import { isSymbolType } from '../core/model/AssetTypes';
import { sortByZ } from '../core/model/Properties';
import type { DrawItem } from './items';

/**
 * One thing sorted into the draw order: an object, or one layer of a placed tilemap (#174) –
 * `layerId` is empty for the object itself. A layer is sorted on its own, so a figure can walk
 * between the ground and the treetops of one map.
 */
export interface DrawSlot {
  id: string;
  layerId: string;
  z: number;
}

/**
 * Back to front: ascending `z`, ties in hierarchy order, and a map's layers right after the map in
 * their list order. With every layer at 0 that is exactly the order of before, where a map was one
 * piece. Symbols are left out, they are drawn above everything.
 */
export function drawSlots(items: readonly DrawItem[]): DrawSlot[] {
  const slots: DrawSlot[] = [];
  for (const item of items) {
    if (isSymbolType(item.type)) continue;
    slots.push({ id: item.id, layerId: '', z: item.z });
    for (const layer of item.tilemap?.layers ?? [])
      slots.push({ id: item.id, layerId: layer.id, z: item.z + layer.z });
  }
  return sortByZ(slots);
}