treaty -


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use crate::{
    any::{TypeName, WithContextLt},
    bijective_higher_ranked_type,
    effect::{Effect, Future},
    hkt::AnySizedSend,
    protocol::{walker::hint::HintMeta, Visitor},
    Flow,
};

use super::VisitResult;

pub trait Sequence<'ctx, E: Effect> {
    fn visit<'a>(
        &'a mut self,
        scope: DynSequenceScope<'a, 'ctx, E>,
    ) -> Future<'a, VisitResult<DynSequenceScope<'a, 'ctx, E>>, E>;
}

bijective_higher_ranked_type! {
    pub type DynSequence['ctx][E]: WithContextLt['ctx][]
    for<'a>
    (dyn Sequence<'ctx, E> + Send + 'a)
    where {
        E: Effect
    }
}

bijective_higher_ranked_type! {
    pub type [][E]: TypeName[][]
    for<'ctx>
    (DynSequence<'ctx, E>)
    where {
        E: Effect
    }
}

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

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

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

bijective_higher_ranked_type! {
    pub type SequenceKnownHkt[][]: AnySizedSend[][] for<'lt> (SequenceKnown)
}

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

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

impl<'ctx, E: Effect> HintMeta<'ctx> for DynSequence<'ctx, E> {
    type Known = SequenceKnownHkt;

    type Hint = SequenceHint;
}

pub fn visit_sequence<'a, 'ctx, E: Effect>(
    visitor: Visitor<'a, 'ctx>,
    scope: DynSequenceScope<'a, 'ctx, E>,
) -> Future<'a, VisitResult<DynSequenceScope<'a, 'ctx, E>>, E> {
    if let Some(object) = visitor.upcast_mut::<DynSequence<'ctx, 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))
    }
}