package contactcheck

import (
	"errors"
	"strings"
	"unicode"

	"github.com/abadojack/whatlanggo"
)

const (
	minMessageRunes = 20
	maxMessageRunes = 8000
	maxNameRunes    = 120

	// Reject non-English only when the detector is fairly confident.
	englishRejectConfidence = 0.80
)

var (
	ErrNotEnglish = errors.New("message must be in English")
	ErrTooShort   = errors.New("message too short")
	ErrTooLong    = errors.New("message too long")
	ErrName       = errors.New("name too long")
)

// ValidateEnglish checks script and language for name + message combined.
func ValidateEnglish(name, message string) error {
	msg := strings.TrimSpace(message)
	nMsg := len([]rune(msg))
	if nMsg < minMessageRunes {
		return ErrTooShort
	}
	if nMsg > maxMessageRunes {
		return ErrTooLong
	}
	if len([]rune(strings.TrimSpace(name))) > maxNameRunes {
		return ErrName
	}

	combined := strings.TrimSpace(name) + "\n\n" + msg
	info := whatlanggo.Detect(combined)

	// Block clearly non-Latin scripts (CJK, Cyrillic, etc.).
	if info.Script != nil && info.Script != unicode.Latin {
		return ErrNotEnglish
	}
	// Allow uncertain detection; block only confident non-English.
	if info.Lang != whatlanggo.Eng && info.IsReliable() {
		return ErrNotEnglish
	}
	if info.Lang != whatlanggo.Eng && info.Confidence >= englishRejectConfidence {
		return ErrNotEnglish
	}
	return nil
}