/*
 * State diagram and cleanup
 * -------------------------
 *
 * If the program exits while a temporary file is active, we want to
 * make sure that we remove it. This is done by remembering the active
 * temporary files in a linked list, `tempfile_list`. An `atexit(3)`
 * handler and a signal handler are registered, to clean up any active
 * temporary files.
 *
 * Because the signal handler can run at any time, `tempfile_list` and
 * the `tempfile` objects that comprise it must be kept in
 * self-consistent states at all times.
 *
 * The possible states of a `tempfile` object are as follows:
 *
 * - Uninitialized. In this state the object's `on_list` field must be
 *   zero but the rest of its contents need not be initialized. As
 *   soon as the object is used in any way, it is irrevocably
 *   registered in `tempfile_list`, and `on_list` is set.
 *
 * - Active, file open (after `create_tempfile()` or
 *   `reopen_tempfile()`). In this state:
 *
 *   - the temporary file exists
 *   - `active` is set
 *   - `filename` holds the filename of the temporary file
 *   - `fd` holds a file descriptor open for writing to it
 *   - `fp` holds a pointer to an open `FILE` object if and only if
 *     `fdopen_tempfile()` has been called on the object
 *   - `owner` holds the PID of the process that created the file
 *
 * - Active, file closed (after `close_tempfile_gently()`). Same
 *   as the previous state, except that the temporary file is closed,
 *   `fd` is -1, and `fp` is `NULL`.
 *
 * - Inactive (after `delete_tempfile()`, `rename_tempfile()`, or a
 *   failed attempt to create a temporary file). In this state:
 *
 *   - `active` is unset
 *   - `filename` is empty (usually, though there are transitory
 *     states in which this condition doesn't hold). Client code should
 *     *not* rely on the filename being empty in this state.
 *   - `fd` is -1 and `fp` is `NULL`
 *   - the object is removed from `tempfile_list` (but could be used again)
 *
 * A temporary file is owned by the process that created it. The
 * `tempfile` has an `owner` field that records the owner's PID. This
 * field is used to prevent a forked process from deleting a temporary
 * file created by its parent.
 */

#include "cache.h"
#include "tempfile.h"
#include "sigchain.h"

static VOLATILE_LIST_HEAD(tempfile_list);

static void remove_tempfiles(int in_signal_handler)
{
        pid_t me = getpid();
        volatile struct volatile_list_head *pos;

        list_for_each(pos, &tempfile_list) {
                struct tempfile *p = list_entry(pos, struct tempfile, list);

                if (!is_tempfile_active(p) || p->owner != me)
                        continue;

                if (p->fd >= 0)
                        close(p->fd);

                if (in_signal_handler)
                        unlink(p->filename.buf);
                else
                        unlink_or_warn(p->filename.buf);

                p->active = 0;
        }
}

static void remove_tempfiles_on_exit(void)
{
        remove_tempfiles(0);
}

static void remove_tempfiles_on_signal(int signo)
{
        remove_tempfiles(1);
        sigchain_pop(signo);
        raise(signo);
}

static struct tempfile *new_tempfile(void)
{
        struct tempfile *tempfile = xmalloc(sizeof(*tempfile));
        tempfile->fd = -1;
        tempfile->fp = NULL;
        tempfile->active = 0;
        tempfile->owner = 0;
        INIT_LIST_HEAD(&tempfile->list);
        strbuf_init(&tempfile->filename, 0);
        return tempfile;
}

static void activate_tempfile(struct tempfile *tempfile)
{
        static int initialized;

        if (is_tempfile_active(tempfile))
                BUG("activate_tempfile called for active object");

        if (!initialized) {
                sigchain_push_common(remove_tempfiles_on_signal);
                atexit(remove_tempfiles_on_exit);
                initialized = 1;
        }

        volatile_list_add(&tempfile->list, &tempfile_list);
        tempfile->owner = getpid();
        tempfile->active = 1;
}

static void deactivate_tempfile(struct tempfile *tempfile)
{
        tempfile->active = 0;
        strbuf_release(&tempfile->filename);
        volatile_list_del(&tempfile->list);
        free(tempfile);
}

/* Make sure errno contains a meaningful value on error */
struct tempfile *create_tempfile(const char *path)
{
        struct tempfile *tempfile = new_tempfile();

        strbuf_add_absolute_path(&tempfile->filename, path);
        tempfile->fd = open(tempfile->filename.buf,
                            O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0666);
        if (O_CLOEXEC && tempfile->fd < 0 && errno == EINVAL)
                /* Try again w/o O_CLOEXEC: the kernel might not support it */
                tempfile->fd = open(tempfile->filename.buf,
                                    O_RDWR | O_CREAT | O_EXCL, 0666);
        if (tempfile->fd < 0) {
                deactivate_tempfile(tempfile);
                return NULL;
        }
        activate_tempfile(tempfile);
        if (adjust_shared_perm(tempfile->filename.buf)) {
                int save_errno = errno;
                error("cannot fix permission bits on %s", tempfile->filename.buf);
                delete_tempfile(&tempfile);
                errno = save_errno;
                return NULL;
        }

        return tempfile;
}

struct tempfile *register_tempfile(const char *path)
{
        struct tempfile *tempfile = new_tempfile();
        strbuf_add_absolute_path(&tempfile->filename, path);
        activate_tempfile(tempfile);
        return tempfile;
}

struct tempfile *mks_tempfile_sm(const char *filename_template, int suffixlen, int mode)
{
        struct tempfile *tempfile = new_tempfile();

        strbuf_add_absolute_path(&tempfile->filename, filename_template);
        tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
        if (tempfile->fd < 0) {
                deactivate_tempfile(tempfile);
                return NULL;
        }
        activate_tempfile(tempfile);
        return tempfile;
}

struct tempfile *mks_tempfile_tsm(const char *filename_template, int suffixlen, int mode)
{
        struct tempfile *tempfile = new_tempfile();
        const char *tmpdir;

        tmpdir = getenv("TMPDIR");
        if (!tmpdir)
                tmpdir = "/tmp";

        strbuf_addf(&tempfile->filename, "%s/%s", tmpdir, filename_template);
        tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
        if (tempfile->fd < 0) {
                deactivate_tempfile(tempfile);
                return NULL;
        }
        activate_tempfile(tempfile);
        return tempfile;
}

struct tempfile *xmks_tempfile_m(const char *filename_template, int mode)
{
        struct tempfile *tempfile;
        struct strbuf full_template = STRBUF_INIT;

        strbuf_add_absolute_path(&full_template, filename_template);
        tempfile = mks_tempfile_m(full_template.buf, mode);
        if (!tempfile)
                die_errno("Unable to create temporary file '%s'",
                          full_template.buf);

        strbuf_release(&full_template);
        return tempfile;
}

FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
{
        if (!is_tempfile_active(tempfile))
                BUG("fdopen_tempfile() called for inactive object");
        if (tempfile->fp)
                BUG("fdopen_tempfile() called for open object");

        tempfile->fp = fdopen(tempfile->fd, mode);
        return tempfile->fp;
}

const char *get_tempfile_path(struct tempfile *tempfile)
{
        if (!is_tempfile_active(tempfile))
                BUG("get_tempfile_path() called for inactive object");
        return tempfile->filename.buf;
}

int get_tempfile_fd(struct tempfile *tempfile)
{
        if (!is_tempfile_active(tempfile))
                BUG("get_tempfile_fd() called for inactive object");
        return tempfile->fd;
}

FILE *get_tempfile_fp(struct tempfile *tempfile)
{
        if (!is_tempfile_active(tempfile))
                BUG("get_tempfile_fp() called for inactive object");
        return tempfile->fp;
}

int close_tempfile_gently(struct tempfile *tempfile)
{
        int fd;
        FILE *fp;
        int err;

        if (!is_tempfile_active(tempfile) || tempfile->fd < 0)
                return 0;

        fd = tempfile->fd;
        fp = tempfile->fp;
        tempfile->fd = -1;
        if (fp) {
                tempfile->fp = NULL;
                if (ferror(fp)) {
                        err = -1;
                        if (!fclose(fp))
                                errno = EIO;
                } else {
                        err = fclose(fp);
                }
        } else {
                err = close(fd);
        }

        return err ? -1 : 0;
}

int reopen_tempfile(struct tempfile *tempfile)
{
        if (!is_tempfile_active(tempfile))
                BUG("reopen_tempfile called for an inactive object");
        if (0 <= tempfile->fd)
                BUG("reopen_tempfile called for an open object");
        tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
        return tempfile->fd;
}

int rename_tempfile(struct tempfile **tempfile_p, const char *path)
{
        struct tempfile *tempfile = *tempfile_p;

        if (!is_tempfile_active(tempfile))
                BUG("rename_tempfile called for inactive object");

        if (close_tempfile_gently(tempfile)) {
                delete_tempfile(tempfile_p);
                return -1;
        }

        if (rename(tempfile->filename.buf, path)) {
                int save_errno = errno;
                delete_tempfile(tempfile_p);
                errno = save_errno;
                return -1;
        }

        deactivate_tempfile(tempfile);
        *tempfile_p = NULL;
        return 0;
}

void delete_tempfile(struct tempfile **tempfile_p)
{
        struct tempfile *tempfile = *tempfile_p;

        if (!is_tempfile_active(tempfile))
                return;

        close_tempfile_gently(tempfile);
        unlink_or_warn(tempfile->filename.buf);
        deactivate_tempfile(tempfile);
        *tempfile_p = NULL;
}