treaty -


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use crate::{
    any::TypeName,
    effect::{Effect, Effective, ErasedEffective},
    higher_ranked_type,
    hkt::Marker,
    protocol::{
        walker::hint::{HintMeta, Meta},
        DynVisitor,
    },
    Flow,
};

use super::VisitResult;

/// Protocol for visiting a sequence.
///
/// This protocol uses a scope to give temporary control to the visitor.
/// The visitor will drive the walker for each item.
pub trait Sequence<'ctx, E: Effect> {
    fn visit<'a>(
        &'a mut self,
        scope: DynSequenceScope<'a, 'ctx, E>,
    ) -> ErasedEffective<'a, VisitResult<DynSequenceScope<'a, 'ctx, E>>, E>;
}

pub struct SequenceProto<E: Effect>(Marker<E>);

higher_ranked_type! {
    impl TypeName {
        impl['a, 'ctx, E] type T['a, 'ctx] for SequenceProto<E> =
            dyn Sequence<'ctx, E> + Send + Sync + 'a
        where {
            E: Effect
        };

        impl['a, 'ctx, E] type HigherRanked['a, 'ctx] for dyn Sequence<'ctx, E> + Send + Sync + 'a =
            SequenceProto<E>
        where {
            E: Effect
        };
    }
}

pub trait SequenceScope<'ctx, E: Effect> {
    fn size_hint(&mut self) -> ErasedEffective<'_, (usize, Option<usize>), E>;

    fn next<'a>(&'a mut self, visitor: DynVisitor<'a, 'ctx>) -> ErasedEffective<'a, Flow, E>;
}

pub type DynSequenceScope<'a, 'ctx, E> = &'a mut (dyn SequenceScope<'ctx, E> + Send + Sync + 'a);

#[derive(Default)]
pub struct SequenceKnown {
    pub len: (usize, Option<usize>),
}

higher_ranked_type! {
    impl Meta {
        impl['a, 'ctx] type T['a, 'ctx] for SequenceKnown =
            SequenceKnown;

        impl['a, 'ctx] type HigherRanked['a, 'ctx] for SequenceKnown =
            SequenceKnown;
    }
}

pub struct SequenceHint {
    pub len: (usize, Option<usize>),
}

higher_ranked_type! {
    impl Meta {
        impl['a, 'ctx] type T['a, 'ctx] for SequenceHint =
            SequenceHint;

        impl['a, 'ctx] type HigherRanked['a, 'ctx] for SequenceHint =
            SequenceHint;
    }
}

impl<E: Effect> HintMeta for SequenceProto<E> {
    type Known = SequenceKnown;

    type Hint = SequenceHint;

    type Effect = E;
}

#[inline(always)]
pub fn visit_sequence<'a, 'ctx, E: Effect>(
    visitor: DynVisitor<'a, 'ctx>,
    scope: DynSequenceScope<'a, 'ctx, E>,
) -> ErasedEffective<'a, VisitResult<DynSequenceScope<'a, 'ctx, E>>, E> {
    if let Some(object) = visitor.0.upcast_mut::<SequenceProto<E>>() {
        // Allow the visitor to give a hint if it wants.
        object.visit(scope)
    } else {
        // If the visitor doesn't support request hint then we continue.
        E::ready(VisitResult::Skipped(scope)).into_erased()
    }
}