use std::fmt;
use std::num::NonZeroU64;

use itertools::Itertools;
use orchid_api_derive::{Coding, Hierarchy};
use orchid_api_traits::Request;

use crate::{
	ExprTicket, Expression, ExtHostReq, FormattingUnit, HostExtReq, OrcResult, SysId, TStrv,
};

#[derive(Clone, Coding)]
pub struct AtomData(pub Vec<u8>);
impl fmt::Debug for AtomData {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		let mut byte_strings = self.0.iter().map(|b| format!("{b:02x}"));
		if self.0.len() < 32 {
			write!(f, "AtomData({})", byte_strings.join(" "))
		} else {
			let data_table =
				byte_strings.chunks(32).into_iter().map(|mut chunk| chunk.join(" ")).join("\n");
			write!(f, "AtomData(\n{}\n)", data_table)
		}
	}
}

/// Unique ID associated with atoms that have an identity
#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq, PartialOrd, Ord, Coding)]
pub struct AtomId(pub NonZeroU64);

/// An atom owned by an implied system. Usually used in responses from a system.
/// This has the same semantics as [Atom] except in that the owner is implied.
#[derive(Clone, Debug, Coding)]
pub struct LocalAtom {
	pub drop: Option<AtomId>,
	pub data: AtomData,
}
impl LocalAtom {
	pub fn associate(self, owner: SysId) -> Atom { Atom { owner, drop: self.drop, data: self.data } }
}

/// An atom representation that can be serialized and sent around. Atoms
/// represent the smallest increment of work.
#[derive(Clone, Debug, Coding)]
pub struct Atom {
	/// Instance ID of the system that created the atom
	pub owner: SysId,
	/// Indicates how the owner should be notified when this atom is dropped.
	/// Construction is always explicit and atoms are never cloned.
	///
	/// Atoms with `drop == None` are also known as trivial, they can be
	/// duplicated and stored with no regard to expression lifetimes. NOTICE
	/// that this only applies to the atom. If it's referenced with an
	/// [ExprTicket], the ticket itself can still expire.
	///
	/// Notice also that the atoms still expire when the system is dropped, and
	/// are not portable across instances of the same system, so this doesn't
	/// imply that the atom is serializable.
	pub drop: Option<AtomId>,
	/// Data stored in the atom. This could be a key into a map, or the raw data
	/// of the atom if it isn't too big.
	pub data: AtomData,
}

/// Attempt to apply an atom as a function to an expression
#[derive(Clone, Debug, Coding, Hierarchy)]
#[extends(AtomReq, HostExtReq)]
pub struct CallRef(pub Atom, pub ExprTicket);
impl Request for CallRef {
	type Response = Expression;
}

/// Attempt to apply an atom as a function, consuming the atom and enabling the
/// library to reuse its datastructures rather than duplicating them. This is an
/// optimization over [CallRef] followed by [AtomDrop].
#[derive(Clone, Debug, Coding, Hierarchy)]
#[extends(AtomReq, HostExtReq)]
pub struct FinalCall(pub Atom, pub ExprTicket);
impl Request for FinalCall {
	type Response = Expression;
}

#[derive(Clone, Debug, Coding, Hierarchy)]
#[extends(AtomReq, HostExtReq)]
pub struct SerializeAtom(pub Atom);
impl Request for SerializeAtom {
	type Response = Option<(Vec<u8>, Vec<ExprTicket>)>;
}

#[derive(Clone, Debug, Hash, PartialEq, Eq, Coding, Hierarchy)]
#[extends(HostExtReq)]
pub struct DeserAtom(pub SysId, pub Vec<u8>, pub Vec<ExprTicket>);
impl Request for DeserAtom {
	type Response = Atom;
}

/// A request blindly routed to the system that provides an atom.
#[derive(Clone, Debug, Coding, Hierarchy)]
#[extends(AtomReq, HostExtReq)]
pub struct Fwded(pub Atom, pub TStrv, pub Vec<u8>);
impl Request for Fwded {
	type Response = Option<Vec<u8>>;
}

#[derive(Clone, Debug, Coding, Hierarchy)]
#[extends(ExtHostReq)]
pub struct Fwd(pub Atom, pub TStrv, pub Vec<u8>);
impl Request for Fwd {
	type Response = Option<Vec<u8>>;
}

#[derive(Clone, Debug, Coding)]
pub enum NextStep {
	Continue(Expression),
	Halt,
}
#[derive(Clone, Debug, Coding, Hierarchy)]
#[extends(AtomReq, HostExtReq)]
pub struct Command(pub Atom);
impl Request for Command {
	type Response = OrcResult<NextStep>;
}

/// Notification that an atom is being dropped because its associated expression
/// isn't referenced anywhere. This should have no effect if the atom's `drop`
/// flag is false.
#[derive(Clone, Debug, Hash, PartialEq, Eq, Coding, Hierarchy)]
#[extends(HostExtReq)]
pub struct AtomDrop(pub SysId, pub AtomId);
impl Request for AtomDrop {
	type Response = ();
}

#[derive(Clone, Debug, Coding, Hierarchy)]
#[extends(AtomReq, HostExtReq)]
pub struct AtomPrint(pub Atom);
impl Request for AtomPrint {
	type Response = FormattingUnit;
}

#[derive(Clone, Debug, Coding, Hierarchy)]
#[extends(ExtHostReq)]
pub struct ExtAtomPrint(pub Atom);
impl Request for ExtAtomPrint {
	type Response = FormattingUnit;
}

/// Requests that apply to an existing atom instance
#[derive(Clone, Debug, Coding, Hierarchy)]
#[extends(HostExtReq)]
#[extendable]
pub enum AtomReq {
	CallRef(CallRef),
	FinalCall(FinalCall),
	Fwded(Fwded),
	Command(Command),
	AtomPrint(AtomPrint),
	SerializeAtom(SerializeAtom),
}
impl AtomReq {
	/// Obtain the first [Atom] argument of the request. All requests in this
	/// subclass have at least one atom argument.
	pub fn get_atom(&self) -> &Atom {
		match self {
			Self::CallRef(CallRef(a, ..))
			| Self::Command(Command(a))
			| Self::FinalCall(FinalCall(a, ..))
			| Self::Fwded(Fwded(a, ..))
			| Self::AtomPrint(AtomPrint(a))
			| Self::SerializeAtom(SerializeAtom(a)) => a,
		}
	}
}