/*
 * Copyright (c) 2011-2017 Contributors to the Eclipse Foundation
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
 * which is available at https://www.apache.org/licenses/LICENSE-2.0.
 *
 * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
 */

package io.vertx.core.file.impl;

import io.netty.buffer.ByteBuf;
import io.vertx.core.AsyncResult;
import io.vertx.core.Future;
import io.vertx.core.Handler;
import io.vertx.core.buffer.Buffer;
import io.vertx.core.file.AsyncFile;
import io.vertx.core.file.FileSystemException;
import io.vertx.core.file.OpenOptions;
import io.vertx.core.impl.Arguments;
import io.vertx.core.impl.ContextImpl;
import io.vertx.core.impl.VertxInternal;
import io.vertx.core.logging.Logger;
import io.vertx.core.logging.LoggerFactory;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousFileChannel;
import java.nio.file.OpenOption;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.nio.file.attribute.FileAttribute;
import java.nio.file.attribute.PosixFilePermissions;
import java.util.HashSet;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;

/**
 *
 * This class is optimised for performance when used on the same event loop that is was passed to the handler with.
 * However it can be used safely from other threads.
 *
 * The internal state is protected using the synchronized keyword. If always used on the same event loop, then
 * we benefit from biased locking which makes the overhead of synchronized near zero.
 *
 * @author <a href="http://tfox.org">Tim Fox</a>
 */
public class AsyncFileImpl implements AsyncFile {

  private static final Logger log = LoggerFactory.getLogger(AsyncFile.class);

  public static final int DEFAULT_READ_BUFFER_SIZE = 8192;

  private final VertxInternal vertx;
  private final AsynchronousFileChannel ch;
  private final ContextImpl context;
  private boolean closed;
  private Runnable closedDeferred;
  private long writesOutstanding;
  private Handler<Throwable> exceptionHandler;
  private Handler<Void> drainHandler;
  private long writePos;
  private int maxWrites = 128 * 1024;    // TODO - we should tune this for best performance
  private int lwm = maxWrites / 2;
  private int readBufferSize = DEFAULT_READ_BUFFER_SIZE;
  private boolean paused;
  private Handler<Buffer> dataHandler;
  private Handler<Void> endHandler;
  private long readPos;
  private boolean readInProgress;

  AsyncFileImpl(VertxInternal vertx, String path, OpenOptions options, ContextImpl context) {
    if (!options.isRead() && !options.isWrite()) {
      throw new FileSystemException("Cannot open file for neither reading nor writing");
    }
    this.vertx = vertx;
    Path file = Paths.get(path);
    HashSet<OpenOption> opts = new HashSet<>();
    if (options.isRead()) opts.add(StandardOpenOption.READ);
    if (options.isWrite()) opts.add(StandardOpenOption.WRITE);
    if (options.isCreate()) opts.add(StandardOpenOption.CREATE);
    if (options.isCreateNew()) opts.add(StandardOpenOption.CREATE_NEW);
    if (options.isSync()) opts.add(StandardOpenOption.SYNC);
    if (options.isDsync()) opts.add(StandardOpenOption.DSYNC);
    if (options.isDeleteOnClose()) opts.add(StandardOpenOption.DELETE_ON_CLOSE);
    if (options.isSparse()) opts.add(StandardOpenOption.SPARSE);
    if (options.isTruncateExisting()) opts.add(StandardOpenOption.TRUNCATE_EXISTING);
    try {
      if (options.getPerms() != null) {
        FileAttribute<?> attrs = PosixFilePermissions.asFileAttribute(PosixFilePermissions.fromString(options.getPerms()));
        ch = AsynchronousFileChannel.open(file, opts, vertx.getWorkerPool(), attrs);
      } else {
        ch = AsynchronousFileChannel.open(file, opts, vertx.getWorkerPool());
      }
      if (options.isAppend()) writePos = ch.size();
    } catch (IOException e) {
      throw new FileSystemException(e);
    }
    this.context = context;
  }

  @Override
  public void close() {
    closeInternal(null);
  }

  @Override
  public void close(Handler<AsyncResult<Void>> handler) {
    closeInternal(handler);
  }

  @Override
  public void end() {
    close();
  }

  @Override
  public synchronized AsyncFile read(Buffer buffer, int offset, long position, int length, Handler<AsyncResult<Buffer>> handler) {
    Objects.requireNonNull(buffer, "buffer");
    Objects.requireNonNull(handler, "handler");
    Arguments.require(offset >= 0, "offset must be >= 0");
    Arguments.require(position >= 0, "position must be >= 0");
    Arguments.require(length >= 0, "length must be >= 0");
    check();
    ByteBuffer bb = ByteBuffer.allocate(length);
    doRead(buffer, offset, bb, position, handler);
    return this;
  }

  @Override
  public AsyncFile write(Buffer buffer, long position, Handler<AsyncResult<Void>> handler) {
    Objects.requireNonNull(handler, "handler");
    return doWrite(buffer, position, handler);
  }

  private synchronized AsyncFile doWrite(Buffer buffer, long position, Handler<AsyncResult<Void>> handler) {
    Objects.requireNonNull(buffer, "buffer");
    Arguments.require(position >= 0, "position must be >= 0");
    check();
    Handler<AsyncResult<Void>> wrapped = ar -> {
      if (ar.succeeded()) {
        checkContext();
        Runnable action;
        synchronized (AsyncFileImpl.this) {
          if (writesOutstanding == 0 && closedDeferred != null) {
            action = closedDeferred;
          } else {
            action = this::checkDrained;
          }
        }
        action.run();
        if (handler != null) {
          handler.handle(ar);
        }
      } else {
        if (handler != null) {
          handler.handle(ar);
        } else {
          handleException(ar.cause());
        }
      }
    };
    ByteBuf buf = buffer.getByteBuf();
    if (buf.nioBufferCount() > 1) {
      doWrite(buf.nioBuffers(), position, wrapped);
    } else {
      ByteBuffer bb = buf.nioBuffer();
      doWrite(bb, position, bb.limit(),  wrapped);
    }
    return this;
  }

  @Override
  public synchronized AsyncFile write(Buffer buffer) {
    int length = buffer.length();
    doWrite(buffer, writePos, null);
    writePos += length;
    return this;
  }

  @Override
  public synchronized AsyncFile setWriteQueueMaxSize(int maxSize) {
    Arguments.require(maxSize >= 2, "maxSize must be >= 2");
    check();
    this.maxWrites = maxSize;
    this.lwm = maxWrites / 2;
    return this;
  }

  @Override
  public synchronized AsyncFile setReadBufferSize(int readBufferSize) {
    this.readBufferSize = readBufferSize;
    return this;
  }

  @Override
  public synchronized boolean writeQueueFull() {
    check();
    return writesOutstanding >= maxWrites;
  }

  @Override
  public synchronized AsyncFile drainHandler(Handler<Void> handler) {
    check();
    this.drainHandler = handler;
    checkDrained();
    return this;
  }

  @Override
  public synchronized AsyncFile exceptionHandler(Handler<Throwable> handler) {
    check();
    this.exceptionHandler = handler;
    return this;
  }

  @Override
  public synchronized AsyncFile handler(Handler<Buffer> handler) {
    check();
    this.dataHandler = handler;
    if (dataHandler != null && !paused && !closed) {
      doRead();
    }
    return this;
  }

  @Override
  public synchronized AsyncFile endHandler(Handler<Void> handler) {
    check();
    this.endHandler = handler;
    return this;
  }

  @Override
  public synchronized AsyncFile pause() {
    check();
    paused = true;
    return this;
  }

  @Override
  public synchronized AsyncFile resume() {
    check();
    if (paused && !closed) {
      paused = false;
      if (dataHandler != null) {
        doRead();
      }
    }
    return this;
  }


  @Override
  public AsyncFile flush() {
    doFlush(null);
    return this;
  }

  @Override
  public AsyncFile flush(Handler<AsyncResult<Void>> handler) {
    doFlush(handler);
    return this;
  }

  @Override
  public synchronized AsyncFile setReadPos(long readPos) {
    this.readPos = readPos;
    return this;
  }

  @Override
  public synchronized AsyncFile setWritePos(long writePos) {
    this.writePos = writePos;
    return this;
  }

  private synchronized void checkDrained() {
    if (drainHandler != null && writesOutstanding <= lwm) {
      Handler<Void> handler = drainHandler;
      drainHandler = null;
      handler.handle(null);
    }
  }

  private void handleException(Throwable t) {
    if (exceptionHandler != null && t instanceof Exception) {
      exceptionHandler.handle(t);
    } else {
      log.error("Unhandled exception", t);

    }
  }

  private synchronized void doWrite(ByteBuffer[] buffers, long position, Handler<AsyncResult<Void>> handler) {
    AtomicInteger cnt = new AtomicInteger();
    AtomicBoolean sentFailure = new AtomicBoolean();
    for (ByteBuffer b: buffers) {
      int limit = b.limit();
      doWrite(b, position, limit, ar -> {
        if (ar.succeeded()) {
          if (cnt.incrementAndGet() == buffers.length) {
            handler.handle(ar);
          }
        } else {
          if (sentFailure.compareAndSet(false, true)) {
            handler.handle(ar);
          }
        }
      });
      position += limit;
    }
  }

  private synchronized void doRead() {
    if (!readInProgress) {
      readInProgress = true;
      Buffer buff = Buffer.buffer(readBufferSize);
      read(buff, 0, readPos, readBufferSize, ar -> {
        if (ar.succeeded()) {
          readInProgress = false;
          Buffer buffer = ar.result();
          if (buffer.length() == 0) {
            // Empty buffer represents end of file
            handleEnd();
          } else {
            readPos += buffer.length();
            handleData(buffer);
            if (!paused && dataHandler != null) {
              doRead();
            }
          }
        } else {
          handleException(ar.cause());
        }
      });
    }
  }

  private synchronized void handleData(Buffer buffer) {
    if (dataHandler != null) {
      checkContext();
      dataHandler.handle(buffer);
    }
  }

  private synchronized void handleEnd() {
    dataHandler = null;
    if (endHandler != null) {
      checkContext();
      endHandler.handle(null);
    }
  }

  private synchronized void doFlush(Handler<AsyncResult<Void>> handler) {
    checkClosed();
    context.executeBlocking(() -> {
      try {
        ch.force(false);
        return null;
      } catch (IOException e) {
        throw new FileSystemException(e);
      }
    }, handler);
  }

  private void doWrite(ByteBuffer buff, long position, long toWrite, Handler<AsyncResult<Void>> handler) {
    if (toWrite == 0) {
      throw new IllegalStateException("Cannot save zero bytes");
    }
    synchronized (this) {
      writesOutstanding += toWrite;
    }
    writeInternal(buff, position, handler);
  }

  private void writeInternal(ByteBuffer buff, long position, Handler<AsyncResult<Void>> handler) {

    ch.write(buff, position, null, new java.nio.channels.CompletionHandler<Integer, Object>() {

      public void completed(Integer bytesWritten, Object attachment) {

        long pos = position;

        if (buff.hasRemaining()) {
          // partial write
          pos += bytesWritten;
          // resubmit
          writeInternal(buff, pos, handler);
        } else {
          // It's been fully written
          context.runOnContext((v) -> {
            synchronized (AsyncFileImpl.this) {
              writesOutstanding -= buff.limit();
            }
            handler.handle(Future.succeededFuture());
          });
        }
      }

      public void failed(Throwable exc, Object attachment) {
        if (exc instanceof Exception) {
          context.runOnContext((v) -> handler.handle(Future.failedFuture(exc)));
        } else {
          log.error("Error occurred", exc);
        }
      }
    });
  }

  private void doRead(Buffer writeBuff, int offset, ByteBuffer buff, long position, Handler<AsyncResult<Buffer>> handler) {

    ch.read(buff, position, null, new java.nio.channels.CompletionHandler<Integer, Object>() {

      long pos = position;

      private void done() {
        context.runOnContext((v) -> {
          buff.flip();
          writeBuff.setBytes(offset, buff);
          handler.handle(Future.succeededFuture(writeBuff));
        });
      }

      public void completed(Integer bytesRead, Object attachment) {
        if (bytesRead == -1) {
          //End of file
          done();
        } else if (buff.hasRemaining()) {
          // partial read
          pos += bytesRead;
          // resubmit
          doRead(writeBuff, offset, buff, pos, handler);
        } else {
          // It's been fully written
          done();
        }
      }

      public void failed(Throwable t, Object attachment) {
        context.runOnContext((v) -> handler.handle(Future.failedFuture(t)));
      }
    });
  }

  private void check() {
    checkClosed();
  }

  private void checkClosed() {
    if (closed) {
      throw new IllegalStateException("File handle is closed");
    }
  }

  private void checkContext() {
    if (!vertx.getContext().equals(context)) {
      throw new IllegalStateException("AsyncFile must only be used in the context that created it, expected: "
          + context + " actual " + vertx.getContext());
    }
  }

  private void doClose(Handler<AsyncResult<Void>> handler) {
    ContextImpl handlerContext = vertx.getOrCreateContext();
    handlerContext.executeBlocking(res -> {
      try {
        ch.close();
        res.complete(null);
      } catch (IOException e) {
        res.fail(e);
      }
    }, handler);
  }

  private synchronized void closeInternal(Handler<AsyncResult<Void>> handler) {
    check();

    closed = true;

    if (writesOutstanding == 0) {
      doClose(handler);
    } else {
      closedDeferred = () -> doClose(handler);
    }
  }

}
