/*
 * sort_list: a stable sort for lists.
 *
 * Time complexity: O(n*log n)
 *   [assuming limited zero-element fragments]
 *
 * Space complexity: O(1).
 *
 * Stable: yes.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "lib.h"
#include "allocate.h"

#undef PARANOIA
#undef COVERAGE

#ifdef PARANOIA
#include <assert.h>
#else
#define assert(x)
#endif

#ifdef COVERAGE
static unsigned char been_there[256];
#define BEEN_THERE(_c)                                  \
  do {                                                  \
        if (!been_there[_c]) {                          \
                been_there[_c] = 1;                     \
                printf ("Been there: %c\n", _c);        \
        }                                               \
  } while (0)
#else
#define BEEN_THERE(_c) do { } while (0)
#endif

// Sort one fragment.  LIST_NODE_NR (==29) is a bit too high for my
// taste for something this simple.  But, hey, it's O(1).
//
// I would use libc qsort for this, but its comparison function
// gets a pointer indirection extra.
static void array_sort(void **ptr, int nr, int (*cmp)(const void *, const void *))
{
        int i;
        for (i = 1; i < nr; i++) {
                void *p = ptr[i];
                if (cmp(ptr[i-1],p) > 0) {
                        int j = i;
                        do {
                                ptr[j] = ptr[j-1];
                                if (!--j)
                                        break;
                        } while (cmp(ptr[j-1], p) > 0);
                        ptr[j] = p;
                }
        }
}

#ifdef PARANOIA
static void verify_seq_sorted (struct ptr_list *l, int n,
                               int (*cmp)(const void *, const void *))
{
        int i = 0;
        const void *a;
        struct ptr_list *head = l;

        while (l->nr == 0) {
                l = l->next;
                if (--n == 0)
                        return;
                assert (l != head);
        }

        a = l->list[0];
        while (n > 0) {
                const void *b;
                if (++i >= l->nr) {
                        i = 0;
                        l = l->next;
                        n--;
                        assert (l != head || n == 0);
                        continue;
                }
                b = l->list[i];
                assert (cmp (a, b) <= 0);
                a = b;
        }
}
#endif


#define FLUSH_TO(b)                                             \
  do {                                                          \
        int nr = (b)->nr;                                       \
        assert (nbuf >= nr);                                    \
        memcpy ((b)->list, buffer, nr * sizeof (void *));       \
        nbuf -= nr;                                             \
        memmove (buffer, buffer + nr, nbuf * sizeof (void *));  \
  } while (0)

#define DUMP_TO(b)                                              \
  do {                                                          \
        assert (nbuf <= (b)->nr);                               \
        memcpy ((b)->list, buffer, nbuf * sizeof (void *));     \
  } while (0)


// Merge two already-sorted sequences of blocks:
//   (b1_1, ..., b1_n)  and  (b2_1, ..., b2_m)
// Since we may be moving blocks around, we return the new head
// of the merged list.
static struct ptr_list *
merge_block_seqs (struct ptr_list *b1, int n,
                  struct ptr_list *b2, int m,
                  int (*cmp)(const void *, const void *))
{
        int i1 = 0, i2 = 0;
        const void *buffer[2 * LIST_NODE_NR];
        int nbuf = 0;
        struct ptr_list *newhead = b1;

        // printf ("Merging %d blocks at %p with %d blocks at %p\n", n, b1, m, b2);

        // Skip empty blocks in b2.
        while (b2->nr == 0) {
                BEEN_THERE('F');
                b2 = b2->next;
                if (--m == 0) {
                        BEEN_THERE('G');
                        return newhead;
                }
        }

        // Do a quick skip in case entire blocks from b1 are
        // already less than smallest element in b2.
        while (b1->nr == 0 ||
               cmp (PTR_ENTRY_NOTAG(b1, b1->nr - 1), PTR_ENTRY_NOTAG(b2,0)) < 0) {
                // printf ("Skipping whole block.\n");
                BEEN_THERE('H');
                b1 = b1->next;
                if (--n == 0) {
                        BEEN_THERE('I');
                        return newhead; 
                }
        }

        while (1) {
                const void *d1 = PTR_ENTRY_NOTAG(b1,i1);
                const void *d2 = PTR_ENTRY_NOTAG(b2,i2);

                assert (i1 >= 0 && i1 < b1->nr);
                assert (i2 >= 0 && i2 < b2->nr);
                assert (b1 != b2);
                assert (n > 0);
                assert (m > 0);

                if (cmp (d1, d2) <= 0) {
                        BEEN_THERE('J');
                        buffer[nbuf++] = d1;
                        // Element from b1 is smaller
                        if (++i1 >= b1->nr) {
                                BEEN_THERE('L');
                                FLUSH_TO(b1);
                                do {
                                        b1 = b1->next;
                                        if (--n == 0) {
                                                BEEN_THERE('O');
                                                while (b1 != b2) {
                                                        BEEN_THERE('P');
                                                        FLUSH_TO(b1);
                                                        b1 = b1->next;
                                                }
                                                assert (nbuf == i2);
                                                DUMP_TO(b2);
                                                return newhead;
                                        }
                                } while (b1->nr == 0);
                                i1 = 0;
                        }
                } else {
                        BEEN_THERE('K');
                        // Element from b2 is smaller
                        buffer[nbuf++] = d2;
                        if (++i2 >= b2->nr) {
                                struct ptr_list *l = b2;
                                BEEN_THERE('M');
                                // OK, we finished with b2.  Pull it out
                                // and plug it in before b1.

                                b2 = b2->next;
                                b2->prev = l->prev;
                                b2->prev->next = b2;
                                l->next = b1;
                                l->prev = b1->prev;
                                l->next->prev = l;
                                l->prev->next = l;

                                if (b1 == newhead) {
                                        BEEN_THERE('N');
                                        newhead = l;
                                }

                                FLUSH_TO(l);
                                b2 = b2->prev;
                                do {
                                        b2 = b2->next;
                                        if (--m == 0) {
                                                BEEN_THERE('Q');
                                                assert (nbuf == i1);
                                                DUMP_TO(b1);
                                                return newhead;
                                        }
                                } while (b2->nr == 0);
                                i2 = 0;
                        }
                }
        }
}


void sort_list(struct ptr_list **plist, int (*cmp)(const void *, const void *))
{
        struct ptr_list *head = *plist, *list = head;
        int blocks = 1;

        if (!head)
                return;

        // Sort all the sub-lists
        do {
                array_sort(list->list, list->nr, cmp);
#ifdef PARANOIA
                verify_seq_sorted (list, 1, cmp);
#endif
                list = list->next;
        } while (list != head);

        // Merge the damn things together
        while (1) {
                struct ptr_list *block1 = head;

                do {
                        struct ptr_list *block2 = block1;
                        struct ptr_list *next, *newhead;
                        int i;

                        for (i = 0; i < blocks; i++) {
                                block2 = block2->next;
                                if (block2 == head) {
                                        if (block1 == head) {
                                                BEEN_THERE('A');
                                                *plist = head;
                                                return;
                                        }
                                        BEEN_THERE('B');
                                        goto next_pass;
                                }                                               
                        }

                        next = block2;
                        for (i = 0; i < blocks; ) {
                                next = next->next;
                                i++;
                                if (next == head) {
                                        BEEN_THERE('C');
                                        break;
                                }
                                BEEN_THERE('D');
                        }

                        newhead = merge_block_seqs (block1, blocks,
                                                    block2, i,
                                                    cmp);
#ifdef PARANOIA
                        verify_seq_sorted (newhead, blocks + i, cmp);
#endif
                        if (block1 == head) {
                                BEEN_THERE('E');
                                head = newhead;
                        }
                        block1 = next;
                } while (block1 != head);
        next_pass:
                blocks <<= 1;
        }
}