#include "cache.h"
#include "repository.h"
#include "refs.h"
#include "object.h"
#include "commit.h"
#include "tag.h"
#include "packfile.h"
#include "object-store.h"
#include "strbuf.h"

struct update_info_ctx {
        FILE *cur_fp;
        FILE *old_fp; /* becomes NULL if it differs from cur_fp */
        struct strbuf cur_sb;
        struct strbuf old_sb;
};

static void uic_mark_stale(struct update_info_ctx *uic)
{
        fclose(uic->old_fp);
        uic->old_fp = NULL;
}

static int uic_is_stale(const struct update_info_ctx *uic)
{
        return uic->old_fp == NULL;
}

static int uic_printf(struct update_info_ctx *uic, const char *fmt, ...)
{
        va_list ap;
        int ret = -1;

        va_start(ap, fmt);

        if (uic_is_stale(uic)) {
                ret = vfprintf(uic->cur_fp, fmt, ap);
        } else {
                ssize_t r;
                struct strbuf *cur = &uic->cur_sb;
                struct strbuf *old = &uic->old_sb;

                strbuf_reset(cur);
                strbuf_vinsertf(cur, 0, fmt, ap);

                strbuf_reset(old);
                strbuf_grow(old, cur->len);
                r = fread(old->buf, 1, cur->len, uic->old_fp);
                if (r != cur->len || memcmp(old->buf, cur->buf, r))
                        uic_mark_stale(uic);

                if (fwrite(cur->buf, 1, cur->len, uic->cur_fp) == cur->len)
                        ret = 0;
        }

        va_end(ap);

        return ret;
}

/*
 * Create the file "path" by writing to a temporary file and renaming
 * it into place. The contents of the file come from "generate", which
 * should return non-zero if it encounters an error.
 */
static int update_info_file(char *path,
                        int (*generate)(struct update_info_ctx *),
                        int force)
{
        char *tmp = mkpathdup("%s_XXXXXX", path);
        int ret = -1;
        int fd = -1;
        FILE *to_close;
        struct update_info_ctx uic = {
                .cur_fp = NULL,
                .old_fp = NULL,
                .cur_sb = STRBUF_INIT,
                .old_sb = STRBUF_INIT
        };

        safe_create_leading_directories(path);
        fd = git_mkstemp_mode(tmp, 0666);
        if (fd < 0)
                goto out;
        to_close = uic.cur_fp = fdopen(fd, "w");
        if (!uic.cur_fp)
                goto out;
        fd = -1;

        /* no problem on ENOENT and old_fp == NULL, it's stale, now */
        if (!force)
                uic.old_fp = fopen_or_warn(path, "r");

        /*
         * uic_printf will compare incremental comparison aginst old_fp
         * and mark uic as stale if needed
         */
        ret = generate(&uic);
        if (ret)
                goto out;

        /* new file may be shorter than the old one, check here */
        if (!uic_is_stale(&uic)) {
                struct stat st;
                long new_len = ftell(uic.cur_fp);
                int old_fd = fileno(uic.old_fp);

                if (new_len < 0) {
                        ret = -1;
                        goto out;
                }
                if (fstat(old_fd, &st) || (st.st_size != (size_t)new_len))
                        uic_mark_stale(&uic);
        }

        uic.cur_fp = NULL;
        if (fclose(to_close))
                goto out;

        if (uic_is_stale(&uic)) {
                if (adjust_shared_perm(tmp) < 0)
                        goto out;
                if (rename(tmp, path) < 0)
                        goto out;
        } else {
                unlink(tmp);
        }
        ret = 0;

out:
        if (ret) {
                error_errno("unable to update %s", path);
                if (uic.cur_fp)
                        fclose(uic.cur_fp);
                else if (fd >= 0)
                        close(fd);
                unlink(tmp);
        }
        free(tmp);
        if (uic.old_fp)
                fclose(uic.old_fp);
        strbuf_release(&uic.old_sb);
        strbuf_release(&uic.cur_sb);
        return ret;
}

static int add_info_ref(const char *path, const struct object_id *oid,
                        int flag, void *cb_data)
{
        struct update_info_ctx *uic = cb_data;
        struct object *o = parse_object(the_repository, oid);
        if (!o)
                return -1;

        if (uic_printf(uic, "%s %s\n", oid_to_hex(oid), path) < 0)
                return -1;

        if (o->type == OBJ_TAG) {
                o = deref_tag(the_repository, o, path, 0);
                if (o)
                        if (uic_printf(uic, "%s %s^{}\n",
                                oid_to_hex(&o->oid), path) < 0)
                                return -1;
        }
        return 0;
}

static int generate_info_refs(struct update_info_ctx *uic)
{
        return for_each_ref(add_info_ref, uic);
}

static int update_info_refs(int force)
{
        char *path = git_pathdup("info/refs");
        int ret = update_info_file(path, generate_info_refs, force);
        free(path);
        return ret;
}

/* packs */
static struct pack_info {
        struct packed_git *p;
        int old_num;
        int new_num;
} **info;
static int num_pack;

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;
                if (!strcmp(pack_basename(p), name))
                        return info[i];
        }
        return NULL;
}

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

/* 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;
        struct strbuf line = STRBUF_INIT;
        int old_cnt = 0;
        int stale = 1;

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

        while (strbuf_getline(&line, fp) != EOF) {
                const char *arg;

                if (!line.len)
                        continue;

                if (skip_prefix(line.buf, "P ", &arg)) {
                        /* P name */
                        if (parse_pack_def(arg, old_cnt++))
                                goto out_stale;
                } else if (line.buf[0] == 'D') {
                        /* we used to emit D but that was misguided. */
                        goto out_stale;
                } else if (line.buf[0] == 'T') {
                        /* we used to emit T but nobody uses it. */
                        goto out_stale;
                } else {
                        error("unrecognized: %s", line.buf);
                }
        }
        stale = 0;

 out_stale:
        strbuf_release(&line);
        fclose(fp);
        return stale;
}

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;

        /* then it does not matter but at least keep the comparison stable */
        if ((*a)->p == (*b)->p)
                return 0;
        else if ((*a)->p < (*b)->p)
                return -1;
        else
                return 1;
}

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

        for (p = get_all_packs(the_repository); p; p = p->next) {
                /* we ignore things on alternate path since they are
                 * not available to the pullers in general.
                 */
                if (!p->pack_local)
                        continue;
                i++;
        }
        num_pack = i;
        info = xcalloc(num_pack, sizeof(struct pack_info *));
        for (i = 0, p = get_all_packs(the_repository); p; p = p->next) {
                if (!p->pack_local)
                        continue;
                assert(i < num_pack);
                info[i] = xcalloc(1, sizeof(struct pack_info));
                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;

        /* renumber them */
        QSORT(info, num_pack, compare_info);
        for (i = 0; i < num_pack; i++)
                info[i]->new_num = i;
}

static void free_pack_info(void)
{
        int i;
        for (i = 0; i < num_pack; i++)
                free(info[i]);
        free(info);
}

static int write_pack_info_file(struct update_info_ctx *uic)
{
        int i;
        for (i = 0; i < num_pack; i++) {
                if (uic_printf(uic, "P %s\n", pack_basename(info[i]->p)) < 0)
                        return -1;
        }
        if (uic_printf(uic, "\n") < 0)
                return -1;
        return 0;
}

static int update_info_packs(int force)
{
        char *infofile = mkpathdup("%s/info/packs", get_object_directory());
        int ret;

        init_pack_info(infofile, force);
        ret = update_info_file(infofile, write_pack_info_file, force);
        free_pack_info();
        free(infofile);
        return ret;
}

/* 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);

        /* remove leftover rev-cache file if there is any */
        unlink_or_warn(git_path("info/rev-cache"));

        return errs;
}