treaty -


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use crate::{
    effect::{Effect, Future},
    higher_ranked_type,
    hkt::AnySend,
    nameable,
    protocol::{walker::hint::HintMeta, Visitor},
    Flow,
};

use super::Status;

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

pub type DynSequence<'a, 'ctx, E> = dyn Sequence<'ctx, E> + Send + 'a;

nameable! {
    pub struct Name['ctx, E] for<'a>;

    impl [E] for DynSequence<'a, 'ctx, E> where {
        E: Effect<'ctx>,
    }
}

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

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

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

higher_ranked_type! {
    pub type SequenceKnownHkt['ctx]: (AnySend) = for<'lt> SequenceKnown
}

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

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

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

    type Hint = SequenceHint;
}

pub fn visit_sequence<'a, 'ctx, E: Effect<'ctx>>(
    visitor: Visitor<'a, 'ctx>,
    scope: DynSequenceScope<'a, 'ctx, E>,
) -> Future<'a, 'ctx, Status, E> {
    if let Some(object) = visitor.upcast_mut::<DynSequence<'_, 'ctx, E>>() {
        // Allow the visitor to give a hint if it wants.
        E::map(object.visit(scope), |flow| match flow {
            Flow::Continue => {
                // The visitor wants the walker to continue to it's normal
                // walking.
                Status::r#continue()
            }
            Flow::Break | Flow::Done => {
                // The visitor is done (either because of an error or because
                // it already used a hint).
                Status::r#break()
            }
        })
    } else {
        // If the visitor doesn't support request hint then we continue.
        E::ready(Status::skipped())
    }
}