<template>
	<view class="u-count-num" :style="{
		fontSize: fontSize + 'rpx',
		color: color
	}">
		{{ displayValue }}
	</view>
</template>

<script>
	/**
	 * alertTips 提示
	 * @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} start-val 开始值
	 * @property {String Number} end-val 结束值
	 * @property {String Number} duration 滚动过程所需的时间，单位ms（默认2000）
	 * @property {Boolean} autoplay 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} use-easing 滚动结束时，是否缓动结尾，见官网说明（默认true）
	 * @property {String} separator 千位分隔符，见官网说明
	 * @property {String} color 字体颜色（默认#303133）
	 * @property {String Number} font-size 字体大小，单位rpx（默认50）
	 * @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",
		props: {
			// 开始的数值，默认从0增长到某一个数
			startVal: {
				type: [Number, String],
				default: 0
			},
			// 要滚动的目标数值，必须
			endVal: {
				type: [Number, String],
				default: 0,
				required: true
			},
			// 滚动到目标数值的动画持续时间，单位为毫秒（ms）
			duration: {
				type: [Number, String],
				default: 2000
			},
			// 设置数值后是否自动开始滚动
			autoplay: {
				type: Boolean,
				default: true
			},
			// 要显示的小数位数
			decimals: {
				type: [Number, String],
				default: 0
			},
			// 是否在即将到达目标数值的时候，使用缓慢滚动的效果
			useEasing: {
				type: Boolean,
				default: true
			},
			// 十进制分割
			decimal: {
				type: [Number, String],
				default: '.'
			},
			// 字体颜色
			color: {
				type: String,
				default: '#303133'
			},
			// 字体大小
			fontSize: {
				type: [Number, String],
				default: 50
			},
			// 千位分隔符，类似金额的分割(￥23,321.05中的",")
			separator: {
				type: String,
				default: ''
			},
		},
		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
			};
		},
		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() {
				this.startTime = null;
				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);
				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) {
				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>
	.u-count-num {
		display: inline-block;
		text-align: center;
	}
</style>
