#include "cache.h"
#include "tree.h"
#include "tree-walk.h"
#include "object-store.h"

static int score_missing(unsigned mode)
{
        int score;

        if (S_ISDIR(mode))
                score = -1000;
        else if (S_ISLNK(mode))
                score = -500;
        else
                score = -50;
        return score;
}

static int score_differs(unsigned mode1, unsigned mode2)
{
        int score;

        if (S_ISDIR(mode1) != S_ISDIR(mode2))
                score = -100;
        else if (S_ISLNK(mode1) != S_ISLNK(mode2))
                score = -50;
        else
                score = -5;
        return score;
}

static int score_matches(unsigned mode1, unsigned mode2)
{
        int score;

        /* Heh, we found SHA-1 collisions between different kind of objects */
        if (S_ISDIR(mode1) != S_ISDIR(mode2))
                score = -100;
        else if (S_ISLNK(mode1) != S_ISLNK(mode2))
                score = -50;

        else if (S_ISDIR(mode1))
                score = 1000;
        else if (S_ISLNK(mode1))
                score = 500;
        else
                score = 250;
        return score;
}

static void *fill_tree_desc_strict(struct tree_desc *desc,
                                   const struct object_id *hash)
{
        void *buffer;
        enum object_type type;
        unsigned long size;

        buffer = read_object_file(hash, &type, &size);
        if (!buffer)
                die("unable to read tree (%s)", oid_to_hex(hash));
        if (type != OBJ_TREE)
                die("%s is not a tree", oid_to_hex(hash));
        init_tree_desc(desc, buffer, size);
        return buffer;
}

static int base_name_entries_compare(const struct name_entry *a,
                                     const struct name_entry *b)
{
        return base_name_compare(a->path, tree_entry_len(a), a->mode,
                                 b->path, tree_entry_len(b), b->mode);
}

/*
 * Inspect two trees, and give a score that tells how similar they are.
 */
static int score_trees(const struct object_id *hash1, const struct object_id *hash2)
{
        struct tree_desc one;
        struct tree_desc two;
        void *one_buf = fill_tree_desc_strict(&one, hash1);
        void *two_buf = fill_tree_desc_strict(&two, hash2);
        int score = 0;

        for (;;) {
                int cmp;

                if (one.size && two.size)
                        cmp = base_name_entries_compare(&one.entry, &two.entry);
                else if (one.size)
                        /* two lacks this entry */
                        cmp = -1;
                else if (two.size)
                        /* two has more entries */
                        cmp = 1;
                else
                        break;

                if (cmp < 0) {
                        /* path1 does not appear in two */
                        score += score_missing(one.entry.mode);
                        update_tree_entry(&one);
                } else if (cmp > 0) {
                        /* path2 does not appear in one */
                        score += score_missing(two.entry.mode);
                        update_tree_entry(&two);
                } else {
                        /* path appears in both */
                        if (!oideq(&one.entry.oid, &two.entry.oid)) {
                                /* they are different */
                                score += score_differs(one.entry.mode,
                                                       two.entry.mode);
                        } else {
                                /* same subtree or blob */
                                score += score_matches(one.entry.mode,
                                                       two.entry.mode);
                        }
                        update_tree_entry(&one);
                        update_tree_entry(&two);
                }
        }
        free(one_buf);
        free(two_buf);
        return score;
}

/*
 * Match one itself and its subtrees with two and pick the best match.
 */
static void match_trees(const struct object_id *hash1,
                        const struct object_id *hash2,
                        int *best_score,
                        char **best_match,
                        const char *base,
                        int recurse_limit)
{
        struct tree_desc one;
        void *one_buf = fill_tree_desc_strict(&one, hash1);

        while (one.size) {
                const char *path;
                const struct object_id *elem;
                unsigned short mode;
                int score;

                elem = tree_entry_extract(&one, &path, &mode);
                if (!S_ISDIR(mode))
                        goto next;
                score = score_trees(elem, hash2);
                if (*best_score < score) {
                        free(*best_match);
                        *best_match = xstrfmt("%s%s", base, path);
                        *best_score = score;
                }
                if (recurse_limit) {
                        char *newbase = xstrfmt("%s%s/", base, path);
                        match_trees(elem, hash2, best_score, best_match,
                                    newbase, recurse_limit - 1);
                        free(newbase);
                }

        next:
                update_tree_entry(&one);
        }
        free(one_buf);
}

/*
 * A tree "oid1" has a subdirectory at "prefix".  Come up with a tree object by
 * replacing it with another tree "oid2".
 */
static int splice_tree(const struct object_id *oid1, const char *prefix,
                       const struct object_id *oid2, struct object_id *result)
{
        char *subpath;
        int toplen;
        char *buf;
        unsigned long sz;
        struct tree_desc desc;
        unsigned char *rewrite_here;
        const struct object_id *rewrite_with;
        struct object_id subtree;
        enum object_type type;
        int status;

        subpath = strchrnul(prefix, '/');
        toplen = subpath - prefix;
        if (*subpath)
                subpath++;

        buf = read_object_file(oid1, &type, &sz);
        if (!buf)
                die("cannot read tree %s", oid_to_hex(oid1));
        init_tree_desc(&desc, buf, sz);

        rewrite_here = NULL;
        while (desc.size) {
                const char *name;
                unsigned short mode;

                tree_entry_extract(&desc, &name, &mode);
                if (strlen(name) == toplen &&
                    !memcmp(name, prefix, toplen)) {
                        if (!S_ISDIR(mode))
                                die("entry %s in tree %s is not a tree", name,
                                    oid_to_hex(oid1));

                        /*
                         * We cast here for two reasons:
                         *
                         *   - to flip the "char *" (for the path) to "unsigned
                         *     char *" (for the hash stored after it)
                         *
                         *   - to discard the "const"; this is OK because we
                         *     know it points into our non-const "buf"
                         */
                        rewrite_here = (unsigned char *)(desc.entry.path +
                                                         strlen(desc.entry.path) +
                                                         1);
                        break;
                }
                update_tree_entry(&desc);
        }
        if (!rewrite_here)
                die("entry %.*s not found in tree %s", toplen, prefix,
                    oid_to_hex(oid1));
        if (*subpath) {
                struct object_id tree_oid;
                hashcpy(tree_oid.hash, rewrite_here);
                status = splice_tree(&tree_oid, subpath, oid2, &subtree);
                if (status)
                        return status;
                rewrite_with = &subtree;
        } else {
                rewrite_with = oid2;
        }
        hashcpy(rewrite_here, rewrite_with->hash);
        status = write_object_file(buf, sz, tree_type, result);
        free(buf);
        return status;
}

/*
 * We are trying to come up with a merge between one and two that
 * results in a tree shape similar to one.  The tree two might
 * correspond to a subtree of one, in which case it needs to be
 * shifted down by prefixing otherwise empty directories.  On the
 * other hand, it could cover tree one and we might need to pick a
 * subtree of it.
 */
void shift_tree(const struct object_id *hash1,
                const struct object_id *hash2,
                struct object_id *shifted,
                int depth_limit)
{
        char *add_prefix;
        char *del_prefix;
        int add_score, del_score;

        /*
         * NEEDSWORK: this limits the recursion depth to hardcoded
         * value '2' to avoid excessive overhead.
         */
        if (!depth_limit)
                depth_limit = 2;

        add_score = del_score = score_trees(hash1, hash2);
        add_prefix = xcalloc(1, 1);
        del_prefix = xcalloc(1, 1);

        /*
         * See if one's subtree resembles two; if so we need to prefix
         * two with a few fake trees to match the prefix.
         */
        match_trees(hash1, hash2, &add_score, &add_prefix, "", depth_limit);

        /*
         * See if two's subtree resembles one; if so we need to
         * pick only subtree of two.
         */
        match_trees(hash2, hash1, &del_score, &del_prefix, "", depth_limit);

        /* Assume we do not have to do any shifting */
        oidcpy(shifted, hash2);

        if (add_score < del_score) {
                /* We need to pick a subtree of two */
                unsigned short mode;

                if (!*del_prefix)
                        return;

                if (get_tree_entry(hash2, del_prefix, shifted, &mode))
                        die("cannot find path %s in tree %s",
                            del_prefix, oid_to_hex(hash2));
                return;
        }

        if (!*add_prefix)
                return;

        splice_tree(hash1, add_prefix, hash2, shifted);
}

/*
 * The user says the trees will be shifted by this much.
 * Unfortunately we cannot fundamentally tell which one to
 * be prefixed, as recursive merge can work in either direction.
 */
void shift_tree_by(const struct object_id *hash1,
                   const struct object_id *hash2,
                   struct object_id *shifted,
                   const char *shift_prefix)
{
        struct object_id sub1, sub2;
        unsigned short mode1, mode2;
        unsigned candidate = 0;

        /* Can hash2 be a tree at shift_prefix in tree hash1? */
        if (!get_tree_entry(hash1, shift_prefix, &sub1, &mode1) &&
            S_ISDIR(mode1))
                candidate |= 1;

        /* Can hash1 be a tree at shift_prefix in tree hash2? */
        if (!get_tree_entry(hash2, shift_prefix, &sub2, &mode2) &&
            S_ISDIR(mode2))
                candidate |= 2;

        if (candidate == 3) {
                /* Both are plausible -- we need to evaluate the score */
                int best_score = score_trees(hash1, hash2);
                int score;

                candidate = 0;
                score = score_trees(&sub1, hash2);
                if (score > best_score) {
                        candidate = 1;
                        best_score = score;
                }
                score = score_trees(&sub2, hash1);
                if (score > best_score)
                        candidate = 2;
        }

        if (!candidate) {
                /* Neither is plausible -- do not shift */
                oidcpy(shifted, hash2);
                return;
        }

        if (candidate == 1)
                /*
                 * shift tree2 down by adding shift_prefix above it
                 * to match tree1.
                 */
                splice_tree(hash1, shift_prefix, hash2, shifted);
        else
                /*
                 * shift tree2 up by removing shift_prefix from it
                 * to match tree1.
                 */
                oidcpy(shifted, &sub2);
}