import debugFactory from 'debug';
import i18n from 'i18n-calypso';
import moment, { LongDateFormatKey } from 'moment';
const debug = debugFactory( 'apps:odyssey' );

const DEFAULT_LANGUAGE = 'en';
const DEFAULT_MOMENT_LOCALE = 'en';
// Only Simple Site has the default locale as 'en'. For atomic/jetpack sites the default locale is 'en-us'.
const SIMPLE_SITE_DEFAULT_LOCALE = 'en';
const ALWAYS_LOAD_WITH_LOCALE = [ 'pt', 'zh' ];
/**
 * inlined from 'calypso/my-sites/site-settings/date-time-format/utils' as the module import the whole moment-timezone library, which is 755k before gzip.
 */
export const phpToMomentMapping = {
	d: 'DD',
	D: 'ddd',
	j: 'D',
	l: 'dddd',
	N: 'E',
	// "S" is andled via custom check
	//S: '',
	w: 'd',
	// Moment.js equivalent of "z" (0 based) is "DDD" (1 based), so it must be adjusted
	//z: 'DDD',
	W: 'W',
	F: 'MMMM',
	m: 'MM',
	M: 'MMM',
	n: 'M',
	// Moment.js has no "t" token equivalent, but a `moment().daysInMonth()` function
	//t: '',
	// Moment.js has no "L" token equivalent, but a `moment().isLeapYear()` function
	//L: '',
	o: 'Y',
	Y: 'YYYY',
	y: 'YY',
	a: 'a',
	A: 'A',
	// Moment.js has no "B" token equivalent, but can be generated nonetheless
	//B: '',
	g: 'h',
	G: 'H',
	h: 'hh',
	H: 'HH',
	i: 'mm',
	s: 'ss',
	u: 'SSSSSS',
	v: 'SSS',
	e: 'z',
	// Moment.js has no "I" token, but a `moment().isDST()` function
	//I: '',
	O: 'ZZ',
	P: 'Z',
	// Moment.js has no "T" token equivalent, but is similar enough to "z"
	T: 'z',
	// Moment.js has no "Z" token equivalent, but can be generated nonetheless
	//Z: '',
	c: 'YYYY-MM-DDTHH:mm-ssZ',
	r: 'ddd, DD MMM YYYY HH:mm:ss ZZ',
	U: 'X',
};

const getLanguageCodeFromLocale = ( localeSlug: string ) => {
	debug( localeSlug );
	if ( localeSlug.indexOf( '-' ) > -1 ) {
		return localeSlug.split( '-' )[ 0 ];
	}
	return localeSlug;
};

const convertPhpToMomentFormat = ( phpFormat: string ): string => {
	const phpToMomentMap = phpToMomentMapping as {
		[ key: string ]: string;
	};

	let momentFormat = '';

	for ( let i = 0; i < phpFormat.length; i++ ) {
		const char = phpFormat.charAt( i );
		if ( phpToMomentMap[ char ] ) {
			momentFormat += phpToMomentMap[ char ];
		} else {
			momentFormat += char;
		}
	}

	return momentFormat;
};

/**
 * WordPress core replaces the longDateFormat with the PHP date format.
 * https://github.com/WordPress/wordpress-develop/blob/1393dc25b54479314acd2162fc39befd84dc46eb/src/wp-includes/script-loader.php#L155
 * This function will convert it back to the moment format.
 *
 * So for Simple sites, the longDateFormat for en is changed to a PHP date format.
 */
const fixLongDateFormatForEn = ( localeSlug: string ) => {
	if ( localeSlug === SIMPLE_SITE_DEFAULT_LOCALE ) {
		const keysReplacedByWordPressCore: LongDateFormatKey[] = [
			'LTS',
			'LT',
			'L',
			'LL',
			'LLL',
			'LLLL',
		];
		const currentLocaleData = moment.localeData();
		const momentLongDateFormat: Partial< { [ key in LongDateFormatKey ]: string } > = {};
		keysReplacedByWordPressCore.forEach( ( key ) => {
			if ( currentLocaleData.longDateFormat( key ) ) {
				momentLongDateFormat[ key ] = convertPhpToMomentFormat(
					currentLocaleData.longDateFormat( key )
				);
			}
		} );
		moment.updateLocale( localeSlug, {
			longDateFormat: momentLongDateFormat as { [ key in LongDateFormatKey ]: string },
		} );
	}
};

const loadMomentLocale = async ( localeSlug: string, languageCode: string, isSimple: boolean ) => {
	return import( `moment/locale/${ localeSlug }` )
		.catch( ( error: Error ) => {
			debug(
				`Encountered an error loading moment locale file for ${ localeSlug }. Falling back to language datetime format.`,
				error
			);
			// Fallback 1 to the language code.
			if ( localeSlug !== languageCode ) {
				localeSlug = languageCode;
				return import( `moment/locale/${ localeSlug }` );
			}
			// Pass it to the next catch block if the language code is the same as the locale slug.
			return Promise.reject( error );
		} )
		.catch( ( error: Error ) => {
			debug(
				`Encountered an error loading moment locale file for ${ localeSlug }. Falling back to US datetime format.`,
				error
			);
			// Fallback 2 to the default US date time format.
			// Interestingly `en` here represents `en-us` locale.
			isSimple && fixLongDateFormatForEn( localeSlug );
			localeSlug = DEFAULT_MOMENT_LOCALE;
		} )
		.then( () => moment.locale( localeSlug ) );
};

const loadLanguageFile = ( languageFileName: string ) => {
	const url = `https://widgets.wp.com/odyssey-stats/v1/languages/${ languageFileName }-v1.1.json`;

	return globalThis.fetch( url ).then( ( response ) => {
		if ( response.ok ) {
			return response.json().then( ( body ) => {
				if ( body ) {
					i18n.setLocale( body );
				}
			} );
		}
		return Promise.reject( response );
	} );
};

export default ( localeSlug: string, isSimple = false ) => {
	const languageCode = getLanguageCodeFromLocale( localeSlug );

	// Load tranlation file if it's not English.
	if ( languageCode !== DEFAULT_LANGUAGE ) {
		const languageFileName = ALWAYS_LOAD_WITH_LOCALE.includes( languageCode )
			? localeSlug
			: languageCode;
		// We don't have to wait for the language file to load before rendering the page, because i18n is using hooks to update translations.
		loadLanguageFile( languageFileName )
			.then( () => debug( `Loaded locale files for ${ languageCode } successfully.` ) )
			.catch( ( error ) =>
				debug(
					`Encountered an error loading locale file for ${ languageCode }. Falling back to English.`,
					error
				)
			);
	}

	// We have to wait for moment locale to load before rendering the page, because otherwise the rendered date time wouldn't get re-rendered.
	// This could be improved in the future with hooks.
	return loadMomentLocale( localeSlug, languageCode, isSimple );
};