/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
    *
   *  http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  package com.opensymphony.xwork2.util;
  
  import org.apache.logging.log4j.Logger;
  import org.apache.logging.log4j.LogManager;
  
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.lang.annotation.Annotation;
  import java.net.URL;
  import java.net.URLDecoder;
  import java.util.Enumeration;
  import java.util.HashSet;
  import java.util.Set;
  import java.util.jar.JarEntry;
  import java.util.jar.JarInputStream;
  
  /**
   * <p>ResolverUtil is used to locate classes that are available in the/a class path and meet
   * arbitrary conditions. The two most common conditions are that a class implements/extends
   * another class, or that is it annotated with a specific annotation. However, through the use
   * of the {@link Test} class it is possible to search using arbitrary conditions.</p>
   *
   * <p>A ClassLoader is used to locate all locations (directories and jar files) in the class
   * path that contain classes within certain packages, and then to load those classes and
   * check them. By default the ClassLoader returned by
   *  {@code Thread.currentThread().getContextClassLoader()} is used, but this can be overridden
   * by calling {@link #setClassLoader(ClassLoader)} prior to invoking any of the {@code find()}
   * methods.</p>
   *
   * <p>General searches are initiated by calling the
   * {@link #find(com.opensymphony.xwork2.util.ResolverUtil.Test, String...)} ()} method and supplying
   * a package name and a Test instance. This will cause the named package <b>and all sub-packages</b>
   * to be scanned for classes that meet the test. There are also utility methods for the common
   * use cases of scanning multiple packages for extensions of particular classes, or classes
   * annotated with a specific annotation.</p>
   *
   * <p>The standard usage pattern for the ResolverUtil class is as follows:</p>
   *
   *<pre>
   *ResolverUtil&lt;ActionBean&gt; resolver = new ResolverUtil&lt;ActionBean&gt;();
   *resolver.findImplementation(ActionBean.class, pkg1, pkg2);
   *resolver.find(new CustomTest(), pkg1);
   *resolver.find(new CustomTest(), pkg2);
   *Collection&lt;ActionBean&gt; beans = resolver.getClasses();
   *</pre> 
   *
   * <p>This class was copied from Stripes - http://stripes.mc4j.org/confluence/display/stripes/Home</p>
   * 
   * @author Tim Fennell
   */
  public class ResolverUtil<T> {
      /** An instance of Log to use for logging in this class. */
      private static final Logger LOG = LogManager.getLogger(ResolverUtil.class);
  
      /**
       * A simple interface that specifies how to test classes to determine if they
       * are to be included in the results produced by the ResolverUtil.
       */
      public static interface Test {
          /**
           * Will be called repeatedly with candidate classes.
           *
           * @param type class type
           * @return True if a class is to be included in the results, false otherwise.
           */
          boolean matches(Class type);
          
          boolean matches(URL resource);
  
          boolean doesMatchClass();
          boolean doesMatchResource();
      }
      
      public static abstract class ClassTest implements Test {
          public boolean matches(URL resource) {
              throw new UnsupportedOperationException();
          }
  
          public boolean doesMatchClass() {
              return true;
         }
         public boolean doesMatchResource() {
             return false;
         }
     }
     
     public static abstract class ResourceTest implements Test {
         public boolean matches(Class cls) {
             throw new UnsupportedOperationException();
         }
 
         public boolean doesMatchClass() {
             return false;
         }
         public boolean doesMatchResource() {
             return true;
         }
     }
 
     /**
      * A Test that checks to see if each class is assignable to the provided class. Note
      * that this test will match the parent type itself if it is presented for matching.
      */
     public static class IsA extends ClassTest {
         private Class parent;
 
         /** Constructs an IsA test using the supplied Class as the parent class/interface.
          * @param parentType the parent type class
          */
         public IsA(Class parentType) { this.parent = parentType; }
 
         /**
          * @param type class type
          * @return true if type is assignable to the parent type supplied in the constructor.
          */
         public boolean matches(Class type) {
             return type != null && parent.isAssignableFrom(type);
         }
 
         @Override public String toString() {
             return "is assignable to " + parent.getSimpleName();
         }
     }
     
     /**
      * A Test that checks to see if each class name ends with the provided suffix.
      */
     public static class NameEndsWith extends ClassTest {
         private String suffix;
 
         /**
          * Constructs a NameEndsWith test using the supplied suffix.
          * @param suffix suffix
          */
         public NameEndsWith(String suffix) { this.suffix = suffix; }
 
         /**
          * @param type class type
          * @return true if type name ends with the suffix supplied in the constructor.
          */
         public boolean matches(Class type) {
             return type != null && type.getName().endsWith(suffix);
         }
 
         @Override public String toString() {
             return "ends with the suffix " + suffix;
         }
     }
 
     /**
      * A Test that checks to see if each class is annotated with a specific annotation. If it
      * is, then the test returns true, otherwise false.
      */
     public static class AnnotatedWith extends ClassTest {
         private Class<? extends Annotation> annotation;
 
         /**
          * Constructs an AnnotatedWith test for the specified annotation type.
          *
          * @param annotation annotation
          */
         public AnnotatedWith(Class<? extends Annotation> annotation) { this.annotation = annotation; }
 
         /**
          * @param type class type
          * @return true if the type is annotated with the class provided to the constructor.
          */
         public boolean matches(Class type) {
             return type != null && type.isAnnotationPresent(annotation);
         }
 
         @Override public String toString() {
             return "annotated with @" + annotation.getSimpleName();
         }
     }
     
     public static class NameIs extends ResourceTest {
         private String name;
         
         public NameIs(String name) { this.name = "/" + name; }
         
         public boolean matches(URL resource) {
             return (resource.getPath().endsWith(name));
         }
         
         @Override public String toString() {
             return "named " + name;
         }
     }
 
     /** The set of matches being accumulated. */
     private Set<Class<? extends T>> classMatches = new HashSet<Class<?extends T>>();
     
     /** The set of matches being accumulated. */
     private Set<URL> resourceMatches = new HashSet<>();
 
     /**
      * The ClassLoader to use when looking for classes. If null then the ClassLoader returned
      * by Thread.currentThread().getContextClassLoader() will be used.
      */
     private ClassLoader classloader;
 
     /**
      * Provides access to the classes discovered so far. If no calls have been made to
      * any of the {@code find()} methods, this set will be empty.
      *
      * @return the set of classes that have been discovered.
      */
     public Set<Class<? extends T>> getClasses() {
         return classMatches;
     }
     
     public Set<URL> getResources() {
         return resourceMatches;
     }
     
 
     /**
      * Returns the classloader that will be used for scanning for classes. If no explicit
      * ClassLoader has been set by the calling, the context class loader will be used.
      *
      * @return the ClassLoader that will be used to scan for classes
      */
     public ClassLoader getClassLoader() {
         return classloader == null ? Thread.currentThread().getContextClassLoader() : classloader;
     }
 
     /**
      * Sets an explicit ClassLoader that should be used when scanning for classes. If none
      * is set then the context classloader will be used.
      *
      * @param classloader a ClassLoader to use when scanning for classes
      */
     public void setClassLoader(ClassLoader classloader) { this.classloader = classloader; }
 
     /**
      * Attempts to discover classes that are assignable to the type provided. In the case
      * that an interface is provided this method will collect implementations. In the case
      * of a non-interface class, subclasses will be collected.  Accumulated classes can be
      * accessed by calling {@link #getClasses()}.
      *
      * @param parent the class of interface to find subclasses or implementations of
      * @param packageNames one or more package names to scan (including subpackages) for classes
      */
     public void findImplementations(Class parent, String... packageNames) {
         if (packageNames == null) return;
 
         Test test = new IsA(parent);
         for (String pkg : packageNames) {
             findInPackage(test, pkg);
         }
     }
     
     /**
      * Attempts to discover classes who's name ends with the provided suffix. Accumulated classes can be
      * accessed by calling {@link #getClasses()}.
      *
      * @param suffix The class name suffix to match
      * @param packageNames one or more package names to scan (including subpackages) for classes
      */
     public void findSuffix(String suffix, String... packageNames) {
         if (packageNames == null) return;
 
         Test test = new NameEndsWith(suffix);
         for (String pkg : packageNames) {
             findInPackage(test, pkg);
         }
     }
 
     /**
      * Attempts to discover classes that are annotated with to the annotation. Accumulated
      * classes can be accessed by calling {@link #getClasses()}.
      *
      * @param annotation the annotation that should be present on matching classes
      * @param packageNames one or more package names to scan (including subpackages) for classes
      */
     public void findAnnotated(Class<? extends Annotation> annotation, String... packageNames) {
         if (packageNames == null) return;
 
         Test test = new AnnotatedWith(annotation);
         for (String pkg : packageNames) {
             findInPackage(test, pkg);
         }
     }
     
     public void findNamedResource(String name, String... pathNames) {
         if (pathNames == null) return;
         
         Test test = new NameIs(name);
         for (String pkg : pathNames) {
             findInPackage(test, pkg);
         }
     }
     
     /**
      * Attempts to discover classes that pass the test. Accumulated
      * classes can be accessed by calling {@link #getClasses()}.
      *
      * @param test the test to determine matching classes
      * @param packageNames one or more package names to scan (including subpackages) for classes
      */
     public void find(Test test, String... packageNames) {
         if (packageNames == null) return;
 
         for (String pkg : packageNames) {
             findInPackage(test, pkg);
         }
     }
 
     /**
      * Scans for classes starting at the package provided and descending into subpackages.
      * Each class is offered up to the Test as it is discovered, and if the Test returns
      * true the class is retained.  Accumulated classes can be fetched by calling
      * {@link #getClasses()}.
      *
      * @param test an instance of {@link Test} that will be used to filter classes
      * @param packageName the name of the package from which to start scanning for
      *        classes, e.g. {@code net.sourceforge.stripes}
      */
     public void findInPackage(Test test, String packageName) {
         packageName = packageName.replace('.', '/');
         ClassLoader loader = getClassLoader();
         Enumeration<URL> urls;
 
         try {
             urls = loader.getResources(packageName);
         }
         catch (IOException ioe) {
             if (LOG.isWarnEnabled()) {
         	LOG.warn("Could not read package: " + packageName, ioe);
             }
             return;
         }
 
         while (urls.hasMoreElements()) {
             try {
                 String urlPath = urls.nextElement().getFile();
                 urlPath = URLDecoder.decode(urlPath, "UTF-8");
 
                 // If it's a file in a directory, trim the stupid file: spec
                 if ( urlPath.startsWith("file:") ) {
                     urlPath = urlPath.substring(5);
                 }
 
                 // Else it's in a JAR, grab the path to the jar
                 if (urlPath.indexOf('!') > 0) {
                     urlPath = urlPath.substring(0, urlPath.indexOf('!'));
                 }
 
                 if (LOG.isInfoEnabled()) {
                     LOG.info("Scanning for classes in [" + urlPath + "] matching criteria: " + test);
                 }
                 File file = new File(urlPath);
                 if ( file.isDirectory() ) {
                     loadImplementationsInDirectory(test, packageName, file);
                 }
                 else {
                     loadImplementationsInJar(test, packageName, file);
                 }
             }
             catch (IOException ioe) {
                 if (LOG.isWarnEnabled()) {
                     LOG.warn("could not read entries", ioe);
                 }
             }
         }
     }
 
 
     /**
      * Finds matches in a physical directory on a filesystem.  Examines all
      * files within a directory - if the File object is not a directory, and ends with <i>.class</i>
      * the file is loaded and tested to see if it is acceptable according to the Test.  Operates
      * recursively to find classes within a folder structure matching the package structure.
      *
      * @param test a Test used to filter the classes that are discovered
      * @param parent the package name up to this directory in the package hierarchy.  E.g. if
      *        /classes is in the classpath and we wish to examine files in /classes/org/apache then
      *        the values of <i>parent</i> would be <i>org/apache</i>
      * @param location a File object representing a directory
      */
     private void loadImplementationsInDirectory(Test test, String parent, File location) {
         File[] files = location.listFiles();
         StringBuilder builder = null;
 
         for (File file : files) {
             builder = new StringBuilder(100);
             builder.append(parent).append("/").append(file.getName());
             String packageOrClass = ( parent == null ? file.getName() : builder.toString() );
 
             if (file.isDirectory()) {
                 loadImplementationsInDirectory(test, packageOrClass, file);
             }
             else if (isTestApplicable(test, file.getName())) {
                 addIfMatching(test, packageOrClass);
             }
         }
     }
 
     private boolean isTestApplicable(Test test, String path) {
         return test.doesMatchResource() || path.endsWith(".class") && test.doesMatchClass();
     }
 
     /**
      * Finds matching classes within a jar files that contains a folder structure
      * matching the package structure.  If the File is not a JarFile or does not exist a warning
      * will be logged, but no error will be raised.
      *
      * @param test a Test used to filter the classes that are discovered
      * @param parent the parent package under which classes must be in order to be considered
      * @param jarfile the jar file to be examined for classes
      */
     private void loadImplementationsInJar(Test test, String parent, File jarfile) {
         try(JarInputStream jarStream = new JarInputStream(new FileInputStream(jarfile))) {
             JarEntry entry;
             while ((entry = jarStream.getNextJarEntry() ) != null) {
                 String name = entry.getName();
                 if (!entry.isDirectory() && name.startsWith(parent) && isTestApplicable(test, name)) {
                     addIfMatching(test, name);
                 }
             }
         } catch (IOException ioe) {
             LOG.error("Could not search jar file '" + jarfile + "' for classes matching criteria: " +
                       test + " due to an IOException", ioe);
         }
     }
 
     /**
      * Add the class designated by the fully qualified class name provided to the set of
      * resolved classes if and only if it is approved by the Test supplied.
      *
      * @param test the test used to determine if the class matches
      * @param fqn the fully qualified name of a class
      */
     protected void addIfMatching(Test test, String fqn) {
         try {
             ClassLoader loader = getClassLoader();
             if (test.doesMatchClass()) {
                 String externalName = fqn.substring(0, fqn.indexOf('.')).replace('/', '.');
                 if (LOG.isDebugEnabled()) {
                     LOG.debug("Checking to see if class " + externalName + " matches criteria [" + test + "]");
                 }
     
                 Class type = loader.loadClass(externalName);
                 if (test.matches(type) ) {
                     classMatches.add( (Class<T>) type);
                 }
             }
             if (test.doesMatchResource()) {
                 URL url = loader.getResource(fqn);
                 if (url == null) {
                     url = loader.getResource(fqn.substring(1));
                 }
                 if (url != null && test.matches(url)) {
                     resourceMatches.add(url);
                 }
             }
         }
         catch (Throwable t) {
             if (LOG.isWarnEnabled()) {
         	LOG.warn("Could not examine class '" + fqn + "' due to a " +
                      t.getClass().getName() + " with message: " + t.getMessage());
             }
         }
     }
 }