<template>
	<view class="signature-wrap">
		<canvas :canvas-id="cid" :id="cid" @touchstart="onTouchStart" @touchmove="onTouchMove" @touchend="onTouchEnd"
			style="height:600rpx" :style="[{ width: formatSize(width)}, customStyle]"></canvas>
		<slot />
	</view>
</template>

<script>
	/**
	 * sign canvas 手写签名
	 * @description 设置线条宽度、颜色，撤回，清空
	 * @tutorial
	 * @property {String} cid canvas id 不设置则默认为 v-sign-时间戳
	 * @property {String, Number} width canvas 宽度
	 * @property {String, Number} height canvas 高度
	 * @property {Object} customStyle 自定义样式
	 * @property {String} lineColor 画笔颜色
	 * @property {Number} lineWidth 画笔大小，权重大于 v-sign-pen 组件设置的画笔大小
	 * @event {Function} init 当创建完 canvas 实例后触发，向外提供 canvas实例，撤回，清空方法
	 * @example <v-sign @init="signInit"></v-sign>
	 */
	import {
		formatSize
	} from './utils'
	// convas 实例
	let canvasCtx

	export default {
		name: 'v-sign',
		props: {
			// canvas id
			cid: {
				type: String,
				default: `v-sign-${Date.now()}`
				// required: true
			},
			// canvas 宽度
			width: {
				type: [String, Number],
				default: '100%'
			},
			// canvas 高度
			height: {
				type: [String, Number],
				default: 300
			},
			// 画笔大小，权重大于 v-sign-pen 组件设置的画笔大小
			lineWidth: {
				type: Number
			},
			// 线颜色
			lineColor: {
				type: String,
				default: '#000'
			},
			// canvas自定义样式
			customStyle: {
				type: Object,
				default: () => ({})
			}
		},
		provide() {
			return {
				getInterface: this.provideInterface
			}
		},
		data() {
			return {
				formatSize,
				lineData: [],
				winWidth: 0,
				winHeight: 0,
				penLineWidth: null, // v-sign-pen 组件设置的画笔大小
			}
		},
		mounted() {
			canvasCtx = uni.createCanvasContext(this.cid, this)
			// 初始化完成，向外暴露接口
			this.$emit('init', this.provideInterface())
			// 获取窗口宽高
			uni.getSystemInfo({
				success: res => {
					this.winWidth = res.windowWidth
					this.winHeight = res.windowHeight
				}
			})
		},
		methods: {
			onTouchStart(e) {
				const pos = e.touches[0]
				this.lineData.push({
					style: {
						color: this.lineColor,
						width: this.lineWidth || this.penLineWidth || 4
					},
					// 屏幕坐标
					coordinates: [{
						type: e.type,
						x: pos.x,
						y: pos.y
					}]
				})
				this.drawLine()
			},
			onTouchMove(e) {
				const pos = e.touches[0]
				this.lineData[this.lineData.length - 1].coordinates.push({
					type: e.type,
					x: pos.x,
					y: pos.y
				})
				this.drawLine()
			},
			onTouchEnd(e) {
				// console.log(e.type, e)
			},
			// 清空画布
			clear() {
				this.lineData = []
				canvasCtx.clearRect(0, 0, this.winWidth, this.winHeight)
				canvasCtx.draw()
			},
			// 撤销
			revoke() {
				this.lineData.pop()
				this.lineData.forEach((item, index) => {
					canvasCtx.beginPath()
					canvasCtx.setLineCap('round')
					canvasCtx.setStrokeStyle(item.style.color)
					canvasCtx.setLineWidth(item.style.width)
					item.coordinates.forEach(pos => {
						if (pos.type == 'touchstart') {
							canvasCtx.moveTo(pos.x, pos.y)
						} else {
							canvasCtx.lineTo(pos.x, pos.y)
						}
					})
					canvasCtx.stroke()
				})
				canvasCtx.draw()
			},
			// 绘制线条
			drawLine() {
				const lineDataLen = this.lineData.length
				if (!lineDataLen) return
				const currentLineData = this.lineData[lineDataLen - 1]
				const coordinates = currentLineData.coordinates
				const coordinatesLen = coordinates.length
				if (!coordinatesLen) return
				let startPos
				let endPos
				if (coordinatesLen < 2) {
					// only start, no move event
					startPos = coordinates[coordinatesLen - 1]
					endPos = {
						x: startPos.x + 1,
						y: startPos.y
					}
				} else {
					startPos = coordinates[coordinatesLen - 2]
					endPos = coordinates[coordinatesLen - 1]
				}

				const style = currentLineData.style
				canvasCtx.beginPath()
				canvasCtx.setLineCap('round')
				canvasCtx.setStrokeStyle(style.color)
				canvasCtx.setLineWidth(style.width)
				canvasCtx.moveTo(startPos.x, startPos.y)
				canvasCtx.lineTo(endPos.x, endPos.y)
				// const P1 = this.caculateBezier(startPos, endPos, centerPos)
				// console.log(P1.x, P1.y)
				// canvasCtx.moveTo(startPos.x, startPos.y)
				// canvasCtx.quadraticCurveTo(P1.x, P1.y, endPos.x, endPos.y)
				canvasCtx.stroke()
				canvasCtx.draw(true)
			},
			canvasToTempFilePath(conf = {}) {
				return new Promise((resolve, reject) => {
					uni.canvasToTempFilePath({
							canvasId: this.cid,
							...conf,
							success: res => {
								resolve(res.tempFilePath)
							},
							fail: err => {
								console.log('fail', err)
								reject(err)
							}
						},
						this
					)
				})
			},
			setLineWidth(numberVal) {
				this.penLineWidth = numberVal
			},
			provideInterface() {
				return {
					cid: this.cid,
					ctx: canvasCtx,
					clear: this.clear,
					revoke: this.revoke,
					canvasToTempFilePath: this.canvasToTempFilePath,
					setLineWidth: this.setLineWidth
				}
			},
			/**
			 * 计算二次贝塞尔曲线 控制点 P1
			 * 起点 P0(x0,y0)、控制点P1(x1, y1)、P2(x2, y2)、曲线上任意点B(x, y)
			 * 二次贝塞尔公式：B(t) = (1-t)²P0 + 2t(1-t)P1 + t²P2
			 * 代入坐标得：
			 * x = (1-t)²*x0 + 2t(1-t)*x1 + t²*x2
			 * y = (1-t)²*y0 + 2t(1-t)*y1 + t²*y2
			 */
			caculateBezier(P0, P2, B, t = 0.5) {
				const {
					x: x0,
					y: y0
				} = P0
				const {
					x: x2,
					y: y2
				} = P2
				const {
					x,
					y
				} = B
				let x1 = (x - (1 - t) * (1 - t) * x0 - t * t * x2) / (2 * t * (1 - t))
				let y1 = (y - (1 - t) * (1 - t) * y0 - t * t * y2) / (2 * t * (1 - t))
				return {
					x: x1,
					y: y1
				}
			}
		}
	}
</script>

<style lang="scss" scoped>
	.signature-wrap {
		position: relative;
	}
</style>
