<?php

namespace CrocWork\Zappy\I18n;

/**
 * Translator class
 *
 * The Translator class provides an implementation for setting the application's
 * locale and providing translations for use in the application ui. This implementation
 * uses a regular expression to check if entered locales conform to a standardized format.
 */
class Translator
{
    /**
     * Regular expression used to check the form of locale strings.
     */
    private const LOCALE_REGEX = '/^[A-Za-z]{2,3}([_-][A-Za-z]{4})?([_-][A-Za-z]{2})?$/';

    /**
     * The default application locale.
     * @var string
     */
    private string $fallbackLocale;

    /**
     * The currently active locale.
     * @var string
     */
    private string $locale;

    /**
     * The path where translation files are stored.
     * @var string
     */
    private string $translationsPath;

    /**
     * The currently loaded translations.
     * @var array
     */
    private array $translations;

    /**
     * Initialize a Translator instance.
     *
     * To initialize a Translator, it must know where translation files are to be found and what
     * locale to set by default on initialization. These values are checked for correctness, upon
     * failure an exception will be thrown.
     *
     * @param string $fallbackLocale
     * @param string $translationsPath
     */
    public function __construct(string $fallbackLocale, string $translationsPath)
    {
        $this->fallbackLocale = $fallbackLocale;
        $this->locale = $this->fallbackLocale;
        $this->translationsPath = $translationsPath;

        if(!file_exists($translationsPath) || !is_dir($translationsPath)) {
            throw new \RuntimeException("Could not initialize translator: invalid translations path.");
        }
    }

    public function provides(): string
    {
        return 'translator';
    }

    /**
     * Get the default locale string.
     * @return string
     */
    public function getFallbackLocale(): string
    {
        return $this->fallbackLocale;
    }

    /**
     * Get the current locale string.
     * @return string
     */
    public function getLocale(): string
    {
        return $this->locale;
    }

    /**
     * Set the current locale string. If the form is invalid, an exception will be thrown.
     * @param string $locale
     * @return $this
     */
    public function setLocale(string $locale): static
    {
        if(!static::checkLocale($locale)) {
            throw new \RuntimeException("Could not set locale: invalid locale format.");
        }

        $this->locale = $locale;
        $this->loadTranslations();
        return $this;
    }

    /**
     * Get a translation from the translation array.
     * @param string $key
     * @param $default
     * @return mixed|null|string
     */
    public function getTranslation(string $key, $default = null)
    {
        if(empty($this->translations)) {
            return $default;
        }

        $keys = explode ('.', $key);

        $value = $this->translations;
        foreach($keys as $index) {
            if(!key_exists($index, $value)) return $default;
            $value = $value[$index];
        }

        return $value;
    }

    /**
     * Check if a locale string has the correct format.
     * @param string $locale
     * @return bool
     */
    public static function checkLocale(string $locale): bool
    {
        return (!empty($locale) && preg_match_all(static::LOCALE_REGEX, $locale));
    }

    /**
     * Load translations for the currently selected locale.
     * @return void
     */
    private function loadTranslations(): void
    {
        $dir = $this->translationsPath;
        $locale = $this->locale;
        $localeDir = $dir . DIRECTORY_SEPARATOR . $locale;

        if(!file_exists($localeDir)) {
            //TODO: is the error really needed?
            throw new \RuntimeException("Unable to load translations; translation directory not found.");
        }

        $files = glob($localeDir . DIRECTORY_SEPARATOR . '*.php');
        if($files === false || empty($files)) {
            return;
        }

        $this->translations = [];
        foreach($files as $file) {
            $translations = require $file;
            $key = basename($file, '.php');
            $this->translations[$key] = $translations;
        }
    }

}