watchparty/server/src/services/StaticPartyService.ts

'use strict';

import crypto from 'crypto';
import { Logger } from '../Logger';
import { StaticPartyStore } from './StaticPartyStore';
import type {
  PersistedStaticParty,
  QueueItem,
  StaticParty,
  StaticPartyDetailDto,
  StaticPartyLink,
  StaticPartyMember,
  StaticPartySummaryDto
} from '../types';

/** A connected participant, as reported by a live session. */
export interface Participant {
  userId: string;
  userName: string;
}

/**
 * Which of `items` the viewer has missed, in the items' own order: every
 * item the group already completed, minus what the viewer watched in-app
 * (`watchedItemIds`) and minus what Emby itself already has as Played for
 * them (`embyPlayedIds` - watched outside this app, or before this party
 * existed). Pure - the one rule this whole feature is about, tested on
 * its own (see staticPartyService.test.ts).
 */
export function computeMissedIds(
  items: QueueItem[],
  completedItemIds: string[],
  watchedItemIds: string[],
  embyPlayedIds: ReadonlySet<string>
): string[] {
  const completed = new Set(completedItemIds);
  const watched = new Set(watchedItemIds);
  return items
    .map((i) => i.itemId)
    .filter((id) => completed.has(id) && !watched.has(id) && !embyPlayedIds.has(id));
}

/**
 * Merges a freshly fetched item list into a static party's existing one:
 * keeps the existing order and every existing item (even one since
 * removed from the source - the group's history shouldn't lose it),
 * refreshes names/images, and appends anything new (a new episode, a
 * playlist addition) at the end in the source's own order. Returns the
 * merged list and how many items were added. Pure.
 */
export function mergeItemLists(existing: QueueItem[], fresh: QueueItem[]): { items: QueueItem[]; added: number } {
  const freshById = new Map(fresh.map((i) => [i.itemId, i]));
  const known = new Set(existing.map((i) => i.itemId));
  const items = existing.map((i) => freshById.get(i.itemId) ?? i);
  const additions = fresh.filter((i) => !known.has(i.itemId));
  return { items: items.concat(additions), added: additions.length };
}

/**
 * Static (persistent) watch parties - a whole series or video playlist a
 * group watches together over several sessions. Remembers the group's own
 * progress (which items it completed, where it stopped) and each member's
 * own (which items they watched), so someone coming back or joining late
 * sees exactly what they missed. See spec/static-watch-party.md.
 *
 * A static party never plays anything itself: each session is an
 * ordinary live Party (PartyService), created by index.ts and linked back
 * here through `party.staticLink` - so the player, sync, shared stream,
 * lobby and host handoff are all reused as-is. This service never imports
 * PartyService (PartyService calls into this one), keeping the dependency
 * one-way.
 *
 * Persisted through StaticPartyStore after every change - one file per
 * party, so only the party that changed is ever rewritten.
 */
class StaticPartyServiceClass {
  /** Every static party, by id. */
  private partiesById = new Map<string, StaticParty>();

  /** Loads every persisted party - once, at startup. */
  public init(): void {
    this.partiesById.clear();
    for (const persisted of StaticPartyStore.load()) {
      this.partiesById.set(persisted.id, { ...persisted, livePartyId: null });
    }
  }

  /** Every static party, most recently active first. */
  public list(): StaticParty[] {
    return Array.from(this.partiesById.values()).sort((a, b) => this.lastActivity(b) - this.lastActivity(a));
  }

  /** One static party, or null. */
  public getById(id: string): StaticParty | null {
    return this.partiesById.get(id) || null;
  }

  /** Creates a static party over `items` - the creator is its first member. */
  public create(
    creator: Participant,
    source: StaticParty['source'],
    name: string,
    imageUrl: string,
    items: QueueItem[]
  ): StaticParty {
    const now = Date.now();
    const sp: StaticParty = {
      id: crypto.randomUUID(),
      name,
      source,
      imageUrl,
      createdByUserId: creator.userId,
      createdUtc: now,
      items,
      group: { nextIndex: 0, resumePositionTicks: 0, completedItemIds: [], lastSessionUtc: null },
      members: {},
      livePartyId: null
    };
    sp.members[creator.userId] = this.newMember(creator);
    this.partiesById.set(sp.id, sp);
    Logger.staticParty(`created id=${sp.id} name="${name}" source=${source.type}:${source.sourceId} items=${items.length} by=${Logger.who(creator.userId, creator.userName)}`);
    this.persist(sp);
    return sp;
  }

  /** Adds `who` as a member - idempotent (refreshes their name only). */
  public join(sp: StaticParty, who: Participant): StaticPartyMember {
    const existing = sp.members[who.userId];
    if (existing) {
      existing.userName = who.userName;
      existing.lastSeenUtc = Date.now();
      this.persist(sp);
      return existing;
    }
    const member = this.newMember(who);
    sp.members[who.userId] = member;
    Logger.staticParty(`joined id=${sp.id} user=${Logger.who(who.userId, who.userName)} members=${Object.keys(sp.members).length}`);
    this.persist(sp);
    return member;
  }

  /** Removes a member - and their progress. The party itself stays, even
   *  empty: only its creator deletes it (see delete()). */
  public leave(sp: StaticParty, userId: string): void {
    const member = sp.members[userId];
    if (!member) return;
    delete sp.members[userId];
    Logger.staticParty(`left id=${sp.id} user=${Logger.who(userId, member.userName)} members=${Object.keys(sp.members).length}`);
    this.persist(sp);
  }

  /** Deletes the party for good - creator only. Returns false (and does
   *  nothing) for anyone else. */
  public delete(sp: StaticParty, userId: string): boolean {
    if (sp.createdByUserId !== userId) {
      Logger.staticParty(`delete refused id=${sp.id} user=${userId} (not the creator)`);
      return false;
    }
    this.partiesById.delete(sp.id);
    Logger.staticParty(`deleted id=${sp.id} name="${sp.name}"`);
    StaticPartyStore.remove(sp.id);
    return true;
  }

  /** Merges a fresh fetch of the source into `sp.items` (see
   *  mergeItemLists) - new episodes/playlist entries appear at the end. */
  public refreshItems(sp: StaticParty, fresh: QueueItem[]): void {
    if (!fresh.length) return;
    const { items, added } = mergeItemLists(sp.items, fresh);
    const changed = added > 0 || items.some((item, i) => item !== sp.items[i]);
    sp.items = items;
    if (added) Logger.staticParty(`refreshed id=${sp.id} +${added} new item(s), total=${items.length}`);
    if (changed) this.persist(sp);
  }

  /** What the group's next session plays: everything from the group's
   *  next item on. Empty once the group has seen everything. */
  public groupQueue(sp: StaticParty): QueueItem[] {
    return sp.items.slice(sp.group.nextIndex);
  }

  /** Records which live party is the group's current session (or none). */
  public setLiveParty(sp: StaticParty, partyId: string | null): void {
    sp.livePartyId = partyId;
    if (partyId) {
      sp.group.lastSessionUtc = Date.now();
      Logger.staticParty(`session started id=${sp.id} partyId=${partyId} at item ${sp.group.nextIndex + 1}/${sp.items.length}`);
      this.persist(sp);
    }
  }

  /**
   * A linked live session finished `itemId` (played to its end, or the
   * host moved past it - the same heuristic as PlaystateService.markPlayed).
   * Every connected participant gets it as watched (and becomes a member
   * if they joined the live session without joining the static party
   * first). In `group` mode the group itself also moves past it; in
   * `catchUp` mode only those participants' own progress changes.
   */
  public onItemCompleted(link: StaticPartyLink, itemId: string, connected: Participant[]): void {
    const sp = this.partiesById.get(link.staticPartyId);
    if (!sp) return; // deleted while a session was still running
    for (const who of connected) {
      const member = sp.members[who.userId] ?? (sp.members[who.userId] = this.newMember(who));
      member.lastSeenUtc = Date.now();
      if (!member.watchedItemIds.includes(itemId)) member.watchedItemIds.push(itemId);
    }
    if (link.mode === 'group') {
      if (!sp.group.completedItemIds.includes(itemId)) sp.group.completedItemIds.push(itemId);
      const index = sp.items.findIndex((i) => i.itemId === itemId);
      if (index >= 0 && index + 1 > sp.group.nextIndex) sp.group.nextIndex = index + 1;
      sp.group.resumePositionTicks = 0;
    }
    Logger.staticParty(`item completed id=${sp.id} mode=${link.mode} item=${itemId} by=[${connected.map((c) => c.userName).join(', ')}] group=${sp.group.completedItemIds.length}/${sp.items.length}`);
    this.persist(sp);
  }

  /** The group session's current position - saved so the next session
   *  resumes there. Ignored for anything but the group's next item. */
  public recordPosition(link: StaticPartyLink, itemId: string, positionTicks: number): void {
    if (link.mode !== 'group') return;
    const sp = this.partiesById.get(link.staticPartyId);
    if (!sp || sp.items[sp.group.nextIndex]?.itemId !== itemId) return;
    if (sp.group.resumePositionTicks === positionTicks) return;
    sp.group.resumePositionTicks = positionTicks;
    this.persist(sp);
  }

  /** A linked live party ended - forget it as the group's live session. */
  public onPartyDestroyed(link: StaticPartyLink, partyId: string): void {
    const sp = this.partiesById.get(link.staticPartyId);
    if (!sp || sp.livePartyId !== partyId) return;
    sp.livePartyId = null;
    Logger.staticParty(`session ended id=${sp.id} partyId=${partyId} resumeAt=item ${sp.group.nextIndex + 1} ${Math.round(sp.group.resumePositionTicks / 10000000)}s`);
    this.persist(sp);
  }

  /** "Marquer comme vu" - `who` becomes a member if they weren't yet. */
  public markWatched(sp: StaticParty, who: Participant, itemId: string): boolean {
    if (!sp.items.some((i) => i.itemId === itemId)) return false;
    const member = sp.members[who.userId] ?? (sp.members[who.userId] = this.newMember(who));
    if (!member.watchedItemIds.includes(itemId)) member.watchedItemIds.push(itemId);
    member.lastSeenUtc = Date.now();
    Logger.staticParty(`marked watched id=${sp.id} user=${Logger.who(who.userId, who.userName)} item=${itemId}`);
    this.persist(sp);
    return true;
  }

  /** `viewerUserId`'s missed items - see computeMissedIds. */
  public missedIds(sp: StaticParty, viewerUserId: string, embyPlayedIds: ReadonlySet<string>): string[] {
    const watched = sp.members[viewerUserId]?.watchedItemIds ?? [];
    return computeMissedIds(sp.items, sp.group.completedItemIds, watched, embyPlayedIds);
  }

  /** The list-view shape of `sp` for `viewerUserId`. `livePartyId` is
   *  passed in already checked against PartyService (still alive). */
  public toSummary(sp: StaticParty, viewerUserId: string, embyPlayedIds: ReadonlySet<string>, livePartyId: string | null): StaticPartySummaryDto {
    return {
      id: sp.id,
      name: sp.name,
      sourceType: sp.source.type,
      imageUrl: sp.imageUrl,
      itemCount: sp.items.length,
      groupWatchedCount: sp.group.completedItemIds.length,
      nextItemName: sp.items[sp.group.nextIndex]?.itemName ?? null,
      memberCount: Object.keys(sp.members).length,
      youAreMember: !!sp.members[viewerUserId],
      youAreCreator: sp.createdByUserId === viewerUserId,
      missedCount: this.missedIds(sp, viewerUserId, embyPlayedIds).length,
      livePartyId
    };
  }

  /** The detail-view shape of `sp` for `viewerUserId`. */
  public toDetail(sp: StaticParty, viewerUserId: string, embyPlayedIds: ReadonlySet<string>, livePartyId: string | null): StaticPartyDetailDto {
    const completed = new Set(sp.group.completedItemIds);
    const viewerWatched = new Set(sp.members[viewerUserId]?.watchedItemIds ?? []);
    return {
      ...this.toSummary(sp, viewerUserId, embyPlayedIds, livePartyId),
      items: sp.items.map((item, index) => ({
        ...item,
        groupState: completed.has(item.itemId) ? 'watched' : index === sp.group.nextIndex ? 'next' : 'upcoming',
        viewerWatched: viewerWatched.has(item.itemId) || embyPlayedIds.has(item.itemId)
      })),
      missedItemIds: this.missedIds(sp, viewerUserId, embyPlayedIds),
      members: Object.values(sp.members).map((m) => ({
        userId: m.userId,
        userName: m.userName,
        watchedCount: m.watchedItemIds.length,
        isCreator: m.userId === sp.createdByUserId
      }))
    };
  }

  /** Writes `sp`'s own file (debounced - see StaticPartyStore). Only the
   *  party that changed is ever rewritten. */
  private persist(sp: StaticParty): void {
    StaticPartyStore.save(sp.id, () => this.snapshotOf(sp));
  }

  /** `sp` minus runtime-only state. */
  private snapshotOf(sp: StaticParty): PersistedStaticParty {
    const { livePartyId: _live, ...persisted } = sp;
    return persisted;
  }

  /** When `sp` last saw anything happen - for list ordering. */
  private lastActivity(sp: StaticParty): number {
    return Math.max(sp.createdUtc, sp.group.lastSessionUtc ?? 0);
  }

  /** A fresh member record for `who`. */
  private newMember(who: Participant): StaticPartyMember {
    const now = Date.now();
    return { userId: who.userId, userName: who.userName, joinedUtc: now, watchedItemIds: [], lastSeenUtc: now };
  }
}

export const StaticPartyService = new StaticPartyServiceClass();