/*
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 {
  type BehaviorSubject,
  combineLatest,
  debounceTime,
  distinctUntilChanged,
  filter,
  ignoreElements,
  map,
  merge,
  type Observable,
  of,
  switchMap,
  tap,
} 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";
import { type LayoutMode } from "../state/LayoutSwitchViewModel";
import { type Behavior } from "../state/Behavior";

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

/**
 * [lotus #4/#30] A host-requested spotlight pin. `id` is the EC media id
 * (`${userId}:${deviceId}`, the same value `io.lotus.call_state` sends the
 * host) and is preferred when present; `userId` alone resolves to the
 * currently-speaking device of that user, else their first device.
 */
export interface ManualSpotlight {
  userId: string;
  id: string | null;
}

/**
 * How long (ms) a pinned participant may be absent from `userMedia$` before
 * the pin is dropped (#16). Long enough to ride out a transient LiveKit
 * reconnect, short enough that a real leave restores speaker-follows promptly.
 */
export const MANUAL_SPOTLIGHT_GONE_MS = 5000;

/**
 * Resolve the pin against the current media list (#30). Pure; the observable
 * wrapper below feeds it the live `speaking` state.
 */
export function resolveManualSpotlight<
  M extends { id: string; userId: string },
>(
  target: ManualSpotlight | null,
  mediaItems: M[],
  speaking: (m: M) => boolean,
): M | undefined {
  if (target === null) return undefined;
  if (target.id !== null) {
    const byId = mediaItems.find((m) => m.id === target.id);
    if (byId) return byId;
    // The pinned device is gone but the user may still be here on another
    // one — fall through to the userId match rather than dropping the pin.
  }
  const devices = mediaItems.filter((m) => m.userId === target.userId);
  if (devices.length <= 1) return devices[0];
  return devices.find(speaking) ?? devices[0];
}

/**
 * The pinned media item, or `undefined` when there is no pin or the pinned
 * participant is not (currently) in the call.
 */
export function pinnedMedia$(
  manualSpotlight$: Observable<ManualSpotlight | null>,
  userMedia$: Observable<UserMediaViewModel[]>,
): Observable<UserMediaViewModel | undefined> {
  return combineLatest([manualSpotlight$, userMedia$]).pipe(
    switchMap(([target, mediaItems]) => {
      if (target === null) return of(undefined);
      const devices = mediaItems.filter((m) => m.userId === target.userId);
      // Only subscribe to speaking$ when there is actually a choice to make.
      const speaking$: Observable<Set<UserMediaViewModel>> =
        devices.length > 1 && !devices.some((m) => m.id === target.id)
          ? combineLatest(devices.map((m) => m.speaking$)).pipe(
              map((flags) => new Set(devices.filter((_, i) => flags[i]))),
            )
          : of(new Set<UserMediaViewModel>());
      return speaking$.pipe(
        map((speaking) =>
          resolveManualSpotlight(target, mediaItems, (m) => speaking.has(m)),
        ),
      );
    }),
    distinctUntilChanged(),
  );
}

/**
 * [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$` auto-selection unchanged and just routes the
 * screenshare/spotlight computation through this wrapper at one call point.
 *
 * Behaviour is IDENTICAL to upstream whenever `manualSpotlight$` 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"); the PiP keeps showing the auto-selected speaker and is
 *    only blanked when that speaker IS the pinned participant (#29).
 *
 * @param autoSpotlightSpeaker$ upstream's speaker-follows auto selection
 * @param manualSpotlight$ host pin, 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 pin)
 */
export function overrideSpotlight$(
  autoSpotlightSpeaker$: Observable<UserMediaViewModel | undefined>,
  manualSpotlight$: Observable<ManualSpotlight | null>,
  screenShares$: Observable<ScreenShareViewModel[]>,
  localUserMediaForPip$: Observable<LocalUserMediaViewModel | undefined>,
  userMedia$: Observable<UserMediaViewModel[]>,
): Observable<SpotlightAndPip> {
  const pinned$ = pinnedMedia$(manualSpotlight$, userMedia$);

  // The effective spotlight speaker: the host-pinned participant when set and
  // still present, otherwise upstream's auto-selected speaker.
  const spotlightSpeaker$ = combineLatest(
    [autoSpotlightSpeaker$, pinned$],
    (auto, pinned) => pinned ?? auto,
  );

  return screenShares$.pipe(
    switchMap((screenShares) => {
      if (screenShares.length > 0)
        // During a screenshare, if the host has explicitly pinned a
        // participant, surface that camera in the spotlight alongside the
        // shared screen (the whole point of "focus camera during screenshare").
        // With no manual pin this is unchanged: the screenshare alone is
        // spotlighted.
        return pinned$.pipe(
          map((pinned) =>
            pinned
              ? {
                  spotlight: [...screenShares, pinned],
                  // [lotus #29] Keep the active-speaker PiP; it is only
                  // redundant when the speaker is the pinned participant.
                  pip$: autoSpotlightSpeaker$.pipe(
                    map((auto) => (auto === pinned ? undefined : auto)),
                  ),
                }
              : { 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)),
          ),
        })),
      );
    }),
  );
}

export interface ManualSpotlightController {
  /** Pin `target`, or clear with `null`. */
  setManualSpotlight: (target: ManualSpotlight | null) => void;
  /**
   * Side effects that must run for the lifetime of the call. Emits nothing;
   * the caller subscribes it through its scope.
   */
  effects$: Observable<never>;
}

/**
 * [lotus #3/#16] State + side effects behind `CallViewModel.setManualSpotlight`.
 *
 *  - #3: a pin only feeds `spotlight$`, which the default grid layout ignores
 *    (and 1:1 layouts bypass entirely), so pinning forces the layout switch to
 *    "spotlight" and remembers the mode it displaced; clearing the pin restores
 *    that mode if the user has not switched layouts themselves meanwhile.
 *  - #16: the pin is dropped when the pinned participant has been absent from
 *    `userMedia$` for {@link MANUAL_SPOTLIGHT_GONE_MS} (a transient reconnect
 *    is shorter than that), and on `leave$`.
 *
 * Pure with respect to its inputs so it can be unit-tested with fake
 * observables; CallViewModel only wires it up.
 *
 * @param manualSpotlight$ the pin state, owned by the caller (it has to exist
 *   before the layout switch does, because `spotlightAndPip$` feeds into it)
 */
export function createManualSpotlight(
  manualSpotlight$: BehaviorSubject<ManualSpotlight | null>,
  userMedia$: Observable<{ userId: string }[]>,
  leave$: Observable<unknown>,
  layout: {
    layout$: Behavior<LayoutMode>;
    setLayout: (mode: LayoutMode) => void;
  },
  goneMs = MANUAL_SPOTLIGHT_GONE_MS,
): ManualSpotlightController {
  // The layout mode we displaced by forcing spotlight, if any.
  let displacedLayout: LayoutMode | null = null;

  const setManualSpotlight = (target: ManualSpotlight | null): void => {
    const hadPin = manualSpotlight$.value !== null;
    manualSpotlight$.next(target);
    if (target !== null) {
      if (!hadPin && layout.layout$.value !== "spotlight") {
        displacedLayout = layout.layout$.value;
        layout.setLayout("spotlight");
      }
    } else if (displacedLayout !== null) {
      // Only restore if the user hasn't picked a layout themselves since.
      if (layout.layout$.value === "spotlight")
        layout.setLayout(displacedLayout);
      displacedLayout = null;
    }
  };

  // #16: pinned user has left for good (absent for `goneMs`), or we hung up.
  const pinnedGone$ = manualSpotlight$.pipe(
    switchMap((target) =>
      target === null
        ? of(false)
        : userMedia$.pipe(
            map((items) => !items.some((m) => m.userId === target.userId)),
            distinctUntilChanged(),
            // A transient absence shorter than goneMs collapses back to
            // `false` before the timer fires and is ignored.
            debounceTime(goneMs),
            filter((gone) => gone),
          ),
    ),
    filter((gone) => gone),
  );
  const effects$ = merge(pinnedGone$, leave$).pipe(
    filter(() => manualSpotlight$.value !== null),
    tap(() => setManualSpotlight(null)),
    ignoreElements(),
  );

  return { setManualSpotlight, effects$ };
}