import { computed, ref, watch } from 'vue'

const STORAGE_KEY = 'voicehub:theme'
type ThemeName = string & {}

const currentTheme = ref<string | null>(null)
const initialized = ref(false)

function isBrowser() {
  return typeof window !== 'undefined' && typeof document !== 'undefined'
}

function getMetaThemeColor() {
  if (!isBrowser()) return null
  return document.querySelector<HTMLMetaElement>('meta[name="theme-color"]')
}

function applyTheme(theme: string) {
  if (!isBrowser()) return

  const root = document.documentElement
  const appRoot = document.querySelector<HTMLElement>('div.app')

  root.setAttribute('data-theme', theme)
  if (appRoot) appRoot.setAttribute('data-theme', theme)

  if (theme === 'dark') {
    root.classList.add('dark')
    root.classList.remove('light')
    root.style.colorScheme = 'dark'
  } else if (theme === 'light') {
    root.classList.add('light')
    root.classList.remove('dark')
    root.style.colorScheme = 'light'
  } else {
    root.classList.remove('dark', 'light')
    root.style.colorScheme = 'light dark'
  }

  const meta = getMetaThemeColor()
  if (meta) {
    if (theme === 'light') {
      meta.content = '#f8fafc'
    } else {
      meta.content = '#111111'
    }
  }

  try {
    localStorage.setItem(STORAGE_KEY, theme)
  } catch {
    /* ignore storage errors */
  }
}

function detectSystemTheme(): 'dark' | 'light' {
  if (!isBrowser()) return 'dark'
  const prefersDark = window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches
  return prefersDark ? 'dark' : 'light'
}

export function useTheme() {
  const config = useRuntimeConfig()

  const enabledThemes = computed<string[]>(() => {
    const list = (config.public?.enabledThemes as unknown) as string[] | undefined
    return Array.isArray(list) && list.length > 0 ? list : ['dark', 'light']
  })

  const defaultTheme = computed<string>(() => {
    const value = config.public?.defaultTheme as string | undefined
    if (value && enabledThemes.value.includes(value)) return value
    return enabledThemes.value.includes('dark') ? 'dark' : enabledThemes.value[0] || 'dark'
  })

  const theme = computed<string>({
    get: () => currentTheme.value ?? defaultTheme.value,
    set: (next: string) => setTheme(next)
  })

  const isDark = computed(() => {
    const t = theme.value
    if (t === 'dark') return true
    if (t === 'light') return false
    return detectSystemTheme() === 'dark'
  })

  function isThemeEnabled(name: string) {
    return enabledThemes.value.includes(name)
  }

  function setTheme(next: string, { persist = true } = {}) {
    let candidate = next
    if (!enabledThemes.value.includes(candidate)) {
      candidate = defaultTheme.value
    }

    if (currentTheme.value === candidate && initialized.value) return

    currentTheme.value = candidate
    applyTheme(candidate)

    if (!persist && isBrowser()) {
      try {
        localStorage.removeItem(STORAGE_KEY)
      } catch {
        /* ignore */
      }
    }
  }

  function toggleTheme() {
    const order = enabledThemes.value.length >= 2 ? enabledThemes.value : ['dark', 'light']
    const current = theme.value
    const idx = order.indexOf(current)
    const next = order[(idx + 1) % order.length]
    setTheme(next)
  }

  function resetToDefault() {
    setTheme(defaultTheme.value, { persist: false })
  }

  function init() {
    if (initialized.value || !isBrowser()) return
    initialized.value = true

    let stored: string | null = null
    try {
      stored = localStorage.getItem(STORAGE_KEY)
    } catch {
      stored = null
    }

    if (stored && enabledThemes.value.includes(stored)) {
      setTheme(stored)
      return
    }

    setTheme(defaultTheme.value, { persist: false })

    if (window.matchMedia) {
      const mql = window.matchMedia('(prefers-color-scheme: dark)')
      const onChange = () => {
        let s: string | null = null
        try {
          s = localStorage.getItem(STORAGE_KEY)
        } catch {
          s = null
        }
        if (!s) {
          setTheme(defaultTheme.value, { persist: false })
        }
      }
      if (typeof mql.addEventListener === 'function') {
        mql.addEventListener('change', onChange)
      } else if (typeof mql.addListener === 'function') {
        mql.addListener(onChange)
      }
    }
  }

  return {
    theme,
    currentTheme,
    defaultTheme,
    enabledThemes,
    isDark,
    isThemeEnabled,
    setTheme,
    toggleTheme,
    resetToDefault,
    init
  }
}