type GenerationKind = "image" | "video";

interface GenerationSlot {
  id: string;
  userKey: string;
  kind: GenerationKind;
  createdAt: number;
}

const DEFAULT_MAX_ACTIVE_GENERATION_TASKS = 3;
const STALE_SLOT_MS = 6 * 60 * 60 * 1000;
const activeSlots = new Map<string, GenerationSlot>();

let userMaxConcurrency: number | null = null;

export function setUserMaxConcurrency(limit: number | null | undefined): void {
  userMaxConcurrency = typeof limit === "number" && limit > 0 ? limit : null;
}

function getEffectiveLimit(): number {
  return userMaxConcurrency ?? DEFAULT_MAX_ACTIVE_GENERATION_TASKS;
}

export function getGenerationUserKey(userId?: string | number | null): string {
  return userId === undefined || userId === null || userId === "" ? "anonymous" : String(userId);
}

function pruneStaleSlots(now = Date.now()): void {
  activeSlots.forEach((slot, id) => {
    if (now - slot.createdAt > STALE_SLOT_MS) {
      activeSlots.delete(id);
    }
  });
}

export function getActiveGenerationTaskCount(userKey: string): number {
  pruneStaleSlots();
  let count = 0;
  activeSlots.forEach((slot) => {
    if (slot.userKey === userKey) count += 1;
  });
  return count;
}

export function claimGenerationSlot(input: {
  userKey: string;
  kind: GenerationKind;
  id?: string;
}): () => void {
  pruneStaleSlots();
  const activeCount = getActiveGenerationTaskCount(input.userKey);
  const effectiveLimit = getEffectiveLimit();
  if (activeCount >= effectiveLimit) {
    throw new Error(`当前账号同时最多生成 ${effectiveLimit} 个图片/视频任务，请等待已有任务完成后再提交。`);
  }

  const id = input.id || `generation-slot-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
  activeSlots.set(id, {
    id,
    userKey: input.userKey,
    kind: input.kind,
    createdAt: Date.now(),
  });

  return () => {
    activeSlots.delete(id);
  };
}

export function releaseGenerationSlot(id: string | undefined | null): void {
  if (!id) return;
  activeSlots.delete(id);
}