using System.Text.Json;
using Google.Protobuf;

namespace DynamicProtobuf.Runtime;

public static class DynamicFieldRegistry
{
    #region Local State
    private static FileSystemWatcher? _fsWatcher;

    private static ProtoJsonRegistry Registry { get; set; } = new();

    private static HashSet<(string, string)> MissingFieldSet { get; set; } = [];

    private static Timer? _reloadTimer;

    private static readonly Lock _reloadLock = new();

    #endregion Local State

    #region Actions
    public static Action<string> OnMissingField { get; set; } = msg => Console.Error.WriteLine("[DynamicProtobuf] [WARN]: " + msg);

    public static Action<string> OnError { get; set; } = msg => Console.Error.WriteLine("[DynamicProtobuf] [ERROR]: " + msg);

    public static event Action<ProtoJsonRegistry>? OnHotReloaded;

    #endregion Actions

    #region Codegen Helper

    public static uint GetXorConst(string fullName, string fieldName)
    {
        return GetField(fullName, fieldName)?.XorConst ?? 0;
    }

    public static bool HasField(string fullName, string fieldName)
    {
        return GetField(fullName, fieldName) != null;
    }

    public static int GetFieldNumber(string fullName, string fieldName)
    {
        return GetField(fullName, fieldName)?.FieldNumber ?? 0;
    }

    public static uint GetTag(string fullName, string fieldName, bool packed = false)
    {
        MessageField? field = GetField(fullName, fieldName);
        if (field == null)
            return 0;
        return (uint)((field.FieldNumber << 3) | (int)field.WireType);
    }

    public static int GetTagSize(string fullName, string fieldName)
    {
        return CodedOutputStream.ComputeTagSize(GetFieldNumber(fullName, fieldName));
    }

    private static MessageField? GetField(string fullName, string fieldName)
    {
        if (Registry.Messages.TryGetValue(fullName, out var fields) && fields.TryGetValue(fieldName, out var field))
        {
            return field;
        }

        if (MissingFieldSet.Add((fullName, fieldName)))
        {
            OnMissingField?.Invoke($"no such field \"{fieldName}\" at message \"{fullName}\"");
        }

        return null;
    }

    #endregion Codegen Helper

    public static void ListenFromFile(string path)
    {
        LoadFromFile(path);

        var directory = Path.GetDirectoryName(path);
        if (string.IsNullOrEmpty(directory)) directory = ".";
        var fileName = Path.GetFileName(path);

        _fsWatcher = new FileSystemWatcher(directory, Path.GetFileName(path))
        {
            NotifyFilter = NotifyFilters.LastWrite | NotifyFilters.Size,
            EnableRaisingEvents = true
        };

        _fsWatcher.Error += (sender, e) =>
        {
            OnError?.Invoke(e.GetException().Message);
        };

        _fsWatcher.Changed += (sender, e) =>
        {
            if (e.ChangeType != WatcherChangeTypes.Changed)
                return;

            lock (_reloadLock)
            {
                _reloadTimer?.Dispose();

                _reloadTimer = new Timer(_ =>
                {
                    try
                    {
                        while (IsFileLocked(path))
                            Thread.Sleep(50);

                        LoadFromFile(path);
                    }
                    catch (Exception ex)
                    {
                        OnError?.Invoke(ex.Message);
                    }
                }, null, 250, Timeout.Infinite);
            }
        };
    }

    public static void LoadFromFile(string path)
    {
        if (!File.Exists(path))
        {
            OnError?.Invoke($"proto json registry file not found: {path}");
            return;
        }

        try
        {
            MissingFieldSet.Clear();

            var json = File.ReadAllText(path);
            var reg = JsonSerializer.Deserialize<ProtoJsonRegistry>(json);

            if (reg != null)
            {
                Registry = reg;
                OnHotReloaded?.Invoke(Registry);
            }
        }
        catch (Exception ex)
        {
            OnError?.Invoke($"failed to load proto json registry: {ex.Message}");
        }
    }

    private static bool IsFileLocked(string path)
    {
        try
        {
            using FileStream file = File.Open(path, FileMode.Open, FileAccess.ReadWrite, FileShare.None);
            return false;
        }
        catch (Exception)
        {
            return true;
        }
    }

}