/*
 * Copyright (C) 2005 Junio C Hamano
 */
#include "cache.h"
#include "diff.h"
#include "diffcore.h"
#include "hash.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 = alloc_filespec(two->path);
        fill_filespec(rename_dst[first].two, two->sha1, two->mode);
        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 short score; /* to remember the break score */
} *rename_src;
static int rename_src_nr, rename_src_alloc;

static struct diff_rename_src *register_rename_src(struct diff_filespec *one,
                                                   unsigned short score)
{
        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].score = score;
        return &(rename_src[first]);
}

static int basename_same(struct diff_filespec *src, struct diff_filespec *dst)
{
        int src_len = strlen(src->path), dst_len = strlen(dst->path);
        while (src_len && dst_len) {
                char c1 = src->path[--src_len];
                char c2 = dst->path[--dst_len];
                if (c1 != c2)
                        return 0;
                if (c1 == '/')
                        return 1;
        }
        return (!src_len || src->path[src_len - 1] == '/') &&
                (!dst_len || dst->path[dst_len - 1] == '/');
}

struct diff_score {
        int src; /* index in rename_src */
        int dst; /* index in rename_dst */
        unsigned short score;
        short name_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.
         */
        unsigned long max_size, delta_size, base_size, src_copied, literal_added;
        unsigned long delta_limit;
        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;

        /*
         * Need to check that source and destination sizes are
         * filled in before comparing them.
         *
         * If we already have "cnt_data" filled in, we know it's
         * all good (avoid checking the size for zero, as that
         * is a possible size - we really should have a flag to
         * say whether the size is valid or not!)
         */
        if (!src->cnt_data && diff_populate_filespec(src, 0))
                return 0;
        if (!dst->cnt_data && diff_populate_filespec(dst, 0))
                return 0;

        max_size = ((src->size > dst->size) ? src->size : dst->size);
        base_size = ((src->size < dst->size) ? src->size : dst->size);
        delta_size = max_size - base_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_limit = (unsigned long)
                (base_size * (MAX_SCORE-minimum_score) / MAX_SCORE);
        if (diffcore_count_changes(src, dst,
                                   &src->cnt_data, &dst->cnt_data,
                                   delta_limit,
                                   &src_copied, &literal_added))
                return 0;

        /* How similar are they?
         * what percentage of material in dst are from source?
         */
        if (!dst->size)
                score = 0; /* should not happen */
        else
                score = (int)(src_copied * MAX_SCORE / max_size);
        return score;
}

static void record_rename_pair(int dst_index, int src_index, int score)
{
        struct diff_filespec *src, *dst;
        struct diff_filepair *dp;

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

        src = rename_src[src_index].one;
        src->rename_used++;
        src->count++;

        dst = rename_dst[dst_index].two;
        dst->count++;

        dp = diff_queue(NULL, src, dst);
        dp->renamed_pair = 1;
        if (!strcmp(src->path, dst->path))
                dp->score = rename_src[src_index].score;
        else
                dp->score = score;
        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_;

        /* sink the unused ones to the bottom */
        if (a->dst < 0)
                return (0 <= b->dst);
        else if (b->dst < 0)
                return -1;

        if (a->score == b->score)
                return b->name_score - a->name_score;

        return b->score - a->score;
}

struct file_similarity {
        int src_dst, index;
        struct diff_filespec *filespec;
        struct file_similarity *next;
};

static int find_identical_files(struct file_similarity *src,
                                struct file_similarity *dst)
{
        int renames = 0;

        /*
         * Walk over all the destinations ...
         */
        do {
                struct diff_filespec *target = dst->filespec;
                struct file_similarity *p, *best;
                int i = 100, best_score = -1;

                /*
                 * .. to find the best source match
                 */
                best = NULL;
                for (p = src; p; p = p->next) {
                        int score;
                        struct diff_filespec *source = p->filespec;

                        /* False hash collission? */
                        if (hashcmp(source->sha1, target->sha1))
                                continue;
                        /* Non-regular files? If so, the modes must match! */
                        if (!S_ISREG(source->mode) || !S_ISREG(target->mode)) {
                                if (source->mode != target->mode)
                                        continue;
                        }
                        /* Give higher scores to sources that haven't been used already */
                        score = !source->rename_used;
                        score += basename_same(source, target);
                        if (score > best_score) {
                                best = p;
                                best_score = score;
                                if (score == 2)
                                        break;
                        }

                        /* Too many identical alternatives? Pick one */
                        if (!--i)
                                break;
                }
                if (best) {
                        record_rename_pair(dst->index, best->index, MAX_SCORE);
                        renames++;
                }
        } while ((dst = dst->next) != NULL);
        return renames;
}

static void free_similarity_list(struct file_similarity *p)
{
        while (p) {
                struct file_similarity *entry = p;
                p = p->next;
                free(entry);
        }
}

static int find_same_files(void *ptr)
{
        int ret;
        struct file_similarity *p = ptr;
        struct file_similarity *src = NULL, *dst = NULL;

        /* Split the hash list up into sources and destinations */
        do {
                struct file_similarity *entry = p;
                p = p->next;
                if (entry->src_dst < 0) {
                        entry->next = src;
                        src = entry;
                } else {
                        entry->next = dst;
                        dst = entry;
                }
        } while (p);

        /*
         * If we have both sources *and* destinations, see if
         * we can match them up
         */
        ret = (src && dst) ? find_identical_files(src, dst) : 0;

        /* Free the hashes and return the number of renames found */
        free_similarity_list(src);
        free_similarity_list(dst);
        return ret;
}

static unsigned int hash_filespec(struct diff_filespec *filespec)
{
        unsigned int hash;
        if (!filespec->sha1_valid) {
                if (diff_populate_filespec(filespec, 0))
                        return 0;
                hash_sha1_file(filespec->data, filespec->size, "blob", filespec->sha1);
        }
        memcpy(&hash, filespec->sha1, sizeof(hash));
        return hash;
}

static void insert_file_table(struct hash_table *table, int src_dst, int index, struct diff_filespec *filespec)
{
        void **pos;
        unsigned int hash;
        struct file_similarity *entry = xmalloc(sizeof(*entry));

        entry->src_dst = src_dst;
        entry->index = index;
        entry->filespec = filespec;
        entry->next = NULL;

        hash = hash_filespec(filespec);
        pos = insert_hash(hash, entry, table);

        /* We already had an entry there? */
        if (pos) {
                entry->next = *pos;
                *pos = entry;
        }
}

/*
 * Find exact renames first.
 *
 * The first round matches up the up-to-date entries,
 * and then during the second round we try to match
 * cache-dirty entries as well.
 */
static int find_exact_renames(void)
{
        int i;
        struct hash_table file_table;

        init_hash(&file_table);
        for (i = 0; i < rename_src_nr; i++)
                insert_file_table(&file_table, -1, i, rename_src[i].one);

        for (i = 0; i < rename_dst_nr; i++)
                insert_file_table(&file_table, 1, i, rename_dst[i].two);

        /* Find the renames */
        i = for_each_hash(&file_table, find_same_files);

        /* .. and free the hash data structure */
        free_hash(&file_table);

        return i;
}

#define NUM_CANDIDATE_PER_DST 4
static void record_if_better(struct diff_score m[], struct diff_score *o)
{
        int i, worst;

        /* find the worst one */
        worst = 0;
        for (i = 1; i < NUM_CANDIDATE_PER_DST; i++)
                if (score_compare(&m[i], &m[worst]) > 0)
                        worst = i;

        /* is it better than the worst one? */
        if (score_compare(&m[worst], o) > 0)
                m[worst] = *o;
}

void diffcore_rename(struct diff_options *options)
{
        int detect_rename = options->detect_rename;
        int minimum_score = options->rename_score;
        int rename_limit = options->rename_limit;
        struct diff_queue_struct *q = &diff_queued_diff;
        struct diff_queue_struct outq;
        struct diff_score *mx;
        int i, j, rename_count;
        int num_create, num_src, dst_cnt;

        if (!minimum_score)
                minimum_score = DEFAULT_RENAME_SCORE;

        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 if (options->single_follow &&
                                 strcmp(options->single_follow, p->two->path))
                                continue; /* not interested */
                        else
                                locate_rename_dst(p->two, 1);
                }
                else if (!DIFF_FILE_VALID(p->two)) {
                        /*
                         * If the source is a broken "delete", and
                         * they did not really want to get broken,
                         * that means the source actually stays.
                         * So we increment the "rename_used" score
                         * by one, to indicate ourselves as a user
                         */
                        if (p->broken_pair && !p->score)
                                p->one->rename_used++;
                        register_rename_src(p->one, p->score);
                }
                else if (detect_rename == DIFF_DETECT_COPY) {
                        /*
                         * Increment the "rename_used" score by
                         * one, to indicate ourselves as a user.
                         */
                        p->one->rename_used++;
                        register_rename_src(p->one, p->score);
                }
        }
        if (rename_dst_nr == 0 || rename_src_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.
         */
        rename_count = find_exact_renames();

        /* Did we only want exact renames? */
        if (minimum_score == MAX_SCORE)
                goto cleanup;

        /*
         * Calculate how many renames are left (but all the source
         * files still remain as options for rename/copies!)
         */
        num_create = (rename_dst_nr - rename_count);
        num_src = rename_src_nr;

        /* All done? */
        if (!num_create)
                goto cleanup;

        /*
         * This basically does a test for the rename matrix not
         * growing larger than a "rename_limit" square matrix, ie:
         *
         *    num_create * num_src > rename_limit * rename_limit
         *
         * but handles the potential overflow case specially (and we
         * assume at least 32-bit integers)
         */
        if (rename_limit <= 0 || rename_limit > 32767)
                rename_limit = 32767;
        if ((num_create > rename_limit && num_src > rename_limit) ||
            (num_create * num_src > rename_limit * rename_limit)) {
                warning("too many files, skipping inexact rename detection");
                goto cleanup;
        }

        mx = xcalloc(num_create * NUM_CANDIDATE_PER_DST, sizeof(*mx));
        for (dst_cnt = i = 0; i < rename_dst_nr; i++) {
                struct diff_filespec *two = rename_dst[i].two;
                struct diff_score *m;

                if (rename_dst[i].pair)
                        continue; /* dealt with exact match already. */

                m = &mx[dst_cnt * NUM_CANDIDATE_PER_DST];
                for (j = 0; j < NUM_CANDIDATE_PER_DST; j++)
                        m[j].dst = -1;

                for (j = 0; j < rename_src_nr; j++) {
                        struct diff_filespec *one = rename_src[j].one;
                        struct diff_score this_src;
                        this_src.score = estimate_similarity(one, two,
                                                             minimum_score);
                        this_src.name_score = basename_same(one, two);
                        this_src.dst = i;
                        this_src.src = j;
                        record_if_better(m, &this_src);
                        diff_free_filespec_blob(one);
                }
                /* We do not need the text anymore */
                diff_free_filespec_blob(two);
                dst_cnt++;
        }

        /* cost matrix sorted by most to least similar pair */
        qsort(mx, dst_cnt * NUM_CANDIDATE_PER_DST, sizeof(*mx), score_compare);

        for (i = 0; i < dst_cnt * NUM_CANDIDATE_PER_DST; i++) {
                struct diff_rename_dst *dst;

                if ((mx[i].dst < 0) ||
                    (mx[i].score < minimum_score))
                        break; /* there is no more usable pair. */
                dst = &rename_dst[mx[i].dst];
                if (dst->pair)
                        continue; /* already done, either exact or fuzzy. */
                if (rename_src[mx[i].src].one->rename_used)
                        continue;
                record_rename_pair(mx[i].dst, mx[i].src, mx[i].score);
                rename_count++;
        }

        for (i = 0; i < dst_cnt * NUM_CANDIDATE_PER_DST; i++) {
                struct diff_rename_dst *dst;

                if ((mx[i].dst < 0) ||
                    (mx[i].score < minimum_score))
                        break; /* there is no more usable pair. */
                dst = &rename_dst[mx[i].dst];
                if (dst->pair)
                        continue; /* already done, either exact or fuzzy. */
                record_rename_pair(mx[i].dst, mx[i].src, mx[i].score);
                rename_count++;
        }
        free(mx);

 cleanup:
        /* At this point, we have found some renames and copies and they
         * are recorded in rename_dst.  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_filepair *pair_to_free = NULL;

                if (!DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two)) {
                        /*
                         * Creation
                         *
                         * We would output this create record if it has
                         * not been turned into a rename/copy already.
                         */
                        struct diff_rename_dst *dst =
                                locate_rename_dst(p->two, 0);
                        if (dst && dst->pair) {
                                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_FILE_VALID(p->one) && !DIFF_FILE_VALID(p->two)) {
                        /*
                         * Deletion
                         *
                         * We would output this delete record if:
                         *
                         * (1) this is a broken delete and the counterpart
                         *     broken create remains in the output; or
                         * (2) this is not a broken delete, and rename_dst
                         *     does not have a rename/copy to move p->one->path
                         *     out of existence.
                         *
                         * Otherwise, the counterpart broken create
                         * has been turned into a rename-edit; or
                         * delete did not have a matching create to
                         * begin with.
                         */
                        if (DIFF_PAIR_BROKEN(p)) {
                                /* broken delete */
                                struct diff_rename_dst *dst =
                                        locate_rename_dst(p->one, 0);
                                if (dst && dst->pair)
                                        /* counterpart is now rename/copy */
                                        pair_to_free = p;
                        }
                        else {
                                if (p->one->rename_used)
                                        /* this path remains */
                                        pair_to_free = p;
                        }

                        if (pair_to_free)
                                ;
                        else
                                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(q->queue);
        *q = outq;
        diff_debug_queue("done collapsing", q);

        for (i = 0; i < rename_dst_nr; i++)
                free_filespec(rename_dst[i].two);

        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;
}