#define _POSIX_C_SOURCE 200809L

#include <errno.h>           /* errno */
#include <fcntl.h>           /* fcntl, mkdirat, open, openat */
#include <stdint.h>          /* uint64_t */
#include <string.h>          /* strlen, memset */
#include <sys/stat.h>        /* opena, openat, mkdirat */
#include <unistd.h>          /* close, unlinkat, write */

/* Napište podprogram ‹largest_files›, kterému je předán:
 *
 *  • popisovač otevřené složky ‹dir_fd›,
 *  • počet hledaných souborů ‹n›,
 *  • odkaz na pole ‹n› čísel, do kterých vyplní velikosti
 *    nalezených největších souborů (v bajtech, v pořadí od
 *    největšího).
 *
 * Uvažujeme pouze obyčejné soubory odkazované přímo předanou
 * složkou. Nezáporná návratová hodnota určuje počet uvažovaných
 * souborů (tzn. počet platných kandidátů), -1 indikuje systémovou
 * chybu. */

int largest_files( int dir_fd, int n, uint64_t *sizes );

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

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

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

    int fd = openat( base_dir, name, O_RDONLY | O_DIRECTORY, 0777 );
    if ( fd == -1 )
        err( 2, "opening directory %s", name );

    return fd;
}

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 ( close( fd ) == -1 )
        warn( "closing %s", name );
}

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

    if ( write( fd, str, strlen( str ) ) == -1 )
        err( 2, "writing file %s", name );

    close_or_warn( fd, name );
}

static void write_files( int dir_fd, char **names, char **contents, int n )
{
    for ( int i = 0; i < n; ++ i )
        write_file( dir_fd, names[ i ], contents[ i ] );
}

static int check_sizes( int n, const uint64_t *s_sizes, const uint64_t *our_sizes )
{
    int correct = 0;

    for ( int i = 0; i < n; ++ i )
        if ( s_sizes[ i ] == our_sizes [ i ] )
            ++ correct;

    return correct;
}

static void unlink_test_files( void )
{
    int dir1, dir2;

    dir1 = openat( AT_FDCWD, "zt.r6_test_dir1", O_DIRECTORY );

    if ( dir1 == -1 )
        return;

    unlink_if_exists( dir1, "zt.r6_a", false );
    unlink_if_exists( dir1, "zt.r6_b", false );
    unlink_if_exists( dir1, "zt.r6_c", false );
    unlink_if_exists( dir1, "zt.r6_d", false );
    unlink_if_exists( dir1, "zt.r6_e", false );
    unlink_if_exists( dir1, "zt.r6_f", false );
    unlink_if_exists( dir1, "zt.r6_g", false );

    dir2 = openat( dir1, "zt.r6_test_dir2", O_DIRECTORY );

    if ( dir2 != -1 )
    {
        unlink_if_exists( dir2, "zt.r6_h", false );

        close_or_warn(    dir2, "zt.r6_test_dir2"       );
        unlink_if_exists( dir1, "zt.r6_test_dir2", true );
    }


    close_or_warn(    dir1,     "zt.r6_test_dir1"       );
    unlink_if_exists( AT_FDCWD, "zt.r6_test_dir1", true );
}

int main( void )
{
    unlink_test_files();

    int dir1, dir2, dir;
    uint64_t sizes[ 10 ] = { 0 };
    char *our_files[] =
    {
        "zt.r6_a", "zt.r6_b", "zt.r6_c", "zt.r6_d", "zt.r6_e"
    };

    char *our_contents[] =
    {
        "All I ever wanted",
        "All I ever needed",
        "Is here in my arms",
        "Words are very unnecessary",
        "They can only do harm",
    };

    uint64_t our_sizes[] =
    {
        strlen( our_contents[ 3 ] ),
        strlen( our_contents[ 4 ] ),
        strlen( our_contents[ 2 ] ),
        strlen( our_contents[ 0 ] ),
        strlen( our_contents[ 1 ] ),
        strlen( our_contents[ 1 ] ),
        0
    };

    dir = open( ".", O_RDONLY );

    if ( dir == -1 )
        err( 2, "opening working directory" );

    close_or_warn( dir, "working directory" );
    assert( largest_files( dir, 1, sizes ) == -1 );

    dir1 = create_and_open_dir( AT_FDCWD, "zt.r6_test_dir1" );

    assert( largest_files( dir1, 5, sizes ) == 0 );

    write_files( dir1, our_files, our_contents, 5 );

    assert( largest_files( dir1, 5, sizes ) == 5 );
    assert( check_sizes( 5, sizes, our_sizes ) == 5 );
    assert( fcntl( dir1, F_GETFD ) != -1 );
    memset( sizes, 0, sizeof( sizes ) );

    assert( largest_files( dir1, 2, sizes ) == 5 );
    assert( check_sizes( 2, sizes, our_sizes ) == 2 );
    assert( fcntl( dir1, F_GETFD ) != -1 );
    memset( sizes, 0, sizeof( sizes ) );

    dir2 = create_and_open_dir( dir1, "zt.r6_test_dir2" );
    if ( linkat( dir1, "zt.r6_a", dir1, "zt.r6_f", 0 ) == -1 )
        err( 2, "creating a link to %s", "zt.r6_a" );

    assert( largest_files( dir1, 10, sizes ) == 6 );
    assert( check_sizes( 6, sizes, our_sizes ) == 6 );
    assert( fcntl( dir1, F_GETFD ) != -1 );
    assert( fcntl( dir2, F_GETFD ) != -1 );

    if ( symlinkat( "zt.r6_b", dir1, "zt.r6_g" ) == -1 )
        err( 2, "creating a symlink to %s", "zt.r6_b" );

    assert( largest_files( dir1, 10, sizes ) == 6 );
    assert( check_sizes( 7, sizes, our_sizes ) == 7 );
    assert( fcntl( dir1, F_GETFD ) != -1 );
    assert( fcntl( dir2, F_GETFD ) != -1 );

    memset( sizes, 0, sizeof( sizes ) );
    assert( largest_files( dir2, 10, sizes ) == 0 );
    assert( sizes[ 0 ] == 0 );
    assert( fcntl( dir1, F_GETFD ) != -1 );
    assert( fcntl( dir2, F_GETFD ) != -1 );

    write_file( dir2, "zt.r6_h", "Life is a fight." );

    memset( sizes, 0, sizeof( sizes ) );
    assert( largest_files( dir2, 10, sizes ) == 1 );
    assert( sizes[ 0 ] == strlen( "Life is a fight." ) );
    assert( sizes[ 1 ] == 0 );

    close_or_warn( dir2, "zt.r6_test_dir2" );
    close_or_warn( dir1, "zt.r6_test_dir1" );

    unlink_test_files();

    return 0;
}