//! This module introduces [`Option`]-like concepts into RADN typesystem using [`Nullable`].

use crate::func::context::*;
use crate::rcore::*;

use super::{inlining::*, point::*, *};

/// Nullable reference type. Made for use as a linking element in data structures.
pub enum Nullable<'a, Ctx: Context<'a>, A: MentionableBase<'a, Ctx>> {
    /// Unlike original Python implementation, stores the factory only in the null case.
    Null(A::Fctr),
    NotNull(Point<'a, Ctx, A>),
}

/// Nullable reference factory.
#[derive(Clone)]
pub struct NullableFactory<F> {
    /// Factory of the referenced object.
    factory: F,
}

impl<'a, Ctx: Context<'a>, A: MentionableBase<'a, Ctx>> Serializable for Nullable<'a, Ctx, A> {
    fn serialize(&self, serializer: &mut dyn Serializer) {
        serializer.write(match self {
            Self::Null(_) => &HASH_ZEROS,
            Self::NotNull(point) => &point.point,
        })
    }
}

impl<'a, Ctx: Context<'a>, A: MentionableBase<'a, Ctx>> MentionableBase<'a, Ctx>
    for Nullable<'a, Ctx, A>
{
    type Fctr = NullableFactory<A::Fctr>;

    fn factory(&self) -> Self::Fctr {
        match self {
            Self::Null(factory) => NullableFactory {
                factory: factory.clone(),
            },
            Self::NotNull(point) => NullableFactory {
                factory: point.origin.factory(),
            },
        }
    }
}

impl<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> MentionableTop<'a, Ctx>
    for Nullable<'a, Ctx, A>
{
    fn points_typed(&self, points: &mut impl PointsVisitor<'a, Ctx>) {
        match self {
            Self::Null(_) => {}
            Self::NotNull(point) => points.visit(point),
        }
    }
}

impl<'a, Ctx: Context<'a>, F: FactoryBase<'a, Ctx>> FactoryBase<'a, Ctx> for NullableFactory<F> {
    type Mtbl = Nullable<'a, Ctx, F::Mtbl>;

    type ParseError = PointParseError;
}

impl<F> ImplMode for NullableFactory<F> {
    type Mode = InliningMode;
}

impl<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> Nullable<'a, Ctx, Nullable<'a, Ctx, A>> {
    /// Reduce [Nullable] nesting.
    pub fn join(&self) -> Resolution<'a, Ctx, Nullable<'a, Ctx, A>> {
        match self {
            Self::Null(nullable_factory) => {
                let NullableFactory { factory } = nullable_factory;
                Ctx::pure(Ok(Rc::new(Nullable::Null(factory.clone()))))
            }
            Self::NotNull(point) => point.resolve(),
        }
    }
}

impl<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> Nullable<'a, Ctx, A> {
    fn from_mentionable(mentionable: Rc<A>) -> Self {
        Self::NotNull(mentionable.into())
    }

    pub fn as_ref(&self) -> Option<&Point<'a, Ctx, A>> {
        match self {
            Nullable::Null(_) => None,
            Nullable::NotNull(point) => Some(point),
        }
    }
}

impl<F> NullableFactory<F> {
    pub fn new(factory: F) -> Self {
        Self { factory }
    }
}

impl<'a, Ctx: Context<'a>, A: MentionableBase<'a, Ctx>> Clone for Nullable<'a, Ctx, A> {
    fn clone(&self) -> Self {
        match self {
            Self::Null(factory) => Self::Null(factory.clone()),
            Self::NotNull(point) => Self::NotNull(point.clone()),
        }
    }
}

impl<'a, Ctx: Context<'a>, F: FactoryBase<'a, Ctx>> CInliningFactory<'a, Ctx>
    for NullableFactory<F>
{
    fn cextension_error(&self, tail: &[u8]) -> Self::ParseError {
        PointParseError::WrongLength(HASH_SIZE + tail.len())
    }

    fn cideserialize<I: InCtx<'a, Ctx>>(&self, inctx: I) -> IParseResult<'a, Ctx, Self, I> {
        let factory = self.factory.clone();
        let (address, inctx) = inctx.icnext_address(|slice| PointParseError::from(slice))?;
        Ok((
            if address.point == HASH_ZEROS {
                Nullable::Null(factory)
            } else {
                Nullable::NotNull(Point::from_address(address, factory, inctx.iresolver()))
            },
            inctx,
        ))
    }
}

impl<F> AlwaysConstSize for NullableFactory<F> {
    const _SIZE: usize = HASH_SIZE;
}

impl<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> From<Rc<A>> for Nullable<'a, Ctx, A> {
    fn from(value: Rc<A>) -> Self {
        Self::from_mentionable(value)
    }
}

impl<'a, Ctx: Context<'a>, A: Mentionable<'a, Ctx>> From<A> for Nullable<'a, Ctx, A> {
    fn from(value: A) -> Self {
        Self::from_mentionable(value.into())
    }
}