// Date
import { keys } from '../utils'

const _padZero = function (value: number): string {
  return value < 10 ? '0' + value : value.toString()
}

const patternLetters = {
  yyyy: 'getFullYear', 
  
  yy: function (date: Date): string {
    return date.getFullYear().toString().slice(2)
  },
  
  y: 'yy',
  
  MM: function (date: Date): string {
    return _padZero(date.getMonth() + 1)
  },
  
  M: function (date: Date): string {
    return (date.getMonth() + 1).toString()
  },
  
  dd: function (date: Date): string {
    return _padZero(date.getDate())
  },
  
  d: 'getDate',
  
  HH: function (date: Date): string {
    return _padZero(date.getHours())
  },
  
  H: 'getHours',
  
  hh: function (date: Date): string {
    return _padZero(date.getHours() % 12)
  },
  
  h: function (date: Date): string {
    return (date.getHours() % 12).toString()
  },
  
  mm: function (date: Date): string {
    return _padZero(date.getMinutes())
  },
  
  m: 'getMinutes',
  
  ss: function (date: Date): string {
    return _padZero(date.getSeconds())
  },
  
  s: 'getSeconds',
  
  SS: function (date: Date): string {
    const ms = date.getMilliseconds()
    return ms < 10 && '00' + ms || ms < 100 && '0' + ms || ms.toString()
  },
  
  S: 'getMilliseconds',
  
  A: function (date: Date): string {
    return date.getHours() < 12 ? 'AM' : 'PM'
  },
  
  a: function (date: Date): string {
    return date.getHours() < 12 ? 'am' : 'pm'
  },
  
  T: 'getTime'
}

const _createFormatRE = function (): string {
  const re: string[] = keys(patternLetters)
  return '(' + re.join('|') + ')'
}

const _formatDate = function (date: Date, format: string): string {
  const formatRE = new RegExp(_createFormatRE(), 'g')
  return format.replace(formatRE, function createNewSubString ($0, flag) {
    return typeof patternLetters[flag] === 'function' 
      ? patternLetters[flag](date) 
      : patternLetters[flag] in patternLetters 
        ? createNewSubString($0, patternLetters[flag]) 
        : date[patternLetters[flag]]()
  })
}

// 生成一个随机的 Date 对象。
const _randomDate = function (min: Date = new Date(0), max: Date = new Date()): Date {
  const randomTS = Math.random() * (max.getTime() - min.getTime())
  return new Date(randomTS)
}

// 返回一个随机的日期字符串。
export const date = function (format: string = 'yyyy-MM-dd'): string {
  return _formatDate(_randomDate(), format)
}

// 返回一个随机的时间字符串。
export const time = function (format: string = 'HH:mm:ss'): string {
  return _formatDate(_randomDate(), format)
}

// 返回一个随机的日期和时间字符串。
export const datetime = function (format: string = 'yyyy-MM-dd HH:mm:ss') {
  return _formatDate(_randomDate(), format)
}

// 返回一个随机的时间戳
export const timestamp = function (): number {
  return Number(_formatDate(_randomDate(), 'T'))
}

// 返回当前的日期和时间字符串。
export const now = function (unit: string, format: string): string {
  // now(unit) now(format)
  if (arguments.length === 1) {
    // now(format)
    if (!/year|month|day|hour|minute|second|week/.test(unit)) {
      format = unit
      unit = ''
    }
  }
  unit = (unit || '').toLowerCase()
  format = format || 'yyyy-MM-dd HH:mm:ss'
  
  const date = new Date()
  
  // 参考自 http://momentjs.cn/docs/#/manipulating/start-of/
  switch (unit) {
    case 'year':
      date.setMonth(0)
      break
    case 'month':
      date.setDate(1)
      break
    case 'week':
      date.setDate(date.getDate() - date.getDay())
      break
    case 'day':
      date.setHours(0)
      break
    case 'hour':
      date.setMinutes(0)
      break
    case 'minute':
      date.setSeconds(0)
      break
    case 'second':
      date.setMilliseconds(0)
  }
  
  return _formatDate(date, format)
}