#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <assert.h>
#include <time.h>

#define BLOCK 1024*1024
#define SIZE 512

#define STEP 64
#define COUNT 1000

int compare (const void *a, const void *b)
{
	return (int)(*(long *)a - *(long*)b);
}

long n_sec (struct timespec *start, struct timespec *stop)
{
	long diff_sec = stop->tv_sec - start->tv_sec;
	long diff_nsec = stop->tv_nsec - start->tv_nsec;
	long wall_nsec = (diff_sec * 1000000000) + diff_nsec;
	return wall_nsec;
}

int main (int argc, char *argv[])
{
	if (argc < 2)
	{
		printf("usage: generate <file name>\n");
		return -1;
	}

	char *name = argv[1];

	int mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
	int flag = O_RDWR | O_CREAT;
	int fd = open(name, flag, mode);
	assert(fd != -1);


	int entries = SIZE / STEP;

	long **table = malloc(sizeof(long*) * entries);

	for (int i = 0; i < entries; ++i)
	{
		table[i] = malloc(sizeof(long) * COUNT);
	}

	for (int c = 0; c < COUNT; c++)
	{
		int b = rand() % BLOCK;
		lseek (fd, b*SIZE, SEEK_SET);

		for (int e = 0; e < entries; e++)
		{
			struct timespec t_start, t_stop;
			int buffer;
			clock_gettime(CLOCK_MONOTONIC, &t_start);
			read(fd, &buffer, sizeof(int));
			clock_gettime(CLOCK_MONOTONIC, &t_stop);
			lseek (fd, STEP - sizeof(int), SEEK_CUR);
			table[e][c]= n_sec(&t_start, &t_stop);
		}
	}

	printf ("#N\tMin\tQ1\tMed\tQ3\tD9\tMax\n");
	for (int e = 0; e < entries; ++e)
	{
		qsort(table[e], COUNT, sizeof(long), compare);
		long min = table[e][0];
		long q1 = table[e][COUNT/4];
		long med = table[e][COUNT/2];
		long q3 = table[e][3 * (COUNT/4)];
		long d9 = table[e][9 * (COUNT/10)];
		long max = table[e][COUNT - 1];
		printf("%d\t%ld\t%ld\t%ld\t%ld\t%ld\t%ld\n",
			e*STEP, min, q1, med, q3, d9, max);

	}


	close (fd);
	printf("done\n");

	return 0;
}