/** "每日新资源"拆成的三种模式(REQ §6.3) */
export type AcquisitionMode = "new_title" | "catch_up" | "upgrade";

export interface ModeInput {
  /** 本地实体;null = 库里没有这部作品 */
  entity: { tracked: boolean; kind: "movie" | "tv" } | null;
  /** 候选覆盖的 content_unit(剧集/综艺);电影留空 */
  releaseUnits: readonly string[];
  /** Slot 中已满足的 content_unit */
  satisfiedUnits: readonly string[];
  /** 电影:该 Slot 是否已满足 */
  slotSatisfied: boolean;
  /** 作品发行/首播日期 YYYY-MM-DD(不是站点上传日期) */
  firstReleaseDate?: string;
  /** 当前时间(ISO),由调用方注入 */
  now: string;
  /** 新作品窗口(天) */
  newTitleWindowDays: number;
  /** evaluateCandidate 对当前资产给出了 upgrade */
  upgradeCandidate?: boolean;
}

export type ModeDecision = { mode: AcquisitionMode; reason: string } | { mode: null; reason: string };

const DAY_MS = 86_400_000;

/**
 * 判定一条候选属于哪种收录模式。
 * - 库里没有:只有发行/首播在窗口内才是新作品;站点今天上传旧片不算新片
 * - 已有剧集:候选覆盖未满足的单元 → 追更补缺;都已满足且可升级 → 升级
 * - 已有电影:Slot 缺口或更优版本 → 升级(独立于上映日期)
 * - 只登记(未追踪)的作品不因新规则隐式变成自动下载
 */
export function determineMode(input: ModeInput): ModeDecision {
  const { entity } = input;
  if (!entity) {
    if (!input.firstReleaseDate) return { mode: null, reason: "release_date_unknown" };
    const released = Date.parse(`${input.firstReleaseDate}T00:00:00Z`);
    const now = Date.parse(input.now);
    if (Number.isNaN(released) || Number.isNaN(now)) return { mode: null, reason: "release_date_unknown" };
    const ageDays = (now - released) / DAY_MS;
    if (ageDays < -1) return { mode: null, reason: "not_yet_released" };
    if (ageDays <= input.newTitleWindowDays) return { mode: "new_title", reason: "released_within_window" };
    return { mode: null, reason: "not_new_release" };
  }
  if (!entity.tracked) return { mode: null, reason: "not_tracked" };
  if (entity.kind === "tv") {
    const satisfied = new Set(input.satisfiedUnits);
    const gaps = input.releaseUnits.filter((u) => !satisfied.has(u));
    if (gaps.length > 0) return { mode: "catch_up", reason: `covers_missing_units:${gaps.length}` };
    if (input.releaseUnits.length === 0) return { mode: null, reason: "no_units_resolved" };
    return input.upgradeCandidate
      ? { mode: "upgrade", reason: "better_version" }
      : { mode: null, reason: "already_satisfied" };
  }
  if (!input.slotSatisfied) return { mode: "upgrade", reason: "slot_gap" };
  return input.upgradeCandidate
    ? { mode: "upgrade", reason: "better_version" }
    : { mode: null, reason: "already_satisfied" };
}