package macro

import (
	"fmt"

	"github.com/hellerve/argos/ast"
)

type Macro struct {
	params      []string
	transformer *ast.AST
}

type MacroEnv map[string]Macro

func NewMacroEnv() MacroEnv {
	return make(MacroEnv)
}

func handleMac(l []*ast.AST, m MacroEnv) (*ast.AST, error) {
	if len(l) != 4 {
		return nil, fmt.Errorf("mac takes 3 arguments")
	}

	nameThunk := l[1]

	if nameThunk.Tag != ast.Symbol {
		return nil, fmt.Errorf("First argument to mac must be symbol, got %s", nameThunk.Pretty())
	}

	name := nameThunk.Val.(string)

	paramsThunk := l[2]

	if paramsThunk.Tag != ast.List {
		return nil, fmt.Errorf("second argument to mac must be list, got %s", paramsThunk.Pretty())
	}

	var params []string

	for _, elem := range paramsThunk.Val.([]*ast.AST) {
		if elem.Tag != ast.Symbol {
			return nil, fmt.Errorf("Invalid value in parameter list to mac: %s", elem.Pretty())
		}
		params = append(params, elem.Val.(string))
	}

	m[name] = Macro{params, l[2]}

	nilVal := ast.AST{ast.Symbol, "nil"}
	return &nilVal, nil
}

func traverse(l *ast.AST, m MacroEnv) (*ast.AST, error) {
	vals := l.Val.([]*ast.AST)
	if len(vals) == 0 {
		return l, nil
	}

	if vals[0].Tag == ast.Symbol && vals[0].Val.(string) == "mac" {
		return handleMac(vals, m)
	}

	return l, nil
}

func Expand(l *ast.AST, m MacroEnv) (*ast.AST, error) {
	if l.Tag != ast.List {
		return l, nil
	}
	return traverse(l, m)
}