/*
*
* Copyright 2005, Lukas Sandstrom <lukass@etek.chalmers.se>
*
* This file is licensed under the GPL v2.
*
*/

#include "cache.h"

static const char pack_redundant_usage[] =
"git-pack-redundant [ --verbose ] [ --alt-odb ] < --all | <.pack filename> ...>";

static int load_all_packs = 0, verbose = 0, alt_odb = 0;

struct llist_item {
        struct llist_item *next;
        char *sha1;
};
static struct llist {
        struct llist_item *front;
        struct llist_item *back;
        size_t size;
} *all_objects; /* all objects which must be present in local packfiles */

static struct pack_list {
        struct pack_list *next;
        struct packed_git *pack;
        struct llist *unique_objects;
        struct llist *all_objects;
} *local_packs = NULL, *altodb_packs = NULL;

struct pll {
        struct pll *next;
        struct pack_list *pl;
        size_t pl_size;
};

static inline void llist_free(struct llist *list)
{
        while((list->back = list->front)) {
                list->front = list->front->next;
                free(list->back);
        }
        free(list);
}

static inline void llist_init(struct llist **list)
{
        *list = xmalloc(sizeof(struct llist));
        (*list)->front = (*list)->back = NULL;
        (*list)->size = 0;
}

static struct llist * llist_copy(struct llist *list)
{
        struct llist *ret;
        struct llist_item *new, *old, *prev;
        
        llist_init(&ret);

        if ((ret->size = list->size) == 0)
                return ret;

        new = ret->front = xmalloc(sizeof(struct llist_item));
        new->sha1 = list->front->sha1;

        old = list->front->next;
        while (old) {
                prev = new;
                new = xmalloc(sizeof(struct llist_item));
                prev->next = new;
                new->sha1 = old->sha1;
                old = old->next;
        }
        new->next = NULL;
        ret->back = new;
        
        return ret;
}

static inline struct llist_item * llist_insert(struct llist *list,
                                        struct llist_item *after, char *sha1)
{
        struct llist_item *new = xmalloc(sizeof(struct llist_item));
        new->sha1 = sha1;
        new->next = NULL;

        if (after != NULL) {
                new->next = after->next;
                after->next = new;
                if (after == list->back)
                        list->back = new;
        } else {/* insert in front */
                if (list->size == 0)
                        list->back = new;
                else
                        new->next = list->front;
                list->front = new;
        }
        list->size++;
        return new;
}

static inline struct llist_item * llist_insert_back(struct llist *list, char *sha1)
{
        return llist_insert(list, list->back, sha1);
}

static inline struct llist_item * llist_insert_sorted_unique(struct llist *list,
                                        char *sha1, struct llist_item *hint)
{
        struct llist_item *prev = NULL, *l;

        l = (hint == NULL) ? list->front : hint;
        while (l) {
                int cmp = memcmp(l->sha1, sha1, 20);
                if (cmp > 0) { /* we insert before this entry */
                        return llist_insert(list, prev, sha1);
                }
                if(!cmp) { /* already exists */
                        return l;
                }
                prev = l;
                l = l->next;
        }
        /* insert at the end */
        return llist_insert_back(list, sha1);
}

/* returns a pointer to an item in front of sha1 */
static inline struct llist_item * llist_sorted_remove(struct llist *list, char *sha1,
                                               struct llist_item *hint)
{
        struct llist_item *prev, *l;

redo_from_start:
        l = (hint == NULL) ? list->front : hint;
        prev = NULL;
        while (l) {
                int cmp = memcmp(l->sha1, sha1, 20);
                if (cmp > 0) /* not in list, since sorted */
                        return prev;
                if(!cmp) { /* found */
                        if (prev == NULL) {
                                if (hint != NULL && hint != list->front) {
                                        /* we don't know the previous element */
                                        hint = NULL;
                                        goto redo_from_start;
                                }
                                list->front = l->next;
                        } else
                                prev->next = l->next;
                        if (l == list->back)
                                list->back = prev;
                        free(l);
                        list->size--;
                        return prev;
                }
                prev = l;
                l = l->next;
        }
        return prev;
}

/* computes A\B */
static void llist_sorted_difference_inplace(struct llist *A,
                                     struct llist *B)
{
        struct llist_item *hint, *b;

        hint = NULL;
        b = B->front;

        while (b) {
                hint = llist_sorted_remove(A, b->sha1, hint);
                b = b->next;
        }
}

static inline struct pack_list * pack_list_insert(struct pack_list **pl,
                                           struct pack_list *entry)
{
        struct pack_list *p = xmalloc(sizeof(struct pack_list));
        memcpy(p, entry, sizeof(struct pack_list));
        p->next = *pl;
        *pl = p;
        return p;
}

static inline size_t pack_list_size(struct pack_list *pl)
{
        size_t ret = 0;
        while(pl) {
                ret++;
                pl = pl->next;
        }
        return ret;
}

static struct pack_list * pack_list_difference(struct pack_list *A,
                                        struct pack_list *B)
{
        struct pack_list *ret, *pl;

        if (A == NULL)
                return NULL;

        pl = B;
        while (pl != NULL) {
                if (A->pack == pl->pack)
                        return pack_list_difference(A->next, B);
                pl = pl->next;
        }
        ret = xmalloc(sizeof(struct pack_list));
        memcpy(ret, A, sizeof(struct pack_list));
        ret->next = pack_list_difference(A->next, B);
        return ret;
}

static void cmp_two_packs(struct pack_list *p1, struct pack_list *p2)
{
        int p1_off, p2_off;
        void *p1_base, *p2_base;
        struct llist_item *p1_hint = NULL, *p2_hint = NULL;
        
        p1_off = p2_off = 256 * 4 + 4;
        p1_base = (void *)p1->pack->index_base;
        p2_base = (void *)p2->pack->index_base;

        while (p1_off <= p1->pack->index_size - 3 * 20 &&
               p2_off <= p2->pack->index_size - 3 * 20)
        {
                int cmp = memcmp(p1_base + p1_off, p2_base + p2_off, 20);
                /* cmp ~ p1 - p2 */
                if (cmp == 0) {
                        p1_hint = llist_sorted_remove(p1->unique_objects,
                                        p1_base + p1_off, p1_hint);
                        p2_hint = llist_sorted_remove(p2->unique_objects,
                                        p1_base + p1_off, p2_hint);
                        p1_off+=24;
                        p2_off+=24;
                        continue;
                }
                if (cmp < 0) { /* p1 has the object, p2 doesn't */
                        p1_off+=24;
                } else { /* p2 has the object, p1 doesn't */
                        p2_off+=24;
                }
        }
}

static void pll_insert(struct pll **pll, struct pll **hint_table)
{
        struct pll *prev;
        int i = (*pll)->pl_size - 1;

        if (hint_table[i] == NULL) {
                hint_table[i--] = *pll;
                for (; i >= 0; --i) {
                        if (hint_table[i] != NULL)
                                break;
                }
                if (hint_table[i] == NULL) /* no elements in list */
                        die("Why did this happen?");
        }

        prev = hint_table[i];
        while (prev->next && prev->next->pl_size < (*pll)->pl_size)
                prev = prev->next;

        (*pll)->next = prev->next;
        prev->next = *pll;
}

/* all the permutations have to be free()d at the same time,
 * since they refer to each other
 */
static struct pll * get_all_permutations(struct pack_list *list)
{
        struct pll *subset, *pll, *new_pll = NULL; /*silence warning*/
        static struct pll **hint = NULL;
        if (hint == NULL)
                hint = xcalloc(pack_list_size(list), sizeof(struct pll *));
                
        if (list == NULL)
                return NULL;

        if (list->next == NULL) {
                new_pll = xmalloc(sizeof(struct pll));
                hint[0] = new_pll;
                new_pll->next = NULL;
                new_pll->pl = list;
                new_pll->pl_size = 1;
                return new_pll;
        }

        pll = subset = get_all_permutations(list->next);
        while (pll) {
                if (pll->pl->pack == list->pack) {
                        pll = pll->next;
                        continue;
                }
                new_pll = xmalloc(sizeof(struct pll));

                new_pll->pl = xmalloc(sizeof(struct pack_list));
                memcpy(new_pll->pl, list, sizeof(struct pack_list));
                new_pll->pl->next = pll->pl;
                new_pll->pl_size = pll->pl_size + 1;
                
                pll_insert(&new_pll, hint);

                pll = pll->next;
        }
        /* add ourself */
        new_pll = xmalloc(sizeof(struct pll));
        new_pll->pl = xmalloc(sizeof(struct pack_list));
        memcpy(new_pll->pl, list, sizeof(struct pack_list));
        new_pll->pl->next = NULL;
        new_pll->pl_size = 1;
        pll_insert(&new_pll, hint);

        return hint[0];
}

static int is_superset(struct pack_list *pl, struct llist *list)
{
        struct llist *diff;

        diff = llist_copy(list);

        while (pl) {
                llist_sorted_difference_inplace(diff,
                                                pl->all_objects);
                if (diff->size == 0) { /* we're done */
                        llist_free(diff);
                        return 1;
                }
                pl = pl->next;
        }
        llist_free(diff);
        return 0;
}

static size_t sizeof_union(struct packed_git *p1, struct packed_git *p2)
{
        size_t ret = 0;
        int p1_off, p2_off;
        void *p1_base, *p2_base;

        p1_off = p2_off = 256 * 4 + 4;
        p1_base = (void *)p1->index_base;
        p2_base = (void *)p2->index_base;

        while (p1_off <= p1->index_size - 3 * 20 &&
               p2_off <= p2->index_size - 3 * 20)
        {
                int cmp = memcmp(p1_base + p1_off, p2_base + p2_off, 20);
                /* cmp ~ p1 - p2 */
                if (cmp == 0) {
                        ret++;
                        p1_off+=24;
                        p2_off+=24;
                        continue;
                }
                if (cmp < 0) { /* p1 has the object, p2 doesn't */
                        p1_off+=24;
                } else { /* p2 has the object, p1 doesn't */
                        p2_off+=24;
                }
        }
        return ret;
}

/* another O(n^2) function ... */
static size_t get_pack_redundancy(struct pack_list *pl)
{
        struct pack_list *subset;
        size_t ret = 0;

        if (pl == NULL)
                return 0;

        while ((subset = pl->next)) {
                while(subset) {
                        ret += sizeof_union(pl->pack, subset->pack);
                        subset = subset->next;
                }
                pl = pl->next;
        }
        return ret;
}

static inline size_t pack_set_bytecount(struct pack_list *pl)
{
        size_t ret = 0;
        while (pl) {
                ret += pl->pack->pack_size;
                ret += pl->pack->index_size;
                pl = pl->next;
        }
        return ret;
}

static void minimize(struct pack_list **min)
{
        struct pack_list *pl, *unique = NULL,
                *non_unique = NULL, *min_perm = NULL;
        struct pll *perm, *perm_all, *perm_ok = NULL, *new_perm;
        struct llist *missing;
        size_t min_perm_size = (size_t)-1, perm_size;

        pl = local_packs;
        while (pl) {
                if(pl->unique_objects->size)
                        pack_list_insert(&unique, pl);
                else
                        pack_list_insert(&non_unique, pl);
                pl = pl->next;
        }
        /* find out which objects are missing from the set of unique packs */
        missing = llist_copy(all_objects);
        pl = unique;
        while (pl) {
                llist_sorted_difference_inplace(missing,
                                                pl->all_objects);
                pl = pl->next;
        }

        /* return if there are no objects missing from the unique set */
        if (missing->size == 0) {
                *min = unique;
                return;
        }

        /* find the permutations which contain all missing objects */
        perm_all = perm = get_all_permutations(non_unique);
        while (perm) {
                if (perm_ok && perm->pl_size > perm_ok->pl_size)
                        break; /* ignore all larger permutations */
                if (is_superset(perm->pl, missing)) {
                        new_perm = xmalloc(sizeof(struct pll));
                        memcpy(new_perm, perm, sizeof(struct pll));
                        new_perm->next = perm_ok;
                        perm_ok = new_perm;
                }
                perm = perm->next;
        }
        
        if (perm_ok == NULL)
                die("Internal error: No complete sets found!\n");

        /* find the permutation with the smallest size */
        perm = perm_ok;
        while (perm) {
                perm_size = pack_set_bytecount(perm->pl);
                if (min_perm_size > perm_size) {
                        min_perm_size = perm_size;
                        min_perm = perm->pl;
                }
                perm = perm->next;
        }
        *min = min_perm;
        /* add the unique packs to the list */
        pl = unique;
        while(pl) {
                pack_list_insert(min, pl);
                pl = pl->next;
        }
}

static void load_all_objects(void)
{
        struct pack_list *pl = local_packs;
        struct llist_item *hint, *l;
        int i;

        llist_init(&all_objects);

        while (pl) {
                i = 0;
                hint = NULL;
                l = pl->all_objects->front;
                while (l) {
                        hint = llist_insert_sorted_unique(all_objects,
                                                          l->sha1, hint);
                        l = l->next;
                }
                pl = pl->next;
        }
        /* remove objects present in remote packs */
        pl = altodb_packs;
        while (pl) {
                llist_sorted_difference_inplace(all_objects, pl->all_objects);
                pl = pl->next;
        }
}

/* this scales like O(n^2) */
static void cmp_local_packs(void)
{
        struct pack_list *subset, *pl = local_packs;

        while ((subset = pl)) {
                while((subset = subset->next))
                        cmp_two_packs(pl, subset);
                pl = pl->next;
        }
}

static void scan_alt_odb_packs(void)
{
        struct pack_list *local, *alt;

        alt = altodb_packs;
        while (alt) {
                local = local_packs;
                while (local) {
                        llist_sorted_difference_inplace(local->unique_objects,
                                                        alt->all_objects);
                        local = local->next;
                }
                alt = alt->next;
        }
}

static struct pack_list * add_pack(struct packed_git *p)
{
        struct pack_list l;
        size_t off;
        void *base;

        if (!p->pack_local && !(alt_odb || verbose))
                return NULL;

        l.pack = p;
        llist_init(&l.all_objects);

        off = 256 * 4 + 4;
        base = (void *)p->index_base;
        while (off <= p->index_size - 3 * 20) {
                llist_insert_back(l.all_objects, base + off);
                off += 24;
        }
        /* this list will be pruned in cmp_two_packs later */
        l.unique_objects = llist_copy(l.all_objects);
        if (p->pack_local)
                return pack_list_insert(&local_packs, &l);
        else
                return pack_list_insert(&altodb_packs, &l);
}

static struct pack_list * add_pack_file(char *filename)
{
        struct packed_git *p = packed_git;

        if (strlen(filename) < 40)
                die("Bad pack filename: %s\n", filename);

        while (p) {
                if (strstr(p->pack_name, filename))
                        return add_pack(p);
                p = p->next;
        }
        die("Filename %s not found in packed_git\n", filename);
}

static void load_all(void)
{
        struct packed_git *p = packed_git;

        while (p) {
                add_pack(p);
                p = p->next;
        }
}

int main(int argc, char **argv)
{
        int i;
        struct pack_list *min, *red, *pl;

        for (i = 1; i < argc; i++) {
                const char *arg = argv[i];
                if(!strcmp(arg, "--")) {
                        i++;
                        break;
                }
                if(!strcmp(arg, "--all")) {
                        load_all_packs = 1;
                        continue;
                }
                if(!strcmp(arg, "--verbose")) {
                        verbose = 1;
                        continue;
                }
                if(!strcmp(arg, "--alt-odb")) {
                        alt_odb = 1;
                        continue;
                }
                if(*arg == '-')
                        usage(pack_redundant_usage);
                else
                        break;
        }

        prepare_packed_git();

        if (load_all_packs)
                load_all();
        else
                while (*(argv + i) != NULL)
                        add_pack_file(*(argv + i++));

        if (local_packs == NULL)
                die("Zero packs found!\n");

        load_all_objects();

        cmp_local_packs();
        if (alt_odb)
                scan_alt_odb_packs();

        minimize(&min);

        if (verbose) {
                fprintf(stderr, "There are %lu packs available in alt-odbs.\n",
                        (unsigned long)pack_list_size(altodb_packs));
                fprintf(stderr, "The smallest (bytewise) set of packs is:\n");
                pl = min;
                while (pl) {
                        fprintf(stderr, "\t%s\n", pl->pack->pack_name);
                        pl = pl->next;
                }
                fprintf(stderr, "containing %lu duplicate objects "
                                "with a total size of %lukb.\n",
                        (unsigned long)get_pack_redundancy(min),
                        (unsigned long)pack_set_bytecount(min)/1024);
                fprintf(stderr, "A total of %lu unique objects were considered.\n",
                        (unsigned long)all_objects->size);
                fprintf(stderr, "Redundant packs (with indexes):\n");
        }
        pl = red = pack_list_difference(local_packs, min);
        while (pl) {
                printf("%s\n%s\n",
                       sha1_pack_index_name(pl->pack->sha1),
                       pl->pack->pack_name);
                pl = pl->next;
        }

        return 0;
}