import { renderIcon } from "discourse-common/lib/icon-library";
import { i18n } from "discourse-i18n";
import DateWithZoneHelper from "./date-with-zone-helper";

const DATETIME_FORMAT = "LLL";
const DATE_FORMAT = "LL";
const FULL_DATETIME_FORMAT = "LLLL";
const TIME_FORMAT = "h:mm A";
const DAY_OF_THE_WEEK_FORMAT = "dddd";
const RANGE_SEPARATOR = "→";
const TIME_ICON = "clock";
const SHORT_FORMAT_DAYS_PERIOD = 1;

export default class LocalDateBuilder {
  constructor(params = {}, localTimezone) {
    this.time = params.time;
    this.date = params.date;
    this.recurring = params.recurring;
    this.sameLocalDayAsFrom = params.sameLocalDayAsFrom;
    this.timezones = Array.from(
      new Set((params.timezones || []).filter(Boolean))
    );
    this.timezone = params.timezone || "UTC";
    this.calendar =
      typeof params.calendar === "undefined" ? true : params.calendar;
    this.displayedTimezone = params.displayedTimezone;
    this.format = params.format || (this.time ? DATETIME_FORMAT : DATE_FORMAT);
    this.countdown = params.countdown;
    this.duration = params.duration;
    this.localTimezone = localTimezone;
  }

  build() {
    const [year, month, day] = this.date.split("-").map((x) => parseInt(x, 10));
    const [hour, minute, second] = (this.time || "")
      .split(":")
      .map((x) => (x ? parseInt(x, 10) : undefined));

    let displayedTimezone;
    if (this.time) {
      displayedTimezone = this.displayedTimezone || this.localTimezone;
    } else {
      displayedTimezone =
        this.displayedTimezone || this.timezone || this.localTimezone;
    }

    let localDate = new DateWithZoneHelper({
      year,
      month: month ? month - 1 : null,
      day,
      hour,
      minute,
      second,
      timezone: this.timezone,
      localTimezone: this.localTimezone,
    });

    if (this.recurring && moment().isAfter(localDate.datetime)) {
      const type = this.recurring.split(".")[1];

      const repetitionsForType = localDate.unitRepetitionsBetweenDates(
        this.recurring,
        moment.tz(this.localTimezone)
      );

      localDate = localDate.add(repetitionsForType, type);
    }

    const previews = this._generatePreviews(localDate, displayedTimezone);
    const hasTime = hour !== undefined;
    return {
      pastEvent:
        !this.recurring &&
        moment.tz(this.localTimezone).isAfter(localDate.datetime),
      formatted: this._applyFormatting(localDate, displayedTimezone, hasTime),
      previews,
      textPreview: this._generateTextPreviews(previews),
    };
  }

  _generateTextPreviews(previews) {
    return previews
      .map((preview) => {
        const formattedZone = this._zoneWithoutPrefix(preview.timezone);
        return `${formattedZone} ${preview.formatted}`;
      })
      .join(", ");
  }

  _generatePreviews(localDate, displayedTimezone) {
    const previewedTimezones = [];

    const timezones = this.timezones.filter(
      (timezone) => !this._isEqualZones(timezone, this.localTimezone)
    );

    previewedTimezones.push({
      timezone: this._zoneWithoutPrefix(this.localTimezone),
      current: true,
      formatted: this._createDateTimeRange(
        DateWithZoneHelper.fromDatetime(
          localDate.datetime,
          localDate.timezone,
          this.localTimezone
        ),
        this.time,
        this.duration
      ),
    });

    if (
      this.timezone &&
      displayedTimezone === this.localTimezone &&
      this.timezone !== displayedTimezone &&
      !this._isEqualZones(displayedTimezone, this.timezone) &&
      !this.timezones.any((t) => this._isEqualZones(t, this.timezone))
    ) {
      timezones.unshift(this.timezone);
    }

    timezones.forEach((timezone) => {
      if (this._isEqualZones(timezone, displayedTimezone)) {
        return;
      }

      if (this._isEqualZones(timezone, this.localTimezone)) {
        timezone = this.localTimezone;
      }

      previewedTimezones.push({
        timezone: this._zoneWithoutPrefix(timezone),
        formatted: this._createDateTimeRange(
          DateWithZoneHelper.fromDatetime(
            localDate.datetime,
            localDate.timezone,
            timezone
          ),
          this.time,
          this.duration
        ),
      });
    });

    return previewedTimezones.uniqBy("timezone");
  }

  _isEqualZones(timezoneA, timezoneB) {
    if ((timezoneA || timezoneB) && (!timezoneA || !timezoneB)) {
      return false;
    }

    if (timezoneA.includes(timezoneB) || timezoneB.includes(timezoneA)) {
      return true;
    }

    return (
      moment.tz(timezoneA).utcOffset() === moment.tz(timezoneB).utcOffset()
    );
  }

  _createDateTimeRange(startRange, time, duration) {
    const [startDate, endDate] = this._calculateDatesForRange(
      startRange,
      time,
      duration
    );
    let formatElements = [
      startDate.format(`${DAY_OF_THE_WEEK_FORMAT}, ${DATE_FORMAT}`),
      this._optionalTimeIcon(startDate, endDate),
      startDate.format(TIME_FORMAT),
    ];
    if (endDate) {
      formatElements = formatElements.concat([
        RANGE_SEPARATOR,
        endDate.format(this._endDateFormat(startDate, endDate)),
      ]);
    }
    return formatElements.filter(Boolean).join(" ");
  }

  _shortFormat(startDate, endDate) {
    return (
      endDate.datetime.diff(startDate.datetime, "days") <
      SHORT_FORMAT_DAYS_PERIOD
    );
  }

  _optionalTimeIcon(startDate, endDate) {
    if (!endDate || this._shortFormat(startDate, endDate)) {
      return `<br />${renderIcon("string", TIME_ICON)}`;
    }
  }

  _endDateFormat(startDate, endDate) {
    return this._shortFormat(startDate, endDate)
      ? TIME_FORMAT
      : FULL_DATETIME_FORMAT;
  }

  _calculateDatesForRange(date, time, duration) {
    // if a time has been given we do not attempt to automatically create a range
    // instead we show only one date with a format showing the time
    if (time && !duration) {
      return [date];
    }
    const dates = [
      date,
      duration ? date.add(duration, "minutes") : date.add(24, "hours"),
    ];
    return duration < 0 ? dates.reverse() : dates;
  }

  _applyFormatting(localDate, displayedTimezone, hasTime) {
    if (this.countdown) {
      const diffTime = moment.tz(this.localTimezone).diff(localDate.datetime);

      if (diffTime < 0) {
        return moment.duration(diffTime).humanize();
      } else {
        return i18n("discourse_local_dates.relative_dates.countdown.passed");
      }
    }

    const sameTimezone = this._isEqualZones(
      displayedTimezone,
      this.localTimezone
    );

    if (this.calendar) {
      const inCalendarRange = moment
        .tz(this.localTimezone)
        .isBetween(
          localDate.subtract(2, "day").datetime,
          localDate.add(1, "day").datetime.endOf("day")
        );

      if (this.sameLocalDayAsFrom) {
        return this._timeOnlyFormat(localDate, displayedTimezone);
      }

      if (inCalendarRange && sameTimezone) {
        const date = localDate.datetimeWithZone(this.localTimezone);

        if (hasTime && date.hours() === 0 && date.minutes() === 0) {
          return date.format("dddd");
        }

        return date.calendar(
          moment.tz(localDate.timezone),
          this._calendarFormats(this.time ? this.time : null)
        );
      }
    }

    if (!sameTimezone) {
      return this._formatWithZone(localDate, displayedTimezone, this.format);
    }

    return localDate.format(this.format);
  }

  _calendarFormats(time) {
    return {
      sameDay: this._translateCalendarKey(time, "today"),
      nextDay: this._translateCalendarKey(time, "tomorrow"),
      lastDay: this._translateCalendarKey(time, "yesterday"),
      sameElse: "L",
    };
  }

  _translateCalendarKey(time, key) {
    const translated = i18n(`discourse_local_dates.relative_dates.${key}`, {
      time: "LT",
    });

    if (time) {
      return translated
        .split("LT")
        .map((w) => `[${w}]`)
        .join("LT");
    } else {
      return `[${translated.replace(" LT", "")}]`;
    }
  }

  _formatTimezone(timezone) {
    return timezone.replace("_", " ").replace("Etc/", "").split("/");
  }

  _zoneWithoutPrefix(timezone) {
    const [part1, part2] = this._formatTimezone(timezone);
    return part2 || part1;
  }

  _formatWithZone(localDate, displayedTimezone, format) {
    let formatted = localDate
      .datetimeWithZone(displayedTimezone)
      .format(format);
    return `${formatted} (${this._zoneWithoutPrefix(displayedTimezone)})`;
  }

  _timeOnlyFormat(localTime, displayedTimezone) {
    return this._formatWithZone(localTime, displayedTimezone, "LT");
  }
}