<?php
/**
 * Locale API: WP_Locale_Switcher class
 *
 * @package WordPress
 * @subpackage i18n
 * @since 4.7.0
 */

/**
 * Core class used for switching locales.
 *
 * @since 4.7.0
 */
class WP_Locale_Switcher {
    /**
     * Locale stack.
     *
     * @since 4.7.0
     * @access private
     * @var string[]
     */
    private $locales = array();

    /**
     * Original locale.
     *
     * @since 4.7.0
     * @access private
     * @var string
     */
    private $original_locale;

    /**
     * Holds all available languages.
     *
     * @since 4.7.0
     * @access private
     * @var array An array of language codes (file names without the .mo extension).
     */
    private $available_languages = array();

    /**
     * Constructor.
     *
     * Stores the original locale as well as a list of all available languages.
     *
     * @since 4.7.0
     */
    public function __construct() {
        $this->original_locale     = is_admin() ? get_user_locale() : get_locale();
        $this->available_languages = array_merge( array( 'en_US' ), get_available_languages() );
    }

    /**
     * Initializes the locale switcher.
     *
     * Hooks into the {@see 'locale'} filter to change the locale on the fly.
     */
    public function init() {
        add_filter( 'locale', array( $this, 'filter_locale' ) );
    }

    /**
     * Switches the translations according to the given locale.
     *
     * @since 4.7.0
     *
     * @param string $locale The locale to switch to.
     * @return bool True on success, false on failure.
     */
    public function switch_to_locale( $locale ) {
        $current_locale = is_admin() ? get_user_locale() : get_locale();
        if ( $current_locale === $locale ) {
            return false;
        }

        if ( ! in_array( $locale, $this->available_languages, true ) ) {
            return false;
        }

        $this->locales[] = $locale;

        $this->change_locale( $locale );

        /**
         * Fires when the locale is switched.
         *
         * @since 4.7.0
         *
         * @param string $locale The new locale.
         */
        do_action( 'switch_locale', $locale );

        return true;
    }

    /**
     * Restores the translations according to the previous locale.
     *
     * @since 4.7.0
     *
     * @return string|false Locale on success, false on failure.
     */
    public function restore_previous_locale() {
        $previous_locale = array_pop( $this->locales );

        if ( null === $previous_locale ) {
            // The stack is empty, bail.
            return false;
        }

        $locale = end( $this->locales );

        if ( ! $locale ) {
            // There's nothing left in the stack: go back to the original locale.
            $locale = $this->original_locale;
        }

        $this->change_locale( $locale );

        /**
         * Fires when the locale is restored to the previous one.
         *
         * @since 4.7.0
         *
         * @param string $locale          The new locale.
         * @param string $previous_locale The previous locale.
         */
        do_action( 'restore_previous_locale', $locale, $previous_locale );

        return $locale;
    }

    /**
     * Restores the translations according to the original locale.
     *
     * @since 4.7.0
     *
     * @return string|false Locale on success, false on failure.
     */
    public function restore_current_locale() {
        if ( empty( $this->locales ) ) {
            return false;
        }

        $this->locales = array( $this->original_locale );

        return $this->restore_previous_locale();
    }

    /**
     * Whether switch_to_locale() is in effect.
     *
     * @since 4.7.0
     *
     * @return bool True if the locale has been switched, false otherwise.
     */
    public function is_switched() {
        return ! empty( $this->locales );
    }

    /**
     * Filters the WordPress install's locale.
     *
     * @since 4.7.0
     *
     * @param string $locale The WordPress install's locale.
     * @return string The locale currently being switched to.
     */
    public function filter_locale( $locale ) {
        $switched_locale = end( $this->locales );

        if ( $switched_locale ) {
            return $switched_locale;
        }

        return $locale;
    }

    /**
     * Load translations for a given locale.
     *
     * When switching to a locale, translations for this locale must be loaded from scratch.
     *
     * @since 4.7.0
     * @access private
     *
     * @global Mo[] $l10n An array of all currently loaded text domains.
     *
     * @param string $locale The locale to load translations for.
     */
    private function load_translations( $locale ) {
        global $l10n;

        $domains = $l10n ? array_keys( $l10n ) : array();

        load_default_textdomain( $locale );

        foreach ( $domains as $domain ) {
            if ( 'default' === $domain ) {
                continue;
            }

            unload_textdomain( $domain );
            get_translations_for_domain( $domain );
        }
    }

    /**
     * Changes the site's locale to the given one.
     *
     * Loads the translations, changes the global `$wp_locale` object and updates
     * all post type labels.
     *
     * @since 4.7.0
     * @access private
     *
     * @global WP_Locale $wp_locale The WordPress date and time locale object.
     *
     * @param string $locale The locale to change to.
     */
    private function change_locale( $locale ) {
        // Reset translation availability information.
        _get_path_to_translation( null, true );

        $this->load_translations( $locale );

        $GLOBALS['wp_locale'] = new WP_Locale();

        /**
         * Fires when the locale is switched to or restored.
         *
         * @since 4.7.0
         *
         * @param string $locale The new locale.
         */
        do_action( 'change_locale', $locale );
    }
}