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

/* Table of rename/copy destinations */

static struct diff_rename_dst {
        struct diff_filespec *two;
        struct diff_filepair *pair;
} *rename_dst;
static int rename_dst_nr, rename_dst_alloc;

static struct diff_rename_dst *locate_rename_dst(struct diff_filespec *two,
                                                 int insert_ok)
{
        int first, last;

        first = 0;
        last = rename_dst_nr;
        while (last > first) {
                int next = (last + first) >> 1;
                struct diff_rename_dst *dst = &(rename_dst[next]);
                int cmp = strcmp(two->path, dst->two->path);
                if (!cmp)
                        return dst;
                if (cmp < 0) {
                        last = next;
                        continue;
                }
                first = next+1;
        }
        /* not found */
        if (!insert_ok)
                return NULL;
        /* insert to make it at "first" */
        if (rename_dst_alloc <= rename_dst_nr) {
                rename_dst_alloc = alloc_nr(rename_dst_alloc);
                rename_dst = xrealloc(rename_dst,
                                      rename_dst_alloc * sizeof(*rename_dst));
        }
        rename_dst_nr++;
        if (first < rename_dst_nr)
                memmove(rename_dst + first + 1, rename_dst + first,
                        (rename_dst_nr - first - 1) * sizeof(*rename_dst));
        rename_dst[first].two = two;
        rename_dst[first].pair = NULL;
        return &(rename_dst[first]);
}

/* Table of rename/copy src files */
static struct diff_rename_src {
        struct diff_filespec *one;
        unsigned src_stays : 1;
} *rename_src;
static int rename_src_nr, rename_src_alloc;

static struct diff_rename_src *register_rename_src(struct diff_filespec *one,
                                                   int src_stays)
{
        int first, last;

        first = 0;
        last = rename_src_nr;
        while (last > first) {
                int next = (last + first) >> 1;
                struct diff_rename_src *src = &(rename_src[next]);
                int cmp = strcmp(one->path, src->one->path);
                if (!cmp)
                        return src;
                if (cmp < 0) {
                        last = next;
                        continue;
                }
                first = next+1;
        }

        /* insert to make it at "first" */
        if (rename_src_alloc <= rename_src_nr) {
                rename_src_alloc = alloc_nr(rename_src_alloc);
                rename_src = xrealloc(rename_src,
                                      rename_src_alloc * sizeof(*rename_src));
        }
        rename_src_nr++;
        if (first < rename_src_nr)
                memmove(rename_src + first + 1, rename_src + first,
                        (rename_src_nr - first - 1) * sizeof(*rename_src));
        rename_src[first].one = one;
        rename_src[first].src_stays = src_stays;
        return &(rename_src[first]);
}

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, 1) || diff_populate_filespec(dst, 1))
                return 0;
        if (src->size != dst->size)
                return 0;
        if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
                return 0;
        if (src->size == dst->size &&
            !memcmp(src->data, dst->data, src->size))
                return 1;
        return 0;
}

struct diff_score {
        int src; /* index in rename_src */
        int dst; /* index in rename_dst */
        int score;
};

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 MAX_SCORE.
         *
         * When there is an exact match, it is considered a better
         * match than anything else; the destination does not even
         * call into this function in that case.
         */
        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;

        if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
                return 0; /* error but caught downstream */

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

        /* A delta that has a lot of literal additions would have
         * big delta_size no matter what else it does.
         */
        if (base_size * (MAX_SCORE-minimum_score) < delta_size * MAX_SCORE)
                return 0;

        /* Estimate the edit size by interpreting delta. */
        delta_size = count_delta(delta, delta_size);
        free(delta);
        if (delta_size == UINT_MAX)
                return 0;

        /*
         * 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 *renq,
                               int dst_index, int src_index, int score)
{
        struct diff_filespec *one, *two, *src, *dst;
        struct diff_filepair *dp;

        if (rename_dst[dst_index].pair)
                die("internal error: dst already matched.");

        src = rename_src[src_index].one;
        one = alloc_filespec(src->path);
        fill_filespec(one, src->sha1, src->mode);

        dst = rename_dst[dst_index].two;
        two = alloc_filespec(dst->path);
        fill_filespec(two, dst->sha1, dst->mode);

        dp = diff_queue(renq, one, two);
        dp->score = score;
        dp->source_stays = rename_src[src_index].src_stays;
        rename_dst[dst_index].pair = dp;
}

/*
 * We sort the rename similarity matrix with the score, in descending
 * order (the most 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 renq, outq;
        struct diff_score *mx;
        int i, j;
        int num_create, num_src, dst_cnt;

        if (!minimum_score)
                minimum_score = DEFAULT_MINIMUM_SCORE;
        renq.queue = NULL;
        renq.nr = renq.alloc = 0;

        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
                                locate_rename_dst(p->two, 1);
                else if (!DIFF_FILE_VALID(p->two))
                        register_rename_src(p->one, 0);
                else if (detect_rename == DIFF_DETECT_COPY)
                        register_rename_src(p->one, 1);
        }
        if (rename_dst_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 < rename_dst_nr; i++) {
                struct diff_filespec *two = rename_dst[i].two;
                for (j = 0; j < rename_src_nr; j++) {
                        struct diff_filespec *one = rename_src[j].one;
                        if (!is_exact_match(one, two))
                                continue;
                        record_rename_pair(&renq, i, j, MAX_SCORE);
                        break; /* we are done with this entry */
                }
        }
        diff_debug_queue("done detecting exact", &renq);

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

        num_create = (rename_dst_nr - renq.nr);
        num_src = rename_src_nr;
        mx = xmalloc(sizeof(*mx) * num_create * num_src);
        for (dst_cnt = i = 0; i < rename_dst_nr; i++) {
                int base = dst_cnt * num_src;
                struct diff_filespec *two = rename_dst[i].two;
                if (rename_dst[i].pair)
                        continue; /* dealt with exact match already. */
                for (j = 0; j < rename_src_nr; j++) {
                        struct diff_filespec *one = rename_src[j].one;
                        struct diff_score *m = &mx[base+j];
                        m->src = j;
                        m->dst = i;
                        m->score = estimate_similarity(one, two,
                                                       minimum_score);
                }
                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++) {
                struct diff_rename_dst *dst = &rename_dst[mx[i].dst];
                if (dst->pair)
                        continue; /* already done, either exact or fuzzy. */
                if (mx[i].score < minimum_score)
                        break; /* there is no more usable pair. */
                record_rename_pair(&renq, mx[i].dst, mx[i].src, mx[i].score);
        }
        free(mx);
        diff_debug_queue("done detecting fuzzy", &renq);

 cleanup:
        /* At this point, we have found some renames and copies and they
         * are kept in renq.  The original list is still in *q.
         */
        outq.queue = NULL;
        outq.nr = outq.alloc = 0;
        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *p = q->queue[i];
                struct diff_rename_dst *dst = locate_rename_dst(p->two, 0);
                struct diff_filepair *pair_to_free = NULL;

                if (dst) {
                        /* creation */
                        if (dst->pair) {
                                /* renq has rename/copy to produce
                                 * this file already, so we do not
                                 * emit the creation record in the
                                 * output.
                                 */
                                diff_q(&outq, dst->pair);
                                pair_to_free = p;
                        }
                        else
                                /* no matching rename/copy source, so record
                                 * this as a creation.
                                 */
                                diff_q(&outq, p);
                }
                else if (!diff_unmodified_pair(p))
                        /* all the usual ones need to be kept */
                        diff_q(&outq, p);
                else
                        /* no need to keep unmodified pairs */
                        pair_to_free = p;

                if (pair_to_free)
                        diff_free_filepair(pair_to_free);
        }
        diff_debug_queue("done copying original", &outq);

        free(renq.queue);
        free(q->queue);
        *q = outq;
        diff_debug_queue("done collapsing", q);

        free(rename_dst);
        rename_dst = NULL;
        rename_dst_nr = rename_dst_alloc = 0;
        free(rename_src);
        rename_src = NULL;
        rename_src_nr = rename_src_alloc = 0;
        return;
}