unit std.io;
import std.sys;

// A writer is a handle and nothing else: an integer the runtime understands.
// It stores no reference and no context pointer, so it is Copy and can be
// passed and returned freely (SPEC 5 R8).
pub enum Writer { Null, Stdout, Stderr }

pub fn write(w: Writer, bytes: []u8) -> usize {
    if w == Writer.Null { return bytes.n; }
    var handle: i32 = 1;
    if w == Writer.Stderr { handle = 2; }
    var done: i32 = 0;
    unsafe { done = sys.raw_write(handle, @ptr_cast(u8, &bytes[0]), bytes.n); }
    if done < 0 { return 0; }
    return done as usize;
}

pub fn print(bytes: []u8) -> usize {
    return write(Writer.Stdout, bytes);
}

pub fn println(bytes: []u8) -> usize {
    let n: usize = write(Writer.Stdout, bytes);
    return n + write(Writer.Stdout, "\n");
}

// Files. A handle is what the operating system gave back; -1 means it did not
// give one. The path has to be NUL terminated because that is what the system
// call wants, and `to_cstr` is how a Ferro string becomes one.

pub fn open_read(path: []mut u8) -> !i32 {
    var handle: i32 = 0;
    unsafe { handle = sys.raw_open(@ptr_cast(u8, &path[0]), 0); }
    if handle == 0 - 1 { return error.NoSuchFile; }
    return handle;
}

pub fn open_write(path: []mut u8) -> !i32 {
    var handle: i32 = 0;
    unsafe { handle = sys.raw_open(@ptr_cast(u8, &path[0]), 1); }
    if handle == 0 - 1 { return error.CannotWrite; }
    return handle;
}

pub fn read(handle: i32, into: []mut u8) -> !usize {
    var got: i32 = 0;
    unsafe { got = sys.raw_read(handle, @ptr_cast(u8, &into[0]), into.n); }
    if got < 0 { return error.ReadFailed; }
    return got as usize;
}

pub fn close(handle: i32) -> void {
    sys.raw_close(handle);
}

/// Put `text` into `buf` with a NUL after it and say how many bytes that took,
/// the NUL included. A system call cannot be told a length, so it needs this.
///
/// The length comes back rather than a slice of `buf`: with two reference-like
/// parameters the signature cannot say which one a returned slice came from,
/// and R8 will not guess.
pub fn to_cstr(buf: []mut u8, text: []u8) -> usize {
    var i: usize = 0;
    while i < text.n {
        if i + 1 >= buf.n { break; }
        buf[i] = text[i];
        i = i + 1;
    }
    if i < buf.n { buf[i] = 0; }
    return i + 1;
}

pub fn write_file(handle: i32, bytes: []u8) -> !usize {
    var done: i32 = 0;
    unsafe { done = sys.raw_write(handle, @ptr_cast(u8, &bytes[0]), bytes.n); }
    if done < 0 { return error.WriteFailed; }
    return done as usize;
}

/// Copy the command line into `buf` and say how long it is. It arrives as one
/// string with the program's own name first; `arg` picks a piece out of it.
pub fn cmdline(buf: []mut u8) -> usize {
    let raw: *u8 = sys.raw_cmdline();
    var i: usize = 0;
    unsafe {
        while i + 1 < buf.n {
            let c: u8 = @volatile_load(raw + i);
            if c == 0 { break; }
            buf[i] = c;
            i = i + 1;
        }
    }
    return i;
}

/// The `n`th whitespace-separated piece of `line`, or an empty slice when
/// there is no such piece. Quoting is not handled; nothing here needs it yet.
pub fn arg(line: []u8, n: usize) -> []u8 {
    var at: usize = 0;
    var seen: usize = 0;
    while at < line.n {
        while at < line.n {
            if line[at] != 32 { break; }
            at = at + 1;
        }
        var stop: usize = at;
        while stop < line.n {
            if line[stop] == 32 { break; }
            stop = stop + 1;
        }
        if stop > at {
            if seen == n { return line[at..stop]; }
            seen = seen + 1;
        }
        at = stop;
    }
    return line[0..0];
}