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

static char *malloc_base(const char *base, int baselen, const char *path, int pathlen)
{
        char *newbase = xmalloc(baselen + pathlen + 2);
        memcpy(newbase, base, baselen);
        memcpy(newbase + baselen, path, pathlen);
        memcpy(newbase + baselen + pathlen, "/", 2);
        return newbase;
}

static char *malloc_fullname(const char *base, int baselen, const char *path, int pathlen)
{
        char *fullname = xmalloc(baselen + pathlen + 1);
        memcpy(fullname, base, baselen);
        memcpy(fullname + baselen, path, pathlen);
        fullname[baselen + pathlen] = 0;
        return fullname;
}

static void show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc,
                       const char *base, int baselen);

static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2, const char *base, int baselen, struct diff_options *opt)
{
        unsigned mode1, mode2;
        const char *path1, *path2;
        const unsigned char *sha1, *sha2;
        int cmp, pathlen1, pathlen2;
        char *fullname;

        sha1 = tree_entry_extract(t1, &path1, &mode1);
        sha2 = tree_entry_extract(t2, &path2, &mode2);

        pathlen1 = tree_entry_len(path1, sha1);
        pathlen2 = tree_entry_len(path2, sha2);
        cmp = base_name_compare(path1, pathlen1, mode1, path2, pathlen2, mode2);
        if (cmp < 0) {
                show_entry(opt, "-", t1, base, baselen);
                return -1;
        }
        if (cmp > 0) {
                show_entry(opt, "+", t2, base, baselen);
                return 1;
        }
        if (!DIFF_OPT_TST(opt, FIND_COPIES_HARDER) && !hashcmp(sha1, sha2) && mode1 == mode2)
                return 0;

        /*
         * If the filemode has changed to/from a directory from/to a regular
         * file, we need to consider it a remove and an add.
         */
        if (S_ISDIR(mode1) != S_ISDIR(mode2)) {
                show_entry(opt, "-", t1, base, baselen);
                show_entry(opt, "+", t2, base, baselen);
                return 0;
        }

        if (DIFF_OPT_TST(opt, RECURSIVE) && S_ISDIR(mode1)) {
                int retval;
                char *newbase = malloc_base(base, baselen, path1, pathlen1);
                if (DIFF_OPT_TST(opt, TREE_IN_RECURSIVE)) {
                        newbase[baselen + pathlen1] = 0;
                        opt->change(opt, mode1, mode2,
                                    sha1, sha2, newbase, 0, 0);
                        newbase[baselen + pathlen1] = '/';
                }
                retval = diff_tree_sha1(sha1, sha2, newbase, opt);
                free(newbase);
                return retval;
        }

        fullname = malloc_fullname(base, baselen, path1, pathlen1);
        opt->change(opt, mode1, mode2, sha1, sha2, fullname, 0, 0);
        free(fullname);
        return 0;
}

/*
 * Is a tree entry interesting given the pathspec we have?
 *
 * Pre-condition: baselen == 0 || base[baselen-1] == '/'
 *
 * Return:
 *  - 2 for "yes, and all subsequent entries will be"
 *  - 1 for yes
 *  - zero for no
 *  - negative for "no, and no subsequent entries will be either"
 */
static int tree_entry_interesting(struct tree_desc *desc, const char *base, int baselen, struct diff_options *opt)
{
        const char *path;
        const unsigned char *sha1;
        unsigned mode;
        int i;
        int pathlen;
        int never_interesting = -1;

        if (!opt->pathspec.nr)
                return 2;

        sha1 = tree_entry_extract(desc, &path, &mode);

        pathlen = tree_entry_len(path, sha1);

        for (i = 0; i < opt->pathspec.nr; i++) {
                const struct pathspec_item *item = opt->pathspec.items+i;
                const char *match = item->match;
                int matchlen = item->len;
                int m = -1; /* signals that we haven't called strncmp() */

                if (baselen >= matchlen) {
                        /* If it doesn't match, move along... */
                        if (strncmp(base, match, matchlen))
                                continue;

                        /*
                         * If the base is a subdirectory of a path which
                         * was specified, all of them are interesting.
                         */
                        if (!matchlen ||
                            base[matchlen] == '/' ||
                            match[matchlen - 1] == '/')
                                return 2;

                        /* Just a random prefix match */
                        continue;
                }

                /* Does the base match? */
                if (strncmp(base, match, baselen))
                        continue;

                match += baselen;
                matchlen -= baselen;

                if (never_interesting) {
                        /*
                         * We have not seen any match that sorts later
                         * than the current path.
                         */

                        /*
                         * Does match sort strictly earlier than path
                         * with their common parts?
                         */
                        m = strncmp(match, path,
                                    (matchlen < pathlen) ? matchlen : pathlen);
                        if (m < 0)
                                continue;

                        /*
                         * If we come here even once, that means there is at
                         * least one pathspec that would sort equal to or
                         * later than the path we are currently looking at.
                         * In other words, if we have never reached this point
                         * after iterating all pathspecs, it means all
                         * pathspecs are either outside of base, or inside the
                         * base but sorts strictly earlier than the current
                         * one.  In either case, they will never match the
                         * subsequent entries.  In such a case, we initialized
                         * the variable to -1 and that is what will be
                         * returned, allowing the caller to terminate early.
                         */
                        never_interesting = 0;
                }

                if (pathlen > matchlen)
                        continue;

                if (matchlen > pathlen) {
                        if (match[pathlen] != '/')
                                continue;
                        if (!S_ISDIR(mode))
                                continue;
                }

                if (m == -1)
                        /*
                         * we cheated and did not do strncmp(), so we do
                         * that here.
                         */
                        m = strncmp(match, path, pathlen);

                /*
                 * If common part matched earlier then it is a hit,
                 * because we rejected the case where path is not a
                 * leading directory and is shorter than match.
                 */
                if (!m)
                        return 1;
        }
        return never_interesting; /* No matches */
}

/* A whole sub-tree went away or appeared */
static void show_tree(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base, int baselen)
{
        int all_interesting = 0;
        while (desc->size) {
                int show;

                if (all_interesting)
                        show = 1;
                else {
                        show = tree_entry_interesting(desc, base, baselen,
                                                      opt);
                        if (show == 2)
                                all_interesting = 1;
                }
                if (show < 0)
                        break;
                if (show)
                        show_entry(opt, prefix, desc, base, baselen);
                update_tree_entry(desc);
        }
}

/* A file entry went away or appeared */
static void show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc,
                       const char *base, int baselen)
{
        unsigned mode;
        const char *path;
        const unsigned char *sha1 = tree_entry_extract(desc, &path, &mode);
        int pathlen = tree_entry_len(path, sha1);

        if (DIFF_OPT_TST(opt, RECURSIVE) && S_ISDIR(mode)) {
                enum object_type type;
                char *newbase = malloc_base(base, baselen, path, pathlen);
                struct tree_desc inner;
                void *tree;
                unsigned long size;

                tree = read_sha1_file(sha1, &type, &size);
                if (!tree || type != OBJ_TREE)
                        die("corrupt tree sha %s", sha1_to_hex(sha1));

                if (DIFF_OPT_TST(opt, TREE_IN_RECURSIVE)) {
                        newbase[baselen + pathlen] = 0;
                        opt->add_remove(opt, *prefix, mode, sha1, newbase, 0);
                        newbase[baselen + pathlen] = '/';
                }

                init_tree_desc(&inner, tree, size);
                show_tree(opt, prefix, &inner, newbase, baselen + 1 + pathlen);

                free(tree);
                free(newbase);
        } else {
                char *fullname = malloc_fullname(base, baselen, path, pathlen);
                opt->add_remove(opt, prefix[0], mode, sha1, fullname, 0);
                free(fullname);
        }
}

static void skip_uninteresting(struct tree_desc *t, const char *base, int baselen, struct diff_options *opt, int *all_interesting)
{
        while (t->size) {
                int show = tree_entry_interesting(t, base, baselen, opt);
                if (show == 2)
                        *all_interesting = 1;
                if (!show) {
                        update_tree_entry(t);
                        continue;
                }
                /* Skip it all? */
                if (show < 0)
                        t->size = 0;
                return;
        }
}

int diff_tree(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
{
        int baselen = strlen(base);
        int all_t1_interesting = 0;
        int all_t2_interesting = 0;

        for (;;) {
                if (DIFF_OPT_TST(opt, QUICK) &&
                    DIFF_OPT_TST(opt, HAS_CHANGES))
                        break;
                if (opt->pathspec.nr) {
                        if (!all_t1_interesting)
                                skip_uninteresting(t1, base, baselen, opt,
                                                   &all_t1_interesting);
                        if (!all_t2_interesting)
                                skip_uninteresting(t2, base, baselen, opt,
                                                   &all_t2_interesting);
                }
                if (!t1->size) {
                        if (!t2->size)
                                break;
                        show_entry(opt, "+", t2, base, baselen);
                        update_tree_entry(t2);
                        continue;
                }
                if (!t2->size) {
                        show_entry(opt, "-", t1, base, baselen);
                        update_tree_entry(t1);
                        continue;
                }
                switch (compare_tree_entry(t1, t2, base, baselen, opt)) {
                case -1:
                        update_tree_entry(t1);
                        continue;
                case 0:
                        update_tree_entry(t1);
                        /* Fallthrough */
                case 1:
                        update_tree_entry(t2);
                        continue;
                }
                die("git diff-tree: internal error");
        }
        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;
        const char *paths[1];
        int i;

        /* 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.raw[0];
        diff_opts.break_opt = opt->break_opt;
        paths[0] = NULL;
        diff_tree_setup_paths(paths, &diff_opts);
        if (diff_setup_done(&diff_opts) < 0)
                die("unable to set up diff options to follow renames");
        diff_tree(t1, t2, base, &diff_opts);
        diffcore_std(&diff_opts);
        diff_tree_release_paths(&diff_opts);

        /* 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.raw[0])) {
                        /* Switch the file-pairs around */
                        q->queue[i] = choice;
                        choice = p;

                        /* Update the path we use from now on.. */
                        diff_tree_release_paths(opt);
                        opt->pathspec.raw[0] = xstrdup(p->one->path);
                        diff_tree_setup_paths(opt->pathspec.raw, opt);

                        /*
                         * 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 = read_object_with_reference(old, tree_type, &size1, NULL);
        if (!tree1)
                die("unable to read source tree (%s)", sha1_to_hex(old));
        tree2 = read_object_with_reference(new, tree_type, &size2, NULL);
        if (!tree2)
                die("unable to read destination tree (%s)", sha1_to_hex(new));
        init_tree_desc(&t1, tree1, size1);
        init_tree_desc(&t2, tree2, size2);
        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)
{
        int retval;
        void *tree;
        unsigned long size;
        struct tree_desc empty, real;

        tree = read_object_with_reference(new, tree_type, &size, NULL);
        if (!tree)
                die("unable to read root tree (%s)", sha1_to_hex(new));
        init_tree_desc(&real, tree, size);

        init_tree_desc(&empty, "", 0);
        retval = diff_tree(&empty, &real, base, opt);
        free(tree);
        return retval;
}

void diff_tree_release_paths(struct diff_options *opt)
{
        free_pathspec(&opt->pathspec);
}

void diff_tree_setup_paths(const char **p, struct diff_options *opt)
{
        init_pathspec(&opt->pathspec, p);
}