/*
 * Odyssey.
 *
 * Scalable PostgreSQL connection pooler.
 *
 * Implementation of reservoir sampling algorithm
*/

#include <stdlib.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <inttypes.h>
#include <assert.h>

#include <machinarium.h>
#include <kiwi.h>
#include <odyssey.h>

void od_hgram_init(od_hgram_t *hgram) {
	memset(hgram, 0, sizeof(*hgram));
}

// Probablisticaly add data point, return 1 is point was actually added to data set, 0 otherwise
int od_hgram_add_data_point(od_hgram_t *hgram, uint64_t point) {
	uint64_t next_position = __sync_fetch_and_add(&hgram->estimated_size, 1);
	if (next_position < OD_HGRAM_DATA_POINTS) {
		hgram->data[next_position] = point;
		return 1;
	}
	next_position = machine_lrand48() % next_position;
	if (next_position < OD_HGRAM_DATA_POINTS){
		hgram->data[next_position] = point;
		return 1;
	}
	return 0;
}

static int cmpfunc_ui32(const void *a, const void *b) {
	if (*(uint32_t *) a < *(uint32_t *) b)
		return 1;
	if (*(uint32_t *) a > *(uint32_t *) b)
		return -1;
	return 0;
}

// Create static copy of reservoir for analysis
void od_hgram_freeze(od_hgram_t *hgram, od_hgram_frozen_t *hgram_tmp) {
	memcpy(hgram_tmp, hgram, sizeof(*hgram));
	hgram->estimated_size = 0;

	qsort(&hgram_tmp->data, OD_HGRAM_DATA_POINTS, sizeof(uint32_t), cmpfunc_ui32);

	if (hgram_tmp->estimated_size > OD_HGRAM_DATA_POINTS) {
		hgram_tmp->estimated_size = OD_HGRAM_DATA_POINTS;
	}
}

// Compute quantile withing static copy of reservoir
uint64_t od_hgram_quantile(od_hgram_frozen_t *frozen, double quantile) {
	assert(quantile > 0);
	assert(quantile <= 1);
	if (frozen->estimated_size == 0)
		return 0;
	return frozen->data[(size_t) (frozen->estimated_size * (1 - quantile))];
}