#define _POSIX_C_SOURCE 200809L

#include <assert.h>    /* assert */
#include <sys/stat.h>  /* mkdirat, openat */
#include <sys/types.h> /* mkdirat, openat */
#include <unistd.h>    /* unlinkat, linkat, close, write, … */
#include <fcntl.h>     /* mkdirat, unlinkat, openat, linkat, … */
#include <string.h>    /* strlen */
#include <stdbool.h>   /* bool */
#include <errno.h>
#include <err.h>

/* Napište podprogram ‹count_unique›, kterému je předán popisovač
 * otevřeného adresáře, a který spočítá, kolik unikátních souborů
 * (které nejsou složkami) je přímo tímto adresářem odkazováno.
 * Nezáporná návratová hodnota určuje počet nalezených souborů, -1
 * indikuje systémovou chybu. */

int count_unique( int dir_fd );

/* ┄┄┄┄┄┄┄ %< ┄┄┄┄┄┄┄┄┄┄ následují testy ┄┄┄┄┄┄┄┄┄┄ %< ┄┄┄┄┄┄┄ */

static void close_or_warn( int fd, const char *name )
{
    if ( close( fd ) == -1 )
        warn( "closing %s", name );
}

static void create_file( int dir_fd, const char *name )
{
    int fd;

    if ( ( fd = openat( dir_fd, name,
                        O_CREAT | O_TRUNC | O_RDWR,
                        0666 ) ) == -1 )
        err( 2, "creating %s", name );

    close_or_warn( fd, name );
}

static void link_file( int dir_fd, const char *old_name,
                       const char *new_name )
{
    if ( linkat( dir_fd, old_name, dir_fd, new_name, 0 ) == -1 )
        err( 2, "linking %s to %s", old_name, new_name );
}

static void unlink_if_exists( int fd, const char *name )
{
    if ( unlinkat( fd, name, 0 ) == -1 && errno != ENOENT )
        err( 2, "unlinking %s", name );
}

static void unlink_test_files( int dir )
{
    unlink_if_exists( dir, "a" );
    unlink_if_exists( dir, "b" );
    unlink_if_exists( dir, "c" );
    unlink_if_exists( dir, "d" );
    unlink_if_exists( dir, "x" );
    unlink_if_exists( dir, "y" );
    unlink_if_exists( dir, "z" );
    unlink_if_exists( dir, "../zt.r2_link" );
}

int main( void )
{
    const char *root_name = "zt.r2_root";
    int root_fd;

    if ( mkdirat( AT_FDCWD, root_name, 0777 ) == -1 &&
         errno != EEXIST )
        err( 2, "creating directory %s", root_name );

    if ( ( root_fd = openat( AT_FDCWD, root_name,
                             O_RDONLY | O_DIRECTORY ) ) == -1 )
        err( 2, "opening directory %s", root_name );

    unlink_test_files( root_fd );

    assert( count_unique( -1 ) == -1 );

    create_file( root_fd, "a" );
    assert( count_unique( root_fd ) == 1 );

    create_file( root_fd, "b" );
    assert( count_unique( root_fd ) == 2 );

    link_file( root_fd, "a", "x" );
    assert( count_unique( root_fd ) == 2 );

    create_file( root_fd, "c" );
    assert( count_unique( root_fd ) == 3 );

    link_file( root_fd, "a", "y" );
    link_file( root_fd, "b", "z" );
    assert( count_unique( root_fd ) == 3 );

    link_file( root_fd, "c", "../zt.r2_link" );
    assert( count_unique( root_fd ) == 3 );

    if ( symlinkat( "a", root_fd, "d" ) == -1 )
        err( 2, "creating symlink d" );

    assert( count_unique( root_fd ) == 4 );

    unlink_test_files( root_fd );
    close_or_warn( root_fd, root_name );

    return 0;
}