using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.Loader;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Emit;

namespace Fission.DotNetCore.Compiler
{
    //adapted from this article http://www.tugberkugurlu.com/archive/compiling-c-sharp-code-into-memory-and-executing-it-with-roslyn
    class FissionCompiler
    {
        public static Function Compile(string code, out List<string> errors)
        {
            errors = new List<string>();

            SyntaxTree syntaxTree = CSharpSyntaxTree.ParseText(code);

            string assemblyName = Path.GetRandomFileName();

            var coreDir = Directory.GetParent(typeof(Enumerable).GetTypeInfo().Assembly.Location);      
            
            List<MetadataReference> references = new List<MetadataReference>
            {
                MetadataReference.CreateFromFile(coreDir.FullName + Path.DirectorySeparatorChar + "mscorlib.dll"),
                MetadataReference.CreateFromFile(typeof(object).GetTypeInfo().Assembly.Location),
                MetadataReference.CreateFromFile(Assembly.GetEntryAssembly().Location),
                MetadataReference.CreateFromFile(typeof(System.Runtime.Serialization.Json.DataContractJsonSerializer).GetTypeInfo().Assembly.Location)
            };

            foreach (var referencedAssembly in Assembly.GetEntryAssembly().GetReferencedAssemblies())
            {
                var assembly = Assembly.Load(referencedAssembly);
                references.Add(MetadataReference.CreateFromFile(assembly.Location));
            }

            CSharpCompilation compilation = CSharpCompilation.Create(
                assemblyName,
                syntaxTrees: new[] { syntaxTree },
                references: references,
                options: new CSharpCompilationOptions(
                    OutputKind.DynamicallyLinkedLibrary,
                    optimizationLevel: OptimizationLevel.Release));

            using (var ms = new MemoryStream())
            {
                EmitResult result = compilation.Emit(ms);

                if (!result.Success)
                {
                    IEnumerable<Diagnostic> failures = result.Diagnostics.Where(diagnostic =>
                        diagnostic.IsWarningAsError ||
                        diagnostic.Severity == DiagnosticSeverity.Error).ToList();

                    foreach (Diagnostic diagnostic in failures)
                    {
                        errors.Add($"{diagnostic.Id}: {diagnostic.GetMessage()}");
                    }
                }
                else
                {
                    ms.Seek(0, SeekOrigin.Begin);

                    Assembly assembly = AssemblyLoadContext.Default.LoadFromStream(ms);
                    var type = assembly.GetType("FissionFunction");
                    var info = type.GetMember("Execute").First() as MethodInfo;
                    return new Function(assembly, type, info);
                }
            }
            return null;
        }
    }
}