package com.ruoyi.device.bts;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;

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

    private final ServerSocket serverSocket;
    private final ExecutorService executor = Executors.newSingleThreadExecutor();
    private final BlockingQueue<String> responses = new LinkedBlockingQueue<>();
    private final List<String> requests = new CopyOnWriteArrayList<>();

    ScriptedBtsTcpSimulator() throws IOException
    {
        serverSocket = new ServerSocket(0);
        executor.submit(this::serve);
    }

    int port()
    {
        return serverSocket.getLocalPort();
    }

    void enqueue(String response)
    {
        responses.add(response);
    }

    List<String> requests()
    {
        return List.copyOf(requests);
    }

    private void serve()
    {
        try (Socket socket = serverSocket.accept())
        {
            while (!socket.isClosed())
            {
                String request = readFrame(socket.getInputStream());
                requests.add(request);
                String response = responses.poll(5, TimeUnit.SECONDS);
                if (response == null) throw new IOException("No scripted BTS response available");
                socket.getOutputStream().write(response.getBytes(StandardCharsets.UTF_8));
                socket.getOutputStream().write(FRAME_END);
                socket.getOutputStream().flush();
            }
        }
        catch (Exception ignored)
        {
        }
    }

    private String readFrame(InputStream input) throws IOException
    {
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        int matched = 0;
        while (true)
        {
            int value = input.read();
            if (value < 0) throw new IOException("Client disconnected");
            if ((byte) value == FRAME_END[matched])
            {
                matched++;
                if (matched == FRAME_END.length) return buffer.toString(StandardCharsets.UTF_8);
                continue;
            }
            if (matched > 0)
            {
                buffer.write(FRAME_END, 0, matched);
                matched = 0;
            }
            buffer.write(value);
        }
    }

    @Override
    public void close() throws Exception
    {
        serverSocket.close();
        executor.shutdownNow();
        executor.awaitTermination(2, TimeUnit.SECONDS);
    }
}