doesn\'t exit';
         }
      } else {
         echo 'Error: Invalid configuration filename format specified.';
      }
   } else {
      echo 'Error: CURL isn\'t available on your system. Read more about CURL - http://www.php.net/manual/en/ref.curl.php.';
   }
?>