import { useCallback, useEffect, useState } from 'react'
import {
  activateProfile,
  createProfile,
  deleteProfile,
  fetchProfiles,
  fetchSettings,
  fetchThemes,
  themeCssUrl,
  updateSettings,
  type ProfileSummary,
  type Settings,
  type Theme,
} from './api'

// `data-*` marker for the single injected `<link>` for the active theme's stylesheet.
const INJECTED_THEME_ATTR = 'data-ottyl-theme-css'

// `"system"` isn't an embedded theme file — it resolves to one of these two at apply time, based
// on the OS light/dark preference.
const SYSTEM_LIGHT_THEME = 'light'
const SYSTEM_DARK_THEME = 'dark'

function resolveTheme(theme: Theme): string {
  if (theme !== 'system') return theme
  const prefersDark = window.matchMedia?.('(prefers-color-scheme: dark)').matches ?? true
  return prefersDark ? SYSTEM_DARK_THEME : SYSTEM_LIGHT_THEME
}

// Injects a `<link>` for the resolved theme's stylesheet, replacing any previously-injected one.
// `webapp/src/index.css`'s `:root` block is the only styling until this loads, so there's no
// flash of unstyled content on first paint.
function applyTheme(theme: Theme) {
  const resolved = resolveTheme(theme)
  document.querySelectorAll(`link[${INJECTED_THEME_ATTR}]`).forEach((el) => el.remove())
  const link = document.createElement('link')
  link.rel = 'stylesheet'
  link.href = themeCssUrl(resolved)
  link.setAttribute(INJECTED_THEME_ATTR, resolved)
  document.head.appendChild(link)
}

// Owns fetching + mutating settings/theme/profile state for the NavMenu panels, and applies the
// selected theme to the document as a side effect so changes are visible immediately, with no reload.
export function useSettingsPanel() {
  const [settings, setSettings] = useState<Settings | null>(null)
  const [themes, setThemes] = useState<string[]>([])
  const [profiles, setProfiles] = useState<ProfileSummary[]>([])
  const [error, setError] = useState<string | null>(null)

  const refreshSettings = useCallback(async () => {
    const next = await fetchSettings()
    setSettings(next)
    return next
  }, [])

  const refreshThemes = useCallback(async () => {
    const next = await fetchThemes()
    setThemes(next)
    return next
  }, [])

  const refreshProfiles = useCallback(async () => {
    const next = await fetchProfiles()
    setProfiles(next)
    return next
  }, [])

  useEffect(() => {
    refreshSettings().catch(() => {})
    refreshThemes().catch(() => {})
    refreshProfiles().catch(() => {})
  }, [refreshSettings, refreshThemes, refreshProfiles])

  useEffect(() => {
    if (!settings) return
    applyTheme(settings.theme)
    if (settings.theme !== 'system') return
    // Re-resolve if the OS preference changes while "system" is selected.
    const media = window.matchMedia?.('(prefers-color-scheme: dark)')
    const onChange = () => applyTheme(settings.theme)
    media?.addEventListener('change', onChange)
    return () => media?.removeEventListener('change', onChange)
  }, [settings])

  const guarded = useCallback((action: () => Promise<void>) => {
    return async () => {
      try {
        setError(null)
        await action()
      } catch (err) {
        setError(err instanceof Error ? err.message : String(err))
      }
    }
  }, [])

  const setTheme = useCallback(
    (theme: Theme) =>
      guarded(async () => {
        const next = await updateSettings({ theme })
        setSettings(next)
      })(),
    [guarded],
  )

  const setMaxLogs = useCallback(
    (maxLogs: number | null) =>
      guarded(async () => {
        const next = await updateSettings({ maxLogs })
        setSettings(next)
      })(),
    [guarded],
  )

  const setNtfySink = useCallback(
    (ntfyTopic: string | null, ntfyServer: string | null) =>
      guarded(async () => {
        const next = await updateSettings({ ntfyTopic, ntfyServer })
        setSettings(next)
      })(),
    [guarded],
  )

  const addProfile = useCallback(
    (name: string) =>
      guarded(async () => {
        await createProfile(name)
        await refreshProfiles()
      })(),
    [guarded, refreshProfiles],
  )

  const removeProfile = useCallback(
    (name: string) =>
      guarded(async () => {
        await deleteProfile(name)
        await Promise.all([refreshProfiles(), refreshSettings()])
      })(),
    [guarded, refreshProfiles, refreshSettings],
  )

  const switchProfile = useCallback(
    (name: string) =>
      guarded(async () => {
        const next = await activateProfile(name)
        setSettings(next)
      })(),
    [guarded],
  )

  return {
    settings,
    themes,
    profiles,
    error,
    setTheme,
    setMaxLogs,
    setNtfySink,
    addProfile,
    removeProfile,
    switchProfile,
  }
}