using System;
using System.Collections.Generic;
using System.Dynamic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using Microsoft.Scripting;
using Microsoft.Scripting.Hosting;
using MQTTnet.Server.Configuration;

namespace MQTTnet.Server.Scripting
{
    public class PythonScriptHostService
    {
        private readonly IDictionary<string, object> _proxyObjects = new ExpandoObject();
        private readonly List<PythonScriptInstance> _scriptInstances = new List<PythonScriptInstance>();
        private readonly string _scriptsPath;
        private readonly ScriptingSettingsModel _scriptingSettings;
        private readonly ILogger<PythonScriptHostService> _logger;
        private readonly ScriptEngine _scriptEngine;
        
        public PythonScriptHostService(ScriptingSettingsModel scriptingSettings, PythonIOStream pythonIOStream, ILogger<PythonScriptHostService> logger)
        {
            _scriptingSettings = scriptingSettings ?? throw new ArgumentNullException(nameof(scriptingSettings));
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));

            _scriptEngine = IronPython.Hosting.Python.CreateEngine();
            _scriptEngine.Runtime.IO.SetOutput(pythonIOStream, Encoding.UTF8);

            _scriptsPath = PathHelper.ExpandPath(scriptingSettings.ScriptsPath);
        }

        public void Configure()
        {
            AddSearchPaths(_scriptEngine);

            TryInitializeScriptsAsync().GetAwaiter().GetResult();
        }

        public void RegisterProxyObject(string name, object @object)
        {
            if (name == null) throw new ArgumentNullException(nameof(name));
            if (@object == null) throw new ArgumentNullException(nameof(@object));

            _proxyObjects.Add(name, @object);
        }

        public void InvokeOptionalFunction(string name, object parameters)
        {
            if (name == null) throw new ArgumentNullException(nameof(name));

            lock (_scriptInstances)
            {
                foreach (var pythonScriptInstance in _scriptInstances)
                {
                    try
                    {
                        pythonScriptInstance.InvokeOptionalFunction(name, parameters);
                    }
                    catch (Exception exception)
                    {
                        _logger.LogError(exception, $"Error while invoking function '{name}' at script '{pythonScriptInstance.Uid}'.");
                    }
                }
            }
        }

        public List<string> GetScriptUids()
        {
            lock (_scriptInstances)
            {
                return _scriptInstances.Select(si => si.Uid).ToList();
            }
        }

        public Task<string> ReadScriptAsync(string uid, CancellationToken cancellationToken)
        {
            if (uid == null) throw new ArgumentNullException(nameof(uid));

            string path;

            lock (_scriptInstances)
            {
                path = _scriptInstances.FirstOrDefault(si => si.Uid == uid)?.Path;
            }

            if (path == null || !File.Exists(path))
            {
                return null;
            }

            return File.ReadAllTextAsync(path, Encoding.UTF8, cancellationToken);
        }

        public async Task WriteScriptAsync(string uid, string code, CancellationToken cancellationToken)
        {
            var path = Path.Combine(_scriptsPath, uid + ".py");

            await File.WriteAllTextAsync(path, code, Encoding.UTF8, cancellationToken).ConfigureAwait(false);
            await TryInitializeScriptsAsync().ConfigureAwait(false);
        }

        public async Task DeleteScriptAsync(string uid)
        {
            var path = Path.Combine(_scriptsPath, uid + ".py");

            if (File.Exists(path))
            {
                File.Delete(path);
                await TryInitializeScriptsAsync().ConfigureAwait(false);
            }
        }

        public async Task TryInitializeScriptsAsync()
        {
            lock (_scriptInstances)
            {
                foreach (var scriptInstance in _scriptInstances)
                {
                    try
                    {
                        scriptInstance.InvokeOptionalFunction("destroy");
                    }
                    catch (Exception exception)
                    {
                        _logger.LogWarning(exception, $"Error while unloading script '{scriptInstance.Uid}'.");
                    }
                }

                _scriptInstances.Clear();
            }

            foreach (var path in Directory.GetFiles(_scriptsPath, "*.py", SearchOption.AllDirectories).OrderBy(file => file))
            {
                await TryInitializeScriptAsync(path).ConfigureAwait(false);
            }
        }

        private async Task TryInitializeScriptAsync(string path)
        {
            var uid = new FileInfo(path).Name.Replace(".py", string.Empty, StringComparison.OrdinalIgnoreCase);

            try
            {
                _logger.LogTrace($"Initializing Python script '{uid}'...");
                var code = await File.ReadAllTextAsync(path).ConfigureAwait(false);

                var scriptInstance = CreateScriptInstance(uid, path, code);
                scriptInstance.InvokeOptionalFunction("initialize");

                lock (_scriptInstances)
                {
                    _scriptInstances.Add(scriptInstance);
                }
                
                _logger.LogInformation($"Initialized script '{uid}'.");
            }
            catch (Exception exception)
            {
                _logger.LogError(exception, $"Error while initializing script '{uid}'.");
            }
        }

        private PythonScriptInstance CreateScriptInstance(string uid, string path, string code)
        {
            var scriptScope = _scriptEngine.CreateScope();

            var source = scriptScope.Engine.CreateScriptSourceFromString(code, SourceCodeKind.File);
            var compiledCode = source.Compile();

            scriptScope.SetVariable("mqtt_net_server", _proxyObjects);
            compiledCode.Execute(scriptScope);
            
            return new PythonScriptInstance(uid, path, scriptScope);
        }

        private void AddSearchPaths(ScriptEngine scriptEngine)
        {
            if (_scriptingSettings.IncludePaths?.Any() != true)
            {
                return;
            }

            var searchPaths = scriptEngine.GetSearchPaths();

            foreach (var path in _scriptingSettings.IncludePaths)
            {
                var effectivePath = PathHelper.ExpandPath(path);

                if (Directory.Exists(effectivePath))
                {
                    searchPaths.Add(effectivePath);
                    _logger.LogInformation($"Added Python lib path: {effectivePath}");
                }
            }

            scriptEngine.SetSearchPaths(searchPaths);
        }
    }
}