import { ref, watchEffect, onMounted } from 'vue'

const STORAGE_KEY = 'lemonboss-theme'

// 'light' | 'dark' | 'auto'
const themeMode = ref(localStorage.getItem(STORAGE_KEY) || 'auto')
const resolvedTheme = ref('dark')

function getSystemTheme() {
  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
}

function applyTheme(theme) {
  resolvedTheme.value = theme
  document.documentElement.setAttribute('data-theme', theme)
}

function resolve() {
  const theme = themeMode.value === 'auto' ? getSystemTheme() : themeMode.value
  applyTheme(theme)
}

export function useTheme() {
  onMounted(() => {
    resolve()
    // Listen for system theme changes
    window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
      if (themeMode.value === 'auto') resolve()
    })
  })

  watchEffect(() => {
    localStorage.setItem(STORAGE_KEY, themeMode.value)
    resolve()
  })

  function setTheme(mode) {
    themeMode.value = mode
  }

  function cycleTheme() {
    const modes = ['light', 'dark', 'auto']
    const idx = modes.indexOf(themeMode.value)
    themeMode.value = modes[(idx + 1) % modes.length]
  }

  return { themeMode, resolvedTheme, setTheme, cycleTheme }
}