type CodexFastStateListener = () => void;

interface CodexFastState {
  enabled: boolean;
  listeners: Set<CodexFastStateListener>;
}

declare global {
  var __killerosCodexFastState: unknown;
}

// Accepts process-global state only when it is safe to reuse across extension versions.
function isCodexFastState(value: unknown): value is CodexFastState {
  return typeof value === "object" && value !== null
    && "enabled" in value && typeof value.enabled === "boolean"
    && "listeners" in value && value.listeners instanceof Set
    && [...value.listeners].every((listener) => typeof listener === "function");
}

const savedState = globalThis.__killerosCodexFastState;
const state: CodexFastState = isCodexFastState(savedState) ? savedState : {
  enabled: typeof savedState === "object" && savedState !== null
    && "enabled" in savedState && savedState.enabled === true,
  listeners: new Set<CodexFastStateListener>(),
};
globalThis.__killerosCodexFastState = state;

export function isCodexFastEnabled(): boolean {
  return state.enabled;
}

export function toggleCodexFast(): boolean {
  state.enabled = !state.enabled;
  for (const listener of [...state.listeners]) listener();
  return state.enabled;
}

export function subscribeCodexFast(listener: CodexFastStateListener): () => void {
  state.listeners.add(listener);
  return () => state.listeners.delete(listener);
}

/** Test-only reset for the process-global state between isolated harnesses. */
export function resetCodexFastState(): void {
  state.enabled = false;
  state.listeners.clear();
}