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

let exprTypes =
    [ { Name = "Sequence"
        Fields = [ { Type = "Expr"; Name = "Left" }; { Type = "Expr"; Name = "Right" } ] }
      { 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" } ] }
      { Name = "If"
        Fields =
          [ { Type = "Expr"; Name = "Condition" }
            { Type = "Expr"; Name = "Then" }
            { Type = "Expr"; Name = "Else" } ] }
      { Name = "Identifier"
        Fields = [ { Type = "Name"; Name = "Value" } ] }
      { Name = "List"
        Fields = [ { Type = "Expr[]"; Name = "Elements" } ] }
      { Name = "Variant"
        Fields = [ { Type = "Name"; Name = "Tag" }; { Type = "Expr?"; Name = "Argument" } ] }
      { Name = "Record"
        Fields =
          [ { Type = "Field[]"
              Name = "Extensions" }
            { Type = "BaseRecord?"; Name = "Base" } ] }
      { Name = "Selector"
        Fields = [ { Type = "Expr"; Name = "Left" }; { Type = "Name"; Name = "FieldName" } ] }
      { Name = "Indexer"
        Fields = [ { Type = "Expr"; Name = "Left" }; { Type = "Expr"; Name = "Index" } ] }
      { Name = "Call"
        Fields = [ { Type = "Expr"; Name = "Left" }; { Type = "Expr?[]"; Name = "Arguments" } ] }
      { Name = "Let"
        Fields =
          [ { Type = "Binding[]"
              Name = "Bindings" }
            { Type = "Expr"; Name = "Body" } ] } ]

let patternTypes =
    [ { Name = "SimplePattern"
        Fields = [ { Type = "Name?"; Name = "Identifier" } ] }
      { Name = "VariantPattern"
        Fields = [ { Type = "Name"; Name = "Tag" }; { Type = "Pattern?"; Name = "Argument" } ] }
      { Name = "FieldPattern"
        Fields = [ { Type = "Name"; Name = "Name" }; { Type = "Pattern?"; Name = "Pattern" } ] }
      { Name = "RecordPattern"
        Fields =
          [ { Type = "FieldPattern[]"
              Name = "Fields" }
            { Type = "SimplePattern?"
              Name = "Rest" } ] } ]

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

let renderIVisitor (sw: System.IO.StreamWriter) (baseName: string) types =
    sw.Write($"public interface I{baseName}Visitor<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 =
    let writeField i field =
        if i > 0 then
            sw.Write(", ")

        sw.Write $"{field.Type} {field.Name}"

    sw.Write $"public partial record {t.Name}("
    List.iteri writeField t.Fields

    sw.Write
        $") : {baseName}()
{{\n"

    sw.Write
        $"\tpublic override T accept<T>(I{baseName}Visitor<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.                                           //
////////////////////////////////////////////////////////////

#nullable enable

namespace Finn.AST;

public abstract record {baseName}() {{
\tpublic abstract T accept<T>(I{baseName}Visitor<T> visitor);
}}\n"

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

renderAST "." "Expr" exprTypes
renderAST "." "Pattern" patternTypes