package html

import (
	"errors"
	"fmt"
	"regexp"
	"strings"
)

var symbolExp = regexp.MustCompile(`^[a-zA-Z][a-zA-Z0-9-_.]*$`)

func validateSymbol(s string) error {
	if !symbolExp.MatchString(s) {
		return errors.New("invalid symbol")
	}

	return nil
}

func validateTagName(name string) error {
	if strings.HasPrefix(name, "!") {
		return nil
	}

	return validateSymbol(name)
}

func validateAttributeName(name string) error {
	return validateSymbol(name)
}

func validate(name string, children []any) error {
	if err := validateTagName(name); err != nil {
		return err
	}

	isDeclaration := strings.HasPrefix(name, "!")
	a, c, rgs := groupChildren(children)
	rg := mergeRenderingGuides(rgs)
	if rg.void && len(c) > 0 {
		return fmt.Errorf("tag %s is void but it has children", name)
	}

	if isDeclaration && len(c) > 0 {
		return fmt.Errorf("declarations cannot have children (%s)", name)
	}

	for _, ai := range a {
		for _, name := range ai.names {
			if isDeclaration {
				continue
			}

			if err := validateAttributeName(name); err != nil {
				return fmt.Errorf("tag %s: %w", name, err)
			}
		}
	}

	for _, ci := range c {
		if tag, ok := ci.(Tag); ok {
			if rg.script {
				return fmt.Errorf("tag %s does not allow child elements", name)
			}

			var v validator
			tag(&v)
			if v.err != nil {
				return v.err
			}

			continue
		}
	}

	return nil
}