/*
 * Helper functions for tree diff generation
 */
#include "cache.h"
#include "diff.h"
#include "diffcore.h"
#include "tree.h"

/*
 * Compare two tree entries, taking into account only path/S_ISDIR(mode),
 * but not their sha1's.
 *
 * NOTE files and directories *always* compare differently, even when having
 *      the same name - thanks to base_name_compare().
 *
 * NOTE empty (=invalid) descriptor(s) take part in comparison as +infty,
 *      so that they sort *after* valid tree entries.
 *
 *      Due to this convention, if trees are scanned in sorted order, all
 *      non-empty descriptors will be processed first.
 */
static int tree_entry_pathcmp(struct tree_desc *t1, struct tree_desc *t2)
{
        struct name_entry *e1, *e2;
        int cmp;

        /* empty descriptors sort after valid tree entries */
        if (!t1->size)
                return t2->size ? 1 : 0;
        else if (!t2->size)
                return -1;

        e1 = &t1->entry;
        e2 = &t2->entry;
        cmp = base_name_compare(e1->path, tree_entry_len(e1), e1->mode,
                                e2->path, tree_entry_len(e2), e2->mode);
        return cmp;
}


/* convert path, t1/t2 -> opt->diff_*() callbacks */
static void emit_diff(struct diff_options *opt, struct strbuf *path,
                      struct tree_desc *t1, struct tree_desc *t2)
{
        unsigned int mode1 = t1 ? t1->entry.mode : 0;
        unsigned int mode2 = t2 ? t2->entry.mode : 0;

        if (mode1 && mode2) {
                opt->change(opt, mode1, mode2, t1->entry.sha1, t2->entry.sha1,
                        1, 1, path->buf, 0, 0);
        }
        else {
                const unsigned char *sha1;
                unsigned int mode;
                int addremove;

                if (mode2) {
                        addremove = '+';
                        sha1 = t2->entry.sha1;
                        mode = mode2;
                } else {
                        addremove = '-';
                        sha1 = t1->entry.sha1;
                        mode = mode1;
                }

                opt->add_remove(opt, addremove, mode, sha1, 1, path->buf, 0);
        }
}


/* new path should be added to diff
 *
 * 3 cases on how/when it should be called and behaves:
 *
 *      !t1,  t2        -> path added, parent lacks it
 *       t1, !t2        -> path removed from parent
 *       t1,  t2        -> path modified
 */
static void show_path(struct strbuf *base, struct diff_options *opt,
                      struct tree_desc *t1, struct tree_desc *t2)
{
        unsigned mode;
        const char *path;
        int pathlen;
        int old_baselen = base->len;
        int isdir, recurse = 0, emitthis = 1;

        /* at least something has to be valid */
        assert(t1 || t2);

        if (t2) {
                /* path present in resulting tree */
                tree_entry_extract(t2, &path, &mode);
                pathlen = tree_entry_len(&t2->entry);
                isdir = S_ISDIR(mode);
        } else {
                /*
                 * a path was removed - take path from parent. Also take
                 * mode from parent, to decide on recursion.
                 */
                tree_entry_extract(t1, &path, &mode);
                pathlen = tree_entry_len(&t1->entry);

                isdir = S_ISDIR(mode);
                mode = 0;
        }

        if (DIFF_OPT_TST(opt, RECURSIVE) && isdir) {
                recurse = 1;
                emitthis = DIFF_OPT_TST(opt, TREE_IN_RECURSIVE);
        }

        strbuf_add(base, path, pathlen);

        if (emitthis)
                emit_diff(opt, base, t1, t2);

        if (recurse) {
                strbuf_addch(base, '/');
                diff_tree_sha1(t1 ? t1->entry.sha1 : NULL,
                               t2 ? t2->entry.sha1 : NULL, base->buf, opt);
        }

        strbuf_setlen(base, old_baselen);
}

static void skip_uninteresting(struct tree_desc *t, struct strbuf *base,
                               struct diff_options *opt)
{
        enum interesting match;

        while (t->size) {
                match = tree_entry_interesting(&t->entry, base, 0, &opt->pathspec);
                if (match) {
                        if (match == all_entries_not_interesting)
                                t->size = 0;
                        break;
                }
                update_tree_entry(t);
        }
}

static int diff_tree(struct tree_desc *t1, struct tree_desc *t2,
                     const char *base_str, struct diff_options *opt)
{
        struct strbuf base;
        int baselen = strlen(base_str);

        /* Enable recursion indefinitely */
        opt->pathspec.recursive = DIFF_OPT_TST(opt, RECURSIVE);

        strbuf_init(&base, PATH_MAX);
        strbuf_add(&base, base_str, baselen);

        for (;;) {
                int cmp;

                if (diff_can_quit_early(opt))
                        break;
                if (opt->pathspec.nr) {
                        skip_uninteresting(t1, &base, opt);
                        skip_uninteresting(t2, &base, opt);
                }
                if (!t1->size && !t2->size)
                        break;

                cmp = tree_entry_pathcmp(t1, t2);

                /* t1 = t2 */
                if (cmp == 0) {
                        if (DIFF_OPT_TST(opt, FIND_COPIES_HARDER) ||
                            hashcmp(t1->entry.sha1, t2->entry.sha1) ||
                            (t1->entry.mode != t2->entry.mode))
                                show_path(&base, opt, t1, t2);

                        update_tree_entry(t1);
                        update_tree_entry(t2);
                }

                /* t1 < t2 */
                else if (cmp < 0) {
                        show_path(&base, opt, t1, /*t2=*/NULL);
                        update_tree_entry(t1);
                }

                /* t1 > t2 */
                else {
                        show_path(&base, opt, /*t1=*/NULL, t2);
                        update_tree_entry(t2);
                }
        }

        strbuf_release(&base);
        return 0;
}

/*
 * Does it look like the resulting diff might be due to a rename?
 *  - single entry
 *  - not a valid previous file
 */
static inline int diff_might_be_rename(void)
{
        return diff_queued_diff.nr == 1 &&
                !DIFF_FILE_VALID(diff_queued_diff.queue[0]->one);
}

static void try_to_follow_renames(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
{
        struct diff_options diff_opts;
        struct diff_queue_struct *q = &diff_queued_diff;
        struct diff_filepair *choice;
        int i;

        /*
         * follow-rename code is very specific, we need exactly one
         * path. Magic that matches more than one path is not
         * supported.
         */
        GUARD_PATHSPEC(&opt->pathspec, PATHSPEC_FROMTOP | PATHSPEC_LITERAL);
#if 0
        /*
         * We should reject wildcards as well. Unfortunately we
         * haven't got a reliable way to detect that 'foo\*bar' in
         * fact has no wildcards. nowildcard_len is merely a hint for
         * optimization. Let it slip for now until wildmatch is taught
         * about dry-run mode and returns wildcard info.
         */
        if (opt->pathspec.has_wildcard)
                die("BUG:%s:%d: wildcards are not supported",
                    __FILE__, __LINE__);
#endif

        /* Remove the file creation entry from the diff queue, and remember it */
        choice = q->queue[0];
        q->nr = 0;

        diff_setup(&diff_opts);
        DIFF_OPT_SET(&diff_opts, RECURSIVE);
        DIFF_OPT_SET(&diff_opts, FIND_COPIES_HARDER);
        diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
        diff_opts.single_follow = opt->pathspec.items[0].match;
        diff_opts.break_opt = opt->break_opt;
        diff_opts.rename_score = opt->rename_score;
        diff_setup_done(&diff_opts);
        diff_tree(t1, t2, base, &diff_opts);
        diffcore_std(&diff_opts);
        free_pathspec(&diff_opts.pathspec);

        /* Go through the new set of filepairing, and see if we find a more interesting one */
        opt->found_follow = 0;
        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *p = q->queue[i];

                /*
                 * Found a source? Not only do we use that for the new
                 * diff_queued_diff, we will also use that as the path in
                 * the future!
                 */
                if ((p->status == 'R' || p->status == 'C') &&
                    !strcmp(p->two->path, opt->pathspec.items[0].match)) {
                        const char *path[2];

                        /* Switch the file-pairs around */
                        q->queue[i] = choice;
                        choice = p;

                        /* Update the path we use from now on.. */
                        path[0] = p->one->path;
                        path[1] = NULL;
                        free_pathspec(&opt->pathspec);
                        parse_pathspec(&opt->pathspec,
                                       PATHSPEC_ALL_MAGIC & ~PATHSPEC_LITERAL,
                                       PATHSPEC_LITERAL_PATH, "", path);

                        /*
                         * The caller expects us to return a set of vanilla
                         * filepairs to let a later call to diffcore_std()
                         * it makes to sort the renames out (among other
                         * things), but we already have found renames
                         * ourselves; signal diffcore_std() not to muck with
                         * rename information.
                         */
                        opt->found_follow = 1;
                        break;
                }
        }

        /*
         * Then, discard all the non-relevant file pairs...
         */
        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *p = q->queue[i];
                diff_free_filepair(p);
        }

        /*
         * .. and re-instate the one we want (which might be either the
         * original one, or the rename/copy we found)
         */
        q->queue[0] = choice;
        q->nr = 1;
}

int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base, struct diff_options *opt)
{
        void *tree1, *tree2;
        struct tree_desc t1, t2;
        unsigned long size1, size2;
        int retval;

        tree1 = fill_tree_descriptor(&t1, old);
        tree2 = fill_tree_descriptor(&t2, new);
        size1 = t1.size;
        size2 = t2.size;
        retval = diff_tree(&t1, &t2, base, opt);
        if (!*base && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && diff_might_be_rename()) {
                init_tree_desc(&t1, tree1, size1);
                init_tree_desc(&t2, tree2, size2);
                try_to_follow_renames(&t1, &t2, base, opt);
        }
        free(tree1);
        free(tree2);
        return retval;
}

int diff_root_tree_sha1(const unsigned char *new, const char *base, struct diff_options *opt)
{
        return diff_tree_sha1(NULL, new, base, opt);
}