#include "cache.h"
#include "diff.h"

static int cached_only = 0;
static int match_nonexisting = 0;
static struct diff_options diff_options;

/* A file entry went away or appeared */
static void show_file(const char *prefix,
                      struct cache_entry *ce,
                      unsigned char *sha1, unsigned int mode)
{
        diff_addremove(&diff_options, prefix[0], ntohl(mode),
                       sha1, ce->name, NULL);
}

static int get_stat_data(struct cache_entry *ce,
                         unsigned char **sha1p, unsigned int *modep)
{
        unsigned char *sha1 = ce->sha1;
        unsigned int mode = ce->ce_mode;

        if (!cached_only) {
                static unsigned char no_sha1[20];
                int changed;
                struct stat st;
                if (lstat(ce->name, &st) < 0) {
                        if (errno == ENOENT && match_nonexisting) {
                                *sha1p = sha1;
                                *modep = mode;
                                return 0;
                        }
                        return -1;
                }
                changed = ce_match_stat(ce, &st);
                if (changed) {
                        mode = create_ce_mode(st.st_mode);
                        sha1 = no_sha1;
                }
        }

        *sha1p = sha1;
        *modep = mode;
        return 0;
}

static void show_new_file(struct cache_entry *new)
{
        unsigned char *sha1;
        unsigned int mode;

        /* New file in the index: it might actually be different in the working copy */
        if (get_stat_data(new, &sha1, &mode) < 0)
                return;

        show_file("+", new, sha1, mode);
}

static int show_modified(struct cache_entry *old,
                         struct cache_entry *new,
                         int report_missing)
{
        unsigned int mode, oldmode;
        unsigned char *sha1;

        if (get_stat_data(new, &sha1, &mode) < 0) {
                if (report_missing)
                        show_file("-", old, old->sha1, old->ce_mode);
                return -1;
        }

        oldmode = old->ce_mode;
        if (mode == oldmode && !memcmp(sha1, old->sha1, 20) &&
            !diff_options.find_copies_harder)
                return 0;

        mode = ntohl(mode);
        oldmode = ntohl(oldmode);

        diff_change(&diff_options, oldmode, mode,
                    old->sha1, sha1, old->name, NULL);
        return 0;
}

static int diff_cache(struct cache_entry **ac, int entries, const char **pathspec)
{
        while (entries) {
                struct cache_entry *ce = *ac;
                int same = (entries > 1) && ce_same_name(ce, ac[1]);

                if (!ce_path_match(ce, pathspec))
                        goto skip_entry;

                switch (ce_stage(ce)) {
                case 0:
                        /* No stage 1 entry? That means it's a new file */
                        if (!same) {
                                show_new_file(ce);
                                break;
                        }
                        /* Show difference between old and new */
                        show_modified(ac[1], ce, 1);
                        break;
                case 1:
                        /* No stage 3 (merge) entry? That means it's been deleted */
                        if (!same) {
                                show_file("-", ce, ce->sha1, ce->ce_mode);
                                break;
                        }
                        /* We come here with ce pointing at stage 1
                         * (original tree) and ac[1] pointing at stage
                         * 3 (unmerged).  show-modified with
                         * report-mising set to false does not say the
                         * file is deleted but reports true if work
                         * tree does not have it, in which case we
                         * fall through to report the unmerged state.
                         * Otherwise, we show the differences between
                         * the original tree and the work tree.
                         */
                        if (!cached_only && !show_modified(ce, ac[1], 0))
                                break;
                        /* fallthru */
                case 3:
                        diff_unmerge(&diff_options, ce->name);
                        break;

                default:
                        die("impossible cache entry stage");
                }

skip_entry:
                /*
                 * Ignore all the different stages for this file,
                 * we've handled the relevant cases now.
                 */
                do {
                        ac++;
                        entries--;
                } while (entries && ce_same_name(ce, ac[0]));
        }
        return 0;
}

/*
 * This turns all merge entries into "stage 3". That guarantees that
 * when we read in the new tree (into "stage 1"), we won't lose sight
 * of the fact that we had unmerged entries.
 */
static void mark_merge_entries(void)
{
        int i;
        for (i = 0; i < active_nr; i++) {
                struct cache_entry *ce = active_cache[i];
                if (!ce_stage(ce))
                        continue;
                ce->ce_flags |= htons(CE_STAGEMASK);
        }
}

static const char diff_cache_usage[] =
"git-diff-index [-m] [--cached] "
"[<common diff options>] <tree-ish> [<path>...]"
COMMON_DIFF_OPTIONS_HELP;

int main(int argc, const char **argv)
{
        const char *tree_name = NULL;
        unsigned char sha1[20];
        const char *prefix = setup_git_directory();
        const char **pathspec = NULL;
        void *tree;
        unsigned long size;
        int ret;
        int allow_options = 1;
        int i;

        diff_setup(&diff_options);
        for (i = 1; i < argc; i++) {
                const char *arg = argv[i];
                int diff_opt_cnt;

                if (!allow_options || *arg != '-') {
                        if (tree_name)
                                break;
                        tree_name = arg;
                        continue;
                }
                        
                if (!strcmp(arg, "--")) {
                        allow_options = 0;
                        continue;
                }
                if (!strcmp(arg, "-r")) {
                        /* We accept the -r flag just to look like git-diff-tree */
                        continue;
                }
                diff_opt_cnt = diff_opt_parse(&diff_options, argv + i,
                                              argc - i);
                if (diff_opt_cnt < 0)
                        usage(diff_cache_usage);
                else if (diff_opt_cnt) {
                        i += diff_opt_cnt - 1;
                        continue;
                }

                if (!strcmp(arg, "-m")) {
                        match_nonexisting = 1;
                        continue;
                }
                if (!strcmp(arg, "--cached")) {
                        cached_only = 1;
                        continue;
                }
                usage(diff_cache_usage);
        }

        pathspec = get_pathspec(prefix, argv + i);

        if (diff_setup_done(&diff_options) < 0)
                usage(diff_cache_usage);

        if (!tree_name || get_sha1(tree_name, sha1))
                usage(diff_cache_usage);

        read_cache();

        mark_merge_entries();

        tree = read_object_with_reference(sha1, "tree", &size, NULL);
        if (!tree)
                die("bad tree object %s", tree_name);
        if (read_tree(tree, size, 1, pathspec))
                die("unable to read tree object %s", tree_name);

        ret = diff_cache(active_cache, active_nr, pathspec);

        diffcore_std(&diff_options);
        diff_flush(&diff_options);
        return ret;
}