type CanvasCapabilityQueueState = {
  tails: Map<string, Promise<unknown>>;
};

declare global {
  var __canvasCapabilityQueueState: CanvasCapabilityQueueState | undefined;
}

function getQueueState() {
  if (!globalThis.__canvasCapabilityQueueState) {
    globalThis.__canvasCapabilityQueueState = { tails: new Map() };
  }
  return globalThis.__canvasCapabilityQueueState;
}

export async function enqueueCanvasCapabilityExecution<T>(params: {
  projectId: string;
  execute: () => Promise<T>;
}): Promise<T> {
  const state = getQueueState();
  const previous = state.tails.get(params.projectId) || Promise.resolve();
  const execution = previous.catch(() => undefined).then(params.execute);
  const settledExecution = execution.then(
    () => undefined,
    () => undefined
  );
  const tail = settledExecution.finally(() => {
    if (state.tails.get(params.projectId) === tail) {
      state.tails.delete(params.projectId);
    }
  });
  state.tails.set(params.projectId, tail);
  return execution;
}

export function getCanvasCapabilityQueueDepth(projectId: string) {
  return getQueueState().tails.has(projectId) ? 1 : 0;
}