/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * 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 com.rnboat.framework.diskcache.lru;

import java.io.Closeable;
import java.io.File;
import java.io.IOException;
import java.io.Reader;
import java.io.StringWriter;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * Junk drawer of utility methods.
 */
public final class Util {
    static final Charset US_ASCII = Charset.forName("US-ASCII");
    static final Charset UTF_8 = Charset.forName("UTF-8");
    static final char[] HEX_CHARS = {
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
    };

    private Util() {
    }

    static String readFully(Reader reader) throws IOException {
        try {
            StringWriter writer = new StringWriter();
            char[] buffer = new char[1024];
            int count;
            while ((count = reader.read(buffer)) != -1) {
                writer.write(buffer, 0, count);
            }
            return writer.toString();
        } finally {
            reader.close();
        }
    }

    /**
     * Deletes the contents of {@code dir}. Throws an IOException if any file
     * could not be deleted, or if {@code dir} is not a readable directory.
     */
    static void deleteContents(File dir) throws IOException {
        File[] files = dir.listFiles();
        if (files == null) {
            throw new IOException("not a readable directory: " + dir);
        }
        for (File file : files) {
            if (file.isDirectory()) {
                deleteContents(file);
            }
            if (!file.delete()) {
                throw new IOException("failed to delete file: " + file);
            }
        }
    }

    public static void closeQuietly(/*Auto*/Closeable closeable) {
        if (closeable != null) {
            try {
                closeable.close();
            } catch (RuntimeException rethrown) {
                throw rethrown;
            } catch (Exception ignored) {
            }
        }
    }

    /**
     * Generates the MD5 digest (32 hex characters) for a given String based on UTF-8.
     */
    public static String md5(String stringToEncode) {
        return digest(stringToEncode, "MD5", "UTF-8");
    }

    /**
     * Generates a digest (hex string) for the given string
     */
    public static String digest(String string, String digestAlgo, String encoding) {
        try {
            MessageDigest digester = MessageDigest.getInstance(digestAlgo);
            digester.update(string.getBytes(encoding));
            return hex(digester.digest());
        } catch (NoSuchAlgorithmException | UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        }
    }

    public static String hex(byte[] bytes) {
        char[] hexChars = new char[bytes.length * 2];
        for (int i = 0; i < bytes.length; i++) {
            int value = bytes[i] & 0xFF;
            hexChars[i * 2] = HEX_CHARS[value >>> 4];
            hexChars[i * 2 + 1] = HEX_CHARS[value & 0x0F];
        }
        return new String(hexChars);
    }
}