package org.simantics.scl.compiler.internal.parsing.utils;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CodingErrorAction;

public class LaxUTF8Reader extends InputStreamReader {
    private static final Charset UTF8 = Charset.forName("UTF-8");
    private static final CharsetDecoder UTF8_DECODER = UTF8.newDecoder();
    
    static {
        UTF8_DECODER.onMalformedInput(CodingErrorAction.REPLACE);
        UTF8_DECODER.onUnmappableCharacter(CodingErrorAction.REPLACE);
        UTF8_DECODER.replaceWith("\ufffd");
    }
    
    /**
     * Skips possible BOM (ef bb bf) in the beginning of the stream.
     */
    private static BufferedInputStream skipBOM(BufferedInputStream stream) throws IOException {
        stream.mark(4);
        if(stream.read() == 0xef)
            if(stream.read() == 0xbb)
                if(stream.read() == 0xbf)
                    return stream;
        stream.reset();
        return stream;
    }

    public LaxUTF8Reader(BufferedInputStream stream) throws IOException {
        super(skipBOM(stream), UTF8_DECODER);
    }
    
    public LaxUTF8Reader(String fileName) throws IOException {
        this(new BufferedInputStream(new FileInputStream(fileName)));
    }
}