// Copyright (c) 2026 Storm Dragon
// SPDX-License-Identifier: GPL-3.0-or-later

package spellcheck

import (
	"os"
	"strings"
	"unicode"
	"unicode/utf8"
)

// Language uses the effective session message locale, with no English fallback.
// LANGUAGE is a translation fallback list, not the session's regional locale.
func Language() string {
	for _, name := range []string{"LC_ALL", "LC_MESSAGES", "LANG"} {
		if value := os.Getenv(name); value != "" {
			return language_tag(value)
		}
	}
	return ""
}

func language_tag(value string) string {
	value, _, _ = strings.Cut(strings.TrimSpace(value), ".")
	value, _, _ = strings.Cut(value, "@")
	if value == "C" || value == "POSIX" {
		return ""
	}
	value = strings.ReplaceAll(value, "-", "_")
	for _, char := range value {
		if !unicode.IsLetter(char) && char != '_' {
			return ""
		}
	}
	return value
}

// Word strips surrounding prose punctuation but leaves structured terminal
// tokens intact so they can be excluded rather than checked as fragments.
func Word(value string) string {
	value = strings.TrimSpace(value)
	if strings.HasPrefix(value, "-") || strings.HasPrefix(value, "#") || strings.HasPrefix(value, "@") ||
		strings.ContainsAny(value, "/\\@_=0123456789") || strings.Contains(value, "://") {
		return ""
	}
	value = strings.TrimFunc(value, func(char rune) bool { return !unicode.IsLetter(char) && !unicode.IsMark(char) })
	if !valid_word(value) {
		return ""
	}
	return value
}

func valid_word(value string) bool {
	if !utf8.ValidString(value) || utf8.RuneCountInString(value) > 128 || value == "" {
		return false
	}
	letters := false
	for _, char := range value {
		if unicode.IsLetter(char) {
			letters = true
		} else if !unicode.IsMark(char) && char != '\'' && char != '’' && char != '-' && char != '‐' {
			return false
		}
	}
	return letters
}

func Separator(char rune) bool {
	return unicode.IsSpace(char) || unicode.IsPunct(char) && !strings.ContainsRune("'.:/@\\_=-’‐#", char)
}