#include <stdio.h>
#include <math.h>

#define DATA_BOUND 3

int F_FRONT = -1;
int F_REAR = -1;
int B_FRONT = -1;
int B_REAR = -1;
unsigned int back_sensor_data[3];
unsigned int front_sensor_data[3];

void sensor_data_init()
{
    int i;
    for (i = 0; i < DATA_BOUND; i++)
    {
        back_sensor_data[i] = 0;
        front_sensor_data[i] = 0;
    }
}

int is_full(int front, int rear)
{
    if ((front == rear + 1) || (front == 0 && rear == DATA_BOUND - 1))
    {
        return 1;
    }
    return 0;
}

int is_empty(int front)
{
    if (front == -1)
    {
        return 1;
    }
    return 0;
}

void enqueue_back(unsigned int data)
{
    if (!is_full(B_FRONT, B_REAR))
    {
        if (B_FRONT == -1)
        {
            B_FRONT = 0;
        }
        B_REAR = (B_REAR + 1) % DATA_BOUND;
        back_sensor_data[B_REAR] = data;
    }
}

unsigned int dequeue_back()
{
    unsigned int data;
    if (is_empty(B_FRONT))
    {
        return -1;
    }
    else
    {
        data = back_sensor_data[B_FRONT];
        if (B_FRONT == B_REAR)
        {
            B_FRONT = -1;
            B_REAR = -1;
        }
        else
        {
            B_FRONT = (B_FRONT + 1) % DATA_BOUND;
        }
    }
    return (data);
}

int main(int argc, char **argv)
{
    enqueue_back(71);
    enqueue_back(57);
    enqueue_back(66);

    unsigned int new_val = 74;

    unsigned int sum = back_sensor_data[0] + 3 * back_sensor_data[1] + 3 * back_sensor_data[2] + new_val;
    printf("result: %d\n", sum / 8);

    printf("removed: %d\n", dequeue_back());
    enqueue_back(new_val);
    enqueue_back(55);

    printf("added: %d\n", back_sensor_data[B_REAR]);
    printf("removed: %d\n", dequeue_back());
    printf("removed: %d\n", dequeue_back());
    printf("removed: %d\n", dequeue_back());
    printf("removed: %d\n", dequeue_back());

    return 0;
}