#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 ‹rcount›, kterému je předán popisovač otevřené
 * složky, a který spočítá, kolik je v takto zadaném podstromě
 * složek (včetně té kořenové). Nezáporná návratová hodnota určuje
 * počet nalezených složek, -1 indikuje systémovou chybu. */

int rcount( int dir_fd );

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

static void mkdir_or_die( int base_dir, const char *name )
{
    if ( mkdirat( base_dir, name, 0777 ) == -1 )
        err( 2, "creating directory %s", name );
}

static int open_or_die( int base_dir, const char *name )
{
    int fd = openat( base_dir, name, O_RDONLY | O_DIRECTORY );

    if ( fd == -1 )
        err( 2, "opening directory %s", name );

    return fd;
}

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

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

static void unlink_test_dirs( const char *root )
{
    int dir = openat( AT_FDCWD, root, O_DIRECTORY );

    if ( dir != -1 )
    {
        unlink_if_exists( dir, "a/x", true );
        unlink_if_exists( dir, "a/y", true );
        unlink_if_exists( dir, "a/loop", false );
        unlink_if_exists( dir, "a", true );
        unlink_if_exists( dir, "b/x", true );
        unlink_if_exists( dir, "b", true );
        unlink_if_exists( dir, "c", true );
        unlink_if_exists( dir, "d", false );
        close_or_warn( dir, root );
    }

    unlink_if_exists( AT_FDCWD, root, true );
}

int main( void )
{
    const char *root_name = "zt.r1_root";
    int root_fd, a_fd;

    unlink_test_dirs( root_name );

    mkdir_or_die( AT_FDCWD, root_name );
    root_fd = open_or_die( AT_FDCWD, root_name );

    mkdir_or_die( root_fd, "a" );
    mkdir_or_die( root_fd, "a/x" );
    mkdir_or_die( root_fd, "a/y" );
    mkdir_or_die( root_fd, "b" );
    mkdir_or_die( root_fd, "b/x" );
    mkdir_or_die( root_fd, "c" );

    a_fd = open_or_die( root_fd, "a" );

    assert( rcount( -1 ) == -1 );
    assert( rcount( root_fd ) == 7 );
    assert( rcount( a_fd ) == 3 );

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

    assert( rcount( root_fd ) == 7 );
    assert( rcount( a_fd ) == 3 );

    if ( symlinkat( "..", a_fd, "loop" ) == -1 )
        err( 2, "creating symlink a/loop" );

    assert( rcount( root_fd ) == 7 );
    assert( rcount( a_fd ) == 3 );

    close_or_warn( a_fd, "zt.r1_root/a" );
    close_or_warn( root_fd, root_name );

    unlink_test_dirs( root_name );

    return 0;
}