export interface AcquisitionBudget {
  maxNewTitlesPerDay?: number;
  maxBytesPerDay?: number;
  maxConcurrent?: number;
}

export interface BudgetUsage {
  newTitlesToday: number;
  bytesToday: number;
  /** 已预留但尚未计入 bytesToday 的计划字节 */
  reservedBytesToday?: number;
  activeDownloads: number;
}

export interface BudgetRequest {
  countsAsNewTitle: boolean;
  bytes?: number;
}

export interface BudgetViolation {
  kind: "new_titles" | "bytes" | "concurrency";
  limit: number;
  current: number;
  requested: number;
}

export interface BudgetDecision {
  decision: "allow" | "deny" | "unknown";
  violations: BudgetViolation[];
  /** 有字节预算但候选体积未知 */
  unknown: "bytes"[];
}

/** 预算检查(每日新增作品数、下载字节、并发)。已知超限 → deny;体积未知 → unknown(不放行) */
export function checkBudget(budget: AcquisitionBudget, usage: BudgetUsage, req: BudgetRequest): BudgetDecision {
  const violations: BudgetViolation[] = [];
  const unknown: "bytes"[] = [];
  if (
    req.countsAsNewTitle &&
    budget.maxNewTitlesPerDay !== undefined &&
    usage.newTitlesToday + 1 > budget.maxNewTitlesPerDay
  )
    violations.push({
      kind: "new_titles",
      limit: budget.maxNewTitlesPerDay,
      current: usage.newTitlesToday,
      requested: 1,
    });
  if (budget.maxBytesPerDay !== undefined) {
    const current = usage.bytesToday + (usage.reservedBytesToday ?? 0);
    if (req.bytes === undefined) unknown.push("bytes");
    else if (current + req.bytes > budget.maxBytesPerDay)
      violations.push({ kind: "bytes", limit: budget.maxBytesPerDay, current, requested: req.bytes });
  }
  if (budget.maxConcurrent !== undefined && usage.activeDownloads + 1 > budget.maxConcurrent)
    violations.push({ kind: "concurrency", limit: budget.maxConcurrent, current: usage.activeDownloads, requested: 1 });
  const decision = violations.length > 0 ? "deny" : unknown.length > 0 ? "unknown" : "allow";
  return { decision, violations, unknown };
}