#define _POSIX_C_SOURCE 200809L

#include <sys/stat.h>  /* mkdirat, openat */
#include <unistd.h>    /* unlinkat, close, write */
#include <fcntl.h>     /* mkdirat, unlinkat, openat, linkat */
#include <string.h>    /* strlen */
#include <stdlib.h>    /* free, malloc, calloc */
#include <string.h>    /* strncpy */
#include <stdbool.h>   /* bool */
#include <errno.h>
#include <assert.h>
#include <err.h>

/* Váš úkol v této přípravě je přímočarý – na vstupu dostanete
 * popisovač otevřené složky, ze kterého vytvoříte zřetězeny seznam
 * jmen. Jména budou uložena v dynamicky alokovaných polích vhodné
 * velikosti. Výsledkem je nulový ukazatel, dojde-li během
 * zpracování složky k chybě, nebo ukazatel na hlavu sestaveného
 * seznamu. */

struct name_list
{
    char *name;
    struct name_list *next;
};

struct name_list *list( int real_dir_fd );

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

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;

    if ( ( fd = openat( dir_fd, name,
                        O_CREAT | O_TRUNC | O_RDWR,
                        0666 ) ) == -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 bool contains( struct name_list *node, const char *name )
{
    while ( node != NULL )
    {
        if ( strcmp( node->name, name ) == 0 )
            return true;

        node = node->next;
    }
    return false;
}

static void check_content( struct name_list *node,
                           const char **names, int size )
{
    if ( node == NULL )
    {
        assert( size == 0 );
        return;
    }

    for ( int i = 0; i < size; ++i )
        assert( contains( node, names[ i ] ) );
}

static void cleanup( struct name_list *head )
{
    while ( head != NULL )
    {
        free( head->name );
        struct name_list *tmp = head->next;
        free( head );
        head = tmp;
    }
}

static void unlink_test_files()
{
    int dir1 = openat( AT_FDCWD, "zt.p3_test_dir1", O_DIRECTORY );
    if ( dir1 != -1 )
    {
        const char *names[] =
        {
            "zt.p3_a", "zt.p3_b", "zt.p3_c",
            "zt.p3_d", "zt.p3_e"
        };

        for ( int i = 0; i < 5; ++i )
            unlink_if_exists( dir1, names[ i ], false );

        close( dir1 );
    }

    unlink_if_exists( AT_FDCWD, "zt.p3_test_dir1", true );
}

int main()
{
    unlink_test_files();

    assert( list( -1 ) == NULL );

    int dir1 = create_and_open_dir( AT_FDCWD, "zt.p3_test_dir1" );

    const char *in_empty[] = { ".", ".." };
    struct name_list *result = list( dir1 );
    check_content( result, in_empty, 2 );
    cleanup( result );

    const char *names[] =
    {
        ".", "..", "zt.p3_a", "zt.p3_b",
        "zt.p3_c", "zt.p3_d", "zt.p3_e"
    };

    const char *contents[] =
    {
        "Nobody said it was easy",
        "It's such a shame for us to part",
        "Nobody said it was easy",
        "No one ever said it would be this hard",
        "Oh, take me back to the start"
    };

    for ( int i = 2; i < 7; ++i )
        write_file( dir1, names[ i ], contents[ i - 2 ] );

    result = list( dir1 );
    check_content( result, names, 7 );
    cleanup( result );

    close_or_warn( dir1, "zt.p3_test_dir1" ); 
    unlink_test_files();

    return 0;
}