/*
 * 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 org.apache.juneau.commons.io;

import static org.apache.juneau.commons.utils.AssertionUtils.*;
import static org.apache.juneau.commons.utils.StringUtils.*;
import static org.apache.juneau.commons.utils.Utils.*;

import java.net.*;
import java.nio.file.*;

/**
 * Represents a directory that can be located either on the classpath or in the file system.
 *
 * <p>
 * This class provides a unified interface for working with directories regardless of their location,
 * allowing code to transparently access files within directories from either the classpath (as resources)
 * or the file system. This is particularly useful in applications that need to work with directory-based
 * resources in both development (file system) and production (packaged JAR) environments.
 *
 * <h5 class='section'>Features:</h5>
 * <ul class='spaced-list'>
 *    <li>Unified directory access - works with both classpath resources and file system directories
 *    <li>File resolution - can resolve files within the directory using relative paths
 *    <li>Transparent resolution - automatically resolves files based on construction parameters
 *    <li>Immutable - directory location cannot be changed after construction
 * </ul>
 *
 * <h5 class='section'>Use Cases:</h5>
 * <ul class='spaced-list'>
 *    <li>Accessing template directories that may be on classpath or file system
 *    <li>Loading configuration files from directories in both development and production
 *    <li>Resolving resources within package directories
 *    <li>Applications that need to support both embedded and external directory access
 * </ul>
 *
 * <h5 class='section'>Usage:</h5>
 * <p class='bjava'>
 *    <jc>// Classpath directory</jc>
 *    LocalDir <jv>classpathDir</jv> = <jk>new</jk> LocalDir(MyClass.<jk>class</jk>, <js>"templates"</js>);
 *    LocalFile <jv>file</jv> = <jv>classpathDir</jv>.resolve(<js>"index.html"</js>);
 *
 *    <jc>// File system directory</jc>
 *    LocalDir <jv>fsDir</jv> = <jk>new</jk> LocalDir(Paths.get(<js>"/var/config"</js>));
 *    LocalFile <jv>file2</jv> = <jv>fsDir</jv>.resolve(<js>"app.properties"</js>);
 *
 *    <jc>// Package directory (null or empty path)</jc>
 *    LocalDir <jv>packageDir</jv> = <jk>new</jk> LocalDir(MyClass.<jk>class</jk>, <jk>null</jk>);
 *    LocalFile <jv>file3</jv> = <jv>packageDir</jv>.resolve(<js>"resource.txt"</js>);
 * </p>
 *
 * <h5 class='section'>Path Resolution:</h5>
 * <p>
 * The {@link #resolve(String)} method resolves files within the directory using relative paths.
 * For classpath directories, the path resolution follows Java resource path conventions:
 * <ul class='spaced-list'>
 *    <li><jk>null</jk> or empty string - resolves relative to the class's package
 *    <li>Absolute path (starts with <js>'/'</js>) - resolves relative to classpath root
 *    <li>Relative path - resolves relative to the specified classpath path
 * </ul>
 *
 * <h5 class='section'>Thread Safety:</h5>
 * <p>
 * This class is immutable and therefore thread-safe. Multiple threads can safely access a LocalDir
 * instance concurrently without synchronization.
 *
 * <h5 class='section'>See Also:</h5><ul>
 *    <li class='jc'>{@link LocalFile} - File counterpart for individual file access
 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/JuneauCommonsIO">I/O Package</a>
 * </ul>
 */
public class LocalDir {

   /**
    * Validates that the specified classpath resource exists and is a file.
    * Note that the behavior of Class.getResource(path) is different when pointing to directories on the classpath.
    * When packaged as a jar, calling Class.getResource(path) on a directory returns null.
    * When unpackaged, calling Class.getResource(path) on a directory returns a URL starting with "file:".
    * We perform a test to make the behavior the same regardless of whether we're packaged or not.
    */
   private static boolean isClasspathFile(URL url) {
      return safeSupplier(() -> {
         if (url == null)
            return false;
         var uri = url.toURI();
         if (uri.toString().startsWith("file:"))
            if (Files.isDirectory(Paths.get(uri)))
               return false;
         return true;
      });
   }

   private final Class<?> clazz;
   private final String clazzPath;
   private final Path path;

   private final int hashCode;

   /**
    * Constructor for classpath directory.
    *
    * <p>
    * Creates a LocalDir that references a directory on the classpath, relative to the specified class.
    * The path resolution follows Java resource path conventions.
    *
    * <h5 class='section'>Path Examples:</h5>
    * <p class='bjava'>
    *    <jc>// Package directory (null or empty)</jc>
    *    LocalDir <jv>dir1</jv> = <jk>new</jk> LocalDir(MyClass.<jk>class</jk>, <jk>null</jk>);
    *    <jc>// Resolves files in same package as MyClass</jc>
    *
    *    <jc>// Absolute path from classpath root</jc>
    *    LocalDir <jv>dir2</jv> = <jk>new</jk> LocalDir(MyClass.<jk>class</jk>, <js>"/com/example/templates"</js>);
    *    <jc>// Resolves files from classpath root</jc>
    *
    *    <jc>// Relative path from class package</jc>
    *    LocalDir <jv>dir3</jv> = <jk>new</jk> LocalDir(MyClass.<jk>class</jk>, <js>"templates"</js>);
    *    <jc>// Resolves files relative to MyClass package</jc>
    * </p>
    *
    * @param clazz The class used to retrieve resources. Must not be <jk>null</jk>.
    * @param clazzPath The subpath. Can be any of the following:
    *                  <ul>
    *                   <li><jk>null</jk> or an empty string - Package of the class
    *                   <li>Absolute path (starts with <js>'/'</js>) - Relative to root package
    *                   <li>Relative path (does not start with <js>'/'</js>) - Relative to class package
    *                  </ul>
    */
   public LocalDir(Class<?> clazz, String clazzPath) {
      this.clazz = assertArgNotNull("clazz", clazz);
      this.clazzPath = "/".equals(clazzPath) ? "/" : nullIfEmpty(trimTrailingSlashes(clazzPath));
      this.path = null;
      this.hashCode = h(clazz, clazzPath);
   }

   /**
    * Constructor for file system directory.
    *
    * <p>
    * Creates a LocalDir that references a directory on the file system using a {@link Path}.
    *
    * <h5 class='section'>Example:</h5>
    * <p class='bjava'>
    *    <jc>// Absolute path</jc>
    *    LocalDir <jv>dir1</jv> = <jk>new</jk> LocalDir(Paths.get(<js>"/var/config"</js>));
    *
    *    <jc>// Relative path</jc>
    *    LocalDir <jv>dir2</jv> = <jk>new</jk> LocalDir(Paths.get(<js>"data/templates"</js>));
    *
    *    <jc>// From File object</jc>
    *    File <jv>f</jv> = <jk>new</jk> File(<js>"output"</js>);
    *    LocalDir <jv>dir3</jv> = <jk>new</jk> LocalDir(<jv>f</jv>.toPath());
    * </p>
    *
    * @param path Filesystem directory location. Must not be <jk>null</jk>.
    */
   public LocalDir(Path path) {
      this.clazz = null;
      this.clazzPath = null;
      this.path = assertArgNotNull("path", path);
      this.hashCode = path.hashCode();
   }

   @Override /* Overridden from Object */
   public boolean equals(Object o) {
      return o instanceof LocalDir o2 && eq(this, o2, (x, y) -> eq(x.clazz, y.clazz) && eq(x.clazzPath, y.clazzPath) && eq(x.path, y.path));
   }

   @Override /* Overridden from Object */
   public int hashCode() {
      return hashCode;
   }

   /**
    * Resolves a file within this directory using the specified relative path.
    *
    * <p>
    * This method attempts to locate a file within the directory. If the file exists and is readable,
    * a {@link LocalFile} instance is returned. If the file does not exist or is not accessible,
    * <jk>null</jk> is returned.
    *
    * <p>
    * For classpath directories, the path is resolved according to the directory's path type:
    * <ul class='spaced-list'>
    *    <li>Package directory (null clazzPath) - path is kept relative
    *    <li>Root directory ("/") - path is made absolute if not already
    *    <li>Absolute clazzPath - resolved path is made absolute
    *    <li>Relative clazzPath - resolved path remains relative
    * </ul>
    *
    * <h5 class='section'>Example:</h5>
    * <p class='bjava'>
    *    LocalDir <jv>dir</jv> = <jk>new</jk> LocalDir(MyClass.<jk>class</jk>, <js>"templates"</js>);
    *
    *    <jc>// Resolve file in directory</jc>
    *    LocalFile <jv>file</jv> = <jv>dir</jv>.resolve(<js>"index.html"</js>);
    *    <jk>if</jk> (<jv>file</jv> != <jk>null</jk>) {
    *       InputStream <jv>is</jv> = <jv>file</jv>.read();
    *    }
    *
    *    <jc>// Resolve file in subdirectory</jc>
    *    LocalFile <jv>file2</jv> = <jv>dir</jv>.resolve(<js>"pages/about.html"</js>);
    * </p>
    *
    * <h5 class='section'>Security Note:</h5>
    * <p>
    * This method does not perform path validation or security checks (e.g., checking for path
    * traversal attacks or malformed values). The caller is responsible for ensuring the path
    * is safe and valid.
    *
    * @param path The relative path to the file to resolve within this directory.
    *             Must be a non-null relative path.
    * @return A {@link LocalFile} instance if the file exists and is readable, or <jk>null</jk> if it does not.
    */
   public LocalFile resolve(String path) {
      assertArgNotNull("path", path);
      if (nn(clazz)) {
         String p;
         if (clazzPath == null) {
            // Relative to class package - keep path relative
            p = path;
         } else if ("/".equals(clazzPath)) {
            // Root - make path absolute
            p = path.startsWith("/") ? path : "/" + path;
         } else if (clazzPath.startsWith("/")) {
            // Absolute clazzPath - make resolved path absolute
            p = clazzPath + '/' + path;
         } else {
            // Relative clazzPath - keep resolved path relative
            p = clazzPath + '/' + path;
         }
         if (isClasspathFile(clazz.getResource(p)))
            return new LocalFile(clazz, p);
      } else {
         var p = this.path.resolve(path);
         if (Files.isReadable(p) && ! Files.isDirectory(p))
            return new LocalFile(p);
      }
      return null;
   }

   @Override /* Overridden from Object */
   public String toString() {
      if (clazz == null)
         return path.toString();
      return cn(clazz) + ":" + clazzPath;
   }
}