using System.IO.Ports;
using System.Text;
using System.Text.RegularExpressions;

namespace Housing.Services;

public sealed class BarcodeScanReceivedEventArgs : EventArgs
{
    public BarcodeScanReceivedEventArgs(string portName, string text, bool isConfirmedPort)
    {
        PortName = portName;
        Text = text;
        IsConfirmedPort = isConfirmedPort;
    }

    public string PortName { get; }
    public string Text { get; }
    public bool IsConfirmedPort { get; }
}

public sealed class SerialBarcodeScanner : IDisposable
{
    private readonly BarcodeScannerSettings _settings;
    private readonly HashSet<string> _excludedPortNames;
    private readonly List<PortSession> _sessions = new();
    private readonly object _sync = new();
    private bool _disposed;
    private string? _confirmedPortName;

    public SerialBarcodeScanner(BarcodeScannerSettings settings, IEnumerable<string> excludedPortNames)
    {
        _settings = settings;
        _excludedPortNames = excludedPortNames
            .Where(portName => !string.IsNullOrWhiteSpace(portName))
            .Select(NormalizePortName)
            .ToHashSet(StringComparer.OrdinalIgnoreCase);
    }

    public event EventHandler<BarcodeScanReceivedEventArgs>? ScanReceived;

    public string? ConfirmedPortName
    {
        get
        {
            lock (_sync)
            {
                return _confirmedPortName;
            }
        }
    }

    public void Start()
    {
        ThrowIfDisposed();

        var candidatePortNames = GetCandidatePortNames();
        if (candidatePortNames.Length == 0)
        {
            throw new InvalidOperationException("No available COM ports for the barcode scanner.");
        }

        var openErrors = new List<string>();
        foreach (var portName in candidatePortNames)
        {
            PortSession? session = null;
            try
            {
                var port = CreateSerialPort(portName);
                session = new PortSession(port, CommitBufferedScan);

                port.DataReceived += SerialPort_DataReceived;
                lock (_sync)
                {
                    _sessions.Add(session);
                }

                port.Open();
                port.DiscardInBuffer();
                port.DiscardOutBuffer();
            }
            catch (Exception ex)
            {
                if (session is not null)
                {
                    lock (_sync)
                    {
                        _sessions.Remove(session);
                    }

                    CloseSession(session);
                }

                openErrors.Add($"{portName}: {ex.Message}");
            }
        }

        int sessionCount;
        lock (_sync)
        {
            sessionCount = _sessions.Count;
        }

        if (sessionCount == 0)
        {
            var detail = openErrors.Count == 0 ? string.Empty : $" ({string.Join("; ", openErrors)})";
            throw new InvalidOperationException($"Could not open a barcode scanner COM port.{detail}");
        }

        if (!BarcodeScannerSettings.IsAutoPort(_settings.PortName) || sessionCount == 1)
        {
            lock (_sync)
            {
                _confirmedPortName = _sessions[0].Port.PortName;
            }
        }
    }

    public void ConfirmPort(string portName)
    {
        if (string.IsNullOrWhiteSpace(portName))
        {
            return;
        }

        List<PortSession> sessionsToClose;
        lock (_sync)
        {
            if (_disposed)
            {
                return;
            }

            var normalizedPortName = NormalizePortName(portName);
            if (!string.IsNullOrWhiteSpace(_confirmedPortName) &&
                !string.Equals(_confirmedPortName, normalizedPortName, StringComparison.OrdinalIgnoreCase))
            {
                return;
            }

            var confirmedSession = _sessions.FirstOrDefault(session =>
                string.Equals(session.Port.PortName, normalizedPortName, StringComparison.OrdinalIgnoreCase));
            if (confirmedSession is null)
            {
                return;
            }

            _confirmedPortName = confirmedSession.Port.PortName;
            sessionsToClose = _sessions
                .Where(session => !ReferenceEquals(session, confirmedSession))
                .ToList();

            _sessions.RemoveAll(session => !ReferenceEquals(session, confirmedSession));
        }

        foreach (var session in sessionsToClose)
        {
            CloseSession(session);
        }
    }

    private SerialPort CreateSerialPort(string portName)
    {
        return new SerialPort(portName, _settings.BaudRate)
        {
            Encoding = Encoding.ASCII,
            NewLine = "\r\n",
            ReadTimeout = _settings.ReadTimeout,
            WriteTimeout = _settings.ReadTimeout,
            DtrEnable = _settings.DtrEnable,
            RtsEnable = _settings.RtsEnable
        };
    }

    private string[] GetCandidatePortNames()
    {
        if (!BarcodeScannerSettings.IsAutoPort(_settings.PortName))
        {
            return new[] { NormalizePortName(_settings.PortName) };
        }

        return SerialPort.GetPortNames()
            .Select(NormalizePortName)
            .Where(portName => !_excludedPortNames.Contains(portName))
            .OrderBy(GetPortNumber)
            .ThenBy(portName => portName, StringComparer.OrdinalIgnoreCase)
            .ToArray();
    }

    private void SerialPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
    {
        if (sender is not SerialPort port)
        {
            return;
        }

        PortSession? session;
        lock (_sync)
        {
            if (_disposed)
            {
                return;
            }

            session = _sessions.FirstOrDefault(item => ReferenceEquals(item.Port, port));
        }

        if (session is null)
        {
            return;
        }

        string text;
        try
        {
            text = port.ReadExisting();
        }
        catch
        {
            return;
        }

        if (string.IsNullOrEmpty(text))
        {
            return;
        }

        var scans = AppendReceivedText(session, text);
        foreach (var scan in scans)
        {
            PublishScan(session, scan);
        }
    }

    private List<string> AppendReceivedText(PortSession session, string text)
    {
        lock (session.Sync)
        {
            session.Buffer.Append(text);
            var scans = DrainCompleteScans(session.Buffer);

            if (session.Buffer.Length > 0)
            {
                var delay = Math.Max(50, _settings.IdleCommitMilliseconds);
                session.CommitTimer.Change(delay, Timeout.Infinite);
            }
            else
            {
                session.CommitTimer.Change(Timeout.Infinite, Timeout.Infinite);
            }

            return scans;
        }
    }

    private void CommitBufferedScan(PortSession session)
    {
        string scan;
        lock (session.Sync)
        {
            scan = NormalizeScanText(session.Buffer.ToString());
            session.Buffer.Clear();
            session.CommitTimer.Change(Timeout.Infinite, Timeout.Infinite);
        }

        PublishScan(session, scan);
    }

    private void PublishScan(PortSession session, string scan)
    {
        scan = NormalizeScanText(scan);
        if (string.IsNullOrWhiteSpace(scan))
        {
            return;
        }

        bool isConfirmedPort;
        lock (_sync)
        {
            if (_disposed || !_sessions.Contains(session))
            {
                return;
            }

            isConfirmedPort = string.Equals(
                _confirmedPortName,
                session.Port.PortName,
                StringComparison.OrdinalIgnoreCase);
        }

        ScanReceived?.Invoke(this, new BarcodeScanReceivedEventArgs(session.Port.PortName, scan, isConfirmedPort));
    }

    private static List<string> DrainCompleteScans(StringBuilder buffer)
    {
        var scans = new List<string>();
        var text = buffer.ToString();
        var start = 0;

        for (var index = 0; index < text.Length; index++)
        {
            if (text[index] != '\r' && text[index] != '\n')
            {
                continue;
            }

            var line = NormalizeScanText(text[start..index]);
            if (line.Length > 0)
            {
                scans.Add(line);
            }

            if (text[index] == '\r' && index + 1 < text.Length && text[index + 1] == '\n')
            {
                index++;
            }

            start = index + 1;
        }

        if (start > 0)
        {
            buffer.Clear();
            if (start < text.Length)
            {
                buffer.Append(text[start..]);
            }
        }

        return scans;
    }

    private static string NormalizeScanText(string text)
    {
        if (string.IsNullOrEmpty(text))
        {
            return string.Empty;
        }

        var builder = new StringBuilder(text.Length);
        foreach (var character in text.Trim())
        {
            if (!char.IsControl(character))
            {
                builder.Append(character);
            }
        }

        return builder.ToString().Trim();
    }

    private static string NormalizePortName(string portName)
    {
        return portName.Trim().ToUpperInvariant();
    }

    private static int GetPortNumber(string portName)
    {
        var match = Regex.Match(portName, @"\d+");
        return match.Success && int.TryParse(match.Value, out var number)
            ? number
            : int.MaxValue;
    }

    private void ThrowIfDisposed()
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
    }

    private void CloseSession(PortSession session)
    {
        try
        {
            session.Port.DataReceived -= SerialPort_DataReceived;
        }
        catch
        {
            // Best effort during shutdown.
        }

        session.Dispose();
    }

    public void Dispose()
    {
        List<PortSession> sessionsToClose;
        lock (_sync)
        {
            if (_disposed)
            {
                return;
            }

            _disposed = true;
            sessionsToClose = _sessions.ToList();
            _sessions.Clear();
        }

        foreach (var session in sessionsToClose)
        {
            CloseSession(session);
        }
    }

    private sealed class PortSession : IDisposable
    {
        private readonly Action<PortSession> _commitBufferedScan;

        public PortSession(SerialPort port, Action<PortSession> commitBufferedScan)
        {
            Port = port;
            _commitBufferedScan = commitBufferedScan;
            CommitTimer = new Timer(_ => _commitBufferedScan(this), null, Timeout.Infinite, Timeout.Infinite);
        }

        public SerialPort Port { get; }
        public StringBuilder Buffer { get; } = new();
        public object Sync { get; } = new();
        public Timer CommitTimer { get; }

        public void Dispose()
        {
            CommitTimer.Dispose();
            Port.Dispose();
        }
    }
}