import type { EntityId } from '../ecs/EntityId';
import type { Cell } from './Cell';
import type { GridMap } from './GridMap';

/** 空间网格索引（按格子桶加速选敌） */
export class SpatialGrid {
    /** 一维桶：index = row * cols + col，空桶为 undefined */
    private readonly _buckets: (EntityId[] | undefined)[];
    /** 实体当前行；未登记为 -1 */
    private readonly _entityRow: number[] = [];
    /** 实体当前列；未登记为 -1 */
    private readonly _entityCol: number[] = [];
    /** query 复用缓冲，仅在下次 query 前有效 */
    private readonly _queryOut: EntityId[] = [];

    /**
     * @param _grid 关联的格子地图
     */
    constructor(private _grid: GridMap) {
        this._buckets = new Array(_grid.rows * _grid.cols);
    }

    /**
     * @param id 实体 ID
     * @param cell 当前所在格子
     */
    updateEntity(id: EntityId, cell: Cell): void {
        const prevRow = this._entityRow[id];
        const prevCol = this._entityCol[id];
        if (prevRow === cell.row && prevCol === cell.col) return;
        if (prevRow != null && prevRow >= 0) {
            this._removeFromBucket(id, prevRow, prevCol);
        }
        this._entityRow[id] = cell.row;
        this._entityCol[id] = cell.col;
        this._addToBucket(id, cell.row, cell.col);
    }

    /** 从空间索引中移除实体 */
    removeEntity(id: EntityId): void {
        const row = this._entityRow[id];
        if (row == null || row < 0) return;
        this._removeFromBucket(id, row, this._entityCol[id]);
        this._entityRow[id] = -1;
        this._entityCol[id] = -1;
    }

    /**
     * @param center 圆心格子
     * @param radiusCells 半径（格）
     * @returns 范围内实体 ID
     */
    queryRadius(center: Cell, radiusCells: number): EntityId[] {
        const out = this._queryOut;
        out.length = 0;
        const rows = this._grid.rows;
        const cols = this._grid.cols;
        const r = Math.ceil(radiusCells);
        const cr = center.row;
        const cc = center.col;
        for (let dr = -r; dr <= r; dr++) {
            const row = cr + dr;
            if (row < 0 || row >= rows) continue;
            for (let dc = -r; dc <= r; dc++) {
                const col = cc + dc;
                if (col < 0 || col >= cols) continue;
                const dRow = cr - row;
                const dCol = cc - col;
                if (Math.sqrt(dRow * dRow + dCol * dCol) > radiusCells) continue;
                this._appendBucket(out, row * cols + col);
            }
        }
        return out.slice();
    }

    /**
     * @returns 全部已登记实体
     */
    queryAll(): EntityId[] {
        const out = this._queryOut;
        out.length = 0;
        const buckets = this._buckets;
        for (let i = 0; i < buckets.length; i++) {
            this._appendBucket(out, i);
        }
        return out.slice();
    }

    /**
     * @param out 输出
     * @param index 桶下标
     */
    private _appendBucket(out: EntityId[], index: number): void {
        const list = this._buckets[index];
        if (!list) return;
        for (let i = 0; i < list.length; i++) out.push(list[i]);
    }

    /**
     * @param id 实体
     * @param row 行
     * @param col 列
     */
    private _addToBucket(id: EntityId, row: number, col: number): void {
        if (row < 0 || row >= this._grid.rows || col < 0 || col >= this._grid.cols) return;
        const index = row * this._grid.cols + col;
        let list = this._buckets[index];
        if (!list) {
            list = [];
            this._buckets[index] = list;
        }
        for (let i = 0; i < list.length; i++) {
            if (list[i] === id) return;
        }
        list.push(id);
    }

    /**
     * @param id 实体
     * @param row 行
     * @param col 列
     */
    private _removeFromBucket(id: EntityId, row: number, col: number): void {
        const index = row * this._grid.cols + col;
        const list = this._buckets[index];
        if (!list) return;
        for (let i = list.length - 1; i >= 0; i--) {
            if (list[i] === id) list.splice(i, 1);
        }
        if (list.length === 0) this._buckets[index] = undefined;
    }
}