/** Policy shared by web and native players; queue ownership stays with the adapter. */
export const EARLY_SKIP_MS = 30_000;
export const WAVE_REFILL_AT = 2;
export type WaveOutcome = 'complete' | 'skip' | 'skip_early' | 'like' | 'dislike';
export interface WaveInfo {
  sessionId: string;
  activity: string | null;
  mood: string | null;
  fallback: boolean;
}
export interface WaveFeedback { track_id: string; outcome: WaveOutcome }
export interface WaveGateway<T> {
  next(sessionId: string, feedback: WaveFeedback[]): Promise<T>;
}

export class WaveCoordinator<T> {
  private sessionId: string | null = null;
  private generation = 0;
  private pending: WaveFeedback[] = [];
  private loading: number | null = null;

  constructor(private readonly gateway: WaveGateway<T>) {}

  get version() { return this.generation; }
  isCurrent(version: number) { return version === this.generation; }

  /** Also invalidates in-flight responses when the context changes within a session. */
  activate(sessionId: string | null) {
    this.sessionId = sessionId;
    this.pending = [];
    this.loading = null;
    return ++this.generation;
  }

  changeContext(sessionId: string) {
    const pending = this.sessionId === sessionId ? this.pending : [];
    const version = this.activate(sessionId);
    this.pending = pending;
    return version;
  }

  note(trackId: string, outcome: WaveOutcome) {
    if (this.sessionId) this.pending.push({ track_id: trackId, outcome });
  }

  async refill(remaining: number, refresh: boolean, apply: (result: T, current: () => boolean) => void | Promise<void>) {
    const id = this.sessionId;
    const version = this.generation;
    if (!id || this.loading === version || (!refresh && remaining > WAVE_REFILL_AT)) return;
    this.loading = version;
    const feedback = this.pending;
    this.pending = [];
    try {
      const result = await this.gateway.next(id, feedback);
      if (this.isCurrent(version)) await apply(result, () => this.isCurrent(version));
    } catch {
      if (this.isCurrent(version)) this.pending = [...feedback, ...this.pending];
    } finally {
      if (this.loading === version) this.loading = null;
    }
  }
}