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Provides common utility functions
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/*
 * Copyright (c) CQSE GmbH
 *
 * 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 org.conqat.lib.commons.filesystem;

import static java.lang.Math.min;

import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.StandardCharsets;

import org.apache.commons.compress.archivers.ArchiveEntry;
import org.apache.commons.compress.archivers.zip.ZipArchiveEntry;
import org.apache.commons.compress.archivers.zip.ZipArchiveInputStream;
import org.apache.commons.compress.archivers.zip.ZipArchiveOutputStream;
import org.conqat.lib.commons.string.StringUtils;

/**
 * Utility methods which deal with the content of Zip files. (Does not support caching.)
 */
public abstract class ZipFileUtils {

	/**
	 * Write entries in chunks of 1 Mchars.
	 * 
	 * Due to UTF-8 encoding, one char may be encoded as up to four byte, so in the worst case, thus
	 * chunk size corresponds to 4 MB.
	 */
	public static final int CHAR_CHUNK_SIZE = (int) ByteUnit.MEBIBYTES.toBytes(1);

	/**
	 * Reads the content of an entry in a ZipFile.
	 *
	 * @throws IOException
	 *             if no entry with the given name exists or no size information is stored for the
	 *             entry.
	 */
	public static byte[] readZipEntryContent(ZipFile zipFile, String entryName) throws IOException {
		ZipArchiveEntry entry = zipFile.getEntry(entryName);
		if (entry == null) {
			throw new IOException("Entry " + entryName + " does not exist in " + zipFile.getName());
		}
		int size = (int) entry.getSize();
		if (size < 0) {
			throw new IOException("Size for entry " + entryName + " not stored in ZIP file " + zipFile.getName());
		}
		byte[] content = new byte[size];

		try (InputStream in = zipFile.getInputStream(entry)) {
			FileSystemUtils.safeRead(in, content);
			return content;
		}
	}

	/** @return The entry for the given entry name as a {@link String} or null. */
	public static String extractEntryAsString(ZipArchiveInputStream zis, String entryName) throws IOException {
		ArchiveEntry entry;
		while ((entry = zis.getNextEntry()) != null) {
			if (entry.getName().equals(entryName)) {
				byte[] content = FileSystemUtils.readStreamBinary(zis);
				return StringUtils.bytesToString(content);
			}
		}
		return null;
	}

	/** Writes a ZIP entry with the given name and content. */
	public static void writeZipEntry(ZipArchiveOutputStream zos, String entryName, CharSequence content)
			throws IOException {
		zos.putArchiveEntry(new ZipArchiveEntry(entryName));

		int beginningOfChunk = 0;
		int endOfContent = content.length();
		while (beginningOfChunk < endOfContent) {
			int endOfChunk = min(beginningOfChunk + CHAR_CHUNK_SIZE, endOfContent);
			CharBuffer contentChunk = CharBuffer.wrap(content, beginningOfChunk, endOfChunk);
			ByteBuffer encodedChunk = StandardCharsets.UTF_8.encode(contentChunk);
			zos.write(encodedChunk.array(), encodedChunk.position(), encodedChunk.limit());
			beginningOfChunk = endOfChunk;
		}

		zos.closeArchiveEntry();
	}
}