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The core random number generators
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package prng.seeds;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.file.StandardOpenOption;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.HashMap;
import java.util.Map;
import java.util.TreeSet;
import prng.SecureRandomProvider;
import prng.config.Config;
import prng.utility.BLOBPrint;

/**
 * Store all seed information in a single file and load it all into memory when needed.
 *
 * @author Simon Greatrix
 */
public class FileStorage extends SeedStorage {

  /** File name where data is stored */
  final File fileName;

  /** Channel for store whilst it is open */
  FileChannel channel = null;

  /** Is the store modified? */
  boolean isModified = false;

  /** Lock on file whilst the store is open */
  FileLock lock = null;

  /** Internal map of storage */
  private final Map storage = new HashMap<>();


  /**
   * Create new file storage instance
   *
   * @throws StorageException if access to the file is denied
   */
  public FileStorage() throws StorageException {
    Config config = Config.getConfig("config", FileStorage.class);
    String file = config.get("file", "./seeds.db");
    file = Config.expand(file);

    fileName = new File(file);
    try {
      AccessController.doPrivileged((PrivilegedAction) () -> {
        if (!fileName.canWrite()) {
          LOG.error("Cannot write to file \"" + fileName.getAbsolutePath() + "\".");
        }
        if (fileName.exists() && !fileName.canRead()) {
          LOG.error("Cannot read from file \"" + fileName.getAbsolutePath() + "\".");
        }
        return null;
      });
    } catch (SecurityException se) {
      SecureRandomProvider.LOG.warn(
          "Lacking permission: 'FilePermission \"" + fileName.getAbsolutePath() + "\", \"delete,write,read\"' - cannot access seed data in file");
      throw new StorageException(
          "Privilege 'FilePermission \"" + fileName.getAbsolutePath() + "\", \"delete,write,read\"' is required to use seed file.",
          se);
    }
  }


  @Override
  protected void closeRaw() throws StorageException {
    if (channel == null || !channel.isOpen()) {
      return;
    }

    try {
      AccessController.doPrivileged((PrivilegedExceptionAction) () -> {
        closeRawWithPrivilege();
        return null;
      });
    } catch (PrivilegedActionException e) {
      // It will be a storage exception
      throw (StorageException) e.getCause();
    } catch (SecurityException se) {
      // Lacking required privilege
      SecureRandomProvider.LOG.warn(
          "Lacking permission: 'FilePermission \"" + fileName.getAbsolutePath() + "\", \"delete,write,read\"' - cannot access seed data in file");
      throw new StorageException(
          "Privilege 'FilePermission \"" + fileName.getAbsolutePath() + "\", \"delete,write,read\"' is required to use seed file.",
          se);
    }
  }


  /**
   * Close the storage after ascerting privilege
   *
   * @throws StorageException if the preferences cannot be written to
   */
  void closeRawWithPrivilege() throws StorageException {
    TreeSet keys = new TreeSet<>(storage.keySet());
    IOException ioe = null;
    try {
      // if not modified, skip straight to the finally block to close the
      // channel
      if (!isModified) {
        return;
      }

      ByteArrayOutputStream buf = new ByteArrayOutputStream(4000);
      DataOutputStream data = new DataOutputStream(buf);
      for (String key : keys) {
        // flag is false for not EOF
        LOG.debug("Writing flag");
        data.writeBoolean(false);

        // write the key
        LOG.debug("Writing key \"{}\"", key);
        data.writeUTF(key);

        // write the value
        byte[] value = storage.get(key);
        if (LOG.isDebugEnabled()) {
          LOG.debug("Writing value:\n{}", BLOBPrint.toString(value));
        }
        data.writeShort(value.length);
        data.write(value);
      }
      // flag is true for EOF
      LOG.debug("Writing final flag");
      data.writeBoolean(true);

      // convert to Buffer and write out in one write
      ByteBuffer bbuf = ByteBuffer.wrap(buf.toByteArray());
      LOG.info("Writing file {}", fileName.getAbsolutePath());
      channel.position(0);
      while (bbuf.hasRemaining()) {
        channel.write(bbuf);
      }
      channel.force(true);
      LOG.info("Write complete");
    } catch (IOException ioe2) {
      ioe = ioe2;
    } finally {
      try {
        // closing the channel releases the lock
        channel.close();
      } catch (IOException ioe2) {
        if (ioe == null) {
          ioe = ioe2;
        } else {
          ioe.addSuppressed(ioe2);
        }
      } finally {
        storage.clear();
        channel = null;
        lock = null;
      }
    }

    if (ioe != null) {
      // delete bad file
      LOG.warn("Deleting bad file \"{}\"", fileName.getAbsolutePath());
      fileName.delete();

      // rethrow exception
      throw new StorageException(
          "Failed to save " + fileName.getAbsolutePath(), ioe);
    }
  }


  @Override
  protected byte[] getRaw(String name) throws StorageException {
    init();
    return storage.get(name);
  }


  /**
   * Initialise this instance, loading the stored seed data
   *
   * @throws StorageException if reading the file fails
   */
  private void init() throws StorageException {
    if (lock != null) {
      return;
    }

    try {
      AccessController.doPrivileged((PrivilegedExceptionAction) () -> {
        initWithPrivilege();
        return null;
      });
    } catch (PrivilegedActionException e) {
      // Storage access failed
      throw (StorageException) e.getCause();
    } catch (SecurityException se) {
      // Lacking required privilege
      SecureRandomProvider.LOG.warn(
          "Lacking permission: 'FilePermission \"" + fileName.getAbsolutePath() + "\", \"delete,write,read\"' - cannot access seed data in file");
      throw new StorageException(
          "Privilege 'FilePermission \"" + fileName.getAbsolutePath() + "\", \"delete,write,read\"' is required to use seed file.",
          se);
    }
  }


  /**
   * Initialise this instance having acquired the requisite privilege.
   *
   * @throws StorageException if the privileges cannot be accessed
   */
  void initWithPrivilege() throws StorageException {
    try {
      File file = fileName;
      LOG.info("Opening file \"{}\"", file.getAbsolutePath());
      // create the file and folder if needed
      if (!file.exists()) {
        if (file.getParentFile().mkdirs()) {
          LOG.info("Created folder \""
              + file.getParentFile().getAbsolutePath() + "\"");
        }
        if (file.createNewFile()) {
          LOG.info("Created file \"" + file.getAbsolutePath() + "\"");
        }
        if (!file.exists()) {
          throw new StorageException("Failed to create file \""
              + file.getAbsolutePath() + "\"", null);
        }
      }

      // check file is usable
      if (!file.isFile()) {
        throw new StorageException("File \"" + file.getAbsolutePath()
            + "\" is not a file.", null);
      }
      if (!file.canWrite()) {
        throw new StorageException("File \"" + file.getAbsolutePath()
            + "\" is not writable.", null);
      }
      if (!file.canRead()) {
        throw new StorageException("File \"" + file.getAbsolutePath()
            + "\" is not readable.", null);
      }

      channel = FileChannel.open(file.toPath(),
          StandardOpenOption.CREATE, StandardOpenOption.READ,
          StandardOpenOption.WRITE, StandardOpenOption.DSYNC);

      // this lock is automatically released when the channel is closed
      lock = channel.lock();

      byte[] buf = new byte[(int) channel.size()];
      storage.clear();
      if (buf.length == 0) {
        return;
      }

      ByteBuffer bbuf = ByteBuffer.wrap(buf);
      channel.position(0);
      while (bbuf.hasRemaining()) {
        channel.read(bbuf);
      }

      ByteArrayInputStream in = new ByteArrayInputStream(buf);
      DataInputStream data = new DataInputStream(in);

      while (true) {
        boolean flag = data.readBoolean();
        if (flag) {
          break;
        }
        LOG.debug("Reading item {}", Integer.valueOf(storage.size()));

        // get the key
        String key = data.readUTF();

        int len = data.readUnsignedShort();
        byte[] value = new byte[len];
        data.readFully(value);

        if (LOG.isDebugEnabled()) {
          LOG.debug("Value for {} is:\n{}", key,
              BLOBPrint.toString(value));
        }
        storage.put(key, value);
      }
      isModified = false;

      LOG.info("File read finished");
    } catch (IOException ioe) {
      throw new StorageException("Loading storage from "
          + fileName.getAbsolutePath() + " failed", ioe);
    }
  }


  @Override
  protected void putRaw(String name, byte[] data) throws StorageException {
    init();
    if (name.length() > 0x8000) {
      throw new StorageException(
          "Maximum key length is 32768, not " + name.length(),
          new IllegalArgumentException("Parameter too long"));
    }
    if (data.length > 0x10000) {
      throw new StorageException(
          "Maximum data length is 65536, not " + data.length,
          new IllegalArgumentException("Parameter too long"));
    }
    isModified = true;
    storage.put(name, data);
  }


  @Override
  protected void remove(String name) {
    storage.remove(name);
  }

}