#include "cache.h"
#include "refs.h"
#include "object.h"
#include "commit.h"
#include "tag.h"
#include "rev-cache.h"

/* refs */
static FILE *info_ref_fp;
static unsigned long info_ref_time;
static int info_ref_is_stale = 0;

static int stat_ref(const char *path, const unsigned char *sha1)
{
        struct stat st;
        if (!stat(path, &st) && info_ref_time < st.st_mtime)
                info_ref_is_stale = 1;
        return 0;
}

static int add_info_ref(const char *path, const unsigned char *sha1)
{
        fprintf(info_ref_fp, "%s        %s\n", sha1_to_hex(sha1), path);
        return 0;
}

static int update_info_refs(int force)
{
        struct stat st;
        char *path0 = strdup(git_path("info/refs"));
        int len = strlen(path0);
        char *path1 = xmalloc(len + 2);

        strcpy(path1, path0);
        strcpy(path1 + len, "+");

        if (!force) {
                if (stat(path0, &st)) {
                        if (errno == ENOENT)
                                info_ref_is_stale = 1;
                        else
                                return error("cannot stat %s", path0);
                }
                else {
                        info_ref_time = st.st_mtime;
                        for_each_ref(stat_ref);
                }
                if (!info_ref_is_stale)
                        return 0;
        }

        safe_create_leading_directories(path0);
        info_ref_fp = fopen(path1, "w");
        if (!info_ref_fp)
                return error("unable to update %s", path0);
        for_each_ref(add_info_ref);
        fclose(info_ref_fp);
        rename(path1, path0);
        free(path0);
        free(path1);
        return 0;
}

/* packs */
static struct pack_info {
        unsigned long latest;
        struct packed_git *p;
        int old_num;
        int new_num;
        int nr_alloc;
        int nr_heads;
        unsigned char (*head)[20];
        char dep[]; /* more */
} **info;
static int num_pack;
static const char *objdir;
static int objdirlen;

static struct object *parse_object_cheap(const unsigned char *sha1)
{
        struct object *o;

        if ((o = parse_object(sha1)) == NULL)
                return NULL;
        if (o->type == commit_type) {
                struct commit *commit = (struct commit *)o;
                free(commit->buffer);
                commit->buffer = NULL;
        }
        return o;
}

static struct pack_info *find_pack_by_name(const char *name)
{
        int i;
        for (i = 0; i < num_pack; i++) {
                struct packed_git *p = info[i]->p;
                /* skip "/pack/" after ".git/objects" */
                if (!strcmp(p->pack_name + objdirlen + 6, name))
                        return info[i];
        }
        return NULL;
}

static struct pack_info *find_pack_by_old_num(int old_num)
{
        int i;
        for (i = 0; i < num_pack; i++)
                if (info[i]->old_num == old_num)
                        return info[i];
        return NULL;
}

static int add_head_def(struct pack_info *this, unsigned char *sha1)
{
        if (this->nr_alloc <= this->nr_heads) {
                this->nr_alloc = alloc_nr(this->nr_alloc);
                this->head = xrealloc(this->head, this->nr_alloc * 20);
        }
        memcpy(this->head[this->nr_heads++], sha1, 20);
        return 0;
}

/* Returns non-zero when we detect that the info in the
 * old file is useless.
 */
static int parse_pack_def(const char *line, int old_cnt)
{
        struct pack_info *i = find_pack_by_name(line + 2);
        if (i) {
                i->old_num = old_cnt;
                return 0;
        }
        else {
                /* The file describes a pack that is no longer here;
                 * dependencies between packs needs to be recalculated.
                 */
                return 1;
        }
}

/* Returns non-zero when we detect that the info in the
 * old file is useless.
 */
static int parse_depend_def(char *line)
{
        unsigned long num;
        char *cp, *ep;
        struct pack_info *this, *that;

        cp = line + 2;
        num = strtoul(cp, &ep, 10);
        if (ep == cp)
                return error("invalid input %s", line);
        this = find_pack_by_old_num(num);
        if (!this)
                return 0;
        while (ep && *(cp = ep)) {
                num = strtoul(cp, &ep, 10);
                if (ep == cp)
                        break;
                that = find_pack_by_old_num(num);
                if (!that)
                        /* The pack this one depends on does not
                         * exist; this should not happen because
                         * we write out the list of packs first and
                         * then dependency information, but it means
                         * the file is useless anyway.
                         */
                        return 1;
                this->dep[that->new_num] = 1;
        }
        return 0;
}

/* Returns non-zero when we detect that the info in the
 * old file is useless.
 */
static int parse_head_def(char *line)
{
        unsigned char sha1[20];
        unsigned long num;
        char *cp, *ep;
        struct pack_info *this;
        struct object *o;

        cp = line + 2;
        num = strtoul(cp, &ep, 10);
        if (ep == cp || *ep++ != ' ')
                return error("invalid input ix %s", line);
        this = find_pack_by_old_num(num);
        if (!this)
                return 1; /* You know the drill. */
        if (get_sha1_hex(ep, sha1) || ep[40] != ' ')
                return error("invalid input sha1 %s (%s)", line, ep);
        if ((o = parse_object_cheap(sha1)) == NULL)
                return error("no such object: %s", line);
        return add_head_def(this, sha1);
}

/* Returns non-zero when we detect that the info in the
 * old file is useless.
 */
static int read_pack_info_file(const char *infofile)
{
        FILE *fp;
        char line[1000];
        int old_cnt = 0;

        fp = fopen(infofile, "r");
        if (!fp)
                return 1; /* nonexisting is not an error. */

        while (fgets(line, sizeof(line), fp)) {
                int len = strlen(line);
                if (line[len-1] == '\n')
                        line[len-1] = 0;

                switch (line[0]) {
                case 'P': /* P name */
                        if (parse_pack_def(line, old_cnt++))
                                goto out_stale;
                        break;
                case 'D': /* D ix dep-ix1 dep-ix2... */
                        if (parse_depend_def(line))
                                goto out_stale;
                        break;
                case 'T': /* T ix sha1 type */
                        if (parse_head_def(line))
                                goto out_stale;
                        break;
                default:
                        error("unrecognized: %s", line);
                        break;
                }
        }
        fclose(fp);
        return 0;
 out_stale:
        fclose(fp);
        return 1;
}

/* We sort the packs according to the date of the latest commit.  That
 * in turn indicates how young the pack is, and in general we would
 * want to depend on younger packs.
 */
static unsigned long get_latest_commit_date(struct packed_git *p)
{
        unsigned char sha1[20];
        struct object *o;
        int num = num_packed_objects(p);
        int i;
        unsigned long latest = 0;

        for (i = 0; i < num; i++) {
                if (nth_packed_object_sha1(p, i, sha1))
                        die("corrupt pack file %s?", p->pack_name);
                if ((o = parse_object_cheap(sha1)) == NULL)
                        die("cannot parse %s", sha1_to_hex(sha1));
                if (o->type == commit_type) {
                        struct commit *commit = (struct commit *)o;
                        if (latest < commit->date)
                                latest = commit->date;
                }
        }
        return latest;
}

static int compare_info(const void *a_, const void *b_)
{
        struct pack_info * const* a = a_;
        struct pack_info * const* b = b_;

        if (0 <= (*a)->old_num && 0 <= (*b)->old_num)
                /* Keep the order in the original */
                return (*a)->old_num - (*b)->old_num;
        else if (0 <= (*a)->old_num)
                /* Only A existed in the original so B is obviously newer */
                return -1;
        else if (0 <= (*b)->old_num)
                /* The other way around. */
                return 1;

        if ((*a)->latest < (*b)->latest)
                return -1;
        else if ((*a)->latest == (*b)->latest)
                return 0;
        else
                return 1;
}

static void init_pack_info(const char *infofile, int force)
{
        struct packed_git *p;
        int stale;
        int i = 0;
        char *dep_temp;

        objdir = get_object_directory();
        objdirlen = strlen(objdir);

        prepare_packed_git();
        for (p = packed_git; p; p = p->next) {
                /* we ignore things on alternate path since they are
                 * not available to the pullers in general.
                 */
                if (strncmp(p->pack_name, objdir, objdirlen) ||
                    strncmp(p->pack_name + objdirlen, "/pack/", 6))
                        continue;
                i++;
        }
        num_pack = i;
        info = xcalloc(num_pack, sizeof(struct pack_info *));
        for (i = 0, p = packed_git; p; p = p->next) {
                if (strncmp(p->pack_name, objdir, objdirlen) ||
                    p->pack_name[objdirlen] != '/')
                        continue;
                info[i] = xcalloc(1, sizeof(struct pack_info) + num_pack);
                info[i]->p = p;
                info[i]->old_num = -1;
                i++;
        }

        if (infofile && !force)
                stale = read_pack_info_file(infofile);
        else
                stale = 1;

        for (i = 0; i < num_pack; i++) {
                if (stale) {
                        info[i]->old_num = -1;
                        memset(info[i]->dep, 0, num_pack);
                        info[i]->nr_heads = 0;
                }
                if (info[i]->old_num < 0)
                        info[i]->latest = get_latest_commit_date(info[i]->p);
        }

        qsort(info, num_pack, sizeof(info[0]), compare_info);
        for (i = 0; i < num_pack; i++)
                info[i]->new_num = i;

        /* we need to fix up the dependency information
         * for the old ones.
         */
        dep_temp = NULL;
        for (i = 0; i < num_pack; i++) {
                int old;

                if (info[i]->old_num < 0)
                        continue;
                if (! dep_temp)
                        dep_temp = xmalloc(num_pack);
                memset(dep_temp, 0, num_pack);
                for (old = 0; old < num_pack; old++) {
                        struct pack_info *base;
                        if (!info[i]->dep[old])
                                continue;
                        base = find_pack_by_old_num(old);
                        if (!base)
                                die("internal error renumbering");
                        dep_temp[base->new_num] = 1;
                }
                memcpy(info[i]->dep, dep_temp, num_pack);
        }
        free(dep_temp);
}

static void write_pack_info_file(FILE *fp)
{
        int i, j;
        for (i = 0; i < num_pack; i++)
                fprintf(fp, "P %s\n", info[i]->p->pack_name + objdirlen + 6);

        for (i = 0; i < num_pack; i++) {
                fprintf(fp, "D %1d", i);
                for (j = 0; j < num_pack; j++) {
                        if ((i == j) || !(info[i]->dep[j]))
                                continue;
                        fprintf(fp, " %1d", j);
                }
                fputc('\n', fp);
        }

        for (i = 0; i < num_pack; i++) {
                struct pack_info *this = info[i];
                for (j = 0; j < this->nr_heads; j++) {
                        struct object *o = lookup_object(this->head[j]);
                        fprintf(fp, "T %1d %s %s\n",
                                i, sha1_to_hex(this->head[j]), o->type);
                }
        }

}

#define REFERENCED 01
#define INTERNAL  02
#define EMITTED   04

static void show(struct object *o, int pack_ix)
{
        /*
         * We are interested in objects that are not referenced,
         * and objects that are referenced but not internal.
         */
        if (o->flags & EMITTED)
                return;

        if (!(o->flags & REFERENCED))
                add_head_def(info[pack_ix], o->sha1);
        else if ((o->flags & REFERENCED) && !(o->flags & INTERNAL)) {
                int i;

                /* Which pack contains this object?  That is what
                 * pack_ix can depend on.  We earlier sorted info
                 * array from youngest to oldest, so try newer packs
                 * first to favor them here.
                 */
                for (i = num_pack - 1; 0 <= i; i--) {
                        struct packed_git *p = info[i]->p;
                        struct pack_entry ent;
                        if (find_pack_entry_one(o->sha1, &ent, p)) {
                                info[pack_ix]->dep[i] = 1;
                                break;
                        }
                }
        }
        o->flags |= EMITTED;
}

static void find_pack_info_one(int pack_ix)
{
        unsigned char sha1[20];
        struct object *o;
        struct object_list *ref;
        int i;
        struct packed_git *p = info[pack_ix]->p;
        int num = num_packed_objects(p);

        /* Scan objects, clear flags from all the edge ones and
         * internal ones, possibly marked in the previous round.
         */
        for (i = 0; i < num; i++) {
                if (nth_packed_object_sha1(p, i, sha1))
                        die("corrupt pack file %s?", p->pack_name);
                if ((o = lookup_object(sha1)) == NULL)
                        die("cannot parse %s", sha1_to_hex(sha1));
                for (ref = o->refs; ref; ref = ref->next)
                        ref->item->flags = 0;
                o->flags = 0;
        }

        /* Mark all the internal ones */
        for (i = 0; i < num; i++) {
                if (nth_packed_object_sha1(p, i, sha1))
                        die("corrupt pack file %s?", p->pack_name);
                if ((o = lookup_object(sha1)) == NULL)
                        die("cannot find %s", sha1_to_hex(sha1));
                for (ref = o->refs; ref; ref = ref->next)
                        ref->item->flags |= REFERENCED;
                o->flags |= INTERNAL;
        }

        for (i = 0; i < num; i++) {
                if (nth_packed_object_sha1(p, i, sha1))
                        die("corrupt pack file %s?", p->pack_name);
                if ((o = lookup_object(sha1)) == NULL)
                        die("cannot find %s", sha1_to_hex(sha1));

                show(o, pack_ix);
                for (ref = o->refs; ref; ref = ref->next)
                        show(ref->item, pack_ix);
        }

}

static void find_pack_info(void)
{
        int i;
        for (i = 0; i < num_pack; i++) {
                /* The packed objects are cast in stone, and a head
                 * in a pack will stay as head, so is the set of missing
                 * objects.  If the repo has been reorganized and we
                 * are missing some packs available back then, we have
                 * already discarded the info read from the file, so
                 * we will find (old_num < 0) in that case.
                 */
                if (0 <= info[i]->old_num)
                        continue;
                find_pack_info_one(i);
        }
}

static int update_info_packs(int force)
{
        char infofile[PATH_MAX];
        char name[PATH_MAX];
        int namelen;
        FILE *fp;

        namelen = sprintf(infofile, "%s/info/packs", get_object_directory());
        strcpy(name, infofile);
        strcpy(name + namelen, "+");

        init_pack_info(infofile, force);
        find_pack_info();

        safe_create_leading_directories(name);
        fp = fopen(name, "w");
        if (!fp)
                return error("cannot open %s", name);
        write_pack_info_file(fp);
        fclose(fp);
        rename(name, infofile);
        return 0;
}

/* rev-cache */
static int record_rev_cache_ref(const char *path, const unsigned char *sha1)
{
        struct object *obj = parse_object(sha1);

        if (!obj)
                return error("ref %s has bad sha %s", path, sha1_to_hex(sha1));
        while (obj && obj->type == tag_type)
                obj = parse_object(((struct tag *)obj)->tagged->sha1);
        if (!obj || obj->type != commit_type)
                /* tag pointing at a non-commit */
                return 0;
        return record_rev_cache(obj->sha1, NULL);
}

static int update_info_revs(int force)
{
        char *path0 = strdup(git_path("info/rev-cache"));
        int len = strlen(path0);
        char *path1 = xmalloc(len + 2);

        strcpy(path1, path0);
        strcpy(path1 + len, "+");

        /* read existing rev-cache */
        if (!force)
                read_rev_cache(path0, NULL, 0);
        safe_create_leading_directories(path0);

        for_each_ref(record_rev_cache_ref);

        /* update the rev-cache database */
        write_rev_cache(path1, force ? "/dev/null" : path0);
        rename(path1, path0);
        free(path1);
        free(path0);
        return 0;
}

/* public */
int update_server_info(int force)
{
        /* We would add more dumb-server support files later,
         * including index of available pack files and their
         * intended audiences.
         */
        int errs = 0;

        errs = errs | update_info_refs(force);
        errs = errs | update_info_packs(force);
        errs = errs | update_info_revs(force);

        return errs;
}