package org.warp.jcwdb;

import com.esotericsoftware.kryo.io.Input;
import com.esotericsoftware.kryo.io.Output;
import it.unimi.dsi.fastutil.longs.*;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.SeekableByteChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.function.Consumer;

public class FileIndexManager implements IndexManager {
	private final SeekableByteChannel dataFileChannel, metadataFileChannel;
	private final FileAllocator fileAllocator;
	private final ByteBuffer metadataByteBuffer = ByteBuffer.allocateDirect(IndexDetails.TOTAL_BYTES);
	private final ByteBuffer maskByteBuffer = ByteBuffer.allocateDirect(Integer.BYTES);
	private volatile boolean closed;
	private final Object closeLock = new Object();
	private final Object metadataByteBufferLock = new Object();
	private final Object maskByteBufferLock = new Object();
	private final Object indicesMapsAccessLock = new Object();

	/**
	 * Edit this using editIndex()
	 * Get using getIndexMetadata()
	 * This hashmap must contain all indices.
	 */
	private final Long2ObjectMap<IndexDetails> loadedIndices;
	/**
	 * Edit this using editIndex()
	 */
	private final LongSet dirtyLoadedIndices, removedIndices;
	private long firstAllocableIndex;

	public FileIndexManager(Path dataFile, Path metadataFile) throws IOException {
		loadedIndices = new Long2ObjectOpenHashMap<>();
		dirtyLoadedIndices = new LongOpenHashSet();
		removedIndices = new LongOpenHashSet();
		if (Files.notExists(dataFile)) {
			Files.createFile(dataFile);
		}
		if (Files.notExists(metadataFile)) {
			Files.createFile(metadataFile);
		}
		dataFileChannel = Files.newByteChannel(dataFile, StandardOpenOption.READ, StandardOpenOption.WRITE);
		metadataFileChannel = Files.newByteChannel(metadataFile, StandardOpenOption.READ, StandardOpenOption.WRITE);
		fileAllocator = new FileAllocator(dataFileChannel);
		firstAllocableIndex = metadataFileChannel.size() / (long) IndexDetails.TOTAL_BYTES;
		if (firstAllocableIndex == 0) {
			firstAllocableIndex = 1;
		}
	}

	@Override
	public <T> T get(long index, DBReader<T> reader) throws IOException {
		checkClosed();
		IndexDetails details = getIndexMetadata(index);
		Input i = new Input(Channels.newInputStream(dataFileChannel.position(details.getOffset())));
		T result = reader.read(i, details.getSize());
		return result;
	}

	@Override
	public int getType(long index) throws IOException {
		return getIndexMetadata(index).getType();
	}

	@Override
	public long getHash(long index) throws IOException {
		return getIndexMetadata(index).getHash();
	}

	@Override
	public <T> IndexDetails set(long index, DBDataOutput<T> data) throws IOException {
		checkClosed();
		final int dataSize = data.getSize();
		final IndexDetails indexDetails = getIndexMetadataUnsafe(index);
		if (indexDetails == null || indexDetails.getSize() < dataSize) {
			// Allocate new space
			return allocateAndWrite(index, data);
		} else {
			// Check if size changed
			if (dataSize < indexDetails.getSize()) {
				// Mark free the unused bytes
				fileAllocator.markFree(indexDetails.getOffset() + dataSize, dataSize);
			}
			// Update index details
			editIndex(index, indexDetails, indexDetails.getOffset(), dataSize, indexDetails.getType(), data.calculateHash());
			// Write data
			writeExact(indexDetails, data);
			// Before returning, return IndexDetails
			return indexDetails;
		}
	}

	@Override
	public <T> long add(DBDataOutput<T> data) throws IOException {
		checkClosed();
		final int size = data.getSize();
		final long offset = fileAllocator.allocate(size);
		final int type = data.getType();
		final long hash = data.calculateHash();
		final IndexDetails indexDetails = new IndexDetails(offset, size, type, hash);
		final long index = createIndexMetadata(indexDetails);
		writeExact(indexDetails, data);
		return index;
	}

	/**
	 * Write the data at index.
	 * The input size must be equal to the index size!
	 *
	 * @param indexDetails
	 * @param data
	 * @throws IOException
	 */
	private void writeExact(final IndexDetails indexDetails, DBDataOutput<?> data) throws IOException {
		final int dataSize = data.getSize();
		if (indexDetails.getSize() != dataSize) {
			throw new IOException("Unable to write " + dataSize + " in a space of " + indexDetails.getSize());
		}
		final long offset = indexDetails.getOffset();

		final Output o = new Output(Channels.newOutputStream(dataFileChannel.position(offset)), dataSize);
		data.getWriter().write(o);
		o.flush();
	}

	private IndexDetails allocateAndWrite(final long index, DBDataOutput<?> w) throws IOException {
		final int size = w.getSize();
		final int type = w.getType();
		final long hash = w.calculateHash();
		final long offset = fileAllocator.allocate(size);
		IndexDetails details = editIndex(index, offset, size, type, hash);
		writeExact(details, w);
		return details;
	}

	@Override
	public void delete(long index) throws IOException {
		checkClosed();
		IndexDetails indexDetails = getIndexMetadataUnsafe(index);
		if (indexDetails != null) {
			fileAllocator.markFree(indexDetails.getOffset(), indexDetails.getSize());
		}
		synchronized (indicesMapsAccessLock) {
			dirtyLoadedIndices.remove(index);
			loadedIndices.remove(index);
			removedIndices.add(index);
		}
	}

	public void flushAndUnload(long index) throws IOException {
		if (removedIndices.contains(index)) {
			synchronized (indicesMapsAccessLock) {
				removedIndices.remove(index);
				dirtyLoadedIndices.remove(index);
				loadedIndices.remove(index);
			}
			// Update indices metadata
			SeekableByteChannel metadata = metadataFileChannel.position(index * IndexDetails.TOTAL_BYTES);
			eraseIndexDetails(metadata);
		}
		boolean isDirty = false;
		IndexDetails indexDetails = null;
		synchronized (indicesMapsAccessLock) {
			if (dirtyLoadedIndices.contains(index)) {
				indexDetails = loadedIndices.get(index);
				dirtyLoadedIndices.remove(index);
			}
		}
		if (isDirty) {
			// Update indices metadata
			SeekableByteChannel metadata = metadataFileChannel.position(index * IndexDetails.TOTAL_BYTES);
			writeIndexDetails(metadata, indexDetails);
		}
		synchronized (indicesMapsAccessLock) {
			loadedIndices.remove(index);
		}
	}

	@Override
	public boolean has(long index) {
		checkClosed();
		try {
			return getIndexMetadataUnsafe(index) != null;
		} catch (IOException ex) {
			ex.printStackTrace();
			return false;
		}
	}

	/**
	 * Edit index data if a change is detected
	 * @param index
	 * @param oldData Old index data to check
	 * @param offset offset
	 * @param size size
	 * @param type type
	 * @param hash hash
	 * @return
	 */
	private IndexDetails editIndex(long index, IndexDetails oldData, long offset, int size, int type, long hash) {
		if (oldData.getOffset() != offset || oldData.getSize() != size || oldData.getType() != type || oldData.getHash() != hash) {
			return editIndex(index, offset, size, type, hash);
		} else {
			return oldData;
		}
	}

	/**
	 * Edit index data
	 * @param index
	 * @param offset
	 * @param size
	 * @param type
	 * @param hash
	 * @return
	 */
	private IndexDetails editIndex(long index, long offset, int size, int type, long hash) {
		IndexDetails indexDetails = new IndexDetails(offset, size, type, hash);
		editIndex(index, indexDetails);
		return indexDetails;
	}

	/**
	 * Edit index data
	 * @param index
	 * @param details
	 */
	private void editIndex(long index, IndexDetails details) {
		synchronized (indicesMapsAccessLock) {
			loadedIndices.put(index, details);
			dirtyLoadedIndices.add(index);
		}
	}

	private long createIndexMetadata(IndexDetails indexDetails) {
		synchronized (indicesMapsAccessLock) {
			long newIndex = firstAllocableIndex++;
			loadedIndices.put(newIndex, indexDetails);
			dirtyLoadedIndices.add(newIndex);
			removedIndices.remove(newIndex);
			return newIndex;
		}
	}

	private IndexDetails getIndexMetadataUnsafe(long index) throws IOException {
		// Return index details if loaded
		IndexDetails details;
		synchronized (indicesMapsAccessLock) {
			details = loadedIndices.getOrDefault(index, null);
		}
		if (details != null) return details;

		// Try to load the details from file
		final long metadataPosition = index * IndexDetails.TOTAL_BYTES;
		if (metadataPosition + IndexDetails.TOTAL_BYTES > metadataFileChannel.size()) {
			// Avoid underflow exception
			return null;
		}
		SeekableByteChannel currentMetadataFileChannel = metadataFileChannel.position(metadataPosition);
		synchronized (metadataByteBufferLock) {
			metadataByteBuffer.rewind();
			currentMetadataFileChannel.read(metadataByteBuffer);
			metadataByteBuffer.rewind();
			// If it's not deleted continue
			if ((metadataByteBuffer.getInt() & IndexDetails.MASK_DELETED) == 0) {
				final long offset = metadataByteBuffer.getLong();
//				final long sizeAndType = metadataByteBuffer.getLong();
//				final int size = (int)(sizeAndType >> 32);
//				final int type = (int)sizeAndType;
				final int size = metadataByteBuffer.getInt();
				final int type = metadataByteBuffer.getInt();
				final long hash = metadataByteBuffer.getLong();
				final IndexDetails indexDetails = new IndexDetails(offset, size, type, hash);
				editIndex(index, indexDetails);
				return indexDetails;
			}
		}

		// No results found. Returning null
		return null;
	}

	private IndexDetails getIndexMetadata(long index) throws IOException {
		IndexDetails details = getIndexMetadataUnsafe(index);
		if (details == null)
			throw new IOException("Index " + index + " not found");
		else
			return details;
	}

	@Override
	public void close() throws IOException {
		if (closed) {
			return;
		}
		synchronized (closeLock) {
			if (closed) {
				return;
			}
			closed = true;
		}

		// Update indices metadata
		SeekableByteChannel metadata = metadataFileChannel;
		long lastIndex = -2;
		synchronized (indicesMapsAccessLock) {
			for (long index : dirtyLoadedIndices) {
				IndexDetails indexDetails = loadedIndices.get(index);
				if (index - lastIndex != 1) {
					metadata = metadata.position(index * IndexDetails.TOTAL_BYTES);
				}
				writeIndexDetails(metadata, indexDetails);
				lastIndex = index;
			}
		}

		// Remove removed indices
		synchronized (indicesMapsAccessLock) {
			for (long index : removedIndices) {
				metadata = metadata.position(index * IndexDetails.TOTAL_BYTES);
				eraseIndexDetails(metadata);
			}
		}
		fileAllocator.close();
	}

	private void writeIndexDetails(SeekableByteChannel position, IndexDetails indexDetails) throws IOException {
		synchronized (metadataByteBufferLock) {
			final int size = indexDetails.getSize();
			final int type = indexDetails.getType();
			final long offset = indexDetails.getOffset();
			final long hash = indexDetails.getHash();
			metadataByteBuffer.rewind();
			metadataByteBuffer.putInt(0);
			metadataByteBuffer.putLong(offset);
			metadataByteBuffer.putInt(size);
			metadataByteBuffer.putInt(type);
			//metadataByteBuffer.putLong((long)size << 32 | type & 0xFFFFFFFFL);
			metadataByteBuffer.putLong(hash);
			metadataByteBuffer.rewind();
			position.write(metadataByteBuffer);
		}
	}

	private void eraseIndexDetails(SeekableByteChannel position) throws IOException {
		synchronized (maskByteBufferLock) {
			maskByteBuffer.rewind();
			maskByteBuffer.putInt(IndexDetails.MASK_DELETED);
			maskByteBuffer.rewind();
			position.write(maskByteBuffer);
		}
	}

	private void checkClosed() {
		if (closed) {
			throw new RuntimeException("Index Manager is closed.");
		}
	}

	@Override
	public long clean() {
		return cleanExtraIndices();
	}

	private long cleanExtraIndices() {
		long removedIndices = 0;
		LongArrayList toUnload = new LongArrayList();
		synchronized (indicesMapsAccessLock) {
			if (loadedIndices.size() > JCWDatabase.MAX_LOADED_REFERENCES) {
				long count = loadedIndices.size();
				LongIterator it = loadedIndices.keySet().iterator();
				while (it.hasNext()) {
					long loadedIndex = it.nextLong();
					if (count < JCWDatabase.MAX_LOADED_REFERENCES * 3l / 2l) {
						break;
					}
					toUnload.add(loadedIndex);
					removedIndices++;
					count--;
				}
			}
		}
		for (long index : toUnload.elements()) {
			try {
				flushAndUnload(index);
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		return removedIndices;
	}
}