DndGamePlayer/app/main/npcs/npcsOverlayStore.ts

import {
  clampNpcsLayout,
  DEFAULT_NPCS_OVERLAY_LAYOUT,
  type NpcId,
  type NpcsOverlayEvent,
  type NpcsOverlayLayout,
  type NpcsOverlayState,
  type NpcsZoomTool,
  zoomNpcsLayoutAt,
} from '../../shared/types';

function emptyState(): NpcsOverlayState {
  return {
    revision: 1,
    activeNpcId: null,
    layout: { ...DEFAULT_NPCS_OVERLAY_LAYOUT },
    zoomTool: null,
  };
}

export class NpcsOverlayStore {
  private state: NpcsOverlayState = emptyState();

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

  clear(): NpcsOverlayState {
    if (this.state.activeNpcId === null && this.state.zoomTool === null) {
      return this.state;
    }
    this.state = {
      revision: this.state.revision + 1,
      activeNpcId: null,
      layout: { ...DEFAULT_NPCS_OVERLAY_LAYOUT },
      zoomTool: null,
    };
    return this.state;
  }

  dispatch(event: NpcsOverlayEvent): NpcsOverlayState {
    switch (event.kind) {
      case 'hide':
        return this.clear();
      case 'show':
        this.state = {
          revision: this.state.revision + 1,
          activeNpcId: event.npcId,
          layout: { ...DEFAULT_NPCS_OVERLAY_LAYOUT },
          zoomTool: this.state.zoomTool,
        };
        return this.state;
      case 'toggle': {
        if (this.state.activeNpcId === event.npcId) {
          return this.clear();
        }
        this.state = {
          revision: this.state.revision + 1,
          activeNpcId: event.npcId,
          layout: { ...DEFAULT_NPCS_OVERLAY_LAYOUT },
          zoomTool: this.state.zoomTool,
        };
        return this.state;
      }
      case 'layout.set': {
        if (this.state.activeNpcId === null) return this.state;
        this.state = {
          ...this.state,
          revision: this.state.revision + 1,
          layout: clampNpcsLayout(event.layout),
        };
        return this.state;
      }
      case 'zoomTool.set': {
        const tool: NpcsZoomTool = event.tool;
        this.state = {
          ...this.state,
          revision: this.state.revision + 1,
          zoomTool: tool,
        };
        return this.state;
      }
      case 'zoomAt': {
        if (this.state.activeNpcId === null || !this.state.zoomTool) return this.state;
        const factor = this.state.zoomTool === 'zoomIn' ? 1.25 : 1 / 1.25;
        const layout: NpcsOverlayLayout = zoomNpcsLayoutAt(
          this.state.layout,
          event.nx,
          event.ny,
          factor,
        );
        this.state = {
          ...this.state,
          revision: this.state.revision + 1,
          layout,
        };
        return this.state;
      }
      default:
        return this.state;
    }
  }

  ensureNpcStillExists(npcIds: ReadonlySet<NpcId>): NpcsOverlayState {
    const active = this.state.activeNpcId;
    if (active === null || npcIds.has(active)) return this.state;
    return this.clear();
  }
}