package org.simantics.databoard.streaming;

import java.io.DataInput;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;

import org.simantics.databoard.Bindings;
import org.simantics.databoard.serialization.Serializer;
import org.simantics.databoard.type.Datatype;
import org.simantics.databoard.util.binary.Endian;
import org.simantics.databoard.util.binary.UTF8;

/**
 * This is an utility class that encapsulates the databoard value decoding scheme.
 * It can be used for streaming value reading.
 */
public class DataReader {
    private static final Serializer DATATYPE_SERIALIZER = Bindings.getSerializerUnchecked(Bindings.getBindingUnchecked( Datatype.class ));

    private final DataInput in;
    
    public DataReader(DataInput in) {
        this.in = in;
    }
    
    public DataReader(InputStream stream) {
        this.in = new DataInputStream(stream);
    }
    
    public boolean readBoolean() throws IOException {
        return in.readByte() != 0;
    }
    
    public byte readByte() throws IOException {
        return in.readByte();
    }
    
    public int readInteger() throws IOException {
        return in.readInt();
    }
    
    public long readLong() throws IOException {
        return in.readLong();
    }
    
    public float readFloat() throws IOException {
        return in.readFloat();
    }
    
    public double readDouble() throws IOException {
        return in.readDouble();
    }
    
    public int readStringLength() throws IOException {
        return Endian.readDynamicUInt32(in);
    }
    
    public String readStringContent(int length) throws IOException {
        return UTF8.readModifiedUTF(in, length); 
    }
    
    public String readString() throws IOException {
        int length = readStringLength();
        return readStringContent(length);
    }
    
    public Datatype readDatatype() throws IOException {
        return (Datatype)DATATYPE_SERIALIZER.deserialize(in);
    }
    
    /**
     * A variable length array is started with the length
     * followed by the serialization of all elements.
     */
    public int beginVariableLengthArray() throws IOException {
        return in.readInt();
    }
    
    /**
     * A map is started with its size followed by 
     * serialization of interleaved keys and values.
     */
    public int beginMap() throws IOException {
        return in.readInt();
    }
    
    /**
     * Starts reading optional value. False is returned,
     * if the optional is null.
     */
    public boolean beginOptional() throws IOException {
        return in.readByte() != 0;
    }
    
    /**
     * Selects the constructor of the union type.
     * It is written as a variable length integer,
     * so the total number of tags is required.
     */
    public int readUnionTag(int tagCount) throws IOException {
        return Endian.getUInt(in, tagCount-1);
    }
    
    /**
     * Reads a record reference. Value 0 indicates that a new record is encountered.
     * In this case reading the reference again returns the id of the new record.
     */
    public int readReferableRecordReference() throws IOException {
        return in.readInt();
    }
}