export type Theme = 'dark' | 'light'

const STORAGE_KEY = 'viewer.theme'
const listeners = new Set<(theme: Theme) => void>()

export function initTheme(): Theme {
  const isAndroidShell =
    typeof (window as unknown as { AndroidViewer?: unknown }).AndroidViewer !== 'undefined'
  let theme: Theme = 'dark'
  try {
    const stored = localStorage.getItem(STORAGE_KEY)
    if (stored === 'light' || stored === 'dark') {
      theme = stored
    } else if (!isAndroidShell && window.matchMedia?.('(prefers-color-scheme: light)').matches) {
      theme = 'light'
    }
  } catch {
    /* ignore */
  }
  applyTheme(theme, false)
  return theme
}

export function getTheme(): Theme {
  return document.documentElement.dataset.theme === 'light' ? 'light' : 'dark'
}

export function setTheme(theme: Theme): void {
  applyTheme(theme, true)
}

export function toggleTheme(): Theme {
  const next: Theme = getTheme() === 'dark' ? 'light' : 'dark'
  setTheme(next)
  return next
}

function applyTheme(theme: Theme, persist: boolean): void {
  document.documentElement.dataset.theme = theme
  document.documentElement.style.colorScheme = theme
  const meta = document.querySelector('meta[name="theme-color"]')
  if (meta) meta.setAttribute('content', theme === 'dark' ? '#0b0e14' : '#f2f5fa')
  if (persist) {
    try {
      localStorage.setItem(STORAGE_KEY, theme)
    } catch {
      /* ignore */
    }
  }
  for (const listener of listeners) listener(theme)
}

export function onThemeChange(listener: (theme: Theme) => void): () => void {
  listeners.add(listener)
  return () => listeners.delete(listener)
}