// https://leetcode.com/problems/design-underground-system/
class UndergroundSystem {
    constructor() {
        this.stationSystem = {};
        this.averageTime = {};
    }

    /**
     * Time O(1) | Space O(1)
     * Records the check-in time and station for a user.
     * @param {number} id - User ID
     * @param {string} stationName - Check-in station name
     * @param {number} t - Check-in time
     * @return {void}
     */
    checkIn(id, stationName, t) {
        this.stationSystem[id] = [stationName, '', t, ''];
    }

    /**
     * Time O(1) | Space O(1)
     * Records the check-out time and station for a user, and calculates the average time.
     * @param {number} id - User ID
     * @param {string} stationName - Check-out station name
     * @param {number} t - Check-out time
     * @return {void}
     */
    checkOut(id, stationName, t) {
        const user = this.stationSystem[id];
        user[1] = stationName;
        user[3] = t;
        const stationHash = `${user[0]}-${user[1]}`;
        if (this.averageTime[stationHash]) {
            this.averageTime[stationHash][0] += 1;
            this.averageTime[stationHash][1] += user[3] - user[2];
        } else {
            this.averageTime[stationHash] = [];
            this.averageTime[stationHash][0] = 1;
            this.averageTime[stationHash][1] = user[3] - user[2];
        }
    }

    /**
     * Time O(1) | Space O(1)
     * Returns the average time taken to travel between two stations.
     * @param {string} startStation - Start station name
     * @param {string} endStation - End station name
     * @return {number} - Average time in hours
     */
    getAverageTime(startStation, endStation) {
        const [rounds, totalHours] =
            this.averageTime[`${startStation}-${endStation}`];
        return totalHours / rounds;
    }
}