class-wp-cldr.php

<?php
/**
 * WP_CLDR class for fetching localization data from Unicode's Common Locale Data Repository
 *
 * The wp-cldr plugin is comprised of the WP_CLDR class, a subset of the reference JSON files from Unicode, and unit tests.
 *
 * @link https://github.com/Automattic/wp-cldr
 *
 * @package wp-cldr
 */

declare( strict_types=1 );

/**
 * This plugin gives WordPress developers easy access to localized country, region, language, currency, time zone, and calendar info from the [Unicode Common Locale Data Repository](http://cldr.unicode.org/).
 *
 * Examples:
 *
 * The default locale is English:
 *
 * ```
 * $cldr = new WP_CLDR();
 * $territories_in_english = $cldr->get_territories();
 * ```
 *
 * You can override the default locale per-call by passing in a language slug in the second parameter:
 *
 * ```
 * $germany_in_arabic = $cldr->get_territory_name( 'DE' , 'ar_AR' );
 * ```
 *
 * Use a convenience parameter during instantiation to change the default locale:
 *
 * ```
 * $cldr = new WP_CLDR( 'fr' );
 * $germany_in_french = $cldr->get_territory_name( 'DE' );
 * $us_dollar_in_french = $cldr->get_currency_name( 'USD' );
 * $canadian_french_in_french = $cldr->get_language_name( 'fr-ca' );
 * $canadian_french_in_english = $cldr->get_language_name( 'fr-ca' , 'en' );
 * $german_in_german = $cldr->get_language_name( 'de_DE' , 'de-DE' );
 * $bengali_in_japanese = $cldr->get_language_name( 'bn_BD' , 'ja_JP' );
 * $us_dollar_symbol_in_simplified_chinese = $cldr->get_currency_symbol( 'USD', 'zh' );
 * $africa_in_french = $cldr->get_territory_name( '002' );
 * ```
 *
 * Switch locales after the object has been created:
 *
 * ```
 * $cldr->set_locale( 'en' );
 * $us_dollar_in_english = $cldr->get_currency_name( 'USD' );
 * ```
 *
 * Testing:
 *
 * The class includes a suite of PHPUnit tests. To run them, call `phpunit` from the plugin directory.
 *
 * @link http://cldr.unicode.org
 * @link https://github.com/unicode-cldr/cldr-json
 *
 * @autounit wp-cldr
 */
class WP_CLDR {
	/**
	 * The current locale.
	 *
	 * @var string
	 */
	private $locale = 'en';

	/**
	 * The in-memory array of localized values.
	 *
	 * @var array
	 */
	private $localized = [];

	/**
	 * Whether or not to use caching.
	 *
	 * @var bool
	 */
	private $use_cache = true;

	/**
	 * The cache group name to use for the WordPress object cache.
	 */
	const CACHE_GROUP = 'wp-cldr';

	/**
	 * The CLDR version, which the class uses to determine path to JSON files.
	 */
	const CLDR_VERSION = '45.0.0';

	/**
	 * Constructs a new instance of the class, including setting defaults for locale and caching.
	 *
	 * @param  string  $locale  Optional. A WordPress locale code.
	 * @param  bool  $use_cache  Optional. Whether to use caching (primarily used to suppress caching for unit testing).
	 */
	public function __construct( string $locale = 'en', bool $use_cache = true ) {
		$this->use_cache = $use_cache;
		$this->set_locale( $locale );
	}

	/**
	 * Sets the locale.
	 *
	 * @param  string  $locale  A WordPress locale code.
	 */
	public function set_locale( string $locale ): void {
		$this->locale = $locale;
		$this->initialize_locale_bucket( $locale );
	}

	/**
	 * Gets CLDR code for the equivalent WordPress locale code.
	 *
	 * @param  string  $wp_locale  A WordPress locale code.
	 *
	 * @return string The equivalent CLDR locale code.
	 */
	public static function get_cldr_locale( string $wp_locale ): string {

		// Some WordPress locales are significantly different from CLDR locales.
		$wp2cldr = [
			'ary'   => 'ar-MA',
			'azb'   => 'az',
			'dzo'   => 'dz',
			'mya'   => 'my',
			'no'    => 'nb',
			'bel'   => 'be',
			'kmr'   => 'ku',
			'kir'   => 'ky',
			'oci'   => 'oc',
			'snd'   => 'sd',
			'tl'    => 'fil',
			'zh-cn' => 'zh-Hans',
			'zh-hk' => 'zh-Hant',
			'zh-sg' => 'zh-Hans',
			'zh-tw' => 'zh-Hant',
			'zh'    => 'zh-Hans',
		];

		// Convert underscores to dashes and everything to lowercase.
		$cleaned_up_wp_locale = '';
		$cleaned_up_wp_locale = str_replace( '_', '-', $wp_locale );
		$cleaned_up_wp_locale = strtolower( $cleaned_up_wp_locale );

		// Check for an exact match in exceptions array.
		if ( isset( $wp2cldr[ $cleaned_up_wp_locale ] ) ) {
			return $wp2cldr[ $cleaned_up_wp_locale ];
		}

		// Capitalize country code and initial letter of script code to match CLDR JSON file names.
		$locale_components = explode( '-', $cleaned_up_wp_locale );
		if ( isset( $locale_components[1] ) && 2 === strlen( $locale_components[1] ) ) {
			$locale_components[1] = strtoupper( $locale_components[1] );
			$cleaned_up_wp_locale = implode( '-', $locale_components );

			return $cleaned_up_wp_locale;
		}
		if ( isset( $locale_components[1] ) && 2 < strlen( $locale_components[1] ) ) {
			$locale_components[1] = ucfirst( $locale_components[1] );
			$cleaned_up_wp_locale = implode( '-', $locale_components );

			return $cleaned_up_wp_locale;
		}

		return $cleaned_up_wp_locale;
	}

	/**
	 * Gets the absolute path of a CLDR JSON file for a given WordPress locale and CLDR data item.
	 *
	 * @param  string  $cldr_locale  A CLDR locale.
	 * @param  string  $bucket  The CLDR data item.
	 *
	 * @return string The absolute path of the CLDR file.
	 */
	public static function get_cldr_json_path( string $cldr_locale, string $bucket ): string {

		$base_path = __DIR__ . '/data/' . self::CLDR_VERSION;

		switch ( $cldr_locale ) {
			case 'supplemental':
				$relative_path = 'supplemental';
				break;

			default:
				$relative_path = "main/$cldr_locale";
				break;
		}

		return "$base_path/$relative_path/$bucket.json";
	}

	/**
	 * Checks to see if there is an installed CLDR JSON file for a given CLDR locale and data item.
	 *
	 * @param  string  $cldr_locale  The CLDR locale.
	 * @param  string  $bucket  The CLDR data item.
	 *
	 * @return bool Whether or not the CLDR JSON file is available.
	 */
	public static function is_cldr_json_available( string $cldr_locale, string $bucket ): bool {
		$cldr_json_file_path = self::get_cldr_json_path( $cldr_locale, $bucket );

		return is_readable( $cldr_json_file_path );
	}

	/**
	 * Loads a CLDR JSON data file.
	 *
	 * @param  string  $cldr_locale  The CLDR locale.
	 * @param  string  $bucket  The CLDR data item.
	 *
	 * @return array An array with the CLDR data from the file, or an empty array if no match with any CLDR data files.
	 */
	public static function get_cldr_json_file( string $cldr_locale, string $bucket ): array {
		$cldr_json_path = self::get_cldr_json_path( $cldr_locale, $bucket );

		if ( self::is_cldr_json_available( $cldr_locale, $bucket ) ) {
			$json_raw     = file_get_contents( $cldr_json_path );
			$json_decoded = json_decode( $json_raw, true );

			return $json_decoded;
		}

		return [];
	}

	/**
	 * Uses fallback logic to get the best available CLDR JSON locale for a given WordPress locale.
	 *
	 * @param  string  $locale  A WordPress locale code.
	 * @param  string  $bucket  The CLDR data item.
	 *
	 * @return string The best available CLDR JSON locale, or an empty string if no JSON locale is available.
	 */
	public static function get_best_available_cldr_json_locale( string $locale, string $bucket ): string {
		$cldr_locale = self::get_cldr_locale( $locale );

		if ( self::is_cldr_json_available( $cldr_locale, $bucket ) ) {
			return $cldr_locale;
		}

		// If there's no language-country locale CLDR file, try falling back to a language-only CLDR file.
		$language_only_cldr_locale = strtok( $cldr_locale, '-_' );
		if ( self::is_cldr_json_available( $language_only_cldr_locale, $bucket ) ) {
			return $language_only_cldr_locale;
		}

		return '';
	}

	/**
	 * Initializes a "bucket" of CLDR data items for a WordPress locale.
	 *
	 * @param  string  $locale  Optional. The locale.
	 * @param  string  $bucket  Optional. The CLDR data item.
	 *
	 * @return bool Whether or not the locale bucket was successfully initialized.
	 */
	private function initialize_locale_bucket( string $locale, string $bucket = 'territories' ): bool {

		$cache_key = "cldr-$locale-$bucket";

		if ( $this->use_cache ) {
			$cached_data = wp_cache_get( $cache_key, self::CACHE_GROUP );
			if ( false !== $cached_data ) {
				$this->localized[ $locale ][ $bucket ] = $cached_data;

				return true;
			}
		}

		$cldr_locale = self::get_best_available_cldr_json_locale( $locale, $bucket );

		if ( empty( $cldr_locale ) ) {
			return false;
		}

		$json_file = self::get_cldr_json_file( $cldr_locale, $bucket );

		// Do some performance-enhancing pre-processing of data items, then put into cache
		// organized by WordPress $locale instead of $cldr_locale (which isn't visible
		// outside this method).
		switch ( $bucket ) {
			case 'territories':
			case 'languages':
				$sorted_array = $json_file['main'][ $cldr_locale ]['localeDisplayNames'][ $bucket ];
				if ( function_exists( 'collator_create' ) ) {
					// Sort data according to locale collation rules.
					$coll = collator_create( $cldr_locale );
					collator_asort( $coll, $sorted_array, Collator::SORT_STRING );
				} else {
					asort( $sorted_array );
				}
				$this->localized[ $locale ][ $bucket ] = $sorted_array;
				break;

			case 'currencies':
				$this->localized[ $locale ][ $bucket ] = $json_file['main'][ $cldr_locale ]['numbers'][ $bucket ];
				break;

			case 'timeZoneNames':
				$this->localized[ $locale ][ $bucket ] = $json_file['main'][ $cldr_locale ]['dates'][ $bucket ];
				break;

			default:
				$this->localized[ $locale ][ $bucket ] = $json_file;
				break;
		}

		if ( $this->use_cache ) {
			wp_cache_set( $cache_key, $this->localized[ $locale ][ $bucket ], self::CACHE_GROUP );
		}

		return true;
	}

	/**
	 * Flushes the WordPress object cache for a single CLDR data item for a single locale.
	 *
	 * @param  string  $locale  A WordPress locale code.
	 * @param  string  $bucket  A CLDR data item.
	 */
	public function flush_wp_cache_for_locale_bucket( string $locale, string $bucket ) {
		$cache_key = "cldr-$locale-$bucket";

		return wp_cache_delete( $cache_key, self::CACHE_GROUP );
	}

	/**
	 * Clears the WordPress object cache for all CLDR data items across all locales.
	 */
	public function flush_all_wp_caches() {
		$this->localized = [];

		$locales           = $this->get_languages();
		$supported_buckets = [ 'territories', 'currencies', 'languages', 'weekData' ];
		foreach ( array_keys( $locales ) as $locale ) {
			foreach ( $supported_buckets as $bucket ) {
				$this->flush_wp_cache_for_locale_bucket( $locale, $bucket );
			}
		}
	}

	/**
	 * Returns a bucket of CLDR data for a locale.
	 *
	 * @param  string  $locale  A WordPress locale code.
	 * @param  string  $bucket  A CLDR data item.
	 *
	 * @return array An associative array with the contents of the locale bucket.
	 */
	private function get_locale_bucket( string $locale, string $bucket ): array {
		if ( empty( $locale ) ) {
			$locale = $this->locale;
		}

		// Check the in-memory array.
		if ( isset( $this->localized[ $locale ][ $bucket ] ) ) {
			return $this->localized[ $locale ][ $bucket ];
		}

		// If it's not in memory, initialize the locale bucket which loads the in-memory array.
		if ( $this->initialize_locale_bucket( $locale, $bucket ) ) {
			return $this->localized[ $locale ][ $bucket ];
		}

		// If the locale bucket cannot be initialized, fall back to English.
		if ( isset( $this->localized['en'][ $bucket ] ) ) {
			return $this->localized['en'][ $bucket ];
		}
		if ( $this->initialize_locale_bucket( 'en', $bucket ) ) {
			return $this->localized['en'][ $bucket ];
		}

		// Since everything else failed, return an empty array.
		return [];
	}

	/**
	 * Gets a localized country or region name.
	 *
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 * @link http://unstats.un.org/unsd/methods/m49/m49regin.htm UN M.49 region codes
	 *
	 * @param  string  $territory_code  An ISO 3166-1 country code, or a UN M.49 region code.
	 * @param  string  $locale  Optional. A WordPress locale code.
	 *
	 * @return string The name of the territory in the provided locale.
	 */
	public function get_territory_name( string $territory_code, string $locale = '' ): string {
		$territories_array = $this->get_territories( $locale );
		if ( isset( $territories_array[ $territory_code ] ) ) {
			return $territories_array[ $territory_code ];
		}

		return '';
	}

	/**
	 * Gets a localized currency symbol.
	 *
	 * @link http://www.iso.org/iso/currency_codes ISO 4217 currency codes
	 *
	 * @param  string  $currency_code  An ISO 4217 currency code.
	 * @param  string  $locale  Optional. A WordPress locale code.
	 *
	 * @return string The symbol for the currency in the provided locale.
	 */
	public function get_currency_symbol( string $currency_code, string $locale = '' ): string {
		$currencies_array = $this->get_locale_bucket( $locale, 'currencies' );
		if ( isset( $currencies_array[ $currency_code ]['symbol'] ) ) {
			return $currencies_array[ $currency_code ]['symbol'];
		}

		return '';
	}

	/**
	 * Gets a localized currency name.
	 *
	 * @link http://www.iso.org/iso/currency_codes ISO 4217 currency codes
	 *
	 * @param  string  $currency_code  An ISO 4217 currency code.
	 * @param  string  $locale  Optional. A WordPress locale code.
	 *
	 * @return string The name of the currency in the provided locale.
	 */
	public function get_currency_name( string $currency_code, string $locale = '' ): string {
		$currencies_array = $this->get_locale_bucket( $locale, 'currencies' );
		if ( isset( $currencies_array[ $currency_code ]['displayName'] ) ) {
			return $currencies_array[ $currency_code ]['displayName'];
		}

		return '';
	}

	/**
	 * Gets a localized language name.
	 *
	 * @link http://www.iso.org/iso/language_codes ISO 639 language codes
	 *
	 * @param  string  $language_code  An ISO 639 language code.
	 * @param  string  $locale  Optional. A WordPress locale code.
	 *
	 * @return string The name of the language in the provided locale.
	 */
	public function get_language_name( string $language_code, string $locale = '' ): string {
		$languages = $this->get_languages( $locale );

		$cldr_matched_language_code = self::get_cldr_locale( $language_code );
		if ( isset( $languages[ $cldr_matched_language_code ] ) ) {
			return $languages[ $cldr_matched_language_code ];
		}

		// If no match for a full language code (e.g. `en-NZ`), check for language code only (e.g. `en`).
		$language_only_cldr_code = strtok( $cldr_matched_language_code, '-_' );
		if ( isset( $languages[ $language_only_cldr_code ] ) ) {
			return $languages[ $language_only_cldr_code ];
		}

		return '';
	}

	/**
	 * Gets all country and region names in a locale.
	 *
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 * @link http://unstats.un.org/unsd/methods/m49/m49regin.htm UN M.49 region codes
	 *
	 * @param  string  $locale  Optional. A WordPress locale code.
	 *
	 * @return array An associative array of ISO 3166-1 alpha-2 country codes and UN M.49 region codes, along with localized names, from CLDR
	 */
	public function get_territories( string $locale = '' ): array {
		return $this->get_locale_bucket( $locale, 'territories' );
	}

	/**
	 * Gets all language names in a locale.
	 *
	 * @link http://www.iso.org/iso/language_codes ISO 639 language codes
	 *
	 * @param  string  $locale  Optional. A WordPress locale code.
	 *
	 * @return array An associative array of ISO 639 codes and localized language names from CLDR
	 */
	public function get_languages( string $locale = '' ): array {
		return $this->get_locale_bucket( $locale, 'languages' );
	}

	/**
	 * Gets the day which typically starts a calendar week in a country.
	 *
	 * @link http://unicode.org/reports/tr35/tr35-dates.html#Week_Data CLDR week data
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 *
	 * @param  string  $country_code  A two-letter ISO 3166 country code.
	 *
	 * @return string The first three characters, in lowercase, of the English name for the day considered to be the start of the week.
	 */
	public function get_first_day_of_week( string $country_code ): string {
		$json_file = $this->get_locale_bucket( 'supplemental', 'weekData' );
		if ( isset( $json_file['supplemental']['weekData']['firstDay'][ $country_code ] ) ) {
			return $json_file['supplemental']['weekData']['firstDay'][ $country_code ];
		}

		return '';
	}

	/**
	 * Gets the currency used in each country worldwide.
	 *
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 * @link http://www.iso.org/iso/currency_codes ISO 4217 currency codes
	 *
	 * @return array An associative array of ISO 3166 country codes and the ISO 4217 code for the currency currently used in each country.
	 */
	public function get_currency_for_all_countries() {
		$json_file = $this->get_locale_bucket( 'supplemental', 'currencyData' );

		// This CLDR item has a history of all the currencies ever used in a country
		// so we need to loop through them to find one without a `_to` ending date
		// and without a `_tender` flag which are always false indicating
		// the currency wasn't legal tender.
		$result = [];
		if ( isset( $json_file['supplemental']['currencyData']['region'] ) ) {
			foreach ( $json_file['supplemental']['currencyData']['region'] as $country_code => $currencies ) {
				foreach ( $currencies as $currency_dates ) {
					if ( ! array_key_exists( '_to', current( $currency_dates ) ) && ! array_key_exists( '_tender',
							current( $currency_dates ) ) ) {
						$result[ $country_code ] = key( $currency_dates );
					}
				}
			}
		}

		return $result;
	}

	/**
	 * Gets the currency currently used in a country.
	 *
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 * @link http://www.iso.org/iso/currency_codes ISO 4217 currency codes
	 *
	 * @param  string  $country_code  A two-letter ISO 3166-1 country code.
	 *
	 * @return string The three-letter ISO 4217 code for the currency currently used in that country.
	 */
	public function get_currency_for_country( string $country_code ): string {
		$currency_for_all_countries = $this->get_currency_for_all_countries();
		if ( isset( $currency_for_all_countries[ $country_code ] ) ) {
			return $currency_for_all_countries[ $country_code ];
		}

		return '';
	}

	/**
	 * Gets the countries that use each currency in use today.
	 *
	 * @link http://www.iso.org/iso/currency_codes ISO 4217 currency codes
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 *
	 * @return array An associative array of ISO 4217 currency codes and then an array of the ISO 3166 codes for countries which currently use each currency.
	 */
	public function get_countries_for_all_currencies() {
		$result                     = [];
		$currency_for_all_countries = $this->get_currency_for_all_countries();
		if ( isset( $currency_for_all_countries ) ) {
			foreach ( $currency_for_all_countries as $country_code => $currency_code ) {
				$result[ $currency_code ][] = $country_code;
			}
		}

		return $result;
	}

	/**
	 * Gets the countries that use a particular currency.
	 *
	 * @link http://www.iso.org/iso/currency_codes ISO 4217 currency codes
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 *
	 * @param  string  $currency_code  A three-letter ISO 4217 currency code.
	 *
	 * @return array The ISO 3166 codes for the countries which currently use the currency.
	 */
	public function get_countries_for_currency( string $currency_code ): array {
		$countries_for_all_currencies = $this->get_countries_for_all_currencies();
		if ( isset( $countries_for_all_currencies[ $currency_code ] ) ) {
			return $countries_for_all_currencies[ $currency_code ];
		}

		return [];
	}

	/**
	 * Gets the countries contained by a region code.
	 *
	 * @link http://www.unicode.org/cldr/charts/latest/supplemental/territory_containment_un_m_49.html CLDR info page on territory containment
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 * @link http://unstats.un.org/unsd/methods/m49/m49regin.htm UN M.49 region codes
	 *
	 * @param  string  $region_code  A UN M.49 region code or a two-letter ISO 3166-1 country code.
	 *
	 * @return array The countries included in that region, or the country if $region_code is a country.
	 */
	public function get_territories_contained( string $region_code ): array {

		// If $region_code is a country code, return it.
		if ( preg_match( '/^[A-Z]{2}$/', $region_code ) ) {
			return [ $region_code ];
		}

		// If it's a region code, recursively find the contained country codes.
		$result = [];
		if ( preg_match( '/^\d{3}$/', $region_code ) ) {
			$json_file = $this->get_locale_bucket( 'supplemental', 'territoryContainment' );
			if ( isset( $json_file['supplemental']['territoryContainment'][ $region_code ]['_contains'] ) ) {
				foreach ( $json_file['supplemental']['territoryContainment'][ $region_code ]['_contains'] as $contained_region ) {
					$result = array_merge( $result, $this->get_territories_contained( $contained_region ) );
				}
			}
		}

		return $result;
	}

	/**
	 * Gets the languages spoken in a country, in descending order of use.
	 *
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 * @link http://www.unicode.org/cldr/charts/latest/supplemental/territory_language_information.html Detail on CLDR language information
	 *
	 * @param  string  $country_code  A two-letter ISO 3166-1 country code.
	 *
	 * @return array An associative array with the key of a language code and the value of the percentage of population which speaks the language in that country.
	 */
	public function get_languages_spoken( string $country_code ): array {
		$json_file = $this->get_locale_bucket( 'supplemental', 'territoryInfo' );
		$result    = [];
		if ( isset( $json_file['supplemental']['territoryInfo'][ $country_code ]['languagePopulation'] ) ) {
			foreach ( $json_file['supplemental']['territoryInfo'][ $country_code ]['languagePopulation'] as $language => $info ) {
				$result[ $language ] = $info['_populationPercent'];
			}
			arsort( $result );
		}

		return $result;
	}

	/**
	 * Gets the most widely spoken language spoken in a country.
	 *
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 * @link http://www.unicode.org/cldr/charts/latest/supplemental/territory_language_information.html Detail on CLDR language information
	 * @link http://www.iso.org/iso/language_codes ISO 639 language codes
	 *
	 * @param  string  $country_code  A two-letter ISO 3166-1 country code.
	 *
	 * @return string The ISO 639 code for the language most widely spoken in the country.
	 */
	public function get_most_spoken_language( string $country_code ): string {
		$languages_spoken = $this->get_languages_spoken( $country_code );
		if ( ! empty( $languages_spoken ) ) {
			return key( $languages_spoken );
		}

		return '';
	}

	/**
	 * Gets GDP, population, and language information for a country.
	 *
	 * @link http://www.iso.org/iso/country_codes ISO 3166 country codes
	 * @link http://www.unicode.org/cldr/charts/latest/supplemental/territory_language_information.html CLDR's territory information
	 *
	 * @param  string  $country_code  A two-letter ISO 3166-1 country code.
	 *
	 * @return array CLDR's territory information.
	 */
	public function get_territory_info( string $country_code ): array {
		$json_file = $this->get_locale_bucket( 'supplemental', 'territoryInfo' );
		if ( isset( $json_file['supplemental']['territoryInfo'][ $country_code ] ) ) {
			return $json_file['supplemental']['territoryInfo'][ $country_code ];
		}

		return [];
	}

	/**
	 * Recursively builds an associative array of the time zone IDs and their localized display names.
	 *
	 * @link http://www.iana.org/time-zones IANA time zone
	 * @link http://unicode.org/reports/tr35/tr35-dates.html#Time_Zone_Names CLDR info on time zone names
	 *
	 * @param  array  $zones  An array of time zone data from CLDR JSON files.
	 * @param  string  $id_start  Optional. The start of the time zone ID (used for recursive calls).
	 *
	 * @return array An associative array of time zone IDs (e.g. `Europe/Istanbul`) and the localized exemplar city names.
	 */
	private function build_cities_array( array $zones, string $id_start = '' ): array {
		$result = [];
		foreach ( $zones as $id => $array ) {
			if ( isset( $array['exemplarCity'] ) ) {
				$result[ $id_start . $id ] = $array['exemplarCity'];
			} elseif ( is_array( $array ) ) {
				$result = array_merge( $result, $this->build_cities_array( $array, $id_start . $id . '/' ) );
			}
		}

		return $result;
	}

	/**
	 * Gets the time zone city names -- aka exemplars -- for a locale.
	 *
	 * @link http://www.iana.org/time-zones IANA time zone
	 * @link http://unicode.org/reports/tr35/tr35-dates.html#Time_Zone_Names CLDR info on time zone names
	 *
	 * @param  string  $locale  Optional. A WordPress locale code.
	 *
	 * @return array As associative array of time zone IDs (e.g. `Europe/Istanbul`) and the localized exemplar city for each.
	 */
	public function get_time_zone_cities( string $locale = '' ): array {
		/**
		 * Since the timezone data is no longer available in timeZoneNames, we need to extract it from cldr-bcp47
		 *
		 * For English or a locale that would fall back to English, we extract timezones from the supplemental timezone file.
		 */
		if ( strtolower( $locale ) === 'en' || ! self::is_cldr_json_available( $locale, 'timeZoneNames' ) ) {

			$timezone_cities = [];
			$timezones_json  = $this->get_locale_bucket( 'supplemental', 'timezone' );
			$timezones_json  = ! empty( $timezones_json['keyword']['u']['tz'] ) ? $timezones_json['keyword']['u']['tz'] : [];
			if ( ! empty( $timezones_json ) ) {
				foreach ( $timezones_json as $timezone_json ) {
					if ( is_array( $timezone_json ) && empty( $timezone_json['_deprecated'] ) ) {
						$city = explode( ',', $timezone_json['_description'] );
						if ( count( $city ) !== 2 ) {
							// Skip timezones that don't have city, country
							continue;
						}
						$city    = trim( $city[0] );
						$aliases = explode( ' ', $timezone_json['_alias'] );
						foreach ( $aliases as $alias ) {
							$timezone_cities[ trim( $alias ) ] = $city;
						}
					}
				}
			}

			return $timezone_cities;
		}

		$time_zone_cities_json = $this->get_locale_bucket( $locale, 'timeZoneNames' );
		if ( ! empty( $time_zone_cities_json['zone'] ) ) {
			return $this->build_cities_array( $time_zone_cities_json['zone'] );
		}

		return [];
	}

	/**
	 * Gets the time zone city name -- aka exemplar -- for a time zone ID.
	 *
	 * @link http://www.iana.org/time-zones IANA time zone
	 * @link http://unicode.org/reports/tr35/tr35-dates.html#Time_Zone_Names CLDR info on time zone names
	 *
	 * @param  string  $time_zone_id  An IANA time zone ID (e.g. `Europe/Istanbul`).
	 * @param  string  $locale  Optional. A WordPress locale code.
	 *
	 * @return string The localized name of the time zone exemplar city.
	 */
	public function get_time_zone_city( string $time_zone_id, string $locale = '' ): string {
		$time_zone_cities = $this->get_time_zone_cities( $locale );

		if ( ! empty( $time_zone_cities[ $time_zone_id ] ) ) {
			return $time_zone_cities[ $time_zone_id ];
		}

		return '';
	}
}