package main

import (
	"fmt"
	"os"
	"strings"
)

func main() {
	if len(os.Args) != 2 {
		fmt.Println("Usage: astgen <output_directory>")
		os.Exit(64)
	}

	d := os.Args[1]

	if _, err := os.Stat(d); os.IsNotExist(err) {
		fmt.Println("Directory does not exist")
		os.Exit(74)
	}

	fmt.Println("Generating AST classes in", d)

	defineAst(d, "Expr", []string{
		"Error    : Value string",
		"Binary   : Left Expr, Operator token.Token, Right Expr",
		"Grouping : Expression Expr",
		"Literal  : Value any",
		"Unary    : Operator token.Token, Right Expr",
		"Variable : Name token.Token",
	})

	defineAst(d, "Stmt", []string{
		"Error        : Value string",
		"Expression   : Expression Expr",
		"Print        : Expression Expr",
		"Var          : Name token.Token, Initializer Expr",
	})
}

func defineAst(outputDir, baseName string, types []string) {
	path := outputDir + "/" + strings.ToLower(baseName) + ".go"

	file, err := os.Create(path)
	if err != nil {
		fmt.Println("Error creating file", path)
		os.Exit(74)
	}
	defer file.Close()

	file.WriteString("package ast\n\n")
	file.WriteString("import \"golox/token\"\n\n")
	defineVisitor(file, baseName, types)

	file.WriteString("type " + baseName + " interface {\n")
	file.WriteString("	Accept(visitor " + baseName + "Visitor[any]) any\n")
	file.WriteString("}\n\n")

	for _, t := range types {
		defineType(file, baseName, t)
	}
}

func defineVisitor(file *os.File, baseName string, types []string) {
	file.WriteString("type " + baseName + "Visitor[T any] interface {\n")

	for _, t := range types {
		typeName := strings.TrimSpace(t[:strings.Index(t, ":")-1])
		paramName := strings.ToLower(typeName[:1]) + strings.ToLower(baseName[:1])
		file.WriteString("	Visit" + typeName + baseName + "(" + paramName + " *" + typeName + baseName + ") T\n")
	}

	file.WriteString("}\n\n")
}

func defineType(file *os.File, baseName, typeString string) {
	typeName := strings.TrimSpace(typeString[:strings.Index(typeString, ":")-1])
	fields := strings.TrimSpace(typeString[strings.Index(typeString, ":")+1:])

	file.WriteString("type " + typeName + baseName + " struct {\n")

	for _, field := range strings.Split(fields, ", ") {
		file.WriteString("	" + field + "\n")
	}

	varName := strings.ToLower(typeName[:1]) + strings.ToLower(baseName[:1])
	file.WriteString("}\n\n")
	file.WriteString("func (" + varName + " *" + typeName + baseName + ") Accept(v " + baseName + "Visitor[any]) any {\n")
	file.WriteString("	return v.Visit" + typeName + baseName + "(" + varName + ")\n")
	file.WriteString("}\n\n")
}