#define _POSIX_C_SOURCE 200809L

#include <errno.h>           /* errno, EEXIST, ENOENT */
#include <fcntl.h>           /* mkdirat, openat, unlinkat */
#include <string.h>          /* strlen */
#include <sys/stat.h>        /* mkdirat */
#include <unistd.h>          /* close, faccessat, unlinkat, write */

/* Napište podprogram ‹prune_empty›, kterému je předán popisovač
 * otevřené složky, a který nalezne a odstraní všechny prázdné
 * podsložky (kdekoliv ve stromě, tzn. ne pouze přímé potomky).
 * Vznikne-li tímto procesem nějaká nově prázdná složka, tato bude
 * podobně odstraněna (netýká se kořenové).
 *
 * Nezáporná návratová hodnota určuje počet odstraněných složek, -1
 * indikuje systémovou chybu. */

int prune_empty( int dir_fd );

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

#include <err.h>             /* err, warn */
#include <stdbool.h>         /* bool, false, true */
#include <assert.h>          /* assert */

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

static void close_or_warn( int fd, const char *name )
{
    if ( fd >= 0 && close( fd ) == -1 )
        warn( "closing %s", name );
}

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

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

    if ( ( fd = openat( dir_fd, name, O_DIRECTORY ) ) == -1 )
        err( 1, "opening newly created directory %s", name );

    return fd;
}

static int create_file( int dir_fd, const char *name )
{
    unlink_if_exists( dir_fd, name, false );
    int fd = openat( dir_fd, name, O_CREAT | O_TRUNC | O_RDWR, 0666 );

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

    return fd;
}

static void write_file( int dir, const char *name, const char *str )
{
    int fd = create_file( dir, name );
    int len = strlen( str );

    if ( write( fd, str, len ) != len )
        err( 2, "writing file %s", name );

    close_or_warn( fd, name );
}

void cleanup( void )
{
    int root_fd = openat( AT_FDCWD, "zt.r5_root", O_DIRECTORY );
    if ( root_fd == -1 )
        return;

    unlink_if_exists( root_fd, "One/Has",      false );
    unlink_if_exists( root_fd, "One/Landmine", true  );
    unlink_if_exists( root_fd, "One",          true  );

    unlink_if_exists( root_fd, "Time/Ticking/Away", true );
    unlink_if_exists( root_fd, "Time/Ticking",      true );
    unlink_if_exists( root_fd, "Time",              true );

    close_or_warn(    root_fd,  "zt.r5_root"       );
    unlink_if_exists( AT_FDCWD, "zt.r5_root", true );
}

int main( void )
{
    cleanup();
    int root_fd = mkdir_or_die( AT_FDCWD, "zt.r5_root" );

    /* Test case 1. */
    assert( ( prune_empty( root_fd ) == 0 ) );

    /* Test case 2. */
    int subdir1 = mkdir_or_die( root_fd, "One"   );
    int subdir2 = mkdir_or_die( root_fd, "Time"  );

    int subdir3 = mkdir_or_die( subdir1, "Landmine" );
    write_file( subdir1, "Has", "Taken My sight"    );

    int subdir4 = mkdir_or_die( subdir2, "Ticking" );
    int subdir5 = mkdir_or_die( subdir4, "Away"    );

    close_or_warn( subdir1, "zt.r5_root/One"               );
    close_or_warn( subdir2, "zt.r5_root/Time"              );
    close_or_warn( subdir3, "zt.r5_root/One/Landmine"      );
    close_or_warn( subdir4, "zt.r5_root/Time/Ticking"      );
    close_or_warn( subdir5, "zt.r5_root/Time/Ticking/Away" );

    assert( ( prune_empty( root_fd ) == 4 ) );

    assert( ( faccessat( root_fd, "One",     F_OK, 0 ) == 0 ) );
    assert( ( faccessat( root_fd, "One/Has", F_OK, 0 ) == 0 ) );

    assert( ( faccessat( root_fd, "One/Landmine", F_OK, 0 ) == -1 ) );
    assert( ( errno == ENOENT ) );

    assert( ( faccessat( root_fd, "Time", F_OK, 0 ) == -1 ) );
    assert( ( errno == ENOENT ) );

    assert( ( faccessat( root_fd, "Time/Ticking", F_OK, 0 ) == -1 ) );
    assert( ( errno == ENOENT ) );

    assert( ( faccessat( root_fd, "Time/Ticking/Away", F_OK, 0 ) == -1 ) );
    assert( ( errno == ENOENT ) );

    /* Test case 3. */
    unlink_if_exists( root_fd, "One/Has", false );

    assert( ( prune_empty( root_fd ) == 1 ) );
    assert( ( faccessat( root_fd, "One", F_OK, 0 ) == -1 ) );
    assert( ( errno == ENOENT ) );

    close_or_warn( root_fd, "zt.r5_root" );

    cleanup();
    return 0;
}