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

static int cached_only = 0;
static int generate_patch = 0;
static int line_termination = '\n';

/* A file entry went away or appeared */
static void show_file(const char *prefix, struct cache_entry *ce, unsigned char *sha1, unsigned int mode)
{
        if (generate_patch)
                diff_addremove(prefix[0], ntohl(mode), sha1, ce->name, NULL);
        else
                printf("%s%06o\tblob\t%s\t%s%c", prefix, ntohl(mode),
                       sha1_to_hex(sha1), ce->name, line_termination);
}

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 (stat(ce->name, &st) < 0)
                        return -1;
                changed = cache_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)
{
        unsigned int mode, oldmode;
        unsigned char *sha1;
        unsigned char old_sha1_hex[60];

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

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

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

        if (generate_patch)
                diff_change(oldmode, mode,
                            old->sha1, sha1, old->name, NULL);
        else {
                strcpy(old_sha1_hex, sha1_to_hex(old->sha1));
                printf("*%06o->%06o\tblob\t%s->%s\t%s%c", oldmode, mode,
                       old_sha1_hex, sha1_to_hex(sha1),
                       old->name, line_termination);
        }
        return 0;
}

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

                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);
                        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;
                        }
                        /* Otherwise we fall through to the "unmerged" case */
                case 3:
                        if (generate_patch)
                                diff_unmerge(ce->name);
                        else
                                printf("U %s%c", ce->name, line_termination);
                        break;

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

                /*
                 * Ignore all the different stages for this file,
                 * we've handled the relevant cases now.
                 */
                do {
                        ac++;
                        entries--;
                } while (entries && 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 char *diff_cache_usage =
"diff-cache [-r] [-z] [-p] [--cached] <tree sha1>";

int main(int argc, char **argv)
{
        unsigned char tree_sha1[20];
        void *tree;
        unsigned long size;

        read_cache();
        while (argc > 2) {
                char *arg = argv[1];
                argv++;
                argc--;
                if (!strcmp(arg, "-r")) {
                        /* We accept the -r flag just to look like diff-tree */
                        continue;
                }
                if (!strcmp(arg, "-p")) {
                        generate_patch = 1;
                        continue;
                }
                if (!strcmp(arg, "-z")) {
                        line_termination = '\0';
                        continue;
                }
                if (!strcmp(arg, "--cached")) {
                        cached_only = 1;
                        continue;
                }
                usage(diff_cache_usage);
        }

        if (argc != 2 || get_sha1(argv[1], tree_sha1))
                usage(diff_cache_usage);

        mark_merge_entries();

        tree = read_object_with_reference(tree_sha1, "tree", &size, 0);
        if (!tree)
                die("bad tree object %s", argv[1]);
        if (read_tree(tree, size, 1))
                die("unable to read tree object %s", argv[1]);

        return diff_cache(active_cache, active_nr);
}