'use strict';

const moment = require('moment-timezone');
const { isMoment } = moment;

const isDate = value =>
  typeof value === 'object' && value instanceof Date && !isNaN(value.getTime());

function getMoment(date, lang, timezone) {
  if (date == null) date = moment();
  if (!isMoment(date)) date = moment(isDate(date) ? date : new Date(date));
  lang = toMomentLocale(lang);

  if (lang) date = date.locale(lang);
  if (timezone) date = date.tz(timezone);

  return date;
}

function toISOString(date) {
  if (date == null) {
    return new Date().toISOString();
  }

  if (date instanceof Date || isMoment(date)) {
    return date.toISOString();
  }

  return new Date(date).toISOString();
}

function dateHelper(date, format) {
  const { config } = this;
  const moment = getMoment(date, getLanguage(this), config.timezone);
  return moment.format(format || config.date_format);
}

function timeHelper(date, format) {
  const { config } = this;
  const moment = getMoment(date, getLanguage(this), config.timezone);
  return moment.format(format || config.time_format);
}

function fullDateHelper(date, format) {
  if (format) {
    const moment = getMoment(date, getLanguage(this), this.config.timezone);
    return moment.format(format);
  }

  return `${this.date(date)} ${this.time(date)}`;
}

function relativeDateHelper(date) {
  const { config } = this;
  const moment = getMoment(date, getLanguage(this), config.timezone);
  return moment.fromNow();
}

function timeTagHelper(date, format) {
  const { config } = this;
  return `<time datetime="${toISOString(date)}">${this.date(date, format, getLanguage(this), config.timezone)}</time>`;
}

function getLanguage(ctx) {
  return ctx.page.lang || ctx.page.language || ctx.config.language;
}

/**
 * Convert Hexo language code to Moment locale code.
 * examples:
 *   default => en
 *   zh-CN => zh-cn
 *
 * Moment defined locales: https://github.com/moment/moment/tree/master/locale
 */
function toMomentLocale(lang) {
  if (lang === undefined) {
    return undefined;
  }

  // moment.locale('') equals moment.locale('en')
  // moment.locale(null) equals moment.locale('en')
  if (!lang || lang === 'en' || lang === 'default') {
    return 'en';
  }
  return lang.toLowerCase().replace('_', '-');
}

exports.date = dateHelper;
exports.date_xml = toISOString;
exports.time = timeHelper;
exports.full_date = fullDateHelper;
exports.relative_date = relativeDateHelper;
exports.time_tag = timeTagHelper;
exports.moment = moment;
exports.toMomentLocale = toMomentLocale;