# coding:utf-8
from collections import deque
from enum import Enum
from math import cos, pi

from PyQt5.QtCore import QDateTime, Qt, QTimer, QPoint
from PyQt5.QtGui import QWheelEvent
from PyQt5.QtWidgets import QApplication, QScrollArea


class ScrollArea(QScrollArea):
    """ 一个可以平滑滚动的区域 """

    def __init__(self, parent=None):
        super().__init__(parent)
        self.fps = 60
        self.duration = 400
        self.stepsTotal = 0
        self.stepRatio = 1.5
        self.acceleration = 1
        self.lastWheelEvent = None
        self.scrollStamps = deque()
        self.stepsLeftQueue = deque()
        self.smoothMoveTimer = QTimer(self)
        self.smoothMode = SmoothMode(SmoothMode.COSINE)
        self.smoothMoveTimer.timeout.connect(self.__smoothMove)

    def setSMoothMode(self, smoothMode):
        """ 设置滚动模式 """
        self.smoothMode = smoothMode

    def wheelEvent(self, e: QWheelEvent):
        """ 实现平滑滚动效果 """
        if self.smoothMode == SmoothMode.NO_SMOOTH:
            super().wheelEvent(e)
            return
        # 将当前时间点插入队尾
        now = QDateTime.currentDateTime().toMSecsSinceEpoch()
        self.scrollStamps.append(now)
        while now - self.scrollStamps[0] > 500:
            self.scrollStamps.popleft()
        # 根据未处理完的事件调整移动速率增益
        accerationRatio = min(len(self.scrollStamps) / 15, 1)
        if not self.lastWheelEvent:
            self.lastWheelEvent = QWheelEvent(e)
        else:
            self.lastWheelEvent = e
        # 计算步数
        self.stepsTotal = self.fps * self.duration / 1000
        # 计算每一个事件对应的移动距离
        delta = e.angleDelta().y() * self.stepRatio
        if self.acceleration > 0:
            delta += delta * self.acceleration * accerationRatio
        # 将移动距离和步数组成列表，插入队列等待处理
        self.stepsLeftQueue.append([delta, self.stepsTotal])
        # 定时器的溢出时间t=1000ms/帧数
        self.smoothMoveTimer.start(1000 / self.fps)

    def __smoothMove(self):
        """ 计时器溢出时进行平滑滚动 """
        totalDelta = 0
        # 计算所有未处理完事件的滚动距离，定时器每溢出一次就将步数-1
        for i in self.stepsLeftQueue:
            totalDelta += self.__subDelta(i[0], i[1])
            i[1] -= 1
        # 如果事件已处理完，就将其移出队列
        while self.stepsLeftQueue and self.stepsLeftQueue[0][1] == 0:
            self.stepsLeftQueue.popleft()
        # 构造滚轮事件
        e = QWheelEvent(self.lastWheelEvent.pos(),
                        self.lastWheelEvent.globalPos(),
                        QPoint(),
                        QPoint(0, totalDelta),
                        round(totalDelta),
                        Qt.Vertical,
                        self.lastWheelEvent.buttons(),
                        Qt.NoModifier)
        # 将构造出来的滚轮事件发送给app处理
        QApplication.sendEvent(self.verticalScrollBar(), e)
        # 如果队列已空，停止滚动
        if not self.stepsLeftQueue:
            self.smoothMoveTimer.stop()

    def __subDelta(self, delta, stepsLeft):
        """ 计算每一步的插值 """
        m = self.stepsTotal / 2
        x = abs(self.stepsTotal - stepsLeft - m)
        # 根据滚动模式计算插值
        res = 0
        if self.smoothMode == SmoothMode.NO_SMOOTH:
            res = 0
        elif self.smoothMode == SmoothMode.CONSTANT:
            res = delta / self.stepsTotal
        elif self.smoothMode == SmoothMode.LINEAR:
            res = 2 * delta / self.stepsTotal * (m - x) / m
        elif self.smoothMode == SmoothMode.QUADRATI:
            res = 3 / 4 / m * (1 - x * x / m / m) * delta
        elif self.smoothMode == SmoothMode.COSINE:
            res = (cos(x * pi / m) + 1) / (2 * m) * delta
        return res


class SmoothMode(Enum):
    """ 滚动模式 """
    NO_SMOOTH = 0
    CONSTANT = 1
    LINEAR = 2
    QUADRATI = 3
    COSINE = 4
