/*
 * 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.commons.configuration2.io;

import java.io.File;
import java.net.URL;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;

/**
 * This class is a subset of org.apache.commons.io.FileUtils, git-svn-id:
 * https://svn.apache.org/repos/asf/commons/proper/io/trunk@1423916 13f79535-47bb-0310-9956-ffa450edef68. The subset is
 * determined by {@link FileLocatorUtils}. The copied constants and methods are <em>literally</em> copied.<br />
 *
 * See CONFIGURATION-521 for a discussion.
 */
final class FileUtils {
    /**
     * The UTF-8 character set, used to decode octets in URLs.
     */
    private static final Charset UTF8 = StandardCharsets.UTF_8;

    /**
     * Convert from a {@code URL} to a {@code File}.
     * <p>
     * From version 1.1 this method will decode the URL. Syntax such as {@code file:///my%20docs/file.txt} will be correctly
     * decoded to {@code /my docs/file.txt}. Starting with version 1.5, this method uses UTF-8 to decode percent-encoded
     * octets to characters. Additionally, malformed percent-encoded octets are handled leniently by passing them through
     * literally.
     *
     * @param url the file URL to convert, {@code null} returns {@code null}
     * @return the equivalent {@code File} object, or {@code null} if the URL's protocol is not {@code file}
     */
    public static File toFile(final URL url) {
        if (url == null || !"file".equalsIgnoreCase(url.getProtocol())) {
            return null;
        }
        String fileName = url.getFile().replace('/', File.separatorChar);
        fileName = decodeUrl(fileName);
        return new File(fileName);
    }

    /**
     * Decodes the specified URL as per RFC 3986, i.e. transforms percent-encoded octets to characters by decoding with the
     * UTF-8 character set. This function is primarily intended for usage with {@link java.net.URL} which unfortunately does
     * not enforce proper URLs. As such, this method will leniently accept invalid characters or malformed percent-encoded
     * octets and simply pass them literally through to the result string. Except for rare edge cases, this will make
     * unencoded URLs pass through unaltered.
     *
     * @param url The URL to decode, may be {@code null}.
     * @return The decoded URL or {@code null} if the input was {@code null}.
     */
    static String decodeUrl(final String url) {
        String decoded = url;
        if (url != null && url.indexOf('%') >= 0) {
            final int n = url.length();
            final StringBuilder buffer = new StringBuilder();
            final ByteBuffer bytes = ByteBuffer.allocate(n);
            for (int i = 0; i < n;) {
                if (url.charAt(i) == '%') {
                    try {
                        do {
                            final byte octet = (byte) Integer.parseInt(url.substring(i + 1, i + 3), 16);
                            bytes.put(octet);
                            i += 3;
                        } while (i < n && url.charAt(i) == '%');
                        continue;
                    } catch (final RuntimeException ignored) {
                        // malformed percent-encoded octet, fall through and
                        // append characters literally
                    } finally {
                        if (bytes.position() > 0) {
                            bytes.flip();
                            buffer.append(UTF8.decode(bytes));
                            bytes.clear();
                        }
                    }
                }
                buffer.append(url.charAt(i++));
            }
            decoded = buffer.toString();
        }
        return decoded;
    }

}
