import {Entity, EntityAccessor} from "../utils/entity";
import {Part} from "./part";
import {RNG} from "../utils/rng";

export type Region = Entity & {
  // aligning axes of the region
  axes: RegionAxis[];

  // current children; expect no overlapped positions
  children: EntityAccessor<Part>[];
}

export type RegionAxis = {
  name: string;
  min?: number;
  max?: number;
  align?: 'start' | 'end' | 'center';
}

/**
 * for each axis, try to remove gaps in positions.
 * - if min exists and align is start, and there are parts at (for example) min+2 and min+4, then move them to min and min+1
 * - if max exists and align is end, and there are parts at (for example) max-2 and max-4, then move them to max-1 and max-3
 * - for center, move parts to the center, possibly creating parts placed at 0.5 positions
 * - sort children so that they're in ascending order on each axes.
 * @param region
 */
export function applyAlign(region: Region){
  for (const axis of region.axes) {
    if (region.children.length === 0) continue;

    // 获取当前轴向上的所有位置
    const positions = region.children.map(accessor => accessor.value.position);
    
    // 根据当前轴的位置排序 children
    region.children.sort((a, b) => {
      const posA = a.value.position[0] ?? 0;
      const posB = b.value.position[0] ?? 0;
      return posA - posB;
    });

    if (axis.align === 'start' && axis.min !== undefined) {
      // 从 min 开始紧凑排列
      region.children.forEach((accessor, index) => {
        const currentPos = accessor.value.position.slice();
        currentPos[0] = axis.min! + index;
        accessor.value.position = currentPos;
      });
    } else if (axis.align === 'end' && axis.max !== undefined) {
      // 从 max 开始向前紧凑排列
      const count = region.children.length;
      region.children.forEach((accessor, index) => {
        const currentPos = accessor.value.position.slice();
        currentPos[0] = axis.max! - (count - 1 - index);
        accessor.value.position = currentPos;
      });
    } else if (axis.align === 'center') {
      // 居中排列
      const count = region.children.length;
      const min = axis.min ?? 0;
      const max = axis.max ?? count - 1;
      const range = max - min;
      const center = min + range / 2;
      
      region.children.forEach((accessor, index) => {
        const currentPos = accessor.value.position.slice();
        // 计算相对于中心的偏移
        const offset = index - (count - 1) / 2;
        currentPos[0] = center + offset;
        accessor.value.position = currentPos;
      });
    }
  }
}

/**
 * shuffle on each axis. for each axis, try to swap position.
 * @param region
 * @param rng
 */
export function shuffle(region: Region, rng: RNG){
  if (region.children.length <= 1) return;

  // Fisher-Yates 洗牌算法
  const children = [...region.children];
  for (let i = children.length - 1; i > 0; i--) {
    const j = rng.nextInt(i + 1);
    // 交换位置
    const posI = children[i].value.position.slice();
    const posJ = children[j].value.position.slice();
    
    children[i].value.position = posJ;
    children[j].value.position = posI;
  }
}