package saccharine

import (
	"fmt"

	"git.maximhutz.com/max/lambda/pkg/iterator"
)

func isVariableToken(t Token) bool {
	return t.Type == TokenVariable
}

func ParseExpression(i *iterator.Iterator[Token]) (Node, error) {
	token, err := i.Pop()
	if err != nil {
		return nil, fmt.Errorf("could not get next token: %w", err)
	}

	switch token.Type {
	case TokenVariable:
		return NewVariable(token.Value), nil
	case TokenDot:
		return nil, fmt.Errorf("token '.' found without a corresponding slash (column %d)", token.Index)
	case TokenSlash:
		tokens := i.PopWhile(isVariableToken)
		variables := []string{}

		for _, token := range tokens {
			variables = append(variables, token.Value)
		}

		if dot, dotErr := i.Pop(); dotErr != nil {
			return nil, fmt.Errorf("could not find parameter terminator: %w", dotErr)
		} else if dot.Type != TokenDot {
			return nil, fmt.Errorf("expected '.', got '%v' (column %d)", dot.Value, dot.Index)
		}

		body, bodyErr := ParseExpression(i)
		if bodyErr != nil {
			return nil, fmt.Errorf("could not parse function body: %w", bodyErr)
		}

		return NewAbstraction(variables, body), nil
	case TokenOpenParen:
		fn, fnErr := ParseExpression(i)
		if fnErr != nil {
			return nil, fmt.Errorf("could not parse call function: %w", fnErr)
		}

		args := []Node{}

		for {
			if next, nextErr := i.Peek(); nextErr == nil && next.Type == TokenCloseParen {
				break
			}

			arg, argErr := ParseExpression(i)
			if argErr != nil {
				return nil, fmt.Errorf("could not parse call argument: %w", argErr)
			}

			args = append(args, arg)
		}

		closing, closingErr := i.Pop()
		if closingErr != nil {
			return nil, fmt.Errorf("could not parse call terminating parenthesis: %w", closingErr)
		} else if closing.Type != TokenCloseParen {
			return nil, fmt.Errorf("expected call terminating parenthesis, got '%v' (column %v)", closing.Value, closing.Index)
		}

		return NewApplication(fn, args), nil
	}

	return nil, fmt.Errorf("unexpected token '%v' (column %d)", token.Value, token.Index)
}

func GetTree(tokens []Token) (Node, error) {
	return ParseExpression(iterator.New(tokens))
}