/*
 * Copyright (C) 2005 Junio C Hamano
 */
#include "cache.h"
#include "diff.h"
#include "diffcore.h"
#include "delta.h"

struct diff_rename_pool {
        struct diff_filespec **s;
        int nr, alloc;
};

static void diff_rename_pool_clear(struct diff_rename_pool *pool)
{
        pool->s = NULL; pool->nr = pool->alloc = 0;
}

static void diff_rename_pool_add(struct diff_rename_pool *pool,
                                 struct diff_filespec *s)
{
        if (S_ISDIR(s->mode))
                return;  /* rename/copy patch for tree does not make sense. */

        if (pool->alloc <= pool->nr) {
                pool->alloc = alloc_nr(pool->alloc);
                pool->s = xrealloc(pool->s,
                                   sizeof(*(pool->s)) * pool->alloc);
        }
        pool->s[pool->nr] = s;
        pool->nr++;
}

static int is_exact_match(struct diff_filespec *src, struct diff_filespec *dst)
{
        if (src->sha1_valid && dst->sha1_valid &&
            !memcmp(src->sha1, dst->sha1, 20))
                return 1;
        if (diff_populate_filespec(src) || diff_populate_filespec(dst))
                /* this is an error but will be caught downstream */
                return 0;
        if (src->size == dst->size &&
            !memcmp(src->data, dst->data, src->size))
                return 1;
        return 0;
}

struct diff_score {
        struct diff_filespec *src;
        struct diff_filespec *dst;
        int score;
        int rank;
};

static int estimate_similarity(struct diff_filespec *src,
                               struct diff_filespec *dst,
                               int minimum_score)
{
        /* src points at a file that existed in the original tree (or
         * optionally a file in the destination tree) and dst points
         * at a newly created file.  They may be quite similar, in which
         * case we want to say src is renamed to dst or src is copied into
         * dst, and then some edit has been applied to dst.
         *
         * Compare them and return how similar they are, representing
         * the score as an integer between 0 and 10000, except
         * where they match exactly it is considered better than anything
         * else.
         */
        void *delta;
        unsigned long delta_size;
        int score;

        delta_size = ((src->size < dst->size) ?
                      (dst->size - src->size) : (src->size - dst->size));

        /* We would not consider rename followed by more than
         * minimum_score/MAX_SCORE edits; that is, delta_size must be smaller
         * than (src->size + dst->size)/2 * minimum_score/MAX_SCORE,
         * which means...
         */

        if ((src->size+dst->size)*minimum_score < delta_size*MAX_SCORE*2)
                return 0;

        delta = diff_delta(src->data, src->size,
                           dst->data, dst->size,
                           &delta_size);
        free(delta);

        /* This "delta" is really xdiff with adler32 and all the
         * overheads but it is a quick and dirty approximation.
         *
         * Now we will give some score to it.  100% edit gets
         * 0 points and 0% edit gets MAX_SCORE points.  That is, every
         * 1/MAX_SCORE edit gets 1 point penalty.  The amount of penalty is:
         *
         * (delta_size * 2 / (src->size + dst->size)) * MAX_SCORE
         *
         */
        score = MAX_SCORE-(MAX_SCORE*2*delta_size/(src->size+dst->size));
        if (score < 0) return 0;
        if (MAX_SCORE < score) return MAX_SCORE;
        return score;
}

static void record_rename_pair(struct diff_queue_struct *outq,
                               struct diff_filespec *src,
                               struct diff_filespec *dst,
                               int rank,
                               int score)
{
        /* The rank is used to sort the final output, because there
         * are certain dependencies.
         *
         *  - rank #0 depends on deleted ones.
         *  - rank #1 depends on kept files before they are modified.
         *  - rank #2 depends on kept files after they are modified;
         *    currently not used.
         *
         * Therefore, the final output order should be:
         *
         *  1. rank #0 rename/copy diffs.
         *  2. deletions in the original.
         *  3. rank #1 rename/copy diffs.
         *  4. additions and modifications in the original.
         *  5. rank #2 rename/copy diffs; currently not used.
         *
         * To achieve this sort order, we give xform_work the number
         * above.
         */
        struct diff_filepair *dp = diff_queue(outq, src, dst);
        dp->xfrm_work = (rank * 2 + 1) | (score<<RENAME_SCORE_SHIFT);
        dst->xfrm_flags |= RENAME_DST_MATCHED;
}

#if 0
static void debug_filespec(struct diff_filespec *s, int x, const char *one)
{
        fprintf(stderr, "queue[%d] %s (%s) %s %06o %s\n",
                x, one,
                s->path,
                s->file_valid ? "valid" : "invalid",
                s->mode,
                s->sha1_valid ? sha1_to_hex(s->sha1) : "");
        fprintf(stderr, "queue[%d] %s size %lu flags %d\n",
                x, one,
                s->size, s->xfrm_flags);
}

static void debug_filepair(const struct diff_filepair *p, int i)
{
        debug_filespec(p->one, i, "one");
        debug_filespec(p->two, i, "two");
        fprintf(stderr, "pair flags %d, orig order %d, score %d\n",
                (p->xfrm_work & ((1<<RENAME_SCORE_SHIFT) - 1)),
                p->orig_order,
                (p->xfrm_work >> RENAME_SCORE_SHIFT));
}

static void debug_queue(const char *msg, struct diff_queue_struct *q)
{
        int i;
        if (msg)
                fprintf(stderr, "%s\n", msg);
        fprintf(stderr, "q->nr = %d\n", q->nr);
        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *p = q->queue[i];
                debug_filepair(p, i);
        }
}
#else
#define debug_queue(a,b) do { ; /*nothing*/ } while(0)
#endif

/*
 * We sort the outstanding diff entries according to the rank (see
 * comment at the beginning of record_rename_pair) and tiebreak with
 * the order in the original input.
 */
static int rank_compare(const void *a_, const void *b_)
{
        const struct diff_filepair *a = *(const struct diff_filepair **)a_;
        const struct diff_filepair *b = *(const struct diff_filepair **)b_;
        int a_rank = a->xfrm_work & ((1<<RENAME_SCORE_SHIFT) - 1);
        int b_rank = b->xfrm_work & ((1<<RENAME_SCORE_SHIFT) - 1);

        if (a_rank != b_rank)
                return a_rank - b_rank;
        return a->orig_order - b->orig_order;
}

/*
 * We sort the rename similarity matrix with the score, in descending
 * order (more similar first).
 */
static int score_compare(const void *a_, const void *b_)
{
        const struct diff_score *a = a_, *b = b_;
        return b->score - a->score;
}

static int needs_to_stay(struct diff_queue_struct *q, int i,
                         struct diff_filespec *it)
{
        /* If it will be used in later entry (either stay or used
         * as the source of rename/copy), we need to copy, not rename.
         */
        while (i < q->nr) {
                struct diff_filepair *p = q->queue[i++];
                if (!p->two->file_valid)
                        continue; /* removed is fine */
                if (strcmp(p->one->path, it->path))
                        continue; /* not relevant */

                /* p has its src set to *it and it is not a delete;
                 * it will be used for in-place change or rename/copy,
                 * so we cannot rename it out.
                 */
                return 1;
        }
        return 0;
}

void diff_detect_rename(struct diff_queue_struct *q,
                        int detect_rename,
                        int minimum_score)
{
        struct diff_queue_struct outq;
        struct diff_rename_pool created, deleted, stay;
        struct diff_rename_pool *(srcs[2]);
        struct diff_score *mx;
        int h, i, j;
        int num_create, num_src, dst_cnt, src_cnt;

        outq.queue = NULL;
        outq.nr = outq.alloc = 0;

        diff_rename_pool_clear(&created);
        diff_rename_pool_clear(&deleted);
        diff_rename_pool_clear(&stay);

        srcs[0] = &deleted;
        srcs[1] = &stay;

        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *p = q->queue[i];
                if (!p->one->file_valid)
                        if (!p->two->file_valid)
                                continue; /* ignore nonsense */
                        else
                                diff_rename_pool_add(&created, p->two);
                else if (!p->two->file_valid)
                        diff_rename_pool_add(&deleted, p->one);
                else if (1 < detect_rename) /* find copy, too */
                        diff_rename_pool_add(&stay, p->one);
        }
        if (created.nr == 0)
                goto cleanup; /* nothing to do */

        /* We really want to cull the candidates list early
         * with cheap tests in order to avoid doing deltas.
         *
         * With the current callers, we should not have already
         * matched entries at this point, but it is nonetheless
         * checked for sanity.
         */
        for (i = 0; i < created.nr; i++) {
                if (created.s[i]->xfrm_flags & RENAME_DST_MATCHED)
                        continue; /* we have matched exactly already */
                for (h = 0; h < sizeof(srcs)/sizeof(srcs[0]); h++) {
                        struct diff_rename_pool *p = srcs[h];
                        for (j = 0; j < p->nr; j++) {
                                if (!is_exact_match(p->s[j], created.s[i]))
                                        continue;
                                record_rename_pair(&outq,
                                                   p->s[j], created.s[i], h,
                                                   MAX_SCORE);
                                break; /* we are done with this entry */
                        }
                }
        }
        debug_queue("done detecting exact", &outq);

        /* Have we run out the created file pool?  If so we can avoid
         * doing the delta matrix altogether.
         */
        if (outq.nr == created.nr)
                goto flush_rest;

        num_create = (created.nr - outq.nr);
        num_src = deleted.nr + stay.nr;
        mx = xmalloc(sizeof(*mx) * num_create * num_src);
        for (dst_cnt = i = 0; i < created.nr; i++) {
                int base = dst_cnt * num_src;
                if (created.s[i]->xfrm_flags & RENAME_DST_MATCHED)
                        continue; /* dealt with exact match already. */
                for (src_cnt = h = 0; h < sizeof(srcs)/sizeof(srcs[0]); h++) {
                        struct diff_rename_pool *p = srcs[h];
                        for (j = 0; j < p->nr; j++, src_cnt++) {
                                struct diff_score *m = &mx[base + src_cnt];
                                m->src = p->s[j];
                                m->dst = created.s[i];
                                m->score = estimate_similarity(m->src, m->dst,
                                                               minimum_score);
                                m->rank = h;
                        }
                }
                dst_cnt++;
        }
        /* cost matrix sorted by most to least similar pair */
        qsort(mx, num_create * num_src, sizeof(*mx), score_compare);
        for (i = 0; i < num_create * num_src; i++) {
                if (mx[i].dst->xfrm_flags & RENAME_DST_MATCHED)
                        continue; /* alreayd done, either exact or fuzzy. */
                if (mx[i].score < minimum_score)
                        continue;
                record_rename_pair(&outq,
                                  mx[i].src, mx[i].dst, mx[i].rank,
                                  mx[i].score);
        }
        free(mx);
        debug_queue("done detecting fuzzy", &outq);

 flush_rest:
        /* At this point, we have found some renames and copies and they
         * are kept in outq.  The original list is still in *q.
         *
         * Scan the original list and move them into the outq; we will sort
         * outq and swap it into the queue supplied to pass that to
         * downstream, so we assign the sort keys in this loop.
         *
         * See comments at the top of record_rename_pair for numbers used
         * to assign xfrm_work.
         *
         * Note that we have not annotated the diff_filepair with any comment
         * so there is nothing other than p to free.
         */
        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *dp, *p = q->queue[i];
                if (!p->one->file_valid) {
                        if (p->two->file_valid) {
                                /* creation */
                                dp = diff_queue(&outq, p->one, p->two);
                                dp->xfrm_work = 4;
                        }
                        /* otherwise it is a nonsense; just ignore it */
                }
                else if (!p->two->file_valid) {
                        /* deletion */
                        dp = diff_queue(&outq, p->one, p->two);
                        dp->xfrm_work = 2;
                }
                else {
                        /* modification, or stay as is */
                        dp = diff_queue(&outq, p->one, p->two);
                        dp->xfrm_work = 4;
                }
                free(p);
        }
        debug_queue("done copying original", &outq);

        /* Sort outq */
        qsort(outq.queue, outq.nr, sizeof(outq.queue[0]), rank_compare);

        debug_queue("done sorting", &outq);

        free(q->queue);
        q->nr = q->alloc = 0;
        q->queue = NULL;

        /* Copy it out to q, removing duplicates. */
        for (i = 0; i < outq.nr; i++) {
                struct diff_filepair *p = outq.queue[i];
                if (!p->one->file_valid) {
                        /* created */
                        if (p->two->xfrm_flags & RENAME_DST_MATCHED)
                                ; /* rename/copy created it already */
                        else
                                diff_queue(q, p->one, p->two);
                }
                else if (!p->two->file_valid) {
                        /* deleted */
                        if (p->one->xfrm_flags & RENAME_SRC_GONE)
                                ; /* rename/copy deleted it already */
                        else
                                diff_queue(q, p->one, p->two);
                }
                else if (strcmp(p->one->path, p->two->path)) {
                        /* rename or copy */
                        struct diff_filepair *dp =
                                diff_queue(q, p->one, p->two);
                        int msglen = (strlen(p->one->path) +
                                      strlen(p->two->path) + 100);
                        int score = (p->xfrm_work >> RENAME_SCORE_SHIFT);
                        dp->xfrm_msg = xmalloc(msglen);

                        /* if we have a later entry that is a rename/copy
                         * that depends on p->one, then we copy here.
                         * otherwise we rename it.
                         */
                        if (needs_to_stay(&outq, i+1, p->one)) {
                                /* copy it */
                                sprintf(dp->xfrm_msg,
                                        "similarity index %d%%\n"
                                        "copy from %s\n"
                                        "copy to %s\n",
                                        (int)(0.5 + score * 100 / MAX_SCORE),
                                        p->one->path, p->two->path);
                        }
                        else {
                                /* rename it, and mark it as gone. */
                                p->one->xfrm_flags |= RENAME_SRC_GONE;
                                sprintf(dp->xfrm_msg,
                                        "similarity index %d%%\n"
                                        "rename old %s\n"
                                        "rename new %s\n",
                                        (int)(0.5 + score * 100 / MAX_SCORE),
                                        p->one->path, p->two->path);
                        }
                }
                else
                        /* otherwise it is a modified (or stayed) entry */
                        diff_queue(q, p->one, p->two);
                free(p);
        }

        free(outq.queue);
        debug_queue("done collapsing", q);

 cleanup:
        free(created.s);
        free(deleted.s);
        free(stay.s);
        return;
}