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There is a newer version: 2021.12.006
package com.devonfw.cobigen.impl.util;

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URI;
import java.nio.file.FileSystem;
import java.nio.file.FileSystemNotFoundException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Collections;

import com.devonfw.cobigen.api.exception.CobiGenRuntimeException;

/**
 * FileSystem utils.
 */
public class FileSystemUtil {

  /**
   * Creates the {@link Path} dependent on the {@link FileSystem} to be retrieved or created due to the {@link URI}
   * declaration. This function will also check whether the target of the {@link URI} is a zip file. When it is, a new
   * {@link FileSystem} will be created (or retrieved if already opened), which represents the zip-file contents.
   *
   * @param targetUri {@link URI}, the {@link Path} should be resolved for.
   * @return the path representing the configuration root
   */
  public static Path createFileSystemDependentPath(URI targetUri) {

    URI workURI = URI.create(targetUri.toString());
    if (FileSystemUtil.isZipFile(workURI)) {
      // reformat URI to be loaded by the zip/jar file system provider
      workURI = URI.create("jar:file:" + new File(workURI).toURI().getPath());
    }

    FileSystem configFileSystem;
    Path configFolder;
    if ("file".equals(workURI.getScheme())) {
      // Windows file system provider only allows "/" as URI to create a new file system... crap...
      configFolder = Paths.get(workURI);
    } else {
      configFileSystem = getOrCreateFileSystem(workURI);
      configFolder = configFileSystem.getPath("/");
    }
    return configFolder;
  }

  /**
   * Creates a new {@link FileSystem} if necessary or retrieves an already opened one for the given {@link URI}
   *
   * @param fileSystemUri {@link URI} of the {@link FileSystem} to be retrieved/created
   * @return the {@link FileSystem} of the given {@link URI}
   */
  public static FileSystem getOrCreateFileSystem(URI fileSystemUri) {

    FileSystem configFileSystem;
    try {
      configFileSystem = FileSystems.getFileSystem(fileSystemUri);
      if (!configFileSystem.isOpen()) {
        throw new FileSystemNotFoundException();
      }
    } catch (FileSystemNotFoundException e) {
      try {
        configFileSystem = FileSystems.newFileSystem(fileSystemUri, Collections.EMPTY_MAP);
      } catch (IOException e1) {
        throw new CobiGenRuntimeException("Unable to create file system from URI " + fileSystemUri, e);
      }
    }
    return configFileSystem;
  }

  /**
   * Determine whether a file is a ZIP File.
   *
   * @param uri {@link URI} to be checked
   * @return true if the file is a zip/jar file
   */
  public static boolean isZipFile(URI uri) {

    File file = new File(uri);
    if (file.isDirectory()) {
      return false;
    }
    if (!file.canRead()) {
      throw new CobiGenRuntimeException("No permission to read file " + file.getAbsolutePath());
    }
    if (file.length() < 4) {
      return false;
    }

    // check "magic number" in the first 4bytes to indicate zip/jar resources
    try (FileInputStream fileInputstream = new FileInputStream(file);
        BufferedInputStream bufferedInputStream = new BufferedInputStream(fileInputstream);
        DataInputStream in = new DataInputStream(bufferedInputStream)) {
      int test = in.readInt();
      in.close();
      return test == 0x504b0304;
    } catch (IOException e) {
      throw new CobiGenRuntimeException("Unable to read file " + file.getAbsolutePath(), e);
    }
  }
}