Class that helps to load resources with dependencies easily, such as JavaScripts, CSSs

ResourceLoader.php

<?php

/**
 * @author Junaid P V (http://junaidpv.in)
 * @license GPLv3
 */

/**
 * Class that helps to load resource easily, such as JavaScripts, CSSs
 * 
 * @version 1.0
 */
class Resource_loader {
	
	private $libraryResources = array();
	private $resources = array();
	
	/**
	 * Add resources that reside on disk.
	 * 
	 * @param array $resources 
	 */
	public function add($resources) {
		foreach ($resources as $name => $resource) {			
			// It is always resource links added with this method
			$tmpArray = array('type' => 'link');
			
			// Add scripts if given
			if (isset($resource['scripts'])) {
				$tmpArray['scripts'] = $this->alwaysArray($resource['scripts']);
			}
			
			// Add styles if given
			if (isset($resource['styles'])) {
				$tmpArray['styles'] = $this->alwaysArray($resource['styles']);
			}
			
			if (isset($resource['dependencies'])) {
				$tmpArray['dependencies'] = $this->alwaysArray(
					$resource['dependencies']
				);
			}
			
			$this->resources[$name] = $tmpArray;
		}
	}
	
	/**
	 * Add library resources.
	 * Resource added by this method will be loaded
	 * when there is at leat one dependance for it
	 * 
	 * @param array $resources 
	 */
	public function addLibrary($resources) {
		foreach ($resources as $name => $resource) {
			// It is always resource links added with this method
			$tmpArray = array('type' => 'link');
			
			// Add scripts if given
			if (isset($resource['scripts'])) {
				$tmpArray['scripts'] = $this->alwaysArray($resource['scripts']);
			}
			
			// Add styles if given
			if (isset($resource['styles'])) {
				$tmpArray['styles'] = $this->alwaysArray($resource['styles']);
			}
			
			if (isset($resource['dependencies'])) {
				$tmpArray['dependencies'] = $this->alwaysArray(
					$resource['dependencies']
				);
			}
			
			$this->libraryResources[$name] = $tmpArray;
		}
	}
	
	/**
	 * Add resouces (JS and CSS) as raw string.
	 * 
	 * @param array $resources 
	 */
	public function addRaw($resources) {
		foreach ($resources as $name => $resource) {
			// It is always raw resources added by this method
			$tmpArray = array('type' => 'raw');
			
			if (isset($resource['scripts'])) {
				$tmpArray['scripts'] = $this->alwaysArray($resource['scripts']);
			}
			if (isset($resource['styles'])) {
				$tmpArray['styles'] = $this->alwaysArray($resource['styles']);
			}
			if (isset($resource['dependencies'])) {
				$tmpArray['dependencies'] = $this->alwaysArray(
					$resource['dependencies']
				);
			}
			
			$this->resources[$name] = $tmpArray;
		}
	}
	
	/**
	 * Add raw library resources.
	 * Resource added by this method will be loaded
	 * when there is at leat one dependance for it
	 * 
	 * @param array $resources 
	 */
	public function addRawLibrary($resources) {
		foreach ($resources as $name => $resource) {
			// It is always raw resources added by this method
			$tmpArray = array('type' => 'raw');
			
			if (isset($resource['scripts'])) {
				$tmpArray['scripts'] = $this->alwaysArray($resource['scripts']);
			}
			if (isset($resource['styles'])) {
				$tmpArray['styles'] = $this->alwaysArray($resource['styles']);
			}
			if (isset($resource['dependencies'])) {
				$tmpArray['dependencies'] =
				$this->alwaysArray($resource['dependencies']);
			}
			
			$this->libraryResources[$name] = $tmpArray;
		}
	}

	
	/**
	 * Returns HTML snippet that can be inserted on web pages
	 * to be send to client.
	 * Caution: This funtion must not be called more than once.
	 * 
	 * @return string
	 */
	public function render() {
		// Get all resources in correct order.
		$ordered = $this->getOrdered();
		
		// Start with a blank html snippet.
		$html = '';
		foreach ($ordered as $res) {
			if ($res['type'] == 'raw') {
				// It is a raw resouce, we need to add the source code.
				if (isset($res['scripts'])) {
					$html .= "\n".'<script type="text/javascript">';
					foreach ($res['scripts'] as $script) {
						$html .= "\n" . $script;
					}
					$html .= '</script>';
				}
				if (isset($res['styles'])) {
					$html .= "\n".'<style type="text/css">';
					foreach ($res['styles'] as $style) {
						$html .= "\n" . $style;
					}
					$html .= '</style>';
				}
			} elseif ($res['type'] == 'link') {
				if (isset($res['scripts'])) {
					foreach ($res['scripts'] as $script) {
						$html .= "\n" . '<script type="text/javascript" src="'
								. $script . '"></script>';
					}
				}
				if (isset($res['styles'])) {
					foreach ($res['styles'] as $style) {
						$html .= "\n"
							. '<link rel="stylesheet" type="text/css" href="'
							. $style . '" />';
					}
				}
			}
		}
		return $html;
	}

	/**
	 * Get resource array having all resources in correct order.
	 */
	private function getOrdered() {
		// Get the unordered resource array.
		$source = $this->resources;
		// Create a blank ordered array to start with.
		$ordered = array();

		// Itereate over all items in unordered resource array to put every
		// item in correct order.
		while (true) {
			if (count($source) == 0) {
				// No more item in $source, let's stop it
				break;
			}
			
			// Get frist item in $source
			$pair = $this->array_kshift($source);
			// and put that item in correct order at $ordered.
			// putItemAtCorrectPosition will manage dependent items.
			$this->putItemAtCorrectPosition($pair[0], $pair[1], $ordered);
		}
		return $ordered;
	}
	
	/**
	 * Put the specified item at correct position in $ordered.
	 * If depended item(s) are in $source they will be put before the item.
	 * 
	 * @param array $item
	 * @param array $ordered
	 * @param array $source 
	 */
	private function putItemAtCorrectPosition($resourceName, $resource, &$ordered) {
		// Let's check about dependecies before putting item in $ordered.
		if (isset($resource['dependencies'])) {
			// Check whether any depended resource in $source
			// since all depended items should be in $ordered before
			// the current item put in.
			foreach ($resource['dependencies'] as $subject) {
				if (array_key_exists($subject, $ordered)) {
					// Depended is already included
					continue;
				}
				else {
					$source = null;
					if (array_key_exists($subject, $this->libraryResources)) {
						// Dependency is on library
						$source = $this->libraryResources;
					}
					elseif (array_key_exists($subject, $this->resources)) {
						// Dependency is on normal resource
						$source = $this->resources;
					}
					else {
						// Depended resource is not available at all.
						// It is mistake and let us throw and
						// exception informing about it.
						throw new Exception(
							"Depended item '$subject' could not be found"
						);
					}

					// Take a copy of it from source 
					$depended = $source[$subject];
					// Remove it from source
					unset($source[$subject]);
					// And put the depended item in $ordered
					// at correct position
					$this->putItemAtCorrectPosition(
						$subject,
						$depended,
						$ordered
					);
				}
			}
		}
		// We have already put every depended items in correct position,
		// so put current item at the end of $ordered.
		$ordered[$resourceName] = $resource;
	}
	
	private function alwaysArray($value) {
		return (is_array($value) ? $value : array($value));
	}
	
	/**
	 * Array shift with key
	 * 
	 * @param array $arr
	 * @return array 
	 */
	private function array_kshift(&$arr) {
		list($k) = array_keys($arr);
		$r  = array($k, $arr[$k]);
		unset($arr[$k]);
		return $r;
	}
	
	/**
	 * Sometimes some libraries needs to be loaded even some other script has
	 * no dependency on them, like posabsolute jquery validation.
	 * 
	 * @param string $name 
	 */
	public function alwaysLoadLibrary($name) {
		if (!array_key_exists($name, $this->resources)) {
			// No need to add if the library is already as normal resource
			
			if(array_key_exists($name, $this->libraryResources)) {
				// Move resource from library to normal
				// so it will be loaded always
				$this->resources[$name] = $this->libraryResources[$name];
				// then remove from library
				unset ($this->libraryResources[$name]);
			}
			else {
				// Resource is not on both library and normal resources
				throw new Exception(
							"Library '$name' not yet added!"
						);
			}
		}
	}

}