#include "ucore/rate_limit.h"

#define SCALE_FACTOR 1000


void uc_ratelimit_init(struct RateLimit *r, long tickets, long period, long current_ts)
{
    r->tickets = tickets;
    r->scaled_tickets = tickets * SCALE_FACTOR;
    r->period = period;
    r->available_tickets = r->scaled_tickets;
    r->last_ts = current_ts;
}

void uc_ratelimit_reset(struct RateLimit *r, long current_ts)
{
    r->available_tickets = r->scaled_tickets;

    if (current_ts)
        r->last_ts = current_ts;
}

int uc_ratelimit_allow(struct RateLimit *r, long current_ts)
{
    int allowed;
    long diff_period;

    //Find elapsed time
    diff_period = current_ts - r->last_ts;

    //If time went backwards, we halt the time for this round
    if (diff_period < 0) 
        diff_period = 0;

    //Calculate the number of tickets that became available since 
    //the last time. (+ ScALE_FACTOR/2 is to round up at halfway points for
    //integer arithmetics)
    r->available_tickets += diff_period  * 
                            ((r->scaled_tickets + SCALE_FACTOR/2) / r->period);

    //throttle handing out tickets
    //
    if (r->available_tickets > r->scaled_tickets) 
        r->available_tickets = r->scaled_tickets;

    //If we have at least onen ticket, we can allow 
    if (r->available_tickets >=  1 * SCALE_FACTOR) {
        r->available_tickets -= 1 * SCALE_FACTOR;
        allowed = 1;
    } else {
        //no more tickets.
        allowed = 0;
    }

    //save this period. 
    r->last_ts = current_ts;

    return allowed;
}

#if 0
int main()
{
    int i;
    struct RateLimit r;
    time_t start;

    uc_ratelimit_init(&r, 10, 60, time(NULL));

    for(i = 0; i < 120; i++) {
        int k;
        long allowed = 0;
        sleep(1);
        for (k = 0; k < 500; k++) 
            allowed += uc_ratelimit_allow(&r, time(NULL));
        printf("%ld of 500 can pass\n", allowed);
    }

    return 0;
}
#endif