package io.trygvis.btree;

import java.io.Closeable;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

import static io.trygvis.btree.HeapPage.blankHeapPage;
import static java.nio.ByteBuffer.allocateDirect;

public class HeapFile implements Closeable {
    private final int PAGE_SIZE;

    private final RandomAccessFile file;
    private final FileChannel channel;

    public HeapFile(int PAGE_SIZE, File file) throws IOException {
        this.PAGE_SIZE = PAGE_SIZE;
        this.file = new RandomAccessFile(file, "rw");

        channel = this.file.getChannel();
    }

    @Override
    public void close() throws IOException {
        channel.force(true);
        file.close();
    }

    public HeapPage loadPage(int page) throws IOException {
        ByteBuffer buffer = allocateDirect(PAGE_SIZE);

        channel.read(buffer, page * PAGE_SIZE);

        return HeapPage.heapPageFromBytes(page, buffer);
    }

    public long writePage(HeapPage page) throws IOException {
        long position;
        if (page.pageNumber == -1) {
            position = channel.size();
        } else {
            position = page.pageNumber * PAGE_SIZE;
        }
        page.bytes.rewind();
        channel.write(page.bytes, position);
        channel.force(true);

        return position / PAGE_SIZE;
    }

    public long pageCount() throws IOException {
        return file.length() / PAGE_SIZE;
    }

    public HeapPage blankPage() {
        return blankHeapPage(allocateDirect(PAGE_SIZE));
    }
}