package com.it_jaros.network_scanner;

import java.io.IOException;
import java.net.*;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.List;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.LockSupport;

public class Scanner {

    private final Counter counter = new Counter();
    private final ProgressBar progressBar = new ProgressBar();
    private final Semaphore socketLimit;
    private final int timeoutInMillis;
    private final long delayInNanos;
    private final int maxWorkersPerHost;
    private final int maxTargetsLimit;

    public Scanner(int socketLimit, int timeoutInMillis, int delayInMillis, int maxWorkersPerHost, int maxTargetsLimit) {
        this.timeoutInMillis = timeoutInMillis;
        this.delayInNanos = TimeUnit.MILLISECONDS.toNanos(Math.max(0, delayInMillis));
        this.socketLimit = new Semaphore(socketLimit);
        this.maxWorkersPerHost = maxWorkersPerHost;
        this.maxTargetsLimit = maxTargetsLimit;
    }

    public List<ScanResult> scan(ScanOptions target) {
        return scanTargets(target.targets(), target.ports());
    }

    public List<ScanResult> scanTargets(List<String> targets, String ports) {
        List<ScanResult> results = new ArrayList<>();
        progressBar.start();
        try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
            List<Future<ScanResult>> futures = new ArrayList<>();
            Semaphore maxTargets = new Semaphore(maxTargetsLimit);
            for (String target : targets) {
                maxTargets.acquireUninterruptibly();
                futures.add(executor.submit(() -> {
                    try {
                        return scanTarget(target, ports);
                    } finally {
                        maxTargets.release();
                    }
                }));
            }

            futures.forEach((Future<ScanResult> f) -> {
                try {
                    results.add(f.get());
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                } catch (ExecutionException e) {
                    System.out.printf("%s -> %s%n", e.getClass().getSimpleName(), e.getMessage());
                }
            });
        }

        progressBar.stop();
        System.out.println("--------------------");
        System.out.println("Finished scan!");
        System.out.println("Stats:");
        System.out.println("Peak concurrent connects: " + counter.max());
        System.out.println("--------------------");
        return results;
    }

    private ScanResult scanTarget(String target, String ports) {
        PortRange portRange = new PortRange(ports);
        AtomicLong portSlotFactory = new AtomicLong(System.nanoTime());
        Semaphore maxWorkers = new Semaphore(maxWorkersPerHost);
        BitSet openPorts = new BitSet(PortRange.MAX_PORT);
        BitSet filteredPorts = new BitSet(PortRange.MAX_PORT);

        Progress progress = new Progress(target, portRange.getTotal(), new AtomicInteger(), new AtomicInteger(), new AtomicInteger() );
        progressBar.submit(progress);

        try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
            List<Future<PortResult>> futures = new ArrayList<>();
            while (portRange.hasNext()) {
                maxWorkers.acquireUninterruptibly();
                final int currentPort = portRange.next();
                futures.add(executor.submit(() -> {
                    try {
                        waitForSlot(portSlotFactory);
                        PortState state = getPortState(target, currentPort);
                        if (state.equals(PortState.OPEN)) {
                            progress.open().incrementAndGet();
                        } else if (state.equals(PortState.FILTERED)) {
                            progress.filtered().incrementAndGet();
                        }
                        return new PortResult(currentPort, state);
                    } finally {
                        maxWorkers.release();
                        progress.done().incrementAndGet();
                    }
                }));
            }

            List<Throwable> errors = new ArrayList<>();
            for (Future<PortResult> f : futures) {
                try {
                    // bitset is not thread-safe, so it is set
                    // outside the other virtual threads that update progress
                    PortResult portResult = f.get();
                    if (portResult.state().equals(PortState.OPEN)) {
                        openPorts.set(portResult.port());
                    } else if (portResult.state().equals(PortState.FILTERED)) {
                        filteredPorts.set(portResult.port());
                    }
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                } catch (ExecutionException e) {
                    errors.add(e);
                }
            }

            if (!errors.isEmpty()) {
                System.out.printf("Errors happened during scan of target %s%nErrors:%s -> %s", target, errors.size(), errors);
            }
        }

        return new ScanResult(target, openPorts, filteredPorts);
    }

    private void waitForSlot(AtomicLong scanSlotFactory) {
        if (delayInNanos > 0) {
            long slot = scanSlotFactory.getAndAdd(delayInNanos);
            long wait = slot - System.nanoTime();
            if (wait > 0)
                LockSupport.parkNanos(wait);
        }
    }

    private PortState getPortState(String target, int port) {
        socketLimit.acquireUninterruptibly();
        counter.inc();
        try (Socket socket = new Socket()) {
            socket.connect(new InetSocketAddress(target, port), timeoutInMillis);
            return PortState.OPEN;
        } catch (NoRouteToHostException ignored) {
            // this can be safely ignored because the port is closed if a host is unreachable
        } catch (SocketTimeoutException ignored) {
            return PortState.FILTERED;
        } catch (ConnectException ignored) {
            return PortState.CLOSED;
        } catch (IOException ignored) {
            // Will happen a lot when scanning for open ports, so not needed
        }  finally {
            counter.dec();
            socketLimit.release();
        }

        return PortState.CLOSED;
    }
}