import {Gpio} from "pigpio";
import {Observable, Subscriber} from "rxjs";

// HC-SR04 ultrasonic sensor
export class PresenceDetector {
    /* presence in cm */
    public isPresent: Observable<number> = new Observable<number>();

    private trigger: Gpio;
    private echo: Gpio;

    // une variable pour sauvegarder le setinterval
    private intervalTrigger: NodeJS.Timeout | null = null;


    // Thresholds for presence detection
    private readonly stepThreshold: number;
    private readonly updateInterval: number;

    // Variables for tracking presence status
    private step: number = 0;
    private timeStep: number = 0;

    // Constants for calculating distance from time
    private readonly MICROSECONDS_PER_CM: number = 1e6 / 34321;
    private readonly MIN_DISTANCE_TIME: number;
    private readonly MAX_DISTANCE_TIME: number;

    // constance rising edge
    private readonly RISING_EDGE: number = 1;
    private readonly FALLING_EDGE: number = 0;

    /**
     * Constructor for PresenceDetector class
     * @param echoPin - GPIO pin number for the echo signal of the sensor
     * @param triggerPin - GPIO pin number for the trigger signal of the sensor
     * @param updateInterval - frequency (in milliseconds) of updates for the presence detection status (default 200)
     * @param staticStateTime - time (in milliseconds) to wait for static state (default 1000)
     * @param minDistance - minimum distance (in centimeters) for presence detection
     * @param maxDistance - maximum distance (in centimeters) for presence detection
     */
    constructor(
        echoPin: number,
        triggerPin: number,
        updateInterval: number = 200,
        minDistance: number = 0,
        maxDistance: number = 9999999,
        staticStateTime: number = 1000
    ) {
        if (!triggerPin || !echoPin) {
            throw new Error("Invalid GPIO parameters");
        }

        if (!staticStateTime || !updateInterval) {
            throw new Error("Invalid distance parameters");
        }

        this.MIN_DISTANCE_TIME = minDistance
            ? minDistance * this.MICROSECONDS_PER_CM * 2
            : 0;
        this.MAX_DISTANCE_TIME = maxDistance
            ? maxDistance * this.MICROSECONDS_PER_CM * 2
            : 0;
        this.stepThreshold = staticStateTime / updateInterval;
        this.updateInterval = updateInterval;
        this.trigger = new Gpio(triggerPin, {mode: Gpio.OUTPUT});
        this.echo = new Gpio(echoPin, {mode: Gpio.INPUT, alert: true});
        this.trigger.digitalWrite(0);

        this.startPresenceDetection();
    }

    /**
     * Starts the loop to detect presence using the HC-SR04 sensor
     * This function listens to the echo pin, and checks the time difference between the
     * rising edge (level 1) and falling edge (level 0) of the echo signal.
     * If the time difference is within the specified min and max distance, it increments
     * the step counter. If the step counter reaches the threshold, it sets the presence
     * status to true. If the time difference is outside of the specified min and max distance,
     * it resets the step counter and sets the presence status to false.
     */
    public startPresenceDetection() {
        let startTick: number;

        // Trigger a distance measurement once per second
        this.intervalTrigger = setInterval(() => {
            this.trigger.trigger(10, 1); // Set trigger high for 10 microseconds
        }, this.updateInterval);

        this.isPresent = new Observable<number>((observer: Subscriber<number>) => {
            this.echo.on("alert", (level: number, tick: number) => {

                if (level === this.RISING_EDGE) {
                    startTick = tick;
                } else {
                    const diff: number = tick - startTick;

                    if (diff <= this.MAX_DISTANCE_TIME
                        && diff >= this.MIN_DISTANCE_TIME) {
                        this.step++;
                    } else {
                        this.step = 0;
                    }

                    if (this.step >= this.stepThreshold) {
                        observer.next(this.calculateDistance(diff));
                    }
                }
            });
        });
    }

    public stopPresenceDetection(): void {
        this.echo.removeAllListeners("alert");
        this.isPresent = new Observable<number>();
        if (this.intervalTrigger) {
            clearInterval(this.intervalTrigger);
        }
    }

    private calculateDistance(timeDiff: number): number {
        return Math.round(timeDiff / (this.MICROSECONDS_PER_CM * 2));
    }
}