// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace SDL.SourceGeneration
{
    [Generator]
    public class FriendlyOverloadGenerator : ISourceGenerator
    {
        public void Initialize(GeneratorInitializationContext context)
        {
            context.RegisterForSyntaxNotifications(() => new UnfriendlyMethodFinder());
        }

        private const string file_header = @"// <auto-generated/>
#nullable enable

using System;

";

        public void Execute(GeneratorExecutionContext context)
        {
            var finder = (UnfriendlyMethodFinder)context.SyntaxReceiver!;

            foreach (var kvp in finder.Methods)
            {
                if (kvp.Value.Count == 0)
                    return;

                string filename = kvp.Key;
                var foundMethods = kvp.Value;

                string className = ClassNameFromMethod(foundMethods.First().NativeMethod);

                var result = new StringBuilder();
                result.Append(file_header);
                result.Append(
                    SyntaxFactory.NamespaceDeclaration(
                                     SyntaxFactory.IdentifierName("SDL"))
                                 .WithMembers(
                                     SyntaxFactory.SingletonList<MemberDeclarationSyntax>(
                                         SyntaxFactory.ClassDeclaration(className)
                                                      .WithModifiers(
                                                          SyntaxFactory.TokenList(
                                                              SyntaxFactory.Token(SyntaxKind.UnsafeKeyword),
                                                              SyntaxFactory.Token(SyntaxKind.PartialKeyword)))
                                                      .WithMembers(SyntaxFactory.List(foundMethods.Select(makeFriendlyMethod)))))
                                 .NormalizeWhitespace());

                context.AddSource(filename, result.ToString());
            }
        }

        private static string ClassNameFromMethod(MethodDeclarationSyntax methodNode)
        {
            if (methodNode.Parent is ClassDeclarationSyntax classDeclaration)
            {
                return classDeclaration.Identifier.Text;
            }

            return "SDL3"; // fallback!
        }

        private static MemberDeclarationSyntax makeFriendlyMethod(GeneratedMethod gm)
        {
            var returnType = gm.RequiredChanges.HasFlag(Changes.ChangeReturnTypeToString)
                ? SyntaxFactory.ParseTypeName("string?")
                : gm.NativeMethod.ReturnType;

            var identifier = gm.RequiredChanges.HasFlag(Changes.TrimUnsafeFromName)
                ? SyntaxFactory.Identifier(gm.NativeMethod.Identifier.ValueText.Replace(Helper.UnsafePrefix, string.Empty))
                : gm.NativeMethod.Identifier;

            return SyntaxFactory.MethodDeclaration(returnType, identifier)
                                .WithModifiers(
                                    SyntaxFactory.TokenList(
                                        SyntaxFactory.Token(SyntaxKind.PublicKeyword),
                                        SyntaxFactory.Token(SyntaxKind.StaticKeyword)))
                                .WithParameterList(
                                    SyntaxFactory.ParameterList(
                                        SyntaxFactory.SeparatedList(transformParams(gm))))
                                .WithBody(
                                    SyntaxFactory.Block(
                                        makeMethodBody(gm)));
        }

        private static IEnumerable<ParameterSyntax> transformParams(GeneratedMethod gm)
        {
            foreach (var param in gm.NativeMethod.ParameterList.Parameters)
            {
                if (param.IsTypeConstCharPtr())
                {
                    Debug.Assert(gm.RequiredChanges.HasFlag(Changes.ChangeParamsToUtf8String));
                    yield return param.WithType(SyntaxFactory.ParseTypeName(Helper.Utf8StringStructName))
                                      .WithAttributeLists(SyntaxFactory.List<AttributeListSyntax>());
                }
                else
                {
                    yield return param.WithAttributeLists(SyntaxFactory.List<AttributeListSyntax>()); // remove [NativeTypeName]
                }
            }
        }

        private const string pointer_suffix = "Ptr";

        private static StatementSyntax makeMethodBody(GeneratedMethod gm)
        {
            var expr = makeReturn(gm);

            foreach (var param in gm.NativeMethod.ParameterList.Parameters.Where(p => p.IsTypeConstCharPtr()).Reverse())
            {
                Debug.Assert(gm.RequiredChanges.HasFlag(Changes.ChangeParamsToUtf8String));

                expr = SyntaxFactory.FixedStatement(
                    SyntaxFactory.VariableDeclaration(
                        SyntaxFactory.ParseTypeName("byte*"),
                        SyntaxFactory.SingletonSeparatedList(
                            SyntaxFactory.VariableDeclarator(
                                             param.Identifier.ValueText + pointer_suffix)
                                         .WithInitializer(
                                             SyntaxFactory.EqualsValueClause(
                                                 SyntaxFactory.IdentifierName(param.Identifier))))),
                    expr);
            }

            return expr;
        }

        private static StatementSyntax makeReturn(GeneratedMethod gm)
        {
            ExpressionSyntax expr;

            if (gm.RequiredChanges.HasFlag(Changes.ChangeReturnTypeToString))
            {
                expr = SyntaxFactory.InvocationExpression(
                                        SyntaxFactory.MemberAccessExpression(
                                            SyntaxKind.SimpleMemberAccessExpression,
                                            SyntaxFactory.IdentifierName("SDL3"),
                                            SyntaxFactory.IdentifierName("PtrToStringUTF8")))
                                    .WithArguments(new[]
                                        {
                                            SyntaxFactory.Argument(makeFunctionCall(gm)),
                                            SyntaxFactory.Argument(SyntaxFactory.LiteralExpression(
                                                gm.RequiredChanges.HasFlag(Changes.FreeReturnedPointer)
                                                    ? SyntaxKind.TrueLiteralExpression
                                                    : SyntaxKind.FalseLiteralExpression))
                                        }
                                    );
            }
            else
            {
                expr = makeFunctionCall(gm);
            }

            if (gm.NativeMethod.ReturnType.IsVoid())
                return SyntaxFactory.ExpressionStatement(expr);

            return SyntaxFactory.ReturnStatement(expr);
        }

        private static InvocationExpressionSyntax makeFunctionCall(GeneratedMethod gm)
        {
            return SyntaxFactory.InvocationExpression(
                                    SyntaxFactory.IdentifierName(gm.NativeMethod.Identifier))
                                .WithArguments(makeArguments(gm));
        }

        private static IEnumerable<ArgumentSyntax> makeArguments(GeneratedMethod gm)
        {
            foreach (var param in gm.NativeMethod.ParameterList.Parameters)
            {
                if (param.IsTypeConstCharPtr())
                {
                    Debug.Assert(gm.RequiredChanges.HasFlag(Changes.ChangeParamsToUtf8String));
                    yield return SyntaxFactory.Argument(SyntaxFactory.IdentifierName(param.Identifier.ValueText + pointer_suffix));
                }
                else
                {
                    yield return SyntaxFactory.Argument(SyntaxFactory.IdentifierName(param.Identifier));
                }
            }
        }
    }
}