esengine/source/src/AI/Pathfinding/AStar/AStarPathfinder.ts

///<reference path="./PriorityQueueNode.ts" />
/**
 * 计算路径给定的IAstarGraph和开始/目标位置
 */
class AStarPathfinder {
    /**
     * 尽可能从开始到目标找到一条路径。如果没有找到路径，则返回null。
     * @param graph 
     * @param start 
     * @param goal 
     */
    public static search<T>(graph: IAstarGraph<T>, start: T, goal: T){
        let foundPath = false;
        let cameFrom = new Map<T, T>();
        cameFrom.set(start, start);

        let costSoFar = new Map<T, number>();
        let frontier = new PriorityQueue<AStarNode<T>>(1000);
        frontier.enqueue(new AStarNode<T>(start), 0);

        costSoFar.set(start, 0);

        while (frontier.count > 0){
            let current = frontier.dequeue();

            if (JSON.stringify(current.data) == JSON.stringify(goal)){
                foundPath = true;
                break;
            }

            graph.getNeighbors(current.data).forEach(next => {
                let newCost = costSoFar.get(current.data) + graph.cost(current.data, next);
                if (!this.hasKey(costSoFar, next) || newCost < costSoFar.get(next)){
                    costSoFar.set(next, newCost);
                    let priority = newCost + graph.heuristic(next, goal);
                    frontier.enqueue(new AStarNode<T>(next), priority);
                    cameFrom.set(next, current.data);
                }
            });
        }

        return foundPath ? this.recontructPath(cameFrom, start, goal) : null;
    }

    private static hasKey<T>(map: Map<T, number>, compareKey: T){
        let iterator = map.keys();
        let r: IteratorResult<T>;
        while (r = iterator.next() , !r.done) {
            if (JSON.stringify(r.value) == JSON.stringify(compareKey))
                return true;
        }

        return false;
    }

    private static getKey<T>(map: Map<T, T>, compareKey: T){
        let iterator = map.keys();
        let valueIterator = map.values();
        let r: IteratorResult<T>;
        let v: IteratorResult<T>;
        while (r = iterator.next(), v = valueIterator.next(), !r.done) {
            if (JSON.stringify(r.value) == JSON.stringify(compareKey))
                return v.value;
        }

        return null;
    }

    /**
     * 从cameFrom字典重新构造路径
     * @param cameFrom 
     * @param start 
     * @param goal 
     */
    public static recontructPath<T>(cameFrom: Map<T, T>, start: T, goal: T): T[]{
        let path = [];
        let current = goal;
        path.push(goal);

        while (current != start){
            current = this.getKey(cameFrom, current);
            path.push(current);
        }

        path.reverse();

        return path;
    }
}

/**
 * 使用PriorityQueue需要的额外字段将原始数据封装在一个小类中
 */
class AStarNode<T> extends PriorityQueueNode {
    public data: T;

    constructor(data: T){
        super();
        this.data = data;
    }
}