//! Basic messages of the Orchid extension API.
//!
//! The protocol is defined over a byte stream, normally the stdin/stdout of the
//! extension. The implementations of [Coding] in this library are considered
//! normative. Any breaking change here or in the default implementations of
//! [Coding] must also increment the version number in the intro strings.
//!
//! 3 different kinds of messages are recognized; request, response, and
//! notification. There are no general ordering guarantees about these, multiple
//! requests, even requests of the same type may be sent concurrently, unless
//! otherwise specified in the request's definition.
//!
//! Each message begins with a u32 length, followed by that many bytes of
//! message content. The first byte of the content is a u64 combined request ID
//! and discriminator, D.
//!
//! - If D = 0, the rest of the content is a notification.
//! - If 0 < D < 2^63, it is a request with identifier D.
//! - If 2^63 <= D, it is a response to request identifier !D.
//!
//! The order of both notifications and requests sent from the same thread must
//! be preserved. Toolkits must ensure that the client code is able to observe
//! the ordering of messages.

use std::io::{Read, Write};

use orchid_api_derive::{Coding, Hierarchy};
use orchid_api_traits::{read_exact, write_exact, Channel, Decode, Encode, MsgSet, Request};

use crate::{atom, expr, intern, parser, system, tree, vfs};

static HOST_INTRO: &[u8] = b"Orchid host, binary API v0\n";
pub struct HostHeader;
impl Decode for HostHeader {
  fn decode<R: Read + ?Sized>(read: &mut R) -> Self {
    read_exact(read, HOST_INTRO);
    Self
  }
}
impl Encode for HostHeader {
  fn encode<W: Write + ?Sized>(&self, write: &mut W) { write_exact(write, HOST_INTRO) }
}

static EXT_INTRO: &[u8] = b"Orchid extension, binary API v0\n";
pub struct ExtensionHeader {
  pub systems: Vec<system::SystemDecl>,
}
impl Decode for ExtensionHeader {
  fn decode<R: Read + ?Sized>(read: &mut R) -> Self {
    read_exact(read, EXT_INTRO);
    Self { systems: Vec::decode(read) }
  }
}
impl Encode for ExtensionHeader {
  fn encode<W: Write + ?Sized>(&self, write: &mut W) {
    write_exact(write, EXT_INTRO);
    self.systems.encode(write)
  }
}

#[derive(Clone, Debug, Copy, Hash, PartialEq, Eq, PartialOrd, Ord, Coding)]
pub struct Ping;
impl Request for Ping {
  type Response = ();
}

/// Requests running from the extension to the host
#[derive(Clone, Coding, Hierarchy)]
#[extendable]
pub enum ExtHostReq {
  Ping(Ping),
  IntReq(intern::IntReq),
  Fwd(atom::Fwd),
  ExprReq(expr::ExprReq),
  SubLex(parser::SubLex),
}

/// Notifications sent from the extension to the host
#[allow(clippy::enum_variant_names)]
#[derive(Debug, Clone, Coding, Hierarchy)]
#[extendable]
pub enum ExtHostNotif {
  ExprNotif(expr::ExprNotif),
}

pub struct ExtHostChannel;
impl Channel for ExtHostChannel {
  type Notif = ExtHostNotif;
  type Req = ExtHostReq;
}

/// Requests running from the host to the extension
#[derive(Clone, Debug, Coding, Hierarchy)]
#[extendable]
pub enum HostExtReq {
  Ping(Ping),
  NewSystem(system::NewSystem),
  Sweep(intern::Sweep),
  AtomReq(atom::AtomReq),
  ParserReq(parser::ParserReq),
  GetConstTree(tree::GetConstTree),
  VfsReq(vfs::VfsReq),
}

/// Notifications sent from the host to the extension
#[derive(Clone, Debug, Coding, Hierarchy)]
#[extendable]
pub enum HostExtNotif {
  SystemDrop(system::SystemDrop),
  AtomDrop(atom::AtomDrop),
  /// The host can assume that after this notif is sent, a correctly written
  /// extension will eventually exit.
  Exit,
}

pub struct HostExtChannel;
impl Channel for HostExtChannel {
  type Notif = HostExtNotif;
  type Req = HostExtReq;
}

/// Message set viewed from the extension's perspective
pub struct ExtMsgSet;
impl MsgSet for ExtMsgSet {
  type In = HostExtChannel;
  type Out = ExtHostChannel;
}

/// Message Set viewed from the host's perspective
pub struct HostMsgSet;
impl MsgSet for HostMsgSet {
  type In = ExtHostChannel;
  type Out = HostExtChannel;
}