export class DateTimeUtil {

  public day: number = 1
  public month: number = 1
  public year: number = 2017
  public hour: number = 0
  public minute: number = 0
  public second: number = 0

  constructor(yearOrDateTimeString: any = 1, month: number = 1, day: number = 1) {
    if (typeof yearOrDateTimeString === 'string') {
      if (
        yearOrDateTimeString.match(DateTimeUtil.dateTimeStringRegex) ||
        yearOrDateTimeString.match(DateTimeUtil.dateStrictStringRegex)
      ) {
        this.setFromString(yearOrDateTimeString)
      }
    } else if (typeof yearOrDateTimeString === 'number') {
      this.setDate(yearOrDateTimeString, month, day)
    }
    return this
  }

  public setDate(year: number, month: number, day: number) {
    this.year = year
    this.month = month
    this.day = day
    return this
  }

  public setFromString(string: string) {
    this.day = DateTimeUtil.getDayFromString(string)
    this.month = DateTimeUtil.getMonthFromString(string)
    this.year = DateTimeUtil.getYearFromString(string)
    if (string.match(DateTimeUtil.dateTimeStringRegex)) {
      this.hour = DateTimeUtil.getHourFromString(string)
      this.minute = DateTimeUtil.getMinuteFromString(string)
      this.second = DateTimeUtil.getSecondFromString(string)
    }
    return this
  }

  // Static
  // Based on mysql datetime.
  private static dateStringRegex = '^([0-9]{4})-(0[0-9]|1[0-2])-([0-2][0-9]|3[0-1])'
  private static dateStrictStringRegex = '^([0-9]{4})-(0[0-9]|1[0-2])-([0-2][0-9]|3[0-1])$'
  private static dateTimeStringRegex = '^([0-9]{4})-(0[0-9]|1[0-2])-([0-2][0-9]|3[0-1]) ([0-1][0-9]|2[0-3]):([0-4][0-9]|5[0-9]):([0-4][0-9]|5[0-9])$'
  private static dayOfWeekStrings = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']
  private static monthStrings = ['January', 'Februrary', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']
  private static numberOfDaysInMonth = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

  static IsDateString(string: string) {
    return string.match(DateTimeUtil.dateStrictStringRegex) ? true : false
  }

  static IsDateTimeString(string: string) {
    return string.match(DateTimeUtil.dateTimeStringRegex) ? true : false
  }

  static getDayFromString(string: string) {
    return Number(string.match(DateTimeUtil.dateStringRegex)[3])
  }

  static getHourFromString(string: string) {
    return Number(string.match(DateTimeUtil.dateTimeStringRegex)[4])
  }

  static getMinuteFromString(string: string) {
    return Number(string.match(DateTimeUtil.dateTimeStringRegex)[5])
  }

  static getMonthFromString(string: string) {
    return Number(string.match(DateTimeUtil.dateStringRegex)[2])
  }

  static getSecondFromString(string: string) {
    return Number(string.match(DateTimeUtil.dateTimeStringRegex)[6])
  }

  static getYearFromString(string: string) {
    return Number(string.match(DateTimeUtil.dateStringRegex)[1])
  }

  static getDayOfWeek(year: number, month: number, day: number) {
    let days = DateTimeUtil.getNumberOfDaysFromYearZero(year, month, day)
    let remainder = (days + 6) % 7
    return remainder + 1
  }

  static getDayOfWeekString(year: number, month: number, day: number) {
    let dayOfWeek = DateTimeUtil.getDayOfWeek(year, month, day)
    return DateTimeUtil.dayOfWeekStrings[dayOfWeek - 1]
  }

  static getNumberOfDaysFromYearZero(year: number, month: number, day: number) {
    let sum = (year * 365) + DateTimeUtil.getNumberOfLeapYears(year)
    sum += DateTimeUtil.getNumberOfDaysInMonth(year, month)
    sum += day
    return sum
  }

  static getNumberOfDaysInMonth(year: number, month: number) {
    if (
      DateTimeUtil.isLeapYear(year) &&
      month === 2
    ) {
      return 29
    } else {
      return DateTimeUtil.numberOfDaysInMonth[month + 1]
    }
  }

  static getNumberOfLeapYears(year: number) {
    let leapYears = Math.floor(year / 4)
    if (year > 100) {
      leapYears -= Math.floor(year / 100)
    }
    if (year > 400) {
      leapYears -= Math.floor(year / 400)
    }
    return leapYears
  }

  static getTotalNumberOfDaysInMonth(year: number, month: number) {
    let sum = 0
    let i = 0
    while (i < month) {
      sum += DateTimeUtil.getNumberOfDaysInMonth(year, i + 1)
      i++
    }
    return sum
  }

  // Returns true if year is a leap year.
  static isLeapYear(year: number) {
    let isLeapYear = false
    if (year % 4 === 0) {
      isLeapYear = true
    }
    // if year % 100 is 0 and year % 400 is not 0
    // isLeapYear = false 
    return isLeapYear
  }

}