use core::fmt::{Debug, Display};

use crate::any::{OwnedStatic, TempBorrowedStatic, TempBorrowedStaticHrt};
use crate::effect::{EffectExt, Effective, EffectiveExt};
use crate::protocol::visitor::{DynRecoverableScope, Recoverable, RecoverableProto};
use crate::{
    any::{AnyTraitObject, TypeName, TypeNameId},
    any_trait,
    effect::{Effect, ErasedEffective, Ss},
    hkt::Invariant,
    protocol::{
        visitor::{tags, Tag, TagProto, Value, ValueProto, VisitResult},
        DynVisitor,
    },
    Builder, BuilderTypes, DynWalkerObjSafe, Flow,
};

pub struct EnumBuilder<'ctx, Info, Mode, E: Effect>
where
    Info: EnumBuildInfo<'ctx, Mode, E>,
{
    inner: Inner<'ctx, Info, Mode, E>,
}

enum Inner<'ctx, Info, Mode, E: Effect>
where
    Info: EnumBuildInfo<'ctx, Mode, E>,
{
    Temp,
    Seed(Info::Seed),
    Builder { builder: Info::Builders },
    Value(Result<Info::T, Info::Error>),
}

pub trait EnumBuildInfo<'ctx, Mode, E: Effect> {
    type Builders: Ss;

    type Seed: Ss;

    type Error: Ss + Debug + Display;

    type ValueT: TypeName::MemberType;

    type T: Ss;

    type VariantMarker: Ss + Copy + Display;

    fn new_builder<'a>(
        seed: Self::Seed,
        variant: Self::VariantMarker,
    ) -> ErasedEffective<'a, Self::Builders, E>;

    fn finish_builder<'a>(
        builder: Self::Builders,
    ) -> ErasedEffective<'a, Result<Self::T, Self::Error>, E>;

    fn from_value<'a>(value: TypeName::T<'a, 'ctx, Self::ValueT>) -> Self::T;

    fn as_visitor<'a>(builder: &'a mut Self::Builders) -> DynVisitor<'a, 'ctx>;

    fn marker_from_name(name: &str) -> Option<Self::VariantMarker>;

    fn marker_from_discriminant(discriminant: u32) -> Option<Self::VariantMarker>;

    fn guess_variant<'a>(
        seed: Self::Seed,
        scope: DynRecoverableScope<'a, 'ctx, E>,
    ) -> ErasedEffective<'a, Result<Self::T, Self::Error>, E>;
}

impl<'ctx, Info, Mode, E: Effect> BuilderTypes for EnumBuilder<'ctx, Info, Mode, E>
where
    Info: EnumBuildInfo<'ctx, Mode, E>,
{
    type Seed = Info::Seed;

    type Error = Info::Error;

    type Value = Info::T;
}

impl<'ctx, Info, Mode, E: Effect> Builder<'ctx, E> for EnumBuilder<'ctx, Info, Mode, E>
where
    Info: EnumBuildInfo<'ctx, Mode, E>,
{
    fn from_seed<'a>(seed: Self::Seed) -> ErasedEffective<'a, Self, E>
    where
        Self: 'a,
    {
        E::ready(Self {
            inner: Inner::Seed(seed),
        })
    }

    fn build<'a>(self) -> ErasedEffective<'a, Result<Self::Value, Self::Error>, E>
    where
        Self: 'a,
    {
        match self.inner {
            Inner::Temp => unreachable!(),
            Inner::Seed(seed) => {
                // what to do...
                todo!()
            }
            Inner::Builder { builder } => Info::finish_builder(builder),
            Inner::Value(value) => E::ready(value),
        }
    }

    fn as_visitor(&mut self) -> DynVisitor<'_, 'ctx> {
        DynVisitor(self)
    }
}

any_trait! {
    impl['ctx, Info, Mode, E] EnumBuilder<'ctx, Info, Mode, E> = [
        ValueProto<Info::ValueT, E>,
        TagProto<tags::Variant, E>,
        RecoverableProto<E>
    ] ref {
        let (_this, _id);
    } else ref {
        None
    } mut {
        let (this, id);

        // If a variant has been chosen, then forward everything to it's builder.
        if matches!(this.inner, Inner::Builder { .. }) {
            match &mut this.inner {
                Inner::Builder { builder } => {
                    return Info::as_visitor(builder).0.upcast_to_id_mut(id)
                }
                _ => unreachable!(),
            }
        }
    } else mut {
        None
    } where
        E: Effect,
        Info: EnumBuildInfo<'ctx, Mode, E>,
}

impl<'ctx, Info, Mode, E: Effect> Recoverable<'ctx, E> for EnumBuilder<'ctx, Info, Mode, E>
where
    Info: EnumBuildInfo<'ctx, Mode, E>,
{
    fn visit<'a>(
        &'a mut self,
        scope: DynRecoverableScope<'a, 'ctx, E>,
    ) -> ErasedEffective<'a, VisitResult, E> {
        match core::mem::replace(&mut self.inner, Inner::Temp) {
            Inner::Seed(seed) => Info::guess_variant(seed, scope).map(|result| {
                self.inner = Inner::Value(result);
                Flow::Done.into()
            }),
            inner => {
                self.inner = inner;
                E::ready(Flow::Continue.into())
            }
        }
    }
}

impl<'ctx, Info, Mode, E: Effect> Value<'ctx, Info::ValueT, E> for EnumBuilder<'ctx, Info, Mode, E>
where
    Info: EnumBuildInfo<'ctx, Mode, E>,
{
    fn visit<'a>(
        &'a mut self,
        value: TypeName::T<'a, 'ctx, Info::ValueT>,
    ) -> ErasedEffective<'a, VisitResult<TypeName::T<'a, 'ctx, Info::ValueT>>, E>
    where
        TypeName::T<'a, 'ctx, Info::ValueT>: Send + Sync + Sized,
        'ctx: 'a,
    {
        self.inner = Inner::Value(Ok(Info::from_value(value)));
        E::ready(Flow::Done.into())
    }
}

impl<'ctx, Info, Mode, E: Effect> Tag<'ctx, tags::Variant, E> for EnumBuilder<'ctx, Info, Mode, E>
where
    Info: EnumBuildInfo<'ctx, Mode, E>,
{
    fn visit<'a: 'c, 'b: 'c, 'c>(
        &'a mut self,
        _kind: tags::Variant,
        walker: DynWalkerObjSafe<'b, 'ctx, E>,
    ) -> ErasedEffective<'c, VisitResult, E> {
        let visitor = VariantVisitor::<Info, Mode, E> { marker: None };

        E::as_ctx((visitor, walker), |(visitor, walker)| {
            walker.walk(DynVisitor(visitor)).cast()
        })
        .then(|((visitor, _), result)| {
            if let Some(variant) = visitor.marker {
                match core::mem::replace(&mut self.inner, Inner::Temp) {
                    // A variant was given so we need to make the builder for
                    // it.
                    Inner::Seed(seed) => Info::new_builder(seed, variant).map(move |builder| {
                        self.inner = Inner::Builder { builder };
                        result.to_done().into()
                    }),
                    inner => {
                        self.inner = inner;
                        E::ready(result.to_done().into())
                    }
                }
            } else {
                E::ready(result.to_done().into())
            }
        })
    }
}

struct VariantVisitor<'ctx, Info, Mode, E: Effect>
where
    Info: EnumBuildInfo<'ctx, Mode, E>,
{
    marker: Option<Info::VariantMarker>,
}

any_trait! {
    impl['ctx, Info, Mode, E] VariantVisitor<'ctx, Info, Mode, E> = [
        ValueProto<TempBorrowedStaticHrt<str>, E>,
        ValueProto<OwnedStatic<u32>, E>,
    ]
    where
        E: Effect,
        Info: EnumBuildInfo<'ctx, Mode, E>,
}

impl<'ctx, Info, Mode, E: Effect> Value<'ctx, TempBorrowedStaticHrt<str>, E>
    for VariantVisitor<'ctx, Info, Mode, E>
where
    Info: EnumBuildInfo<'ctx, Mode, E>,
{
    fn visit<'a>(
        &'a mut self,
        TempBorrowedStatic(value): TypeName::T<'a, 'ctx, TempBorrowedStaticHrt<str>>,
    ) -> ErasedEffective<'a, VisitResult<TypeName::T<'a, 'ctx, TempBorrowedStaticHrt<str>>>, E>
    where
        TypeName::T<'a, 'ctx, TempBorrowedStaticHrt<str>>: Send + Sync + Sized,
        'ctx: 'a,
    {
        if let Some(variant) = Info::marker_from_name(value) {
            self.marker = Some(variant);

            E::ready(Flow::Done.into())
        } else {
            E::ready(Flow::Continue.into())
        }
    }
}

impl<'ctx, Info, Mode, E: Effect> Value<'ctx, OwnedStatic<u32>, E>
    for VariantVisitor<'ctx, Info, Mode, E>
where
    Info: EnumBuildInfo<'ctx, Mode, E>,
{
    fn visit<'a>(
        &'a mut self,
        OwnedStatic(value): TypeName::T<'a, 'ctx, OwnedStatic<u32>>,
    ) -> ErasedEffective<'a, VisitResult<TypeName::T<'a, 'ctx, OwnedStatic<u32>>>, E>
    where
        TypeName::T<'a, 'ctx, OwnedStatic<u32>>: Send + Sync + Sized,
        'ctx: 'a,
    {
        if let Some(variant) = Info::marker_from_discriminant(value) {
            self.marker = Some(variant);

            E::ready(Flow::Done.into())
        } else {
            E::ready(Flow::Continue.into())
        }
    }
}