// 季总集数账本(对照 MP __resolve_effective_total_episode / __resolve_total_episode_decrease /
// SubscribeEpisodesRefresh 只升注入):纯函数,来源值由调用方给。

export type EpisodeTotalSource = "tmdb" | "injected" | "manual" | "covered_floor" | "previous";

export interface EpisodeTotalInput {
  /** 账本里现有的总集数(null = 未知) */
  previous: number | null;
  /** 元数据(TMDB)本次给出的集数;0 / null = 未公布 */
  fresh?: number | null;
  /** 插件/Agent 注入值:只升不降 */
  injected?: number | null;
  /** 已存在(入库覆盖)的最高集号:回退时不得低于它 */
  coveredMax?: number | null;
  /** 人工锁定:锁定后元数据与注入都不再改写 */
  locked?: boolean;
}

export interface EpisodeTotalResult {
  total: number | null;
  /** 总集数是否已知(未知时追更不结束) */
  known: boolean;
  source: EpisodeTotalSource;
  changed: boolean;
  /** 元数据回退被已有最高集号兜住 */
  clampedByCovered: boolean;
}

const pos = (v: number | null | undefined): number | null =>
  typeof v === "number" && Number.isFinite(v) && v > 0 ? Math.floor(v) : null;

/**
 * 解析总集数:
 * - 锁定 → 保持现值;
 * - 元数据变大 → 采用(追更范围扩大);元数据变小 → 取 max(新值, 已存在最高集号)(防 TMDB 临时回退误完成);
 * - 注入值只升;元数据未公布(0/null)→ 保持现值,现值也没有 → 未知。
 */
export function resolveEpisodeTotal(input: EpisodeTotalInput): EpisodeTotalResult {
  const prev = pos(input.previous);
  const covered = pos(input.coveredMax);
  const keep = (source: EpisodeTotalSource = "previous"): EpisodeTotalResult => ({
    total: prev,
    known: prev !== null,
    source,
    changed: false,
    clampedByCovered: false,
  });
  if (input.locked) return keep("manual");
  const fresh = pos(input.fresh);
  const injected = pos(input.injected);
  let total = prev;
  let source: EpisodeTotalSource = "previous";
  let clamped = false;
  if (fresh !== null) {
    if (prev === null || fresh >= prev) {
      total = fresh;
      source = "tmdb";
    } else {
      const floor = Math.max(fresh, covered ?? 0);
      total = floor;
      source = floor === fresh ? "tmdb" : "covered_floor";
      clamped = floor !== fresh;
    }
  }
  if (injected !== null && (total === null || injected > total)) {
    total = injected;
    source = "injected";
    clamped = false;
  }
  if (total === null && covered !== null) {
    // 没有任何来源:已见过的最高集只说明"至少这么多",不当作已知总数
    return { total: null, known: false, source: "previous", changed: false, clampedByCovered: false };
  }
  return { total, known: total !== null, source, changed: total !== prev, clampedByCovered: clamped };
}