/*
Copyright 2026 Lotus Guild

SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
Please see LICENSE in the repository root for full details.
*/

import { combineLatest, map, type Observable, of, switchMap } from "rxjs";

import { type UserMediaViewModel } from "../state/media/UserMediaViewModel";
import { type ScreenShareViewModel } from "../state/media/ScreenShareViewModel";
import { type MediaViewModel } from "../state/media/MediaViewModel";
import { type LocalUserMediaViewModel } from "../state/media/LocalUserMediaViewModel";

interface SpotlightAndPip {
  spotlight: MediaViewModel[];
  pip$: Observable<UserMediaViewModel | undefined>;
}

/**
 * [lotus #4] Manual spotlight override.
 *
 * Wraps upstream's auto-selected spotlight speaker so a host can pin a specific
 * participant (via the `io.lotus.focus_participant` widget action). Kept as a
 * pure function OUTSIDE CallViewModel so CallViewModel stays byte-close to
 * upstream and rebases cleanly: CallViewModel keeps its original
 * `spotlightSpeaker$` auto-selection unchanged and just routes the
 * screenshare/spotlight computation through this wrapper at one call point.
 *
 * Behaviour is IDENTICAL to upstream whenever `manualSpotlightUserId$` stays
 * `null` (the default). When it names a participant that is still present:
 *  - with no screenshare, that participant is spotlighted instead of the
 *    auto-selected active speaker;
 *  - during a screenshare, that participant's camera is surfaced in the
 *    spotlight ALONGSIDE the shared screen (#4 / A5 "focus camera during
 *    screenshare"), and the redundant PiP is hidden.
 *
 * @param autoSpotlightSpeaker$ upstream's speaker-follows auto selection
 * @param manualSpotlightUserId$ host-pinned userId, or `null` for auto (default)
 * @param screenShares$ current screen-share view models
 * @param localUserMediaForPip$ local media suitable for the PiP
 * @param userMedia$ all user media in the call (to resolve the pinned userId)
 */
export function overrideSpotlight$(
  autoSpotlightSpeaker$: Observable<UserMediaViewModel | undefined>,
  manualSpotlightUserId$: Observable<string | null>,
  screenShares$: Observable<ScreenShareViewModel[]>,
  localUserMediaForPip$: Observable<LocalUserMediaViewModel | undefined>,
  userMedia$: Observable<UserMediaViewModel[]>,
): Observable<SpotlightAndPip> {
  // The effective spotlight speaker: the host-pinned participant when set and
  // still present, otherwise upstream's auto-selected speaker.
  const spotlightSpeaker$ = combineLatest([
    autoSpotlightSpeaker$,
    manualSpotlightUserId$,
    userMedia$,
  ]).pipe(
    map(([auto, manualUserId, mediaItems]) => {
      if (manualUserId !== null) {
        const pinned = mediaItems.find((m) => m.userId === manualUserId);
        if (pinned) return pinned;
      }
      return auto;
    }),
  );

  return screenShares$.pipe(
    switchMap((screenShares) => {
      if (screenShares.length > 0)
        // During a screenshare, if the host has explicitly pinned a
        // participant, surface that camera in the spotlight alongside the
        // shared screen (the whole point of "focus camera during screenshare").
        // With no manual pin this is unchanged: the screenshare alone is
        // spotlighted.
        return combineLatest([manualSpotlightUserId$, userMedia$]).pipe(
          map(([manualUserId, mediaItems]) => {
            const pinned =
              manualUserId !== null
                ? mediaItems.find((m) => m.userId === manualUserId)
                : undefined;
            return pinned
              ? { spotlight: [...screenShares, pinned], pip$: of(undefined) }
              : { spotlight: screenShares, pip$: spotlightSpeaker$ };
          }),
        );

      return spotlightSpeaker$.pipe(
        map((speaker) => ({
          spotlight: speaker ? [speaker] : [],
          // Hide PiP if redundant (i.e. if local user is already in spotlight)
          pip$: localUserMediaForPip$.pipe(
            map((m) => (m === speaker ? undefined : m)),
          ),
        })),
      );
    }),
  );
}