<template>
  <text
    class="u-count-num"
    :style="{
      fontSize: $u.addUnit(fontSize),
      fontWeight: bold ? bold : 'normal',
      color: color
    }"
  >
    {{ displayValue }}
  </text>
</template>

<script>
import props from './props.js'
/**
 * countTo 数字滚动
 * @description 该组件一般用于需要滚动数字到某一个值的场景，目标要求是一个递增的值。
 * @tutorial https://www.uviewui.com/components/countTo.html
 * @property {String | Number}	startVal	开始的数值，默认从0增长到某一个数（默认 0 ）
 * @property {String | Number}	endVal		要滚动的目标数值，必须 （默认 0 ）
 * @property {String | Number}	duration	滚动到目标数值的动画持续时间，单位为毫秒（ms） （默认 2000 ）
 * @property {Boolean}			autoplay	设置数值后是否自动开始滚动 （默认 true ）
 * @property {String | Number}	decimals	要显示的小数位数，见官网说明（默认 0 ）
 * @property {Boolean}			useEasing	滚动结束时，是否缓动结尾，见官网说明（默认 true ）
 * @property {String}			decimal		十进制分割 （ 默认 "." ）
 * @property {String}			color		字体颜色（ 默认 '#606266' )
 * @property {String | Number}	fontSize	字体大小，单位px（ 默认 22 ）
 * @property {Boolean}			bold		字体是否加粗（默认 false ）
 * @property {String}			separator	千位分隔符，见官网说明
 * @event {Function} end 数值滚动到目标值时触发
 * @example <u-count-to ref="uCountTo" :end-val="endVal" :autoplay="autoplay"></u-count-to>
 */
export default {
  name: 'u-count-to',
  data() {
    return {
      localStartVal: this.startVal,
      displayValue: this.formatNumber(this.startVal),
      printVal: null,
      paused: false, // 是否暂停
      localDuration: Number(this.duration),
      startTime: null, // 开始的时间
      timestamp: null, // 时间戳
      remaining: null, // 停留的时间
      rAF: null,
      lastTime: 0 // 上一次的时间
    }
  },
  mixins: [uni.$u.mpMixin, uni.$u.mixin, props],
  computed: {
    countDown() {
      return this.startVal > this.endVal
    }
  },
  watch: {
    startVal() {
      this.autoplay && this.start()
    },
    endVal() {
      this.autoplay && this.start()
    }
  },
  mounted() {
    this.autoplay && this.start()
  },
  methods: {
    easingFn(t, b, c, d) {
      return (c * (-Math.pow(2, (-10 * t) / d) + 1) * 1024) / 1023 + b
    },
    requestAnimationFrame(callback) {
      const currTime = new Date().getTime()
      // 为了使setTimteout的尽可能的接近每秒60帧的效果
      const timeToCall = Math.max(0, 16 - (currTime - this.lastTime))
      const id = setTimeout(() => {
        callback(currTime + timeToCall)
      }, timeToCall)
      this.lastTime = currTime + timeToCall
      return id
    },
    cancelAnimationFrame(id) {
      clearTimeout(id)
    },
    // 开始滚动数字
    start() {
      this.localStartVal = this.startVal
      this.startTime = null
      this.localDuration = this.duration
      this.paused = false
      this.rAF = this.requestAnimationFrame(this.count)
    },
    // 暂定状态，重新再开始滚动；或者滚动状态下，暂停
    reStart() {
      if (this.paused) {
        this.resume()
        this.paused = false
      } else {
        this.stop()
        this.paused = true
      }
    },
    // 暂停
    stop() {
      this.cancelAnimationFrame(this.rAF)
    },
    // 重新开始(暂停的情况下)
    resume() {
      if (!this.remaining) return
      this.startTime = 0
      this.localDuration = this.remaining
      this.localStartVal = this.printVal
      this.requestAnimationFrame(this.count)
    },
    // 重置
    reset() {
      this.startTime = null
      this.cancelAnimationFrame(this.rAF)
      this.displayValue = this.formatNumber(this.startVal)
    },
    count(timestamp) {
      if (!this.startTime) this.startTime = timestamp
      this.timestamp = timestamp
      const progress = timestamp - this.startTime
      this.remaining = this.localDuration - progress
      if (this.useEasing) {
        if (this.countDown) {
          this.printVal =
            this.localStartVal -
            this.easingFn(
              progress,
              0,
              this.localStartVal - this.endVal,
              this.localDuration
            )
        } else {
          this.printVal = this.easingFn(
            progress,
            this.localStartVal,
            this.endVal - this.localStartVal,
            this.localDuration
          )
        }
      } else {
        if (this.countDown) {
          this.printVal =
            this.localStartVal -
            (this.localStartVal - this.endVal) *
              (progress / this.localDuration)
        } else {
          this.printVal =
            this.localStartVal +
            (this.endVal - this.localStartVal) *
              (progress / this.localDuration)
        }
      }
      if (this.countDown) {
        this.printVal =
          this.printVal < this.endVal ? this.endVal : this.printVal
      } else {
        this.printVal =
          this.printVal > this.endVal ? this.endVal : this.printVal
      }
      this.displayValue = this.formatNumber(this.printVal) || 0
      if (progress < this.localDuration) {
        this.rAF = this.requestAnimationFrame(this.count)
      } else {
        this.$emit('end')
      }
    },
    // 判断是否数字
    isNumber(val) {
      return !isNaN(parseFloat(val))
    },
    formatNumber(num) {
      // 将num转为Number类型，因为其值可能为字符串数值，调用toFixed会报错
      num = Number(num)
      num = num.toFixed(Number(this.decimals))
      num += ''
      const x = num.split('.')
      let x1 = x[0]
      const x2 = x.length > 1 ? this.decimal + x[1] : ''
      const rgx = /(\d+)(\d{3})/
      if (this.separator && !this.isNumber(this.separator)) {
        while (rgx.test(x1)) {
          x1 = x1.replace(rgx, '$1' + this.separator + '$2')
        }
      }
      return x1 + x2
    },
    destroyed() {
      this.cancelAnimationFrame(this.rAF)
    }
  }
}
</script>

<style lang="scss" scoped>
@import '../../libs/css/components.scss';

.u-count-num {
  /* #ifndef APP-NVUE */
  display: inline-flex;
  /* #endif */
  text-align: center;
}
</style>