website/includes/translation.php

<?php
/**
 * Translation System
 * Handles multi-language support for Finnish and English
 */

class Translation {
    private static $instance = null;
    private $translations = [];
    private $currentLanguage = 'en';
    private $defaultLanguage = 'en';
    private $supportedLanguages = ['en' => 'English', 'fi' => 'Finnish'];
    
    private function __construct() {
        $this->detectLanguage();
        $this->loadTranslations();
    }
    
    public static function getInstance() {
        if (self::$instance === null) {
            self::$instance = new self();
        }
        return self::$instance;
    }
    
    private function detectLanguage() {
        // Check if language is set in session
        if (isset($_SESSION['language']) && isset($this->supportedLanguages[$_SESSION['language']])) {
            $this->currentLanguage = $_SESSION['language'];
            return;
        }
        
        // Check URL parameter
        if (isset($_GET['lang']) && isset($this->supportedLanguages[$_GET['lang']])) {
            $this->currentLanguage = $_GET['lang'];
            $_SESSION['language'] = $this->currentLanguage;
            return;
        }
        
        // Redirect to same page without language parameter to apply new language
        if (isset($_GET['lang']) && isset($this->supportedLanguages[$_GET['lang']])) {
            // Remove language parameter from URL to prevent infinite redirect loops
            $currentUrl = $_SERVER['REQUEST_URI'];
            $urlWithoutLang = strtok($currentUrl, '?')[0];
            
            // Redirect to same page without language parameter
            if ($urlWithoutLang !== false) {
                header('Location: ' . $urlWithoutLang . '?lang=' . $_GET['lang']);
                exit;
            }
        }
        
        // Check browser language preference
        if (isset($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
            $browserLang = substr($_SERVER['HTTP_ACCEPT_LANGUAGE'], 0, 2);
            if (isset($this->supportedLanguages[$browserLang])) {
                $this->currentLanguage = $browserLang;
                $_SESSION['language'] = $this->currentLanguage;
                return;
            }
        }
        
        // Check configuration default
        if (defined('DEFAULT_LANGUAGE') && isset($this->supportedLanguages[DEFAULT_LANGUAGE])) {
            $this->currentLanguage = DEFAULT_LANGUAGE;
            return;
        }
        
        // Fall back to default language
        $this->currentLanguage = $this->defaultLanguage;
    }
    
    private function loadTranslations() {
        $langFile = __DIR__ . '/../languages/' . $this->currentLanguage . '.php';
        
        if (file_exists($langFile)) {
            $this->translations = require $langFile;
        } else {
            // Fall back to default language if current language file doesn't exist
            $defaultLangFile = __DIR__ . '/../languages/' . $this->defaultLanguage . '.php';
            if (file_exists($defaultLangFile)) {
                $this->translations = require $defaultLangFile;
            }
        }
    }
    
    public function translate($key, $params = []) {
        if (isset($this->translations[$key])) {
            $translation = $this->translations[$key];
            
            // Replace parameters in translation
            foreach ($params as $param => $value) {
                $translation = str_replace(':' . $param, $value, $translation);
            }
            
            return $translation;
        }
        
        // Return key if translation not found
        return $key;
    }
    
    public function getCurrentLanguage() {
        return $this->currentLanguage;
    }
    
    public function getSupportedLanguages() {
        return $this->supportedLanguages;
    }
    
    public function setLanguage($language) {
        if (isset($this->supportedLanguages[$language])) {
            $this->currentLanguage = $language;
            $_SESSION['language'] = $language;
            $this->loadTranslations();
            return true;
        }
        return false;
    }
    
    public function getLanguageSwitcher($currentPath = '') {
        $switcher = '<div class="language-switcher">';
        $switcher .= '<span class="language-label">' . $this->translate('language') . ':</span>';
        
        foreach ($this->supportedLanguages as $code => $name) {
            $url = $currentPath;
            $separator = strpos($url, '?') !== false ? '&' : '?';
            $switcherUrl = $url . $separator . 'lang=' . $code;
            
            $class = $code === $this->currentLanguage ? 'active' : '';
            $switcher .= '<a href="' . htmlspecialchars($switcherUrl) . '" class="language-link ' . $class . '">' . $name . '</a>';
        }
        
        $switcher .= '</div>';
        return $switcher;
    }
}

// Global translation function for convenience
function t($key, $params = []) {
    return Translation::getInstance()->translate($key, $params);
}

// Get current language
function getCurrentLanguage() {
    return Translation::getInstance()->getCurrentLanguage();
}

// Get supported languages
function getSupportedLanguages() {
    return Translation::getInstance()->getSupportedLanguages();
}