#include "cache.h"
#include "diff.h"
#include "commit.h"
#include "patch-ids.h"

static int commit_patch_id(struct commit *commit, struct diff_options *options,
                    unsigned char *sha1)
{
        if (commit->parents)
                diff_tree_sha1(commit->parents->item->object.sha1,
                               commit->object.sha1, "", options);
        else
                diff_root_tree_sha1(commit->object.sha1, "", options);
        diffcore_std(options);
        return diff_flush_patch_id(options, sha1);
}

static uint32_t take2(const unsigned char *id)
{
        return ((id[0] << 8) | id[1]);
}

/*
 * Conventional binary search loop looks like this:
 *
 *      do {
 *              int mi = (lo + hi) / 2;
 *              int cmp = "entry pointed at by mi" minus "target";
 *              if (!cmp)
 *                      return (mi is the wanted one)
 *              if (cmp > 0)
 *                      hi = mi; "mi is larger than target"
 *              else
 *                      lo = mi+1; "mi is smaller than target"
 *      } while (lo < hi);
 *
 * The invariants are:
 *
 * - When entering the loop, lo points at a slot that is never
 *   above the target (it could be at the target), hi points at a
 *   slot that is guaranteed to be above the target (it can never
 *   be at the target).
 *
 * - We find a point 'mi' between lo and hi (mi could be the same
 *   as lo, but never can be the same as hi), and check if it hits
 *   the target.  There are three cases:
 *
 *    - if it is a hit, we are happy.
 *
 *    - if it is strictly higher than the target, we update hi with
 *      it.
 *
 *    - if it is strictly lower than the target, we update lo to be
 *      one slot after it, because we allow lo to be at the target.
 *
 * When choosing 'mi', we do not have to take the "middle" but
 * anywhere in between lo and hi, as long as lo <= mi < hi is
 * satisfied.  When we somehow know that the distance between the
 * target and lo is much shorter than the target and hi, we could
 * pick mi that is much closer to lo than the midway.
 */
static int patch_pos(struct patch_id **table, int nr, const unsigned char *id)
{
        int hi = nr;
        int lo = 0;
        int mi = 0;

        if (!nr)
                return -1;

        if (nr != 1) {
                unsigned lov, hiv, miv, ofs;

                for (ofs = 0; ofs < 18; ofs += 2) {
                        lov = take2(table[0]->patch_id + ofs);
                        hiv = take2(table[nr-1]->patch_id + ofs);
                        miv = take2(id + ofs);
                        if (miv < lov)
                                return -1;
                        if (hiv < miv)
                                return -1 - nr;
                        if (lov != hiv) {
                                /*
                                 * At this point miv could be equal
                                 * to hiv (but id could still be higher);
                                 * the invariant of (mi < hi) should be
                                 * kept.
                                 */
                                mi = (nr-1) * (miv - lov) / (hiv - lov);
                                if (lo <= mi && mi < hi)
                                        break;
                                die("oops");
                        }
                }
                if (18 <= ofs)
                        die("cannot happen -- lo and hi are identical");
        }

        do {
                int cmp;
                cmp = hashcmp(table[mi]->patch_id, id);
                if (!cmp)
                        return mi;
                if (cmp > 0)
                        hi = mi;
                else
                        lo = mi + 1;
                mi = (hi + lo) / 2;
        } while (lo < hi);
        return -lo-1;
}

#define BUCKET_SIZE 190 /* 190 * 21 = 3990, with slop close enough to 4K */
struct patch_id_bucket {
        struct patch_id_bucket *next;
        int nr;
        struct patch_id bucket[BUCKET_SIZE];
};

int init_patch_ids(struct patch_ids *ids)
{
        memset(ids, 0, sizeof(*ids));
        diff_setup(&ids->diffopts);
        ids->diffopts.recursive = 1;
        if (diff_setup_done(&ids->diffopts) < 0)
                return error("diff_setup_done failed");
        return 0;
}

int free_patch_ids(struct patch_ids *ids)
{
        struct patch_id_bucket *next, *patches;

        free(ids->table);
        for (patches = ids->patches; patches; patches = next) {
                next = patches->next;
                free(patches);
        }
        return 0;
}

static struct patch_id *add_commit(struct commit *commit,
                                   struct patch_ids *ids,
                                   int no_add)
{
        struct patch_id_bucket *bucket;
        struct patch_id *ent;
        unsigned char sha1[20];
        int pos;

        if (commit_patch_id(commit, &ids->diffopts, sha1))
                return NULL;
        pos = patch_pos(ids->table, ids->nr, sha1);
        if (0 <= pos)
                return ids->table[pos];
        if (no_add)
                return NULL;

        pos = -1 - pos;

        bucket = ids->patches;
        if (!bucket || (BUCKET_SIZE <= bucket->nr)) {
                bucket = xcalloc(1, sizeof(*bucket));
                bucket->next = ids->patches;
                ids->patches = bucket;
        }
        ent = &bucket->bucket[bucket->nr++];
        hashcpy(ent->patch_id, sha1);

        if (ids->alloc <= ids->nr) {
                ids->alloc = alloc_nr(ids->nr);
                ids->table = xrealloc(ids->table, sizeof(ent) * ids->alloc);
        }
        if (pos < ids->nr)
                memmove(ids->table + pos + 1, ids->table + pos,
                        sizeof(ent) * (ids->nr - pos));
        ids->nr++;
        ids->table[pos] = ent;
        return ids->table[pos];
}

struct patch_id *has_commit_patch_id(struct commit *commit,
                                     struct patch_ids *ids)
{
        return add_commit(commit, ids, 1);
}

struct patch_id *add_commit_patch_id(struct commit *commit,
                                     struct patch_ids *ids)
{
        return add_commit(commit, ids, 0);
}