/**
 * Real Browser Environment Dark Mode Flicker Test
 *
 * This test attempts to simulate real browser refresh scenarios including:
 * 1. SSR HTML generation phase
 * 2. Client-side JavaScript loading
 * 3. Theme system initialization
 * 4. CSS styles application timing
 */

import { render, screen, waitFor } from '@testing-library/react'
import { ThemeProvider } from 'next-themes'
import { useEffect, useState } from 'react'
import useTheme from '@/hooks/use-theme'

const DARK_MODE_MEDIA_QUERY = /prefers-color-scheme:\s*dark/i

// Setup browser environment for testing
const setupMockEnvironment = (storedTheme: string | null, systemPrefersDark = false) => {
  if (typeof window === 'undefined')
    return

  try {
    window.localStorage.clear()
  }
  catch {
    // ignore if localStorage has been replaced by a throwing stub
  }

  if (storedTheme === null)
    window.localStorage.removeItem('theme')
  else
    window.localStorage.setItem('theme', storedTheme)

  document.documentElement.removeAttribute('data-theme')

  const mockMatchMedia: typeof window.matchMedia = (query: string) => {
    const listeners = new Set<(event: MediaQueryListEvent) => void>()
    const isDarkQuery = DARK_MODE_MEDIA_QUERY.test(query)
    const matches = isDarkQuery ? systemPrefersDark : false

    const handleAddListener = (listener: (event: MediaQueryListEvent) => void) => {
      listeners.add(listener)
    }

    const handleRemoveListener = (listener: (event: MediaQueryListEvent) => void) => {
      listeners.delete(listener)
    }

    const handleAddEventListener = (_event: string, listener: EventListener) => {
      if (typeof listener === 'function')
        listeners.add(listener as (event: MediaQueryListEvent) => void)
    }

    const handleRemoveEventListener = (_event: string, listener: EventListener) => {
      if (typeof listener === 'function')
        listeners.delete(listener as (event: MediaQueryListEvent) => void)
    }

    const handleDispatchEvent = (event: Event) => {
      listeners.forEach(listener => listener(event as MediaQueryListEvent))
      return true
    }

    const mediaQueryList: MediaQueryList = {
      matches,
      media: query,
      onchange: null,
      addListener: handleAddListener,
      removeListener: handleRemoveListener,
      addEventListener: handleAddEventListener,
      removeEventListener: handleRemoveEventListener,
      dispatchEvent: handleDispatchEvent,
    }

    return mediaQueryList
  }

  vi.spyOn(window, 'matchMedia').mockImplementation(mockMatchMedia)
}

// Helper function to create timing page component
const createTimingPageComponent = (
  timingData: Array<{ phase: string, timestamp: number, styles: { backgroundColor: string, color: string } }>,
) => {
  const recordTiming = (phase: string, styles: { backgroundColor: string, color: string }) => {
    timingData.push({
      phase,
      timestamp: performance.now(),
      styles,
    })
  }

  const TimingPageComponent = () => {
    const [mounted, setMounted] = useState(false)
    const { theme } = useTheme()
    const isDark = mounted ? theme === 'dark' : false

    const currentStyles = {
      backgroundColor: isDark ? '#1f2937' : '#ffffff',
      color: isDark ? '#ffffff' : '#000000',
    }

    recordTiming(mounted ? 'CSR' : 'Initial', currentStyles)

    useEffect(() => {
      setMounted(true)
    }, [])

    return (
      <div
        data-testid="timing-page"
        style={currentStyles}
      >
        <div data-testid="timing-status">
          Phase:
          {' '}
          {mounted ? 'CSR' : 'Initial'}
          {' '}
          | Theme:
          {' '}
          {theme}
          {' '}
          | Visual:
          {' '}
          {isDark ? 'dark' : 'light'}
        </div>
      </div>
    )
  }

  return TimingPageComponent
}

// Helper function to create CSS test component
const createCSSTestComponent = (
  cssStates: Array<{ className: string, timestamp: number }>,
) => {
  const recordCSSState = (className: string) => {
    cssStates.push({
      className,
      timestamp: performance.now(),
    })
  }

  const CSSTestComponent = () => {
    const [mounted, setMounted] = useState(false)
    const { theme } = useTheme()
    const isDark = mounted ? theme === 'dark' : false

    const className = `min-h-screen ${isDark ? 'bg-gray-900 text-white' : 'bg-white text-black'}`

    recordCSSState(className)

    useEffect(() => {
      setMounted(true)
    }, [])

    return (
      <div
        data-testid="css-component"
        className={className}
      >
        <div data-testid="css-classes">
          Classes:
          {className}
        </div>
      </div>
    )
  }

  return CSSTestComponent
}

// Helper function to create performance test component
const createPerformanceTestComponent = (
  performanceMarks: Array<{ event: string, timestamp: number }>,
) => {
  const recordPerformanceMark = (event: string) => {
    performanceMarks.push({ event, timestamp: performance.now() })
  }

  const PerformanceTestComponent = () => {
    const [mounted, setMounted] = useState(false)
    const { theme } = useTheme()

    recordPerformanceMark('component-render')

    useEffect(() => {
      recordPerformanceMark('mount-start')
      setMounted(true)
      recordPerformanceMark('mount-complete')
    }, [])

    useEffect(() => {
      if (theme)
        recordPerformanceMark('theme-available')
    }, [theme])

    return (
      <div data-testid="performance-test">
        Mounted:
        {' '}
        {mounted.toString()}
        {' '}
        | Theme:
        {' '}
        {theme || 'loading'}
      </div>
    )
  }

  return PerformanceTestComponent
}

// Simulate real page component based on Dify's actual theme usage
const PageComponent = () => {
  const [mounted, setMounted] = useState(false)
  const { theme } = useTheme()

  useEffect(() => {
    setMounted(true)
  }, [])

  // Simulate common theme usage pattern in Dify
  const isDark = mounted ? theme === 'dark' : false

  return (
    <div data-theme={isDark ? 'dark' : 'light'}>
      <div
        data-testid="page-content"
        style={{ backgroundColor: isDark ? '#1f2937' : '#ffffff' }}
      >
        <h1 style={{ color: isDark ? '#ffffff' : '#000000' }}>
          Dify Application
        </h1>
        <div data-testid="theme-indicator">
          Current Theme:
          {' '}
          {mounted ? theme : 'unknown'}
        </div>
        <div data-testid="visual-appearance">
          Appearance:
          {' '}
          {isDark ? 'dark' : 'light'}
        </div>
      </div>
    </div>
  )
}

const TestThemeProvider = ({ children }: { children: React.ReactNode }) => (
  <ThemeProvider
    attribute="data-theme"
    defaultTheme="system"
    enableSystem
    disableTransitionOnChange
  >
    {children}
  </ThemeProvider>
)

describe('Real Browser Environment Dark Mode Flicker Test', () => {
  beforeEach(() => {
    vi.restoreAllMocks()
    vi.clearAllMocks()
    if (typeof window !== 'undefined') {
      try {
        window.localStorage.clear()
      }
      catch {
        // ignore when localStorage is replaced with an error-throwing stub
      }
      document.documentElement.removeAttribute('data-theme')
    }
  })

  describe('Page Refresh Scenario Simulation', () => {
    it('simulates complete page loading process with dark theme', async () => {
      // Setup: User previously selected dark mode
      setupMockEnvironment('dark')

      render(
        <TestThemeProvider>
          <PageComponent />
        </TestThemeProvider>,
      )

      // Check initial client-side rendering state
      const initialState = {
        theme: screen.getByTestId('theme-indicator').textContent,
        appearance: screen.getByTestId('visual-appearance').textContent,
      }
      console.log('Initial client state:', initialState)

      // Wait for theme system to fully initialize
      await waitFor(() => {
        expect(screen.getByTestId('theme-indicator'))!.toHaveTextContent('Current Theme: dark')
      })

      const finalState = {
        theme: screen.getByTestId('theme-indicator').textContent,
        appearance: screen.getByTestId('visual-appearance').textContent,
      }
      console.log('Final state:', finalState)

      // Document the state change - this is the source of flicker
      console.log('State change detection: Initial -> Final')
    })

    it('handles light theme correctly', async () => {
      setupMockEnvironment('light')

      render(
        <TestThemeProvider>
          <PageComponent />
        </TestThemeProvider>,
      )

      await waitFor(() => {
        expect(screen.getByTestId('theme-indicator'))!.toHaveTextContent('Current Theme: light')
      })

      expect(screen.getByTestId('visual-appearance'))!.toHaveTextContent('Appearance: light')
    })

    it('handles system theme with dark preference', async () => {
      setupMockEnvironment('system', true) // system theme, dark preference

      render(
        <TestThemeProvider>
          <PageComponent />
        </TestThemeProvider>,
      )

      await waitFor(() => {
        expect(screen.getByTestId('theme-indicator'))!.toHaveTextContent('Current Theme: dark')
      })

      expect(screen.getByTestId('visual-appearance'))!.toHaveTextContent('Appearance: dark')
    })

    it('handles system theme with light preference', async () => {
      setupMockEnvironment('system', false) // system theme, light preference

      render(
        <TestThemeProvider>
          <PageComponent />
        </TestThemeProvider>,
      )

      await waitFor(() => {
        expect(screen.getByTestId('theme-indicator'))!.toHaveTextContent('Current Theme: light')
      })

      expect(screen.getByTestId('visual-appearance'))!.toHaveTextContent('Appearance: light')
    })

    it('handles no stored theme (defaults to system)', async () => {
      setupMockEnvironment(null, false) // no stored theme, system prefers light

      render(
        <TestThemeProvider>
          <PageComponent />
        </TestThemeProvider>,
      )

      await waitFor(() => {
        expect(screen.getByTestId('theme-indicator'))!.toHaveTextContent('Current Theme: light')
      })
    })

    it('measures timing window of style changes', async () => {
      setupMockEnvironment('dark')

      const timingData: Array<{ phase: string, timestamp: number, styles: any }> = []
      const TimingPageComponent = createTimingPageComponent(timingData)

      render(
        <TestThemeProvider>
          <TimingPageComponent />
        </TestThemeProvider>,
      )

      await waitFor(() => {
        expect(screen.getByTestId('timing-status'))!.toHaveTextContent('Phase: CSR')
      })

      // Analyze timing and style changes
      console.log('\n=== Style Change Timeline ===')
      timingData.forEach((data, index) => {
        console.log(`${index + 1}. ${data.phase}: bg=${data.styles.backgroundColor}, color=${data.styles.color}`)
      })

      // Check if there are style changes (this is visible flicker)
      const hasStyleChange = timingData.length > 1
        && timingData[0]!.styles.backgroundColor !== timingData[timingData.length - 1]!.styles.backgroundColor

      if (hasStyleChange)
        console.log('⚠️  Style changes detected - this causes visible flicker')
      else
        console.log('✅ No style changes detected')

      expect(timingData.length).toBeGreaterThan(1)
    })
  })

  describe('CSS Application Timing Tests', () => {
    it('checks CSS class changes causing flicker', async () => {
      setupMockEnvironment('dark')

      const cssStates: Array<{ className: string, timestamp: number }> = []
      const CSSTestComponent = createCSSTestComponent(cssStates)

      render(
        <TestThemeProvider>
          <CSSTestComponent />
        </TestThemeProvider>,
      )

      await waitFor(() => {
        expect(screen.getByTestId('css-classes'))!.toHaveTextContent('bg-gray-900 text-white')
      })

      console.log('\n=== CSS Class Change Detection ===')
      cssStates.forEach((state, index) => {
        console.log(`${index + 1}. ${state.className}`)
      })

      // Check if CSS classes have changed
      const hasCSSChange = cssStates.length > 1
        && cssStates[0]!.className !== cssStates[cssStates.length - 1]!.className

      if (hasCSSChange) {
        console.log('⚠️  CSS class changes detected - may cause style flicker')
        console.log(`From: "${cssStates[0]!.className}"`)
        console.log(`To: "${cssStates[cssStates.length - 1]!.className}"`)
      }

      expect(hasCSSChange).toBe(true) // We expect to see this change
    })
  })

  describe('Edge Cases and Error Handling', () => {
    it('handles localStorage access errors gracefully', async () => {
      setupMockEnvironment(null)

      const mockStorage = {
        getItem: vi.fn(() => {
          throw new Error('LocalStorage access denied')
        }),
        setItem: vi.fn(),
        removeItem: vi.fn(),
        clear: vi.fn(),
      }

      Object.defineProperty(window, 'localStorage', {
        value: mockStorage,
        configurable: true,
      })

      try {
        render(
          <TestThemeProvider>
            <PageComponent />
          </TestThemeProvider>,
        )

        // Should fallback gracefully without crashing
        await waitFor(() => {
          expect(screen.getByTestId('theme-indicator'))!.toBeInTheDocument()
        })

        // Should default to light theme when localStorage fails
        // Should default to light theme when localStorage fails
        expect(screen.getByTestId('visual-appearance'))!.toHaveTextContent('Appearance: light')
      }
      finally {
        Reflect.deleteProperty(window, 'localStorage')
      }
    })

    it('handles invalid theme values in localStorage', async () => {
      setupMockEnvironment('invalid-theme-value')

      render(
        <TestThemeProvider>
          <PageComponent />
        </TestThemeProvider>,
      )

      await waitFor(() => {
        expect(screen.getByTestId('theme-indicator'))!.toBeInTheDocument()
      })

      // Should handle invalid values gracefully
      const themeIndicator = screen.getByTestId('theme-indicator')
      expect(themeIndicator)!.toBeInTheDocument()
    })
  })

  describe('Performance and Regression Tests', () => {
    it('verifies ThemeProvider position fix reduces initialization delay', async () => {
      const performanceMarks: Array<{ event: string, timestamp: number }> = []

      setupMockEnvironment('dark')

      expect(window.localStorage.getItem('theme')).toBe('dark')

      const PerformanceTestComponent = createPerformanceTestComponent(performanceMarks)

      render(
        <TestThemeProvider>
          <PerformanceTestComponent />
        </TestThemeProvider>,
      )

      await waitFor(() => {
        expect(screen.getByTestId('performance-test'))!.toHaveTextContent('Theme: dark')
      })

      // Analyze performance timeline
      console.log('\n=== Performance Timeline ===')
      performanceMarks.forEach((mark) => {
        console.log(`${mark.event}: ${mark.timestamp.toFixed(2)}ms`)
      })

      expect(performanceMarks.length).toBeGreaterThan(3)
    })
  })

  describe('Solution Requirements Definition', () => {
    it('defines technical requirements to eliminate flicker', () => {
      const technicalRequirements = {
        ssrConsistency: 'SSR and CSR must render identical initial styles',
        synchronousDetection: 'Theme detection must complete synchronously before first render',
        noStyleChanges: 'No visible style changes should occur after hydration',
        performanceImpact: 'Solution should not significantly impact page load performance',
        browserCompatibility: 'Must work consistently across all major browsers',
      }

      console.log('\n=== Technical Requirements ===')
      Object.entries(technicalRequirements).forEach(([key, requirement]) => {
        console.log(`${key}: ${requirement}`)
        expect(requirement).toBeDefined()
      })

      // A successful solution should pass all these requirements
    })
  })
})
