Genarrative/src/components/game-shell/useSceneTransitionModel.ts

import { useCallback, useEffect, useRef, useState } from 'react';

import type {
  GameState,
  StoryMoment,
} from '../../types';

export type SceneTransitionPhase = 'idle' | 'exiting' | 'entering';
export type SceneTransitionTriggerMode = 'scene-change' | 'content-change';

type SceneTransitionRequest = {
  mode: SceneTransitionTriggerMode;
  baselineSceneId: string | null;
  baselineContentKey: string;
  exitComplete: boolean;
};

const DEFAULT_SCENE_SWITCH_EXIT_MS = 5000;
const DEFAULT_SCENE_SWITCH_ENTRY_MS = 5930;

export const SCENE_TRANSITION_FUNCTION_MODES: Partial<Record<string, SceneTransitionTriggerMode>> = {
  idle_travel_next_scene: 'scene-change',
  camp_travel_home_scene: 'scene-change',
  idle_explore_forward: 'content-change',
  idle_follow_clue: 'content-change',
};

function buildSceneTransitionContentKey(gameState: GameState, currentStory: StoryMoment | null) {
  const sceneId = gameState.currentScenePreset?.id ?? 'scene:none';
  const encounterKey = gameState.currentEncounter
    ? `${gameState.currentEncounter.kind}:${gameState.currentEncounter.id ?? gameState.currentEncounter.npcName ?? 'unknown'}`
    : 'encounter:none';
  const monsterKey = gameState.sceneMonsters
    .map(monster => `${monster.id}:${monster.renderKind}:${monster.xMeters}:${monster.animation}`)
    .join('|');
  const storyKey = currentStory
    ? `${currentStory.displayMode ?? 'story'}:${currentStory.text ?? ''}:${currentStory.dialogue?.length ?? 0}`
    : 'story:none';
  return [sceneId, encounterKey, monsterKey, storyKey].join('::');
}

export function useSceneTransitionModel(params: {
  gameState: GameState;
  currentStory: StoryMoment | null;
  openingCampSceneId: string | null;
}) {
  const {
    gameState,
    currentStory,
    openingCampSceneId,
  } = params;
  const [renderGameState, setRenderGameState] = useState(gameState);
  const [renderCurrentStory, setRenderCurrentStory] = useState(currentStory);
  const [sceneTransitionPhase, setSceneTransitionPhase] = useState<SceneTransitionPhase>('idle');
  const [sceneTransitionToken, setSceneTransitionToken] = useState(0);
  const [sceneTransitionDurations, setSceneTransitionDurations] = useState({
    exitMs: DEFAULT_SCENE_SWITCH_EXIT_MS,
    entryMs: DEFAULT_SCENE_SWITCH_ENTRY_MS,
  });

  const pendingScenePayloadRef = useRef<{ gameState: GameState; currentStory: StoryMoment | null }>({
    gameState,
    currentStory,
  });
  const sceneTransitionTimerIdsRef = useRef<number[]>([]);
  const sceneTransitionRequestRef = useRef<SceneTransitionRequest | null>(null);

  useEffect(() => {
    return () => {
      sceneTransitionTimerIdsRef.current.forEach(timerId => window.clearTimeout(timerId));
      sceneTransitionTimerIdsRef.current = [];
      sceneTransitionRequestRef.current = null;
    };
  }, []);

  const startSceneEntering = useCallback((payload: { gameState: GameState; currentStory: StoryMoment | null }) => {
    sceneTransitionTimerIdsRef.current.forEach(timerId => window.clearTimeout(timerId));
    sceneTransitionTimerIdsRef.current = [];
    sceneTransitionRequestRef.current = null;
    setRenderGameState(payload.gameState);
    setRenderCurrentStory(payload.currentStory);
    setSceneTransitionToken(current => current + 1);
    setSceneTransitionPhase('entering');

    const entryTimerId = window.setTimeout(() => {
      setSceneTransitionPhase('idle');
    }, sceneTransitionDurations.entryMs);
    sceneTransitionTimerIdsRef.current.push(entryTimerId);
  }, [sceneTransitionDurations.entryMs]);

  const beginSceneTransition = useCallback((mode: SceneTransitionTriggerMode) => {
    if (sceneTransitionPhase !== 'idle') return;

    pendingScenePayloadRef.current = { gameState, currentStory };
    sceneTransitionTimerIdsRef.current.forEach(timerId => window.clearTimeout(timerId));
    sceneTransitionTimerIdsRef.current = [];
    sceneTransitionRequestRef.current = {
      mode,
      baselineSceneId: renderGameState.currentScenePreset?.id ?? gameState.currentScenePreset?.id ?? null,
      baselineContentKey: buildSceneTransitionContentKey(renderGameState, renderCurrentStory),
      exitComplete: false,
    };
    setSceneTransitionPhase('exiting');

    const exitTimerId = window.setTimeout(() => {
      const request = sceneTransitionRequestRef.current;
      if (!request) return;
      request.exitComplete = true;

      const pendingPayload = pendingScenePayloadRef.current;
      const isReady = request.mode === 'scene-change'
        ? (pendingPayload.gameState.currentScenePreset?.id ?? null) !== request.baselineSceneId
        : buildSceneTransitionContentKey(pendingPayload.gameState, pendingPayload.currentStory) !== request.baselineContentKey;

      if (isReady) {
        startSceneEntering(pendingPayload);
      }
    }, sceneTransitionDurations.exitMs);
    sceneTransitionTimerIdsRef.current.push(exitTimerId);
  }, [
    currentStory,
    gameState,
    renderCurrentStory,
    renderGameState,
    sceneTransitionDurations.exitMs,
    sceneTransitionPhase,
    startSceneEntering,
  ]);

  useEffect(() => {
    pendingScenePayloadRef.current = { gameState, currentStory };

    const request = sceneTransitionRequestRef.current;
    if (sceneTransitionPhase === 'exiting' && request?.exitComplete) {
      const isReady = request.mode === 'scene-change'
        ? (gameState.currentScenePreset?.id ?? null) !== request.baselineSceneId
        : buildSceneTransitionContentKey(gameState, currentStory) !== request.baselineContentKey;
      if (isReady) {
        startSceneEntering({ gameState, currentStory });
      }
      return;
    }

    if (sceneTransitionPhase !== 'exiting') {
      setRenderGameState(gameState);
      setRenderCurrentStory(currentStory);
    }
  }, [currentStory, gameState, sceneTransitionPhase, startSceneEntering]);

  useEffect(() => {
    if (sceneTransitionPhase !== 'idle') {
      return;
    }
    if (renderGameState.playerCharacter) {
      return;
    }
    if (!gameState.playerCharacter || gameState.currentScene !== 'Story') {
      return;
    }
    if (gameState.storyHistory.length > 0) {
      return;
    }
    if (!openingCampSceneId || gameState.currentScenePreset?.id !== openingCampSceneId) {
      return;
    }

    startSceneEntering({ gameState, currentStory });
  }, [
    currentStory,
    gameState,
    openingCampSceneId,
    renderGameState.playerCharacter,
    sceneTransitionPhase,
    startSceneEntering,
  ]);

  return {
    visibleGameState: sceneTransitionPhase === 'idle' ? gameState : renderGameState,
    visibleCurrentStory: sceneTransitionPhase === 'idle' ? currentStory : renderCurrentStory,
    sceneTransitionPhase,
    sceneTransitionToken,
    setSceneTransitionDurations,
    beginSceneTransition,
  };
}