#include <math.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <limits.h>

#include "sorters.h"
#include "common.h"
#include "counts.h"

static inline void *tail(char *base, size_t nmel, size_t width)
{
	return base + (nmel-1) * width;
}

/* get index of last block whose head is less than the previous block's tail */
static size_t last_overlap(char *base, size_t bcount, size_t bwidth, size_t width, cmpfun cmp)
{
	struct counts snapshot = counts[CURRENT];

	for (char *cur = tail(base, bcount, bwidth); --bcount; cur -= bwidth)
		if (cmp(cur - width, cur) > 0) break;

	add_counts(counts + LAST_OVERLAP, &snapshot);
	return bcount;
}

size_t merge(char *buf, char *a, char *b, size_t bufnmel, size_t anmel, size_t bnmel, size_t width, cmpfun cmp)
{
	struct counts snapshot = counts[CURRENT];

	char  *a_end   = a   + width * anmel;
	char  *b_end   = b   + width * bnmel;
	char  *buf_end = buf + width * bufnmel;
	size_t count;

	while (bnmel) {
		for (count = 0; cmp(a_end-width, b_end-width) > 0; count++) {
			anmel   -= 1;
			bufnmel -= 1;
			a_end   -= width;
			buf_end -= width;
		}
		swap(a_end, buf_end, count*width);

		do {
			for (count = 0; bnmel && count < bufnmel && cmp(a_end-width, b_end-width) <= 0; count++) {
				bnmel   -= 1;
				b_end   -= width;
				buf_end -= width;
			}
			swap(b_end, buf_end, count*width);
		} while (count == bufnmel);
	}

	add_counts(counts + MERGE, &snapshot);
	return anmel;
}

void grailsort(void *unsorted, size_t nmel, size_t width, cmpfun cmp)
{
	char *base = unsorted;

	if (nmel <= MAX_SORTNET) {
		sorting_network(base, nmel, width, cmp);
		return;
	}

	size_t blknmel = sqrt(nmel);               /* elements in a block */
	size_t bufnmel = blknmel + nmel % blknmel; /* elements in the buffer */
	size_t bwidth  = blknmel * width;          /* size of a block in bytes */
	size_t blocks  = nmel / blknmel - 1;       /* number of blocks in a + b */
	size_t acount  = blocks / 2;
	size_t bcount  = blocks - acount;

	char *a   = base;
	char *b   = a + acount * bwidth;
	char *buf = b + bcount * bwidth;

	grailsort(a, acount * blknmel, width, cmp);
	grailsort(b, bcount * blknmel, width, cmp);

	/* sort all the a and b blocks together by their head elements */
	grailsort(base, blocks, bwidth, cmp);

	/* merge, starting from the end and working towards the beginning */
	size_t last_nmel = blknmel;
	while (blocks > 1) {
		size_t overlap = last_overlap(base, blocks, bwidth, width, cmp);

		if (!overlap) break;

		char *block_a = base + bwidth * (overlap-1);
		char *block_b = base + bwidth *  overlap;
		size_t bnmel  = (blocks - overlap - 1) * blknmel + last_nmel;

		last_nmel = merge(buf, block_a, block_b, bufnmel, blknmel, bnmel, width, cmp);
		buf       = block_a + last_nmel * width;
		blocks    = overlap;
	}

	struct counts snapshot = counts[CURRENT];
	rotate(base, buf-base + bufnmel*width, buf-base);
	add_counts(counts + MOVE_BUFFER, &snapshot);

	grailsort(base, bufnmel, width, cmp);
	distribute_buffer(base, bufnmel, nmel - bufnmel, width, cmp);

#if 0
	assert_sorted(base, nmel, width, cmp);
#endif
}