using System.Text;

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Text;

namespace MfGames.Nitride.Generators;

/// <summary>
/// Implements a source generator that creates the additional properties
/// and methods for a singleton component including the constructor and
/// instance methods, along with extension methods for adding them to entities.
/// </summary>
[Generator]
public class SingletonComponentSourceGenerator
    : ClassAttributeSourceGeneratorBase<SingletonComponentSyntaxReceiver>
{
    protected override SingletonComponentSyntaxReceiver CreateSyntaxReceiver(
        GeneratorInitializationContext context)
    {
        return new SingletonComponentSyntaxReceiver(context);
    }

    protected override void GenerateClassFile(
        GeneratorExecutionContext context,
        ClassAttributeReference unit)
    {
        // Pull out some fields.
        ClassDeclarationSyntax cds = unit.ClassDeclaration;

        // Create the partial class.
        StringBuilder buffer = new();
        buffer.AppendLine("#nullable enable");

        // Copy the using statements from the file.
        foreach (UsingDirectiveSyntax? uds in unit.UsingDirectiveList)
        {
            buffer.AppendLine(uds.ToString());
        }

        buffer.AppendLine();

        // Create the namespace.
        SyntaxToken cls = cds.Identifier;

        buffer.AppendLine(
            string.Join(
                "\n",
                $"using MfGames.Gallium;",
                $"",
                $"namespace {unit.Namespace}",
                $"{{",
                $"    public partial class {cls}",
                $"    {{",
                $"        static {cls}()",
                $"         {{",
                $"             Instance = new {cls}();",
                $"         }}",
                $"",
                $"        private {cls}()",
                $"         {{",
                $"         }}",
                $"",
                $"        public static {cls} Instance {{ get; }}",
                $"    }}",
                $"",
                $"    public static class {cls}Extensions",
                $"    {{",
                $"        public static bool Has{cls}(this Entity entity)",
                $"        {{",
                $"            return entity.Has<{cls}>();",
                $"        }}",
                $"",
                $"        public static Entity Remove{cls}(this Entity entity)",
                $"        {{",
                $"            return entity.Remove<{cls}>();",
                $"        }}",
                $"",
                $"        public static Entity Set{cls}(this Entity entity)",
                $"        {{",
                $"            return entity.Set({cls}.Instance);",
                $"        }}",
                $"    }}",
                $"}}",
                ""));

        // Create the source text and write out the file.
        var sourceText = SourceText.From(buffer.ToString(), Encoding.UTF8);
        context.AddSource(cls + ".Generated.cs", sourceText);
    }
}