type Field = { Type: string; Name: string }
type Type = { Name: string; Fields: list<Field> }

let types =
    [ { Name = "Binary"
        Fields =
          [ { Type = "Expr"; Name = "Left" }
            { Type = "Token"; Name = "Op" }
            { Type = "Expr"; Name = "Right" } ] }
      { Name = "Grouping"
        Fields = [ { Type = "Expr"; Name = "Expression" } ] }
      { Name = "Literal"
        Fields =
          [ { Type = "System.Object"
              Name = "Value" } ] }
      { Name = "Unary"
        Fields = [ { Type = "Token"; Name = "Op" }; { Type = "Expr"; Name = "Right" } ] } ]

let visitorMethod baseName t = $"visit{t.Name}{baseName}"

let renderIVisitor (sw: System.IO.StreamWriter) (baseName: string) types =
    sw.Write($"public interface IVisitor<T> {{\n")

    for t in types do
        sw.Write($"\tT {visitorMethod baseName t}({t.Name} {baseName.ToLower()});\n")

    sw.Write("}\n")

let renderType (sw: System.IO.StreamWriter) baseName t =
    sw.Write
        $"public class {t.Name} : {baseName}
{{\n"

    for f in t.Fields do
        sw.Write $"\tpublic required {f.Type} {f.Name} {{ get; init; }}\n"

    sw.Write
        $"\tpublic override T accept<T>(IVisitor<T> visitor)
\t{{
\t\treturn visitor.{visitorMethod baseName t}(this);
\t}}\n"

    sw.Write("}\n")

let renderAST outputDir baseName types =
    let path = System.IO.Path.Combine(outputDir, baseName + ".g.cs")
    use sw = new System.IO.StreamWriter(path)

    sw.Write
        $"////////////////////////////////////////////////////////////
// THIS FILE IS GENERATED.                                //
// DO NOT EDIT.                                           //
////////////////////////////////////////////////////////////

using System;
namespace Finn.AST;

public abstract class {baseName} {{
\tpublic abstract T accept<T>(IVisitor<T> visitor);
}}\n"

    renderIVisitor sw baseName types
    List.iter (renderType sw baseName) types

renderAST "." "Expr" types