package ie.dcu.plugin;

import java.io.*;
import java.net.*;
import java.util.*;

import org.xml.sax.*;
import org.xml.sax.helpers.*;

public class PluginLoader {
	public static final String SPECFILE = "plugin.xml";
	
	private final File root;
	private final Map<String, String> metadata;
	private final List<JarResource> jarFiles;
	private URLClassLoader pluginClassLoader;
	
	public PluginLoader(File root) {
		this.root = root;
		this.metadata = new HashMap<String, String>();
		this.jarFiles = new ArrayList<JarResource>();
		
		// Extract plugin name
		String name = root.getName();
		int idx = name.lastIndexOf('.');
		if (idx > 1) {
			name = name.substring(0, idx);
		}
		metadata.put("name", name);
	}
	
	public File getRootFolder() {
		return root;
	}
	
	public File getSpecFile() {
		return new File(root, SPECFILE);
	}
	
	public Map<String, String> getMetadata() {
		return metadata;
	}
	
	public String getMetaValue(String key) {
		return metadata.get(key);
	}
	
	public Plugin load() throws PluginException {
		try {
			loadMetadata();
			loadJars();
			return new Plugin(root, metadata, pluginClassLoader);
		} catch (SAXException e) {
			throw new PluginException(e);
		} catch (IOException e) {
			throw new PluginException(e);
		}
	}
	
	public Class<?> loadClass(String name) throws ClassNotFoundException {
		if (pluginClassLoader == null) {
			throw new IllegalStateException("load() not called");
		}
		return pluginClassLoader.loadClass(name);
	}

	private void addJarFile(String path) throws MalformedURLException {
		jarFiles.add(new JarResource(root, path));
	}

	private void addMetadata(String key, String value) {
		metadata.put(key, value);
	}

	private void loadMetadata() throws SAXException, IOException {
		BufferedReader reader = new BufferedReader(
			new FileReader(getSpecFile()));
		try {
			InputSource source = new InputSource(reader);
			XMLReader xmlreader = XMLReaderFactory.createXMLReader();
			xmlreader.setContentHandler(new SaxHandler());
			xmlreader.parse(source);
		} finally {
			reader.close();
		}
	}

	private void loadJars() {
		URL[] jarUrls = new URL[jarFiles.size()];
		int i = 0;
		for (JarResource resource : jarFiles) {
			jarUrls[i++] = resource.url;
		}
		ClassLoader parent = getClass().getClassLoader();
		pluginClassLoader = new PluginClassLoader(root, jarUrls, parent);
	}

	private class SaxHandler extends DefaultHandler {
		private Attributes attrs;
		private String elem;
		
		String getMandatoryAttribute(String name) throws SAXException {
			String value = attrs.getValue(name);
			if (value == null) {
				exception("Missing mandatory attribute '%s'", name);
			}
			return value;
		}
		
		private void exception(String message, Object ... args) 
			throws SAXException {
			String a = String.format(message, args);
			String m = String.format("In element <%s>: %s", elem, a);
			throw new SAXException(m);
		}

		public void startElement(String uri, String localName, String name,
			Attributes attributes) throws SAXException {
			elem = name;
			attrs = attributes;
			parseElem();
		}

		private void parseElem() throws SAXException {
			if (elem.equals("meta")) {
				String name = getMandatoryAttribute("name");
				String value = getMandatoryAttribute("value");
				addMetadata(name, value);
			} else if (elem.equals("jar")) {
				String path = getMandatoryAttribute("file");
				try {
					addJarFile(path);
				} catch (MalformedURLException e) {
					throw new SAXException(e);
				}
				 
			} else {
				// Ignore other elements
			}
		}
	}
}

class JarResource {
	public final File file;
	public final URI uri;
	public final URL url;

	public JarResource(File root, String path) throws MalformedURLException {
		if (new File(path).isAbsolute()) {
			this.file = new File(path);
		} else {
			this.file = new File(root, path);
		}
		uri = file.toURI();
		url = uri.toURL();
	}
}