first commit

src/core/theme.ts

@@ -0,0 +1,56 @@
+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)
+}