using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Scripting;
using Microsoft.CodeAnalysis.Scripting;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Tango.Scripting
{
    /// <summary>
    /// Represents a C# scripting engine capable of executing C# scripts using the Roslyn engine.
    /// </summary>
    public class ScriptEngine
    {
        private CancellationTokenSource _cancaller;
        private OnExecuteParameters _onExecuteParameters;
        public List<Type> ReferencedAssemblies { get; private set; }

        /// <summary>
        /// Initializes a new instance of the <see cref="ScriptEngine"/> class.
        /// </summary>
        /// <param name="parameters">The parameters.</param>
        public ScriptEngine(OnExecuteParameters parameters)
        {
            _onExecuteParameters = parameters;
            ReferencedAssemblies = new List<Type>();
        }

        /// <summary>
        /// Runs the specified code.
        /// </summary>
        /// <param name="code">The code.</param>
        /// <returns></returns>
        public async Task Run(String code, String workingFolder)
        {
            try
            {
                code = ReplaceIncludes(code, workingFolder);
            }
            catch (Exception ex)
            {
                throw ex;
            }

            var options = CreateOptions();

            String methodParameters = CreateMethodParameters();

            _cancaller = new CancellationTokenSource();

            await CSharpScript.RunAsync(
               code +
               Environment.NewLine +
               Environment.NewLine +
               "await Task.Factory.StartNew(() => { OnExecute(" + methodParameters + "); });", options: options, globals: _onExecuteParameters, cancellationToken: _cancaller.Token);
        }

        public Task<List<CompilerError>> Compile(String code, String workingFolder)
        {
            return Task.Factory.StartNew<List<CompilerError>>(() =>
            {
                try
                {
                    code = ReplaceIncludes(code, workingFolder);
                }
                catch (Exception ex)
                {
                    return new List<CompilerError>() { new CompilerError() { Error = ex.Message } };
                }

                var options = CreateOptions();

                String methodParameters = CreateMethodParameters();

                _cancaller = new CancellationTokenSource();

                var script = CSharpScript.Create(
                   code, options: options, globalsType: _onExecuteParameters.GetType());

                var results = script.Compile();

                return results.Where(x => x.Severity == DiagnosticSeverity.Error).ToList().Select(x => new CompilerError() { Error = x.ToString() }).ToList();
            });
        }

        private String CreateMethodParameters()
        {
            return String.Join(", ", _onExecuteParameters.GetType().GetFields(BindingFlags.Public | BindingFlags.Instance).Select(x => x.Name));
        }

        private String ReplaceIncludes(String code, String workingFolder)
        {
            if (Directory.Exists(workingFolder))
            {
                Environment.CurrentDirectory = workingFolder;
            }

            List<String> lines = code.ToLines();

            for (int i = 0; i < lines.Count; i++)
            {
                var line = lines[i];

                if (line.Trim().StartsWith("include"))
                {
                    String path = line.Replace("include", "").Trim().Replace("\"", "");

                    if (!File.Exists(path))
                    {
                        throw new FileNotFoundException("Could not locate include file '" + path + "'.");
                    }

                    String content = ReplaceIncludes(File.ReadAllText(path), Path.GetDirectoryName(path));

                    if (content.Contains("OnExecute("))
                    {
                        throw new InvalidProgramException(String.Format("Include file '{0}' contains and OnExecute method. Please remove it before trying to compile.", path));
                    }

                    lines[i] = content;
                }
            }

            code = ClearnUsings(String.Join(Environment.NewLine, lines));

            return code;
        }

        private String ClearnUsings(String code)
        {
            List<String> usings = new List<string>();

            List<String> lines = code.ToLines();

            foreach (var line in lines)
            {
                if (line.Trim().StartsWith("using"))
                {
                    usings.Add(line);
                }
            }

            lines.RemoveAll(x => x.Trim().StartsWith("using"));

            return String.Join(Environment.NewLine, usings.Distinct()) + String.Join(Environment.NewLine, lines);
        }

        private ScriptOptions CreateOptions()
        {
            //My References.
            var options = ScriptOptions.Default;

            //My Assemblies.
            options = options.AddReferences(typeof(Form).Assembly.Location);
            options = options.AddReferences(typeof(Enumerable).Assembly.Location);
            options = options.AddReferences(typeof(ScriptEngine).Assembly.Location);

            foreach (var asm in ReferencedAssemblies)
            {
                options = options.AddReferences(asm.Assembly.Location);
            }

            //Imports.
            options = options.AddImports(
            "System",
            "System.Collections.Generic",
            "System.Linq",
            "System.Text",
            "System.Diagnostics",
            "System.Windows.Forms"
            );

            return options;
        }

        /// <summary>
        /// Stops this instance.
        /// </summary>
        public void Stop()
        {
            _cancaller.Cancel();
        }
    }
}