/*
    *    Copyright 2009-2021 the original author or authors.
    *
    *    Licensed 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 org.apache.ibatis.io;
  
  import java.io.IOException;
  import java.lang.annotation.Annotation;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Set;
  
  import org.apache.ibatis.logging.Log;
  import org.apache.ibatis.logging.LogFactory;
  
  /**
   * <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(Test, String)} 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>
   *
   * @author Tim Fennell
   * @param <T>
   *          the generic type
   */
  public class ResolverUtil<T> {
  
    /**
     * An instance of Log to use for logging in this class.
     */
    private static final Log log = LogFactory.getLog(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 interface Test {
  
      /**
       * Will be called repeatedly with candidate classes. Must return True if a class
       * is to be included in the results, false otherwise.
       *
       * @param type
       *          the type
       * @return true, if successful
       */
      boolean matches(Class<?> type);
    }
  
    /**
     * 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 implements Test {
  
      /** The parent. */
      private Class<?> parent;
  
      /**
       * Constructs an IsA test using the supplied Class as the parent class/interface.
       *
       * @param parentType
       *          the parent type
       */
      public IsA(Class<?> parentType) {
       this.parent = parentType;
     }
 
     /** Returns true if type is assignable to the parent type supplied in the constructor. */
     @Override
     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 is annotated with a specific annotation. If it
    * is, then the test returns true, otherwise false.
    */
   public static class AnnotatedWith implements Test {
 
     /** The annotation. */
     private Class<? extends Annotation> annotation;
 
     /**
      * Constructs an AnnotatedWith test for the specified annotation type.
      *
      * @param annotation
      *          the annotation
      */
     public AnnotatedWith(Class<? extends Annotation> annotation) {
       this.annotation = annotation;
     }
 
     /** Returns true if the type is annotated with the class provided to the constructor. */
     @Override
     public boolean matches(Class<?> type) {
       return type != null && type.isAnnotationPresent(annotation);
     }
 
     @Override
     public String toString() {
       return "annotated with @" + annotation.getSimpleName();
     }
   }
 
   /** The set of matches being accumulated. */
   private Set<Class<? extends T>> matches = 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 matches;
   }
 
   /**
    * 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
    * @return the resolver util
    */
   public ResolverUtil<T> findImplementations(Class<?> parent, String... packageNames) {
     if (packageNames == null) {
       return this;
     }
 
     Test test = new IsA(parent);
     for (String pkg : packageNames) {
       find(test, pkg);
     }
 
     return this;
   }
 
   /**
    * Attempts to discover classes that are annotated with 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
    * @return the resolver util
    */
   public ResolverUtil<T> findAnnotated(Class<? extends Annotation> annotation, String... packageNames) {
     if (packageNames == null) {
       return this;
     }
 
     Test test = new AnnotatedWith(annotation);
     for (String pkg : packageNames) {
       find(test, pkg);
     }
 
     return this;
   }
 
   /**
    * 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}
    * @return the resolver util
    */
   public ResolverUtil<T> find(Test test, String packageName) {
     String path = getPackagePath(packageName);
 
     try {
       List<String> children = VFS.getInstance().list(path);
       for (String child : children) {
         if (child.endsWith(".class")) {
           addIfMatching(test, child);
         }
       }
     } catch (IOException ioe) {
       log.error("Could not read package: " + packageName, ioe);
     }
 
     return this;
   }
 
   /**
    * Converts a Java package name to a path that can be looked up with a call to
    * {@link ClassLoader#getResources(String)}.
    *
    * @param packageName
    *          The Java package name to convert to a path
    * @return the package path
    */
   protected String getPackagePath(String packageName) {
     return packageName == null ? null : packageName.replace('.', '/');
   }
 
   /**
    * 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
    */
   @SuppressWarnings("unchecked")
   protected void addIfMatching(Test test, String fqn) {
     try {
       String externalName = fqn.substring(0, fqn.indexOf('.')).replace('/', '.');
       ClassLoader loader = getClassLoader();
       if (log.isDebugEnabled()) {
         log.debug("Checking to see if class " + externalName + " matches criteria [" + test + "]");
       }
 
       Class<?> type = loader.loadClass(externalName);
       if (test.matches(type)) {
         matches.add((Class<T>) type);
       }
     } catch (Throwable t) {
       log.warn("Could not examine class '" + fqn + "'" + " due to a "
           + t.getClass().getName() + " with message: " + t.getMessage());
     }
   }
 }