// The signed-in admin's UI preferences: the theme (system, light or dark)
// and the admin language. The server keeps them per admin (GET /auth/me
// preferences, PUT /account/preferences); the last choices are also cached in
// localStorage under THEME_KEY and LOCALE_KEY, so boot applies the theme
// before the first await (the shell never renders in the wrong theme) and
// loads the strings in the chosen language. Only the codes are stored;
// tokens and record data never are (T-261016-0fm-08).
import { readonly, ref } from 'vue'
import { api } from '../api/client'
import type { AdminProfile } from '../api/types'
import { currentLocale, loadStrings, t } from '../app/i18n'
import { applyColorScheme, isThemeChoice, THEME_CHOICES, type ThemeChoice } from '../app/theme'
import { showToast } from './useToasts'

export const THEME_KEY = 'summer-admin.theme'
export const LOCALE_KEY = 'summer-admin.locale'

/** A short locale code: letters with an optional region, e.g. pl or pt-BR. */
const LOCALE_SHAPE = /^[A-Za-z]{2,8}(?:[-_][A-Za-z0-9]{1,8})?$/

const theme = ref<ThemeChoice>('system')
let stopTheme: () => void = () => undefined

/** The theme currently applied. */
export const themeChoice = readonly(theme)

const localePref = ref('')

/** The admin language the server stores; "" follows the request locale. */
export const localePreference = readonly(localePref)

function storage(): Storage | null {
  try {
    return typeof window === 'undefined' ? null : window.localStorage
  } catch {
    return null
  }
}

function cache(key: string, value: string | null): void {
  try {
    if (value === null) {
      storage()?.removeItem(key)
    } else {
      storage()?.setItem(key, value)
    }
  } catch {
    // Storage may be full or disabled; the choice still holds for the session.
  }
}

/** Caches a theme; system, the default, is stored as an absent key. */
function cacheTheme(choice: ThemeChoice): void {
  cache(THEME_KEY, choice === 'system' ? null : choice)
}

/** The cached theme when it is a valid choice, else system. */
export function cachedTheme(): ThemeChoice {
  try {
    const value = storage()?.getItem(THEME_KEY)
    return isThemeChoice(value) ? value : 'system'
  } catch {
    return 'system'
  }
}

/** The cached admin language when it is a locale-shaped code, else "". */
export function cachedLocale(): string {
  try {
    const value = storage()?.getItem(LOCALE_KEY) ?? ''
    return value.length <= 16 && LOCALE_SHAPE.test(value) ? value : ''
  } catch {
    return ''
  }
}

/** Page reload indirection, so tests can stub it. */
export const page = {
  reload(): void {
    window.location.reload()
  },
}

/** Applies a theme, replacing the previous one's media subscription. */
export function applyTheme(choice: ThemeChoice): void {
  stopTheme()
  theme.value = choice
  stopTheme = typeof window === 'undefined' ? () => undefined : applyColorScheme(window, choice)
}

/** The choice after current in the rail button's cycle. */
export function nextTheme(current: ThemeChoice): ThemeChoice {
  const index = THEME_CHOICES.indexOf(current)
  return THEME_CHOICES[(index + 1) % THEME_CHOICES.length] ?? 'system'
}

/**
 * Applies and caches a theme at once and saves it on the server. When the
 * save fails the previous theme comes back and a danger toast says so.
 */
export async function setTheme(choice: ThemeChoice): Promise<void> {
  const previous = theme.value
  applyTheme(choice)
  cacheTheme(choice)
  let ok = false
  try {
    const { response } = await api.PUT('/account/preferences', { body: { theme: choice } })
    ok = response.ok
  } catch {
    ok = false
  }
  if (ok) {
    return
  }
  // A later click owns the theme now; only this request's choice is undone.
  if (theme.value === choice) {
    applyTheme(previous)
    cacheTheme(previous)
  }
  showToast(t('backend::lang.myaccount.preferences_failed'), 'danger')
}

/** Moves to the next theme: system, light, dark, system. */
export function cycleTheme(): Promise<void> {
  return setTheme(nextTheme(theme.value))
}

/**
 * Applies the preferences of a freshly loaded profile (boot and sign-in), so
 * a second browser of the same admin shows the same theme.
 */
export async function applyProfilePreferences(profile: AdminProfile | null): Promise<void> {
  const prefs = (profile as { preferences?: Partial<AdminProfile['preferences']> } | null)?.preferences
  if (!prefs) {
    return
  }
  if (isThemeChoice(prefs.theme)) {
    if (prefs.theme !== theme.value) {
      applyTheme(prefs.theme)
    }
    cacheTheme(prefs.theme)
  }
  if (typeof prefs.locale === 'string') {
    localePref.value = prefs.locale
    if (prefs.locale !== '' && prefs.locale !== currentLocale.value) {
      await loadStrings(prefs.locale).catch(() => undefined)
    }
    cache(LOCALE_KEY, prefs.locale === '' ? null : prefs.locale)
  }
}

/**
 * Saves the admin language and reloads the page, so strings, navigation,
 * settings, schemas and field types all come back in it at once (a form
 * with unsaved changes asks first through its beforeunload prompt). The
 * current preference does nothing; a failed save shows a danger toast.
 */
export async function setLocale(code: string): Promise<void> {
  if (code === localePref.value) {
    return
  }
  let ok = false
  try {
    const { response } = await api.PUT('/account/preferences', { body: { locale: code } })
    ok = response.ok
  } catch {
    ok = false
  }
  if (!ok) {
    showToast(t('backend::lang.myaccount.preferences_failed'), 'danger')
    return
  }
  localePref.value = code
  cache(LOCALE_KEY, code === '' ? null : code)
  page.reload()
}

export function usePreferences() {
  return {
    theme: themeChoice,
    locale: localePreference,
    setTheme,
    cycleTheme,
    setLocale,
  }
}