import { View, Text, Image } from '@tarojs/components'
import Taro from '@tarojs/taro'
import { useEffect, useRef, useState } from 'react'
import { getTheme, resolveTheme, setDetectedSystemTheme } from '../utils/store'
import { THEME_CHANGE_EVENT } from '../context/ThemeContext'
import { applyPageBackground } from '../utils/themeBackground'
import { assetUrl } from '../utils/asset'
import { clampPercent, getTabBarFrame, hasDragged, tabIndexAtPercent } from './tabBarGeometry'
import './index.scss'

const TABS = [
  { pagePath: '/pages/index/index', label: '首页', icon: assetUrl('/icon/首页.svg'), iconActive: assetUrl('/icon/首页-fill.svg') },
  { pagePath: '/pages/shop/index', label: '商品', icon: assetUrl('/icon/商品.svg'), iconActive: assetUrl('/icon/商品-fill.svg') },
  { pagePath: '/pages/designList/index', label: '设计清单', icon: assetUrl('/icon/调色盘.svg'), iconActive: assetUrl('/icon/调色盘-fill.svg') },
  { pagePath: '/pages/orders/index', label: '订单', icon: assetUrl('/icon/包裹.svg'), iconActive: assetUrl('/icon/包裹-fill.svg') },
  { pagePath: '/pages/profile/index', label: '我的', icon: assetUrl('/icon/个人.svg'), iconActive: assetUrl('/icon/个人-fill.svg') }
]

const TAB_CENTER_STEP = 100 / TABS.length
const DRAG_THRESHOLD_PX = 12

function matchTab(path: string): string {
  const idx = TABS.findIndex((t) => path.endsWith(t.pagePath))
  return TABS[idx >= 0 ? idx : 0].pagePath
}

function currentTabPath(): string {
  const router = Taro.getCurrentInstance().router
  const path = router && router.path ? router.path : 'pages/index/index'
  return matchTab(path)
}

type ThemeChangeApi = {
  onThemeChange?: (listener: (res: { theme?: string }) => void) => void
  offThemeChange?: (listener: (res: { theme?: string }) => void) => void
}

export default function CustomTabBar() {
  const [resolvedTheme, setResolvedTheme] = useState<'light' | 'dark'>(resolveTheme(getTheme()))

  // 微信自定义 tabBar 不会自动感知 page 路由变化，用 state 保持选中态响应式
  const [activeTab, setActiveTab] = useState<string>(currentTabPath)
  const [dragPercent, setDragPercent] = useState<number | null>(null)
  const [isDragging, setIsDragging] = useState<boolean>(false)
  const isDraggingRef = useRef<boolean>(false)
  const dragPercentRef = useRef<number | null>(null)
  const startXRef = useRef<number>(0)
  const barFrameRef = useRef<{ left: number; width: number } | null>(null)

  useEffect(() => {
    const handler = (t: 'light' | 'dark') => setResolvedTheme(t)
    Taro.eventCenter.on(THEME_CHANGE_EVENT, handler)
    return () => {
      Taro.eventCenter.off(THEME_CHANGE_EVENT, handler)
    }
  }, [])

  // 自定义 tabBar 不处在 React Tree 里，额外直接监听系统主题，保证“跟随系统”时也即时切换
  useEffect(() => {
    const handler = (res: { theme?: string }) => {
      if (res && (res.theme === 'dark' || res.theme === 'light')) {
        setDetectedSystemTheme(res.theme)
        if (getTheme() === 'auto') {
          setResolvedTheme(res.theme)
        }
      }
    }
    const themeApi = Taro as typeof Taro & ThemeChangeApi
    if (themeApi.onThemeChange) {
      themeApi.onThemeChange(handler)
    }
    return () => {
      if (themeApi.offThemeChange) {
        themeApi.offThemeChange(handler)
      }
    }
  }, [])

  // 其它入口(如页面内部调用 switchTab)也会回到 tabBar，收到事件后重新同步选中态
  useEffect(() => {
    const handler = (path?: string) => {
      const router = Taro.getCurrentInstance().router
      const currentPath = router && router.path ? router.path : 'pages/index/index'
      setActiveTab(matchTab(path || currentPath))
    }
    Taro.eventCenter.on('tabBarChange', handler)
    return () => {
      Taro.eventCenter.off('tabBarChange', handler)
    }
  }, [])

  // tabBar 是 tab 页切换时必定会挂载/更新的组件：在这里也刷新一次页面背景，
  // 兜底处理“登录后切到受保护页面”时自定义导航区背景，避免残留白色
  useEffect(() => {
    applyPageBackground(resolvedTheme)
  }, [resolvedTheme])

  const switchTab = (url: string) => {
    setActiveTab(matchTab(url))
    Taro.switchTab({ url })
    Taro.eventCenter.trigger('tabBarChange', url)
  }

  const startDrag = (e: any) => {
    const touch = e.touches && e.touches[0]
    if (!touch) return
    const frame = getTabBarFrame(Taro.getSystemInfoSync().windowWidth)
    barFrameRef.current = frame
    startXRef.current = touch.clientX
    isDraggingRef.current = false
    setIsDragging(false)
    dragPercentRef.current = null
    setDragPercent(null)
  }

  const moveDrag = (e: any) => {
    const frame = barFrameRef.current
    const touch = e.touches && e.touches[0]
    if (!frame || !touch) return
    if (!isDraggingRef.current) {
      if (!hasDragged(startXRef.current, touch.clientX, DRAG_THRESHOLD_PX)) return
      isDraggingRef.current = true
      setIsDragging(true)
    }
    const nextPercent = clampPercent(((touch.clientX - frame.left) / frame.width) * 100)
    dragPercentRef.current = nextPercent
    setDragPercent(nextPercent)
  }

  const endDrag = (e: any) => {
    const frame = barFrameRef.current
    if (!frame) return
    let targetIndex: number
    if (isDraggingRef.current) {
      targetIndex = tabIndexAtPercent(dragPercentRef.current ?? 0, TABS.length)
      isDraggingRef.current = false
      setIsDragging(false)
      Taro.nextTick(() => {
        dragPercentRef.current = null
        setDragPercent(null)
      })
    } else {
      const touch = e.changedTouches && e.changedTouches[0]
      const x = touch ? touch.clientX : startXRef.current
      targetIndex = tabIndexAtPercent(clampPercent(((x - frame.left) / frame.width) * 100), TABS.length)
    }
    const target = TABS[targetIndex]
    if (target && target.pagePath !== activeTab) switchTab(target.pagePath)
    barFrameRef.current = null
    startXRef.current = 0
  }

  const cancelDrag = () => {
    barFrameRef.current = null
    startXRef.current = 0
    isDraggingRef.current = false
    setIsDragging(false)
    dragPercentRef.current = null
    setDragPercent(null)
  }

  const activeIndex = Math.max(0, TABS.findIndex((t) => t.pagePath === activeTab))

  return (
    <View className={`tab-bar-root theme-${resolvedTheme}`}>
      <View className='tab-bar-gradient' />
      <View
        className={`custom-tab-bar theme-${resolvedTheme}`}
        onTouchStart={startDrag}
        onTouchMove={moveDrag}
        onTouchEnd={endDrag}
        onTouchCancel={cancelDrag}
        catchMove
      >
        <View className='tab-bar-caustic' />
        <View className='tab-bar-rim' />
        <View
          className={`tab-indicator ${isDragging ? 'dragging' : ''}`}
          style={{ left: dragPercent === null ? `${(activeIndex + 0.5) * TAB_CENTER_STEP}%` : `${dragPercent}%` }}
        />
        {TABS.map((tab) => {
          const isActive = tab.pagePath === activeTab
          return (
            <View key={tab.pagePath} className={`tab-item ${isActive ? 'active' : ''}`}>
              <Image className={`tab-icon-img ${isActive ? 'active' : ''}`} src={isActive ? tab.iconActive : tab.icon} mode='aspectFit' />
              <Text className='tab-label'>{tab.label}</Text>
            </View>
          )
        })}
      </View>
    </View>
  )
}