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

export type Region = Entity & {
  // aligning axes of the region, expect a part's position to have a matching number of elements
  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){
  if (region.children.length === 0) return;

  // Process each axis independently while preserving spatial relationships
  for (let axisIndex = 0; axisIndex < region.axes.length; axisIndex++) {
    const axis = region.axes[axisIndex];
    if (!axis.align) continue;

    // Collect all unique position values on this axis, preserving original order
    const positionValues = new Set<number>();
    for (const accessor of region.children) {
      positionValues.add(accessor.value.position[axisIndex] ?? 0);
    }

    // Sort position values
    const sortedPositions = Array.from(positionValues).sort((a, b) => a - b);

    // Create position mapping: old position -> new position
    const positionMap = new Map<number, number>();

    if (axis.align === 'start' && axis.min !== undefined) {
      // Compact from min, preserving relative order
      sortedPositions.forEach((pos, index) => {
        positionMap.set(pos, axis.min! + index);
      });
    } else if (axis.align === 'end' && axis.max !== undefined) {
      // Compact towards max
      const count = sortedPositions.length;
      sortedPositions.forEach((pos, index) => {
        positionMap.set(pos, axis.max! - (count - 1 - index));
      });
    } else if (axis.align === 'center') {
      // Center alignment
      const count = sortedPositions.length;
      const min = axis.min ?? 0;
      const max = axis.max ?? count - 1;
      const range = max - min;
      const center = min + range / 2;

      sortedPositions.forEach((pos, index) => {
        const offset = index - (count - 1) / 2;
        positionMap.set(pos, center + offset);
      });
    }

    // Apply position mapping to all parts
    for (const accessor of region.children) {
      const currentPos = accessor.value.position[axisIndex] ?? 0;
      accessor.value.position[axisIndex] = positionMap.get(currentPos) ?? currentPos;
    }
  }

  // Sort children by all axes at the end
  region.children.sort((a, b) => {
    for (let i = 0; i < region.axes.length; i++) {
      const diff = (a.value.position[i] ?? 0) - (b.value.position[i] ?? 0);
      if (diff !== 0) return diff;
    }
    return 0;
  });
}

/**
 * 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);
    // 交换两个 part 的整个 position 数组
    const temp = children[i].value.position;
    children[i].value.position = children[j].value.position;
    children[j].value.position = temp;
  }
}