// @flow

import * as React from 'react'
import { useEffect, useState } from 'react'
import dateParser from './dateParser'
import defaultFormatter from './defaultFormatter'

export type Unit =
  | 'second'
  | 'minute'
  | 'hour'
  | 'day'
  | 'week'
  | 'month'
  | 'year'
export type Suffix = 'ago' | 'from now'
export type Formatter = (
  value: number,
  unit: Unit,
  suffix: Suffix,
  epochMilliseconds: number,
  nextFormatter: () => React.Node,
  now: () => number,
) => React.Node

export type Props = $ReadOnly<{
  /** If the component should update itself over time */
  live?: boolean,
  /** minimum amount of time in seconds between re-renders */
  minPeriod?: number,
  /** Maximum time between re-renders in seconds. The component should update at least once every `x` seconds */
  maxPeriod?: number,
  /** The container to render the string into. You could use a string like `span` or a custom component */
  component?: string | React.ComponentType<mixed>,
  /**
   * A title used for setting the title attribute if a <time> HTML Element is used.
   */
  title?: string,
  /** A function to decide how to format the date.
   * If you use this, react-timeago is basically acting like a glorified setInterval for you.
   */
  formatter?: Formatter,
  /** The Date to display. An actual Date object or something that can be fed to new Date */
  date: string | number | Date,
  /** A function that returns what Date.now would return. Primarily for server
   * date: string | number | Date		 +   * rendering.
   */
  now?: () => number,
  ...
}>

// Just some simple constants for readability
const MINUTE = 60
const HOUR = MINUTE * 60
const DAY = HOUR * 24
const WEEK = DAY * 7
const MONTH = DAY * 30
const YEAR = DAY * 365

const defaultNow = () => Date.now();

export default function TimeAgo({
  date,
  formatter = defaultFormatter,
  component = 'time',
  live = true,
  minPeriod = 0,
  maxPeriod = WEEK,
  title,
  now = defaultNow,
  ...passDownProps
}: Props): null | React.MixedElement {
  const [timeNow, setTimeNow] = useState(now())
  useEffect(() => {
    if (!live) {
      return
    }
    const tick = (): 0 | TimeoutID => {
      const then = dateParser(date).valueOf()
      if (!then) {
        console.warn('[react-timeago] Invalid Date provided')
        return 0
      }
      const seconds = Math.round(Math.abs(timeNow - then) / 1000)

      const unboundPeriod =
        seconds < MINUTE
          ? 1000
          : seconds < HOUR
          ? 1000 * MINUTE
          : seconds < DAY
          ? 1000 * HOUR
          : 1000 * WEEK

      const period = Math.min(
        Math.max(unboundPeriod, minPeriod * 1000),
        maxPeriod * 1000,
      )

      if (period) {
        return setTimeout(() => {
          setTimeNow(now())
        }, period)
      }

      return 0
    }
    const timeoutId = tick()
    return () => {
      if (timeoutId) {
        clearTimeout(timeoutId)
      }
    }
  }, [date, live, maxPeriod, minPeriod, now, timeNow])

  const Komponent = component
  const then = dateParser(date).valueOf()
  if (!then) {
    return null
  }

  const seconds = Math.round(Math.abs(timeNow - then) / 1000)
  const suffix = then < timeNow ? 'ago' : 'from now'

  const [value, unit] =
    seconds < MINUTE
      ? [Math.round(seconds), 'second']
      : seconds < HOUR
      ? [Math.round(seconds / MINUTE), 'minute']
      : seconds < DAY
      ? [Math.round(seconds / HOUR), 'hour']
      : seconds < WEEK
      ? [Math.round(seconds / DAY), 'day']
      : seconds < MONTH
      ? [Math.round(seconds / WEEK), 'week']
      : seconds < YEAR
      ? [Math.round(seconds / MONTH), 'month']
      : [Math.round(seconds / YEAR), 'year']

  const passDownTitle =
    typeof title === 'undefined'
      ? typeof date === 'string'
        ? date
        : dateParser(date).toISOString().substr(0, 16).replace('T', ' ')
      : title

  const spreadProps =
    Komponent === 'time'
      ? { ...passDownProps, dateTime: dateParser(date).toISOString() }
      : passDownProps

  const nextFormatter = defaultFormatter.bind(null, value, unit, suffix)

  return (
    <Komponent {...spreadProps} title={passDownTitle}>
      {formatter(value, unit, suffix, then, nextFormatter, now)}
    </Komponent>
  )
}