/**
 * @author Aleksey Terzi
 *
 */

package com.encrox.instancedregions.chunkmap;

import java.io.IOException;

public class ChunkReader {
	private byte[] data;
	private int bitsPerBlock;
	private long maxValueMask; 
	private int byteIndex;
	private int bitIndex;
	private long buffer;
	
	public ChunkReader(byte[] data) {
		this.data = data;
		this.byteIndex = 0;
		this.bitIndex = 0;
	}
	
	public int getByteIndex() {
		return this.byteIndex;
	}
	
	public void skip(int count) {
		this.byteIndex += count;
		this.bitIndex = 0;
	}
	
	public void setBitsPerBlock(int bitsPerBlock) {
		this.bitsPerBlock = bitsPerBlock;
		this.maxValueMask = (1L << this.bitsPerBlock) - 1;
	}
	
	public int readBlockBits() throws IOException {
		if(this.bitIndex == 0 || this.bitIndex >= 64) {
			readLong();
			this.bitIndex = 0;
		}
		
		int leftBits = 64 - this.bitIndex;
		long result = this.buffer >>> this.bitIndex;
		
		if(leftBits >= this.bitsPerBlock) {
			this.bitIndex += this.bitsPerBlock;
		} else {
			readLong();
			
			result |= this.buffer << leftBits;
			
			this.bitIndex = this.bitsPerBlock - leftBits;
		}
		
		return (int)(result & this.maxValueMask);
	}
	
	private void readLong() throws IOException {
		if(this.byteIndex + 7 >= this.data.length) {
			throw new IOException("No data to read.");
		}
		
		this.buffer = ((this.data[this.byteIndex] & 0xffL) << 56)
				| ((this.data[this.byteIndex + 1] & 0xffL) << 48)
				| ((this.data[this.byteIndex + 2] & 0xffL) << 40)
				| ((this.data[this.byteIndex + 3] & 0xffL) << 32)
				| ((this.data[this.byteIndex + 4] & 0xffL) << 24)
				| ((this.data[this.byteIndex + 5] & 0xffL) << 16)
				| ((this.data[this.byteIndex + 6] & 0xffL) << 8)
				| (this.data[this.byteIndex + 7] & 0xffL);
		
		this.byteIndex += 8;
	}
	
	public int readVarInt() throws IOException {
        int value = 0;
        int size = 0;
        int b;
        
        while(((b = readByte()) & 0x80) == 0x80) {
            value |= (b & 0x7F) << (size++ * 7);
            
            if(size > 5) {
                throw new IOException("Invalid VarInt.");
            }
        }

        return value | ((b & 0x7F) << (size * 7));
    }
	
	public int readByte() throws IOException {
		if(this.byteIndex >= this.data.length) {
			throw new IOException("No data to read.");
		}
		
		return this.data[this.byteIndex++] & 0xff;
	}
}