package com.battery.device.bts;

import java.io.ByteArrayOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;

final class BtsFrameReader
{
    private static final byte[] FRAME_END = "#\r\n".getBytes(StandardCharsets.UTF_8);

    private BtsFrameReader()
    {
    }

    static byte[] read(InputStream input, int maxPayloadBytes) throws IOException
    {
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        int matched = 0;
        while (true)
        {
            int value = input.read();
            if (value < 0) throw new EOFException("BTS connection closed before the frame ended");
            if ((byte) value == FRAME_END[matched])
            {
                matched++;
                if (matched == FRAME_END.length) return buffer.toByteArray();
                continue;
            }
            if (matched > 0)
            {
                for (int i = 0; i < matched; i++) append(buffer, FRAME_END[i], maxPayloadBytes);
                matched = 0;
                if ((byte) value == FRAME_END[0])
                {
                    matched = 1;
                    continue;
                }
            }
            append(buffer, value, maxPayloadBytes);
        }
    }

    private static void append(ByteArrayOutputStream buffer, int value, int maxPayloadBytes)
            throws FrameTooLargeException
    {
        if (buffer.size() >= maxPayloadBytes) throw new FrameTooLargeException();
        buffer.write(value);
    }

    static final class FrameTooLargeException extends IOException
    {
        private static final long serialVersionUID = 1L;
    }
}