import type { AmPm, FormattedPartial, LocalizedTimePartials } from './types'

/**
 * Converts a 12-hour time format to a 24-hour time format.
 * @param {('am' | 'pm')} abbr The abbreviation indicating AM or PM.
 * @param {number} hour The hour to be converted.
 * @returns {number} The hour in 24-hour format.
 */
export const convert12hTo24h = (abbr: AmPm, hour: number): number => {
  if (abbr === 'am' && hour === 12) {
    return 0
  }

  if (abbr === 'am') {
    return hour
  }

  if (abbr === 'pm' && hour === 12) {
    return 12
  }

  return hour + 12
}

/**
 * Converts a 24-hour time format to a 12-hour format.
 * @param {number} hour The hour to be converted.
 * @returns {number} The hour in 12-hour format.
 */
export const convert24hTo12h = (hour: number): number => hour % 12 || 12

/**
 * Converts a time input into a Date object.
 * @param {Date | string | null | undefined} time The time input to be converted.
 * @returns {Date | null} The converted Date object or null if the input is falsy.
 */
export const convertTimeToDate = (time: Date | string | null | undefined): Date | null =>
  time ? (time instanceof Date ? time : new Date(`1970-01-01 ${time}`)) : null

/**
 * Retrieves the AM/PM part of the specified date according to the given locale.
 * @param {Date} date The date from which to extract the AM/PM part.
 * @param {string} locale The locale to use for formatting.
 * @returns {string} 'am' or 'pm' based on the given date and locale.
 */
export const getAmPm = (date: Date, locale: string): AmPm => {
  if (date.toLocaleTimeString(locale).includes('AM')) {
    return 'am'
  }

  if (date.toLocaleTimeString(locale).includes('PM')) {
    return 'pm'
  }

  return date.getHours() >= 12 ? 'pm' : 'am'
}

/**
 * Formats an array of time values (hours, minutes, or seconds) according to the specified locale and partial.
 * @param {number[]} values An array of time values to format.
 * @param {string} locale The locale to use for formatting.
 * @param {('hour' | 'minute' | 'second')} partial The type of time value to format.
 * @returns {Array} An array of objects with the original value and its localized label.
 */
export const formatTimePartials = (
  values: number[],
  locale: string,
  partial: 'hour' | 'minute' | 'second'
): FormattedPartial[] => {
  const date = new Date()
  const forceTwoDigit = shouldUseTwoDigitHour(locale)
  const formatter = new Intl.DateTimeFormat(locale, {
    hour: forceTwoDigit ? '2-digit' : 'numeric',
    minute: '2-digit',
    second: '2-digit',
  })

  return values.map((value) => {
    if (partial === 'hour') {
      date.setHours(value)
    }

    if (partial === 'minute') {
      date.setMinutes(value)
    }

    if (partial === 'second') {
      date.setSeconds(value)
    }

    return {
      value,
      label: formatter.formatToParts(date).find((part) => part.type === partial)?.value || '',
    }
  })
}

/**
 * Generates localized time partials (hours, minutes, seconds) based on the given parameters.
 * @param {string} locale The locale to use for generating localized time partials.
 * @param {'auto' | boolean} ampm Determines whether to use 12-hour or 24-hour format. 'auto' decides based on locale.
 * @param {boolean | number[] | Function} hours An array of hours, a boolean, or a function to generate hours.
 * @param {boolean | number[] | Function} minutes An array of minutes, a boolean, or a function to generate minutes.
 * @param {boolean | number[] | Function} seconds An array of seconds, a boolean, or a function to generate seconds.
 * @returns {LocalizedTimePartials} An object containing arrays of localized time partials and a boolean indicating if 12-hour format is used.
 */
export const getLocalizedTimePartials = (
  locale: string,
  ampm: 'auto' | boolean = 'auto',
  hours: boolean | number[] | ((hour: number) => number[]) = [],
  minutes: boolean | number[] | ((minute: number) => number[]) = [],
  seconds: boolean | number[] | ((second: number) => number[]) = []
): LocalizedTimePartials => {
  const hour12 = (ampm === 'auto' && isAmPm(locale)) || ampm === true

  const listOfHours =
    Array.isArray(hours) && hours.length > 0
      ? hours
      : typeof hours === 'function'
        ? Array.from({ length: hour12 ? 12 : 24 }, (_, i) => (hour12 ? i + 1 : i)).filter((hour) =>
            hours(hour)
          )
        : Array.from({ length: hour12 ? 12 : 24 }, (_, i) => (hour12 ? i + 1 : i))

  const listOfMinutes =
    Array.isArray(minutes) && minutes.length > 0
      ? minutes
      : typeof minutes === 'function'
        ? Array.from({ length: 60 }, (_, i) => i).filter((minute) => minutes(minute))
        : Array.from({ length: 60 }, (_, i) => i)

  const listOfSeconds =
    Array.isArray(seconds) && seconds.length > 0
      ? seconds
      : typeof seconds === 'function'
        ? Array.from({ length: 60 }, (_, i) => i).filter((second) => seconds(second))
        : Array.from({ length: 60 }, (_, i) => i)

  return {
    listOfHours: formatTimePartials(listOfHours, locale, 'hour'),
    listOfMinutes: formatTimePartials(listOfMinutes, locale, 'minute'),
    listOfSeconds: formatTimePartials(listOfSeconds, locale, 'second'),
    hour12,
  }
}

/**
 * Gets the selected hour from a date object in either 12-hour or 24-hour format based on locale and preference.
 * @param {Date | null} date The date object from which to extract the hour. If null, the function returns an empty string.
 * @param {string} locale The locale to use when determining whether to return in 12-hour or 24-hour format.
 * @param {'auto' | boolean} ampm Determines the format of the hour returned. 'auto' decides based on locale, true forces 12-hour format, and false forces 24-hour format.
 * @returns {string | number} The hour in the specified format or an empty string if the date is null.
 */
export const getSelectedHour = (
  date: Date | null,
  locale: string,
  ampm: 'auto' | boolean = 'auto'
): number | string =>
  date
    ? (ampm === 'auto' && isAmPm(locale)) || ampm === true
      ? convert24hTo12h(date.getHours())
      : date.getHours()
    : ''

/**
 * Gets the selected minutes from a date object.
 * @param {Date | null} date The date object from which to extract the minutes. If null, the function returns an empty string.
 * @returns {string | number} The minutes from the date or an empty string if the date is null.
 */
export const getSelectedMinutes = (date: Date | null): number | string =>
  date ? date.getMinutes() : ''

/**
 * Gets the selected seconds from a date object.
 * @param {Date | null} date The date object from which to extract the seconds. If null, the function returns an empty string.
 * @returns {string | number} The seconds from the date or an empty string if the date is null.
 */
export const getSelectedSeconds = (date: Date | null): number | string =>
  date ? date.getSeconds() : ''

/**
 * Determines if the given locale uses AM/PM format.
 * @param {string} locale The locale to check.
 * @returns {boolean} True if the locale uses AM/PM format, otherwise false.
 */
export const isAmPm = (locale: string): boolean =>
  ['am', 'AM', 'pm', 'PM'].some((el) => new Date().toLocaleString(locale).includes(el))

/**
 * Validates if the given string represents a valid time.
 * @param {string} time The time string to validate.
 * @returns {boolean} True if the string is a valid time, otherwise false.
 */
export const isValidTime = (time: string): boolean => {
  const d = new Date(`1970-01-01T${time}`)
  return d instanceof Date && !Number.isNaN(d.getTime())
}

/**
 * Checks whether the given locale formats the hour "9" with a leading zero ("09")
 * when using `hour: 'numeric'` in `toLocaleTimeString`.
 *
 * This helps determine if you should force `hour: '2-digit'` for consistent formatting.
 *
 * @param {string} locale - The locale code (e.g., "en-US", "pl-PL").
 * @returns {boolean} `true` if the formatted hour starts with a leading zero, otherwise `false`.
 */
export const shouldUseTwoDigitHour = (locale: string): boolean => {
  const d = new Date(2020, 0, 1, 7, 5, 7) // 7:05:07
  const formatted = d.toLocaleTimeString(locale)

  return formatted.startsWith('0') // check if the hour starts with "0"
}