api.cpp

#include "api.h"
#include "parson/parson.h"

#include <curl/curl.h>
#include <math.h>
#include <stdlib.h>
#include <pthread.h>
#include <string.h>
#include <unistd.h>

// define maximum viewing distance in nautical miles
#define MAX_DISTANCE 20.0

// define intervall in seconds after which a plane is removed if there is no more data about it
#define PLANE_TIMEOUT 30

// define URLs
#define URL_BALANCE "http://www.flightradar24.com/balance.json"
#define URL_ZONES "http://www.flightradar24.com/js/zones.js.php"
#define URL_ZONE_INFIX "/zones/fcgi/"
#define URL_ZONE_SUFFIX "_all.json"

// define indices of relevant aircraft properties for parsing
#define ARRAY_INDEX_LATITUDE 1
#define ARRAY_INDEX_LONGITUDE 2
#define ARRAY_INDEX_HEADING 3
#define ARRAY_INDEX_ALTITUDE 4
#define ARRAY_INDEX_SPEED 5
#define ARRAY_INDEX_SQUAWK 6
#define ARRAY_INDEX_ICAO_TYPE 8
#define ARRAY_INDEX_REGISTRATION 9
#define ARRAY_INDEX_VERTICAL_SPEED 15
#define ARRAY_INDEX_ICAO_ID 16

// define radius of the earth in nautical miles
#define RADIUS_EARTH 3440.07

// external variables
std::map<std::string, Plane*> planes;
pthread_mutex_t planesMutex;

// global variables
static char *lastZone = NULL;
static double userLatitude = 48.3537449, userLongitude = 11.7860028; // Munich
//static double latitude = 0.0, longitude = 0.0;
//static double userLatitude = 51.5286416 , userLongitude = -0.1015987; // London
//static double userLatitude = 50.4433421, userLongitude = -4.9443987; // Cornwall
//static double userLatitude = 50.9987326, userLongitude = 13.9867738; // Dresden
//static double userLatitude = 37.7577, userLongitude = -122.4376; // San Francisco
//static double userLatitude = 40.7033127, userLongitude = -73.979681; // New York
//static double userLatitude = 34.0204989, userLongitude = -118.4117325; // Los Angeles
//static double userLatitude = 49.8152995, userLongitude = 6.13332; // Luxemburg
//static double userLatitude = -33.7969235, userLongitude = 150.9224326; //Sydney
//static double userLatitude = 47.4812134, userLongitude = 19.1303031; // Budapest
static pthread_t thread = 0;
static pthread_mutex_t positionMutex;

// define UrlData struct used by libcurl
struct UrlData
{
    size_t size;
    char* data;
};

// WriteData function used by libcurl
static size_t WriteData(void *ptr, size_t size, size_t nmemb, UrlData *data)
{
    size_t index = data->size;
    size_t n = (size * nmemb);

    data->size += (size * nmemb);

    char *tmp = (char*) realloc(data->data, data->size + 1);

    if(tmp != NULL)
        data->data = tmp;
    else
    {
        if(data->data != NULL)
        {
            free(data->data);
            data->data = NULL;
        }

        return 0;
    }

    memcpy((data->data + index), ptr, n);
    data->data[data->size] = '\0';

    return size * nmemb;
}

// retrieves a url with libcurl and returns the content
static char *GetUrl(const char *url)
{
    CURL *curl = NULL;

    UrlData data;
    data.size = 0;
    data.data = (char*) malloc(4096);

    if(data.data != NULL)
    {
        data.data[0] = '\0';

        curl = curl_easy_init();
        if (curl != NULL)
        {
            curl_easy_setopt(curl, CURLOPT_URL, url);
            curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteData);
            curl_easy_setopt(curl, CURLOPT_WRITEDATA, &data);
            curl_easy_perform(curl);
            curl_easy_cleanup(curl);
        }
    }

    return data.data;
}

// define json_value_value type used by Parson
typedef union json_value_value
{
    char *string;
    double number;
    JSON_Object *object;
    JSON_Array *array;
    int boolean;
    int null;
} JSON_Value_Value;

// define json_value_t struct used by Parson
struct json_value_t
{
    JSON_Value_Type type;
    JSON_Value_Value value;
};

// retrieves the balancer url with the lowest load, if there are several balancers with the same load one of these is randomly selected
static char *GetBalancerUrl(void)
{
    char *bestUrl = NULL;

    char *balance = GetUrl(URL_BALANCE);
    if (balance != NULL)
    {
        JSON_Value *rootJson = json_parse_string(balance);
        free(balance);
        balance = NULL;

        if (rootJson != NULL && rootJson->type == JSONObject)
        {
            JSON_Object *serversJson = json_value_get_object(rootJson);

            if (serversJson != NULL)
            {
                size_t serverCount = json_object_get_count(serversJson);
                int bestLoad = 0;

                for (int i = 0; i < serverCount; i++)
                {
                    const char *url = json_object_get_name(serversJson, i);

                    JSON_Value *value = json_object_get_value(serversJson, url);

                    if (value != NULL && value->type == JSONNumber)
                    {
                        int load = (int) json_object_get_number(serversJson, url);

                        if (load != 0 && (bestUrl == NULL || load <= bestLoad/* || (load == bestLoad && rand() % 2)*/))
                        {
                            if (bestUrl != NULL)
                            {
                                free(bestUrl);
                                bestUrl = NULL;
                            }

                            bestUrl = (char*) malloc(strlen(url) + 1);
                            if (bestUrl != NULL)
                                strcpy(bestUrl, url);

                            bestLoad = load;
                        }
                    }
                }
            }

            json_value_free(rootJson);
            rootJson = NULL;
        }
    }

    return bestUrl;
}

// converts from degrees to radians
inline static double DegreesToRadians(double degrees)
{
    return degrees * (M_PI / 180.0);
}

// converts from degrees to radians
inline static double RadiansToDegrees(double radians)
{
    return radians * (180.0 / M_PI);
}

// calculates the midpoint between two given coordinates
static void GetMidpoint(double *latitudeMidpoint, double *longitudeMidpoint, double latiudeA, double longitudeA, double latiudeB, double longitudeB)
{
    double dLongitude = DegreesToRadians(longitudeB - longitudeA);
    double bX = cos(DegreesToRadians(latiudeB)) * cos(dLongitude);
    double bY = cos(DegreesToRadians(latiudeB)) * sin(dLongitude);

    *latitudeMidpoint = RadiansToDegrees(atan2(sin(DegreesToRadians(latiudeA)) + sin(DegreesToRadians(latiudeB)), sqrt((cos(DegreesToRadians(latiudeA)) + bX) * (cos(DegreesToRadians(latiudeA)) + bX) + bY * bY)));

    *longitudeMidpoint = longitudeA + RadiansToDegrees(atan2(bY, cos(DegreesToRadians(latiudeA)) + bX));
}

// calculates the distance between two coordinates in nautical miles
static double GetDistance(double latiudeA, double longitudeA, double latiudeB, double longitudeB)
{
    double dLatitude = latiudeB - latiudeA;
    double dLongitude = longitudeB - longitudeA;

    double a = pow(sin(DegreesToRadians(dLatitude / 2.0)), 2) + cos(DegreesToRadians(latiudeA)) * cos(DegreesToRadians(latiudeB)) * pow(sin(DegreesToRadians(dLongitude / 2.0)), 2);
    double c = 2.0 * atan2(sqrt(a), sqrt(1.0 - a));

    return c * RADIUS_EARTH;
}

// parses a JSON object containing zones and calculates the zone that fits the given latitude and longitude best, bestDistance is used internally and contains the distance from the midpoint of the selected zone
static void ParseZones(char **bestZone, double *bestDistance, JSON_Object *zonesJson, double latitude, double longitude)
{
    *bestDistance = -1.0;

    if (zonesJson != NULL)
    {
        size_t zoneCount = json_object_get_count(zonesJson);

        for (int i = 0; i < zoneCount; i++)
        {
            const char *zoneName = json_object_get_name(zonesJson, i);
            JSON_Value *valueJson = json_object_get_value(zonesJson, zoneName);

            if (valueJson != NULL && valueJson->type == JSONObject)
            {
                JSON_Object *zoneJson = json_value_get_object(valueJson);
                double topLeftX = 0.0, topLeftY = 0.0, bottomRightX = 0.0, bottomRightY = 0.0;
                JSON_Object *subzonesJson = NULL;

                size_t propertyCount = json_object_get_count(zoneJson);
                for (int j = 0; j < propertyCount; j++)
                {
                    const char *propertyName = json_object_get_name(zoneJson, j);
                    JSON_Value *propertyJson = json_object_get_value(zoneJson, propertyName);

                    if (propertyJson != NULL)
                    {
                        if (propertyJson->type == JSONNumber)
                        {
                            double number = json_value_get_number(propertyJson);

                            if (strcmp(propertyName, "tl_x") == 0)
                                topLeftX = number;
                            else if (strcmp(propertyName, "tl_y") == 0)
                                topLeftY = number;
                            else if (strcmp(propertyName, "br_x") == 0)
                                bottomRightX = number;
                            else if (strcmp(propertyName, "br_y") == 0)
                                bottomRightY = number;
                        }
                        else if (propertyJson->type == JSONObject && (strcmp(propertyName, "subzones") == 0))
                            subzonesJson = json_value_get_object(propertyJson);
                    }
                }

                if (topLeftX != 0.0 && topLeftY != 0.0 && bottomRightX != 0.0 && bottomRightY != 0.0 && longitude > topLeftX && latitude < topLeftY && longitude < bottomRightX && latitude > bottomRightY)
                {
                    double latitudeMidpoint = 0.0, longitudeMidpoint = 0.0;
                    GetMidpoint(&latitudeMidpoint, &longitudeMidpoint, topLeftY, topLeftX, bottomRightY, bottomRightX);
                    double distance = GetDistance(latitudeMidpoint, longitudeMidpoint, latitude, longitude);
//                    printf("Distance from %s = %f\n", zoneName, distance);
                    if (*bestDistance == -1.0 || distance < *bestDistance)
                    {
                        if (*bestZone != NULL)
                        {
                            free(*bestZone);
                            *bestZone = NULL;
                        }

                        if (subzonesJson != NULL)
                        {
                            char *bestSubzone = NULL;
                            double subzoneDistance = -1.0;
                            ParseZones(&bestSubzone, &subzoneDistance, subzonesJson, latitude, longitude);

                            if (bestSubzone != NULL && subzoneDistance != -1.0)
                            {
                                *bestDistance = subzoneDistance;
                                *bestZone = bestSubzone;
                            }
                        }

                        if (*bestZone == NULL)
                        {
                            *bestDistance = distance;
                            *bestZone = (char*) malloc(strlen(zoneName) + 1);
                            if (*bestZone != NULL)
                                strcpy(*bestZone, zoneName);
                        }
                    }
                }
            }
        }
    }
}

// returns the name of the zone that fits the given latitude and longitude best
static char *GetZoneName(double latitude, double longitude)
{
    char *zoneName = NULL;
    char *zones = GetUrl(URL_ZONES);

    if (zones != NULL)
    {
        JSON_Value *rootJson = json_parse_string(zones);
        free(zones);
        zones = NULL;

        if (rootJson != NULL)
        {
            if (rootJson->type == JSONObject)
            {
                double bestDistance = -1.0;
                ParseZones(&zoneName, &bestDistance, json_value_get_object(rootJson), latitude, longitude);
            }

            json_value_free(rootJson);
            rootJson = NULL;
        }
    }

    return zoneName;
}

// updates the planes map, planes not seen for a defined intervall are removed from the map and only planes within a defined distance from the given latitude and longited
static void UpdatePlanes(char *balancerUrl, char *zoneName, double latitude, double longitude)
{
    time_t currentTime = time(NULL);

    if (currentTime != ((time_t) -1))
    {
        pthread_mutex_lock(&planesMutex);
        for (std::map<std::string, Plane*>::iterator p = planes.begin(); p != planes.end(); ++p)
        {
            Plane *plane = p->second;
            if (currentTime - plane->lastSeen > PLANE_TIMEOUT)
            {
                //printf("Removing: %s - CurrentTime = %d - LastSeen = %d\n", p->first.c_str(), (int) currentTime, (int) plane->lastSeen);
                free(plane);
                plane = NULL;
                planes.erase(p->first);
            }
        }
        pthread_mutex_unlock(&planesMutex);

        char url[strlen(balancerUrl) + strlen(URL_ZONE_INFIX) + strlen(zoneName) + strlen(URL_ZONE_SUFFIX)];
        sprintf(url, "%s%s%s%s", balancerUrl, URL_ZONE_INFIX, zoneName, URL_ZONE_SUFFIX);

        char *zone = GetUrl(url);
        if (zone != NULL)
        {
            int cmp = 1;
            if (lastZone != NULL)
                cmp = strcmp(zone, lastZone);

            if (cmp != 0)
            {
                JSON_Value *rootJson = json_parse_string(zone);
                lastZone = zone;

                if (rootJson != NULL)
                {
                    if (rootJson->type == JSONObject)
                    {
                        JSON_Object *aircraftJson = json_value_get_object(rootJson);
                        if (aircraftJson != NULL)
                        {
                            size_t aircraftCount = json_object_get_count(aircraftJson);
                            for (int i = 0; i < aircraftCount; i++)
                            {
                                const char *id = json_object_get_name(aircraftJson, i);
                                if (id != NULL)
                                {
                                    JSON_Value *value = json_object_get_value(aircraftJson, id);

                                    if (value != NULL && value->type == JSONArray)
                                    {
                                        JSON_Array *propertiesJson = json_value_get_array(value);

                                        if (propertiesJson != NULL)
                                        {
                                            const char *registration = NULL, *icaoId = NULL, *icaoType = NULL, *squawk = NULL;
                                            double latitudePlane = 0.0, longitudePlane = 0.0, altitude = 0.0;
                                            float heading = 0.0f;
                                            int speed = 0, verticalSpeed = 0;

                                            int propertyCount = json_array_get_count(propertiesJson);
                                            for (int k = 0; k < propertyCount; k++)
                                            {
                                                JSON_Value *valueJson = json_array_get_value(propertiesJson, k);

                                                if (valueJson != NULL)
                                                {
                                                    switch (k)
                                                    {
                                                    case ARRAY_INDEX_LATITUDE:
                                                        latitudePlane = json_value_get_number(valueJson);
                                                        break;
                                                    case ARRAY_INDEX_LONGITUDE:
                                                        longitudePlane = json_value_get_number(valueJson);
                                                        break;
                                                    case ARRAY_INDEX_ALTITUDE:
                                                        altitude = json_value_get_number(valueJson);
                                                        break;
                                                    case ARRAY_INDEX_HEADING:
                                                        heading = (float) json_value_get_number(valueJson);
                                                        break;
                                                    case ARRAY_INDEX_SPEED:
                                                        speed = (int) json_value_get_number(valueJson);
                                                        break;
                                                    case ARRAY_INDEX_SQUAWK:
                                                        squawk = json_value_get_string(valueJson);
                                                        break;
                                                    case ARRAY_INDEX_ICAO_TYPE:
                                                        icaoType = json_value_get_string(valueJson);
                                                        break;
                                                    case ARRAY_INDEX_REGISTRATION:
                                                        registration = json_value_get_string(valueJson);
                                                        break;
                                                    case ARRAY_INDEX_VERTICAL_SPEED:
                                                        verticalSpeed = (int) json_value_get_number(valueJson);
                                                        break;
                                                    case ARRAY_INDEX_ICAO_ID:
                                                        icaoId = json_value_get_string(valueJson);
                                                        break;
                                                    }
                                                }
                                            }

                                            if (latitudePlane != 0.0 && longitudePlane != 0.0 && GetDistance(latitude, longitude, latitudePlane, longitudePlane) <= MAX_DISTANCE)
                                            {
                                                Plane *plane = NULL;

                                                pthread_mutex_lock(&planesMutex);
                                                std::map<std::string, Plane*>::iterator p = planes.find(id);
                                                if (p != planes.end())
                                                    plane = p->second;
                                                else
                                                {
                                                    plane = (Plane*) malloc(sizeof(*plane));
                                                    if (plane != NULL)
                                                        planes[std::string(id)] = plane;
                                                }

                                                if (plane != NULL)
                                                {
                                                    if (registration == NULL || strlen(registration) == 0)
                                                        registration = "Unknown";
                                                    if (icaoId == NULL || strlen(icaoId) == 0)
                                                        icaoId = "Unknown";
                                                    if (icaoType == NULL || strlen(icaoType) == 0)
                                                        icaoType = "UKN";
                                                    if (squawk == NULL || strlen(squawk) == 0)
                                                        squawk = "0000";
                                                    strncpy(plane->registration, registration, sizeof(plane->registration) / sizeof(char));
                                                    strncpy(plane->icaoId, icaoId, sizeof(plane->icaoId) / sizeof(char));
                                                    strncpy(plane->icaoType, icaoType, sizeof(plane->icaoType) / sizeof(char));
                                                    strncpy(plane->squawk, squawk, sizeof(plane->squawk) / sizeof(char));
                                                    if (plane->latitude != latitudePlane)
                                                    {
                                                        plane->latitude = latitudePlane;
                                                        plane->interpolatedLatitude = 0.0;
                                                    }
                                                    if (plane->longitude != longitudePlane)
                                                    {
                                                        plane->longitude = longitudePlane;
                                                        plane->interpolatedLongitude = 0.0;
                                                    }
                                                    if (plane->altitude != altitude)
                                                    {
                                                        plane->altitude = altitude;
                                                        plane->interpolatedAltitude = -1000.0;
                                                    }
                                                    plane->pitch = 0.0f;
                                                    plane->roll = 0.0f;
                                                    plane->heading = heading;
                                                    plane->speed = speed;
                                                    plane->verticalSpeed = verticalSpeed;
                                                    plane->lastSeen = currentTime;
                                                }
                                                pthread_mutex_unlock(&planesMutex);
                                            }
                                        }
                                    }
                                }
                            }
                        }

                        json_value_free(rootJson);
                        rootJson = NULL;
                    }
                }
            }
        }
    }
}

// thread function that handels the update process
static void *UpdateThreadFunction(void *ptr)
{
    srand(time(NULL));

    while (true)
    {
        pthread_mutex_lock(&positionMutex);
        double latitude = userLatitude, longitude = userLongitude;
        pthread_mutex_unlock(&positionMutex);

        char *balancerUrl = GetBalancerUrl();
//        printf("URL -> %s\n", balancerUrl);
        if (balancerUrl != NULL)
        {
            char *zoneName = GetZoneName(latitude, longitude);
            if (zoneName != NULL)
            {
//                printf("ZONE -> %s\n", zoneName);
                UpdatePlanes(balancerUrl, zoneName, latitude, longitude);
                free(zoneName);
                zoneName = NULL;
            }

            free(balancerUrl);
            balancerUrl = NULL;
        }

        sleep(3);
    }
}

// provides safe writing access to the users position
void SetPosition(double latitude, double longitude)
{
    pthread_mutex_lock(&positionMutex);
    userLatitude = latitude;
    userLongitude = longitude;
    pthread_mutex_unlock(&positionMutex);
}

// initilializes the update thread and the mutexes
void Init(void)
{
    pthread_mutex_init(&planesMutex, 0);
    pthread_mutex_init(&positionMutex, 0);
    pthread_create(&thread, NULL, UpdateThreadFunction, NULL);
}

// uninitializes the reserved memory, thread and mutexes
void Cleanup(void)
{
    pthread_mutex_lock(&planesMutex);
    for (std::map<std::string, Plane*>::iterator p = planes.begin(); p != planes.end(); ++p)
    {
        Plane *plane = p->second;
        free(plane);
        plane = NULL;
        planes.erase(p->first);
    }
    pthread_mutex_unlock(&planesMutex);
    pthread_cancel(thread);
    pthread_mutex_destroy(&planesMutex);
    pthread_mutex_destroy(&positionMutex);

    if (lastZone != NULL)
        free(lastZone);
}

/*int main(void)
{
    Init();

    while(true)
    {
        printf("\033[2J\033[1;1H");
        printf("PlaneCount = %d\n\n", (int) planes.size());

        pthread_mutex_lock(&planesMutex);
        for (std::map<std::string, Plane*>::iterator p = planes.begin(); p != planes.end(); ++p)
        {
            Plane *plane = p->second;
            printf("Plane %s:\n Registration = %s\n ICAO ID = %s\n ICAO Type = %s\n Squawk = %s\n Latitude = %f\n Longitude = %f\n Altitude = %f\n Heading = %f\n Speed = %d\n Vertical Speed = %d\n\n", p->first.c_str(), plane->registration, plane->icaoId, plane->icaoType, plane->squawk, plane->latitude, plane->longitude, plane->altitude, plane->heading, plane->speed, plane->verticalSpeed);
        }
        pthread_mutex_unlock(&planesMutex);

        sleep(1);
    }

    Cleanup();

    return 0;
}*/