ThemeController

export class ThemeController {
  readonly #capabilities: TerminalCapabilities;
  readonly #observers = new Set<() => void>();
  #theme: Theme;

  constructor(theme: Theme, capabilities: TerminalCapabilities) {
    this.#capabilities = capabilities;
    this.#theme = normalizeTheme(theme, capabilities);
  }

  get(): Theme {
    return this.#theme;
  }

  set(theme: Theme | ThemeFactory): Theme {
    const selected = typeof theme === "function" ? theme(this.#theme) : theme;
    const next = normalizeTheme(selected, this.#capabilities);
    if (next === this.#theme) return next;
    this.#theme = next;
    for (const observer of this.#observers) observer();
    return next;
  }

  observe(observer: () => void): () => void {
    this.#observers.add(observer);
    return () => this.#observers.delete(observer);
  }
}