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

use effectful::{bound::{IsSend, IsSync}, closure::Capture, effective::Effective, environment::{DynBind, Environment, NativeForm}, higher_ranked::Mut, tri};

use crate::{
    any::{OwnedStatic, TempBorrowedStatic, TempBorrowedStaticHrt, TypeName},
    any_trait,
    hkt::Marker,
    protocol::{
        visitor::{
            tags, DynSequenceScope, EffectiveVisitExt as _, RequestHint, RequestHintProto,
            Sequence, SequenceHint, SequenceProto, Tag, TagConst, TagHint, TagProto, Value,
            ValueProto, VisitResult,
        },
        walker::hint::hint_protocol,
        AsVisitor, DynVisitor, DynWalker,
    },
    Builder, BuilderTypes, DynWalkerObjSafe, Flow,
};

use super::NoopVisitor;

/// A builder for a struct.
pub struct StructBuilder<'ctx, Info, Mode, E: Environment>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{
    inner: Inner<'ctx, Info, Mode, E>,
}

unsafe impl<'ctx, Info, Mode, E: Environment> IsSend<E::NeedSend> for StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{}

unsafe impl<'ctx, Info, Mode, E: Environment> IsSync<E::NeedSync> for StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{}

enum Inner<'ctx, Info, Mode, E: Environment>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{
    Temp,
    Seed(Info::Seed),
    Builders {
        /// The builders for all the struct's fields.
        builders: Info::Builders,

        /// The kind of struct the builder is expecting.
        kind: StructKind,
    },
    Value(Info::T),
}

/// Structs are either tuple-like or map-like.
enum StructKind {
    /// A tuple-like struct uses the order of the fields.
    Tuple,

    /// A map-like struct uses field names.
    Map,
}

/// Information about how a struct type interacts with the [`StructBuilder`].
///
/// This trait is *not* implemented by the struct type itself to allow many
/// of these to exist per struct.
///
/// The `Mode` generic allows implementations to change depending on the mode the user gives.
/// It is not used by the trait directly.
pub trait StructTypeInfo<'ctx, Mode: 'ctx, E: Environment>: 'static {
    /// A struct of builders for each field.
    type Builders: DynBind<E>;

    /// The seed value needed to make the builders.
    type Seed: DynBind<E>;

    /// An enum of the fields.
    ///
    /// These markers act in place of the field names.
    type FieldMarker: DynBind<E> + Copy + Display;

    /// The error type that can be generated while building the struct.
    type Error: DynBind<E> + Debug + Display;

    /// The kind of type for enabling the direct value protocol.
    type ValueT: TypeName::MemberType<E>;

    /// The struct type this info is for.
    type T: DynBind<E>;

    const FIELD_COUNT: usize;

    /// Create a set of builders from a seed value.
    fn new_builders<'a>(seed: Self::Seed) -> NativeForm<'a, Self::Builders, E>;

    /// Finish building the struct value.
    fn from_builders<'a>(
        builders: Self::Builders,
    ) -> NativeForm<'a, Result<Self::T, Self::Error>, E>;

    /// Get the visitor for a field.
    ///
    /// This is how [`StructBuilder`] picks a field builder to use.
    fn as_visitor<'a>(
        marker: Self::FieldMarker,
        builders: &'a mut Self::Builders,
    ) -> DynVisitor<'a, 'ctx, E>;

    /// Get a field marker from the index of the field.
    ///
    /// This should be the definition order as seen in the Rust source code.
    fn marker_from_index(index: usize) -> Option<Self::FieldMarker>;

    /// Get a field marker from a field name.
    fn marker_from_name(name: &str) -> Option<Self::FieldMarker>;

    /// Get the value from the value protocol.
    fn from_value<'a>(value: TypeName::T<'a, 'ctx, Self::ValueT, E>) -> Self::T;
}

/// Error that [`StructBuilder`] returns.
pub struct StructError<'ctx, Info, M, E: Environment>
where
    Info: StructTypeInfo<'ctx, M, E>,
{
    /// Error from the struct info definition.
    error: Info::Error,
}

unsafe impl<'ctx, Info, Mode, E: Environment> IsSend<E::NeedSend> for StructError<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{}

unsafe impl<'ctx, Info, Mode, E: Environment> IsSync<E::NeedSync> for StructError<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{}

impl<'ctx, Info, Mode, E: Environment> StructError<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{
    fn from_field_err(error: Info::Error) -> Self {
        Self { error }
    }
}

impl<'ctx, Info, Mode, E: Environment> Debug for StructError<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.debug_tuple("StructError").field(&self.error).finish()
    }
}

impl<'ctx, Info, Mode, E: Environment> Display for StructError<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        Display::fmt(&self.error, f)
    }
}

impl<'ctx, Info, Mode, E: Environment> BuilderTypes<E> for StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{
    type Seed = Info::Seed;

    type Error = StructError<'ctx, Info, Mode, E>;

    type Value = Info::T;
}

impl<'ctx, Info, Mode: 'ctx, E: Environment> StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{
    fn make_builders<'e>(&'e mut self) -> NativeForm<'e, (), E>
    where
        'ctx: 'e,
    {
        match core::mem::replace(&mut self.inner, Inner::Temp) {
            Inner::Seed(seed) => Info::new_builders(seed).map(Capture(self).fun_once(|this, builders, _| {
                this.inner = Inner::Builders {
                    builders,
                    kind: StructKind::Tuple,
                };
            })).cast(),
            inner => {
                self.inner = inner;

                E::value(()).cast()
            }
        }
    }
}

impl<'ctx, Info, Mode: 'ctx, E: Environment> Builder<'ctx, E> for StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
    for<'b, 'c> TypeName::T<'b, 'c, Info::ValueT, E>: IsSync<E::NeedSend>,
{
    fn from_seed<'a>(seed: Self::Seed) -> NativeForm<'a, Self, E>
    where
        Self: 'a,
    {
        E::value(Self {
            inner: Inner::Seed(seed),
        }).cast()
    }

    fn build<'a>(self) -> NativeForm<'a, Result<Self::Value, Self::Error>, E>
    where
        Self: 'a,
    {
        match self.inner {
            Inner::Temp => unreachable!(),
            Inner::Seed(seed) => {
                // We may be able to make a value from just the seed.
                Info::new_builders(seed)
                    .then(Capture(()).fun_once(|_, builders, _| Info::from_builders(builders)))
                    .map(Capture(()).fun_once(|_, result, _| result.map_err(StructError::from_field_err))).cast()
            }
            Inner::Builders { builders, .. } => {
                // Create the value from the builders.
                Info::from_builders(builders)
                    .map(Capture(()).fun_once(|_, result, _| result.map_err(StructError::from_field_err)))
                    .cast()
            }
            // Use the value as is.
            Inner::Value(value) => E::value(Ok(value)).cast(),
        }
    }
}

impl<'ctx, Info, Mode: 'ctx, E: Environment> AsVisitor<'ctx, E> for StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
    for<'b, 'c> TypeName::T<'b, 'c, Info::ValueT, E>: IsSync<E::NeedSend>,
{
    fn as_visitor<'a>(&'a mut self) -> DynVisitor<'a, 'ctx, E>
    where
        'ctx: 'a,
    {
        DynVisitor(self)
    }
}

any_trait! {
    impl['ctx, Info, Mode][E] StructBuilder<'ctx, Info, Mode, E> = [
        RequestHintProto<E>,
        ValueProto<Info::ValueT, E>,
        TagProto<tags::Struct, E>,
        TagProto<tags::Map, E>,
        SequenceProto<E>
    ] where
        E: Environment,
        Info: StructTypeInfo<'ctx, Mode, E>,
        for<'b, 'c> TypeName::T<'b, 'c, Info::ValueT, E>: IsSync<E::NeedSend>,
        Mode: 'ctx,
}

impl<'ctx, Info, Mode: 'ctx, E> RequestHint<'ctx, E> for StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
    for<'b, 'c> TypeName::T<'b, 'c, Info::ValueT, E>: IsSync<E::NeedSend>,
    E: Environment,
{
    #[inline(always)]
    fn request_hint<'this: 'e, 'walker: 'e, 'e>(
        &'this mut self,
        walker: DynWalker<'walker, 'ctx, E>,
    ) -> NativeForm<'e, VisitResult, E>
    where
        'ctx: 'this + 'walker,
    {
        E::value((self, walker))
        .update(Capture(()).fun_once_hrt::<Mut<_>, _>(|_, (this, walker), _| {
            // Start with a hint to use the value protocol to directly transfer the
            // struct value.
            hint_protocol::<ValueProto<Info::ValueT, E>, _>(walker.cast(), *this, ()).cast()
        }))
        .if_not_finished(|(this, walker)| {
            // Next hint that the struct protocol should be used to switch into
            // map-like if the walker supports it.
            hint_protocol::<TagProto<tags::Struct, E>, _>(
                walker.cast(),
                *this,
                TagHint { kind: TagConst },
            )
            .cast()
        })
        .if_skipped(|(this, walker)| {
            // If the struct hint didn't work,
            // then hint that the map protocol should be used to switch into
            // map-like if the walker supports it.
            hint_protocol::<TagProto<tags::Map, E>, _>(
                walker.cast(),
                *this,
                TagHint { kind: TagConst },
            )
            .cast()
        })
        .if_not_finished(|(this, walker)| {
            // Lastly hint to use a sequence to get the field values.
            // We hint with the exact number of fields we are expecting.
            hint_protocol::<SequenceProto<E>, _>(
                walker.cast(),
                *this,
                SequenceHint {
                    len: (Info::FIELD_COUNT, Some(Info::FIELD_COUNT)),
                },
            )
            .cast()
        })
        .map(Capture(()).fun_once(|_, (_, x), _| x))
        .cast()
    }
}

/// Allows for a walker to directly give the struct value.
///
/// This skips needing to go through each field individually.
impl<'ctx, Info, Mode, E> Value<'ctx, Info::ValueT, E> for StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
    E: Environment,
    for<'a> TypeName::T<'a, 'ctx, Info::ValueT, E>: DynBind<E>,
{
    fn visit<'a>(
        &'a mut self,
        value: TypeName::T<'a, 'ctx, Info::ValueT, E>,
    ) -> NativeForm<'a, VisitResult<TypeName::T<'a, 'ctx, Info::ValueT, E>>, E>
    where
        TypeName::T<'a, 'ctx, Info::ValueT, E>: Sized,
        'ctx: 'a,
    {
        // Get the value from what we got from the walker.
        self.inner = Inner::Value(Info::from_value(value));

        // Since we have the struct value we are done.
        E::value(Flow::Done.into()).cast()
    }
}

/// Allows for the walker to use field names.
///
/// By default [`StructBuilder`] expects a tuple-like struct.
impl<'ctx, Info, Mode: 'ctx, E> Tag<'ctx, tags::Struct, E> for StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
    E: Environment,
{
    fn visit<'this: 'e, 'walker: 'e, 'e>(
        &'this mut self,
        _kind: tags::Struct,
        walker: DynWalkerObjSafe<'walker, 'ctx, E>,
    ) -> NativeForm<'e, VisitResult, E> {
        // If this protocol is used then we need to create the builders.
        E::value(self)
        .update(Capture(()).fun_once_hrt::<Mut<_>, _>(|_, this, _| this.make_builders().cast()))
        .then(Capture(walker).fun_once(|walker, (this, _), _| {
            if let Inner::Builders { kind, .. } = &mut this.inner {
                // This signals to go into map mode for the sequence.
                *kind = StructKind::Map;
            }

            // Walk the walker so nothing complains.
            NoopVisitor::walk_dyn(walker)
        }))
        .cast()
    }
}

/// Allows for the walker to use field names.
///
/// By default [`StructBuilder`] expects a tuple-like struct.
impl<'ctx, Info, Mode: 'ctx, E> Tag<'ctx, tags::Map, E> for StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
    E: Environment,
{
    fn visit<'this: 'e, 'walker: 'e, 'e>(
        &'this mut self,
        _kind: tags::Map,
        walker: DynWalkerObjSafe<'walker, 'ctx, E>,
    ) -> NativeForm<'e, VisitResult, E> {
        // If this protocol is used then we need to create the builders.
        E::value(self).update(Capture(()).fun_once_hrt::<Mut<_>, _>(|_, this, _| this.make_builders().cast())).then(Capture(walker).fun_once(|walker, (this, _), _| {
            if let Inner::Builders { kind, .. } = &mut this.inner {
                // This signals to go into map mode for the sequence.
                *kind = StructKind::Map;
            }

            // Walk the walker so nothing complains.
            NoopVisitor::walk_dyn(walker)
        }))
        .cast()
    }
}

/// Main protocol allowing a sequence of field values.
///
/// By default this will use each sequence element as a field value.
///
/// If the [`tags::Struct`] or [`tags::Map`] tags are used then this will expect
/// a sequence of key value pairs. Where the key is the field name.
impl<'ctx, Info, Mode: 'ctx, E> Sequence<'ctx, E> for StructBuilder<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
    E: Environment,
{
    fn visit<'a: 'c, 'b: 'c, 'c>(
        &'a mut self,
        scope: DynSequenceScope<'b, 'ctx, E>,
    ) -> NativeForm<'c, VisitResult, E>
    where
        'ctx: 'a + 'b + 'c,
    {
        // If this protocol is used then we need to create the builders.
        E::value(self)
            .update(Capture(()).fun_once_hrt::<Mut<_>, _>(|_, this, _| this.make_builders().cast()))
            .update(Capture(()).fun_once_hrt::<Mut<_>, _>(|_, (this, _), _| {
                match &mut this.inner {
                    // We should treat the sequence as just values.
                    Inner::Builders {
                        builders,
                        kind: StructKind::Tuple,
                    } => {
                        // Tuple-like is based on the index of the field.
                        let mut index = 0;

                        // Loop through all the fields getting a value for each one.
                        E::repeat_map((scope, builders), move |(scope, builders)| {
                            // Get the marker for the field at this index.
                            let marker = tri!(Info::marker_from_index(index));

                            // Move to the next field for the next iteration.
                            index += 1;

                            // Select the visitor for this field.
                            let visitor = Info::as_visitor(marker, builders);

                            // Visit the next item in the sequence.
                            scope.next(visitor).map(Flow::to_control_flow).cast()
                        })
                    }
                    // We should treat the sequence as key value pairs.
                    Inner::Builders {
                        builders,
                        kind: StructKind::Map,
                    } => {
                        // A visitor that knows how to use field names.
                        let visitor = FieldVisitor::<Info, Mode, E> {
                            builders,
                            marker: None,
                            _marker: Default::default(),
                        };

                        // Loop through all the elements in the sequence.
                        // Each key value pair will be mapped to a field.
                        E::repeat_map((visitor, scope), |(visitor, scope)| {
                            // Visit the next element of the sequence.
                            // When there are no more items in the sequence then the loop ends.
                            scope
                                .next(DynVisitor(visitor))
                                .map(Flow::to_control_flow)
                                .cast()
                        })
                    }
                    // If we don't have the builders ... we can't do anything.
                    // This would only happen if the walker gives the value directly
                    // then gives a sequence.
                    _ => E::value(Flow::Done).cast(),
                }
                .map(Into::into)
                .cast()
            }))
            .map(Capture(()).fun_once(|_, (_, x), _| x))
            .cast()
    }
}

struct FieldVisitor<'a, 'ctx, I: StructTypeInfo<'ctx, M, E>, M, E: Environment> {
    builders: &'a mut I::Builders,
    marker: Option<I::FieldMarker>,
    _marker: Marker<E>,
}

unsafe impl<'a, 'ctx, Info, Mode, E: Environment> IsSend<E::NeedSend> for FieldVisitor<'a, 'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{}

unsafe impl<'a, 'ctx, Info, Mode, E: Environment> IsSync<E::NeedSync> for FieldVisitor<'a, 'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{}

any_trait! {
    impl['ctx, 'a, I, M][E] FieldVisitor<'a, 'ctx, I, M, E> = [
        TagProto<tags::Key, E>,
    ] ref {
        let (_this, _id);
    } else ref {
        None
    } mut {
        let (this, id);
    } else mut {
        this.marker.and_then(|marker| {
            I::as_visitor(marker, this.builders).0.upcast_to_id_mut(id)
        })
    } where
        E: Environment,
        I: StructTypeInfo<'ctx, M, E>,
}

impl<'d, 'ctx, I, M, E> Tag<'ctx, tags::Key, E> for FieldVisitor<'d, 'ctx, I, M, E>
where
    E: Environment,
    I: StructTypeInfo<'ctx, M, E>,
{
    fn visit<'a: 'c, 'b: 'c, 'c>(
        &'a mut self,
        _key: tags::Key,
        walker: DynWalkerObjSafe<'b, 'ctx, E>,
    ) -> NativeForm<'c, VisitResult, E> {
        let visitor = NameVisitor::<I, M, E> {
            field_marker: None,
            _marker: Default::default(),
        };

        E::ready((self, visitor, walker))
            .as_ctx(|(_, visitor, walker)| walker.walk(DynVisitor(visitor)).cast())
            .map(|((this, visitor, _), flow)| {
                this.marker = visitor.field_marker;
                flow.to_continue().into()
            })
    }
}

struct NameVisitor<'ctx, I: StructTypeInfo<'ctx, M, E>, M, E: Environment> {
    field_marker: Option<I::FieldMarker>,
    _marker: Marker<E>,
}

unsafe impl<'ctx, Info, Mode, E: Environment> IsSend<E::NeedSend> for NameVisitor<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{}

unsafe impl<'ctx, Info, Mode, E: Environment> IsSync<E::NeedSync> for NameVisitor<'ctx, Info, Mode, E>
where
    Info: StructTypeInfo<'ctx, Mode, E>,
{}

any_trait! {
    impl['ctx, I, M][E] NameVisitor<'ctx, I, M, E> = [
        ValueProto<OwnedStatic<usize>, E>,
        ValueProto<TempBorrowedStaticHrt<str>, E>,
        ValueProto<OwnedStatic<&'static str>, E>,
    ] where
        E: Environment,
        I: StructTypeInfo<'ctx, M, E>,
}

impl<'ctx, I, M, E> Value<'ctx, OwnedStatic<usize>, E> for NameVisitor<'ctx, I, M, E>
where
    E: Environment,
    I: StructTypeInfo<'ctx, M, E>,
{
    fn visit<'a>(
        &'a mut self,
        OwnedStatic(index): TypeName::T<'a, 'ctx, OwnedStatic<usize>, E>,
    ) -> NativeForm<'a, VisitResult<TypeName::T<'a, 'ctx, OwnedStatic<usize>, E>>, E>
    where
        TypeName::T<'a, 'ctx, OwnedStatic<usize>, E>: Sized,
        'ctx: 'a,
    {
        self.field_marker = I::marker_from_index(index);

        E::ready(VisitResult::Control(Flow::Done))
    }
}

impl<'ctx, I, M, E> Value<'ctx, TempBorrowedStaticHrt<str>, E> for NameVisitor<'ctx, I, M, E>
where
    E: Environment,
    I: StructTypeInfo<'ctx, M, E>,
{
    fn visit<'a>(
        &'a mut self,
        TempBorrowedStatic(name): TypeName::T<'a, 'ctx, TempBorrowedStaticHrt<str>, E>,
    ) -> NativeForm<'a, VisitResult<TypeName::T<'a, 'ctx, TempBorrowedStaticHrt<str>, E>>, E>
    where
        TypeName::T<'a, 'ctx, TempBorrowedStaticHrt<str>, E>: Sized,
        'ctx: 'a,
    {
        self.field_marker = I::marker_from_name(name);

        E::ready(VisitResult::Control(Flow::Done))
    }
}

impl<'ctx, I, M, E> Value<'ctx, OwnedStatic<&'static str>, E> for NameVisitor<'ctx, I, M, E>
where
    E: Environment,
    I: StructTypeInfo<'ctx, M, E>,
{
    fn visit<'a>(
        &'a mut self,
        OwnedStatic(name): TypeName::T<'a, 'ctx, OwnedStatic<&'static str>, E>,
    ) -> NativeForm<'a, VisitResult<TypeName::T<'a, 'ctx, OwnedStatic<&'static str>, E>>, E>
    where
        TypeName::T<'a, 'ctx, TempBorrowedStaticHrt<str>, E>: Sized,
        'ctx: 'a,
    {
        self.field_marker = I::marker_from_name(name);

        E::ready(VisitResult::Control(Flow::Done))
    }
}