/*
 * Copyright (C) 2024 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 android.util;

import android.annotation.Nullable;

import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * Bits and pieces copied from hidden API of android.os.FileUtils.
 *
 * @hide
 */
public class FileUtils {
    /**
     * Read a text file into a String, optionally limiting the length.
     *
     * @param file     to read (will not seek, so things like /proc files are OK)
     * @param max      length (positive for head, negative of tail, 0 for no limit)
     * @param ellipsis to add of the file was truncated (can be null)
     * @return the contents of the file, possibly truncated
     * @throws IOException if something goes wrong reading the file
     * @hide
     */
    public static @Nullable String readTextFile(@Nullable File file, @Nullable int max,
            @Nullable String ellipsis) throws IOException {
        InputStream input = new FileInputStream(file);
        // wrapping a BufferedInputStream around it because when reading /proc with unbuffered
        // input stream, bytes read not equal to buffer size is not necessarily the correct
        // indication for EOF; but it is true for BufferedInputStream due to its implementation.
        BufferedInputStream bis = new BufferedInputStream(input);
        try {
            long size = file.length();
            if (max > 0 || (size > 0 && max == 0)) {  // "head" mode: read the first N bytes
                if (size > 0 && (max == 0 || size < max)) max = (int) size;
                byte[] data = new byte[max + 1];
                int length = bis.read(data);
                if (length <= 0) return "";
                if (length <= max) return new String(data, 0, length);
                if (ellipsis == null) return new String(data, 0, max);
                return new String(data, 0, max) + ellipsis;
            } else if (max < 0) {  // "tail" mode: keep the last N
                int len;
                boolean rolled = false;
                byte[] last = null;
                byte[] data = null;
                do {
                    if (last != null) rolled = true;
                    byte[] tmp = last;
                    last = data;
                    data = tmp;
                    if (data == null) data = new byte[-max];
                    len = bis.read(data);
                } while (len == data.length);

                if (last == null && len <= 0) return "";
                if (last == null) return new String(data, 0, len);
                if (len > 0) {
                    rolled = true;
                    System.arraycopy(last, len, last, 0, last.length - len);
                    System.arraycopy(data, 0, last, last.length - len, len);
                }
                if (ellipsis == null || !rolled) return new String(last);
                return ellipsis + new String(last);
            } else {  // "cat" mode: size unknown, read it all in streaming fashion
                ByteArrayOutputStream contents = new ByteArrayOutputStream();
                int len;
                byte[] data = new byte[1024];
                do {
                    len = bis.read(data);
                    if (len > 0) contents.write(data, 0, len);
                } while (len == data.length);
                return contents.toString();
            }
        } finally {
            bis.close();
            input.close();
        }
    }

    /**
     * Perform an fsync on the given FileOutputStream. The stream at this
     * point must be flushed but not yet closed.
     *
     * @hide
     */
    public static boolean sync(FileOutputStream stream) {
        try {
            if (stream != null) {
                stream.getFD().sync();
            }
            return true;
        } catch (IOException e) {
        }
        return false;
    }
}