function main() {
    server.log("Main function...");
    photo_pin <- hardware.pin7;
    photo_pin.configure(ANALOG_IN);
    
    flash_pin <- hardware.pin8;
    flash_pin.configure(DIGITAL_OUT);
    flash_pin.write(0);
    
    led_pin <- hardware.pin2;
    led_pin.configure(DIGITAL_OUT);
    led_pin.write(0);
    
    local flash_delay = 0.2;
    local sensitivity = 0.3;
    
    function setFlashDelay(delay) {
        flash_delay = delay / 1000.0;
        server.log("Set flash delay: " + flash_delay);
    }
    
    function setSensitivity(sense) {
        sensitivity = sense / 100.0;
        server.log("Set sense sensitivity: " + sensitivity);
    }
    
    agent.on("set.delay", setFlashDelay);
    agent.on("set.sensitivity", setSensitivity);
    
    function getLightLevel() {
        local photo1 = photo_pin.read();
        led_pin.write(1);
        imp.sleep(0.0001);
        local photo2 = photo_pin.read();
        led_pin.write(0);
        
        local light_diff = photo1 - photo2; // the smaller the value, the bigger the obstacle; 0 with opaque obstacle
        return light_diff
    }
    
    local light_level_mean = getLightLevel();
    
    function fireTheFlash() {
        flash_pin.write(1);
        imp.sleep(0.1);
        flash_pin.write(0);
        light_level_mean = getLightLevel();
        adjustLightMean();
    }
    
    function adjustLightMean() {
        local light_level = getLightLevel();
        if ((light_level + (light_level * (sensitivity / 2.0))) < light_level_mean) {
           light_level_mean = (light_level_mean * 0.9) + (light_level * 0.1)
           imp.wakeup(0.1, adjustLightMean);
       } else {
           imp.wakeup(0.1, checkLightBeam);
       }
    }
    
    function checkLightBeam() {
       local light_level = getLightLevel();
       //server.log("checkLightBeam: "+ light_level +", "+ light_level_mean);
       if ((light_level + (light_level * sensitivity)) < light_level_mean) {
           // obstacle detected
           imp.wakeup(flash_delay, fireTheFlash);
       } else {
           light_level_mean = (light_level_mean * 0.999) + (light_level * 0.001)
           imp.wakeup(0.001, checkLightBeam);
       }
    }

    adjustLightMean();
}

main();