DndGamePlayer/app/main/players/sceneNpcTokensSessionStore.ts

import {
  clampNpcTokenSessionScale,
  DEFAULT_NPC_TOKEN_SESSION_SCALE,
  type SceneNpcTokensSessionEvent,
  type SceneNpcTokensSessionState,
} from '../../shared/types/appPlayers';

function emptyState(revision = 1): SceneNpcTokensSessionState {
  return {
    revision,
    byPlacementId: {},
    scale: DEFAULT_NPC_TOKEN_SESSION_SCALE,
  };
}

export class SceneNpcTokensSessionStore {
  private state: SceneNpcTokensSessionState = emptyState();

  getState(): SceneNpcTokensSessionState {
    return this.state;
  }

  reset(): SceneNpcTokensSessionState {
    if (
      Object.keys(this.state.byPlacementId).length === 0 &&
      this.state.scale === DEFAULT_NPC_TOKEN_SESSION_SCALE
    ) {
      return this.state;
    }
    this.state = emptyState(this.state.revision + 1);
    return this.state;
  }

  dispatch(event: SceneNpcTokensSessionEvent): SceneNpcTokensSessionState {
    switch (event.kind) {
      case 'clear':
        return this.reset();
      case 'setScale': {
        const scale = clampNpcTokenSessionScale(event.scale);
        if (this.state.scale === scale) return this.state;
        this.state = {
          ...this.state,
          revision: this.state.revision + 1,
          scale,
        };
        return this.state;
      }
      case 'move': {
        const placementId = String(event.placementId ?? '');
        if (!placementId) return this.state;
        const nx = Math.max(0, Math.min(1, event.nx));
        const ny = Math.max(0, Math.min(1, event.ny));
        if (!Number.isFinite(nx) || !Number.isFinite(ny)) return this.state;
        const prev = this.state.byPlacementId[placementId];
        if (prev && prev.nx === nx && prev.ny === ny) return this.state;
        this.state = {
          revision: this.state.revision + 1,
          byPlacementId: {
            ...this.state.byPlacementId,
            [placementId]: { nx, ny },
          },
          scale: this.state.scale,
        };
        return this.state;
      }
      default: {
        const _exhaustive: never = event;
        void _exhaustive;
        return this.state;
      }
    }
  }
}