/*
 *  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
 *
 *    https://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.grails.io.support;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.URL;

/**
 * Interface for a resource descriptor that abstracts from the actual
 * type of underlying resource, such as a file or class path resource.
 *
 * <p>An InputStream can be opened for every resource if it exists in
 * physical form, but a URL or File handle can just be returned for
 * certain resources. The actual behavior is implementation-specific.
 *
 * @author Juergen Hoeller
 * @since 28.12.2003
 * @see #getURL()
 * @see #getURI()
 * @see #getFile()
 */
public interface Resource {

    /**
     * An input stream
     * @return The input stream
     */
    InputStream getInputStream() throws IOException;

    /**
     * Return whether this resource actually exists in physical form.
     * <p>This method performs a definitive existence check, whereas the
     * existence of a <code>Resource</code> handle only guarantees a
     * valid descriptor handle.
     */
    boolean exists();

    /**
     * Return whether the contents of this resource can be read,
     * e.g. via {@link #getInputStream()} or {@link #getFile()}.
     * <p>Will be <code>true</code> for typical resource descriptors;
     * note that actual content reading may still fail when attempted.
     * However, a value of <code>false</code> is a definitive indication
     * that the resource content cannot be read.
     * @see #getInputStream()
     */
    boolean isReadable();

    /**
     * Return a URL handle for this resource.
     * @throws java.io.IOException if the resource cannot be resolved as URL,
     * i.e. if the resource is not available as descriptor
     */
    URL getURL() throws IOException;

    /**
     * Return a URI handle for this resource.
     * @throws IOException if the resource cannot be resolved as URI,
     * i.e. if the resource is not available as descriptor
     */
    URI getURI() throws IOException;

    /**
     * Return a File handle for this resource.
     * @throws IOException if the resource cannot be resolved as absolute
     * file path, i.e. if the resource is not available in a file system
     */
    File getFile() throws IOException;

    /**
     * Determine the content length for this resource.
     * @throws IOException if the resource cannot be resolved
     * (in the file system or as some other known physical resource type)
     */
    long contentLength() throws IOException;

    /**
     * Determine the last-modified timestamp for this resource.
     * @throws IOException if the resource cannot be resolved
     * (in the file system or as some other known physical resource type)
     */
    long lastModified() throws IOException;

    /**
     * Determine a filename for this resource, i.e. typically the last
     * part of the path: for example, "myfile.txt".
     * <p>Returns <code>null</code> if this type of resource does not
     * have a filename.
     */
    String getFilename();

    /**
     * Return a description for this resource,
     * to be used for error output when working with the resource.
     * <p>Implementations are also encouraged to return this value
     * from their <code>toString</code> method.
     * @see java.lang.Object#toString()
     */
    String getDescription();

    /**
     * Creates a new resource relative to this one
     *
     * @param relativePath The relative path
     * @return The new resource
     */
    Resource createRelative(String relativePath);
}
