// ///// Example //////////////////
import io.directories.*;

main() {
    for (x in directoryListing("/home"))
        println(x);
}

// ////////////////////////////////
import libc.*;
import unix.errno.*;



//
// directoryListing
//

directoryListing(x) = map(direntPointerToString, direntSequence(x));

private direntPointerToString(x) = String(Pointer[Int8](&x^.d_name));



//
// DirentSequence
//

private record DirentSequence {
    dirp : Pointer[DIR];
}

[T | String?(T)]
direntSequence(x:T) = DirentSequence(cstring(x));

overload DirentSequence(x:Pointer[CChar]) {
    var ret = DirentSequence(opendir(x));
    if (null?(ret.dirp)) {
        throw errno();
    }
    return ret;
}

overload iterator(x:DirentSequence) = DirentIterator(x.dirp, false, null(Struct_dirent));



//
// DirentIterator
//

private record DirentIterator {
    dirp : Pointer[DIR];
    queued? : Bool;
    entry : Pointer[Struct_dirent];
}

overload destroy(x:DirentIterator) {
    if (closedir(x.dirp) > 0)
        throw errno();
}

overload hasNext?(x:DirentIterator) {
    if (not x.queued?) {
        x.queued? = true;

        if (not(null?(x.entry)))
            destroy(x.entry);

        var returnCode = readdir_r(x.dirp, allocateMemory(Struct_dirent, 1), &x.entry);

        if (returnCode != 0)
            throw returnCode;
    }
    return not(null?(x.entry));
}

overload next(x:DirentIterator) {
    if (not x.queued?)
        hasNext?(x);
    x.queued? = false;
    return x.entry;
}