/*
 * 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;  /* no trees, please */

        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, base_size;
        int score;

        /* We deal only with regular files.  Symlink renames are handled
         * only when they are exact matches --- in other words, no edits
         * after renaming.
         */
        if (!S_ISREG(src->mode) || !S_ISREG(dst->mode))
                return 0;

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

        /* We would not consider edits that change the file size so
         * drastically.  delta_size must be smaller than
         * (MAX_SCORE-minimum_score)/MAX_SCORE * min(src->size, dst->size).
         * Note that base_size == 0 case is handled here already
         * and the final score computation below would not have a
         * divide-by-zero issue.
         */
        if (base_size * (MAX_SCORE-minimum_score) < delta_size * MAX_SCORE)
                return 0;

        delta = diff_delta(src->data, src->size,
                           dst->data, dst->size,
                           &delta_size);
        /*
         * We currently punt here, but we may later end up parsing the
         * delta to really assess the extent of damage.  A big consecutive
         * remove would produce small delta_size that affects quite a
         * big portion of the file.
         */
        free(delta);

        /*
         * Now we will give some score to it.  100% edit gets 0 points
         * and 0% edit gets MAX_SCORE points.
         */
        score = MAX_SCORE - (MAX_SCORE * delta_size / base_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)
{
        /*
         * These ranks are used to sort the final output, because there
         * are certain dependencies:
         *
         *  1. rename/copy that depends on deleted ones.
         *  2. deletions in the original.
         *  3. rename/copy that depends on the pre-edit image of kept files.
         *  4. additions, modifications and no-modifications in the original.
         *  5. rename/copy that depends on the post-edit image of kept files
         *     (note that we currently do not detect such rename/copy).
         *
         * The downstream diffcore transformers are free to reorder
         * the entries as long as they keep file pairs that has the
         * same p->one->path in earlier rename_rank to appear before
         * later ones.
         *
         * To the final output routine, and in the diff-raw format
         * output, a rename/copy that is based on a path that has a
         * later entry that shares the same p->one->path and is not a
         * deletion is a copy.  Otherwise it is a rename.
         */

        struct diff_filepair *dp = diff_queue(outq, src, dst);
        dp->rename_rank = rank * 2 + 1;
        dp->score = score;
        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,
                DIFF_FILE_VALID(s) ? "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 rank %d, orig order %d, score %d\n",
                p->rename_rank, p->orig_order, p->score);
}

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->rename_rank;
        int b_rank = b->rename_rank;

        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;
}

int diff_scoreopt_parse(const char *opt)
{
        int diglen, num, scale, i;
        if (opt[0] != '-' || (opt[1] != 'M' && opt[1] != 'C'))
                return -1; /* that is not a -M nor -C option */
        diglen = strspn(opt+2, "0123456789");
        if (diglen == 0 || strlen(opt+2) != diglen)
                return 0; /* use default */
        sscanf(opt+2, "%d", &num);
        for (i = 0, scale = 1; i < diglen; i++)
                scale *= 10;

        /* user says num divided by scale and we say internally that
         * is MAX_SCORE * num / scale.
         */
        return MAX_SCORE * num / scale;
}

void diffcore_rename(int detect_rename, int minimum_score)
{
        struct diff_queue_struct *q = &diff_queued_diff;
        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;

        if (!minimum_score)
                minimum_score = DEFAULT_MINIMUM_SCORE;
        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 (!DIFF_FILE_VALID(p->one))
                        if (!DIFF_FILE_VALID(p->two))
                                continue; /* unmerged */
                        else
                                diff_rename_pool_add(&created, p->two);
                else if (!DIFF_FILE_VALID(p->two))
                        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.
         */
        for (i = 0; i < created.nr; i++) {
                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)
                        break; /* there is not any more diffs applicable. */
                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 rename_rank.
         */
        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *dp, *p = q->queue[i];
                if (!DIFF_FILE_VALID(p->one)) {
                        /* creation or unmerged entries */
                        dp = diff_queue(&outq, p->one, p->two);
                        dp->rename_rank = 4;
                }
                else if (!DIFF_FILE_VALID(p->two)) {
                        /* deletion */
                        dp = diff_queue(&outq, p->one, p->two);
                        dp->rename_rank = 2;
                }
                else {
                        /* modification, or stay as is */
                        dp = diff_queue(&outq, p->one, p->two);
                        dp->rename_rank = 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 (!DIFF_FILE_VALID(p->one)) {
                        /* created or unmerged */
                        if (p->two->xfrm_flags & RENAME_DST_MATCHED)
                                ; /* rename/copy created it already */
                        else
                                diff_queue(q, p->one, p->two);
                }
                else if (!DIFF_FILE_VALID(p->two)) {
                        /* deleted */
                        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);
                        dp->score = p->score;
                }
                else
                        /* otherwise it is a modified (or "stay") 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;
}