treaty -


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use effectful::{
    effective::{Canonical, Effective},
    environment::{Environment, InEnvironment},
    higher_ranked::Rank1,
    DynBind, SendSync,
};

use crate::{
    any::type_name,
    protocol::{walker::hint::HintMeta, 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<'src, E: Environment>: DynBind<E> {
    fn visit<'r>(
        &'r mut self,
        scope: DynSequenceScope<'r, 'src, E>,
    ) -> Canonical<'r, VisitResult, E>;
}

impl<'u, 'src, E> type_name::Lower<'u, 'src, &'u &'src ()> for dyn Sequence<'static, E>
where
    E: Environment,
{
    type Lowered = dyn Sequence<'src, E> + 'u;
}

impl<'u, 'src, E> type_name::Raise<'u, 'src, &'u &'src ()> for dyn Sequence<'src, E> + 'u
where
    E: Environment,
{
    type Raised = dyn Sequence<'static, E>;
}

impl<E: Environment> HintMeta for dyn Sequence<'static, E> {
    type Known = Rank1<SequenceKnown>;

    type Hint = Rank1<SequenceHint>;
}

impl<E: Environment> InEnvironment for dyn Sequence<'static, E> {
    type Env = E;
}

pub trait SequenceScope<'src, E: Environment>: DynBind<E> {
    fn size_hint(&mut self) -> Canonical<'_, (usize, Option<usize>), E>;

    fn next<'r>(&'r mut self, visitor: DynVisitor<'r, 'src, E>) -> Canonical<'r, Flow, E>;
}

pub type DynSequenceScope<'r, 'src, E> = &'r mut dyn SequenceScope<'src, E>;

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

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

#[inline(always)]
pub fn visit_sequence<'r, 'src, E: Environment>(
    visitor: DynVisitor<'r, 'src, E>,
    scope: DynSequenceScope<'r, 'src, E>,
) -> Canonical<'r, VisitResult, E> {
    if let Some(object) = visitor
        .into_inner()
        .as_any_trait_mut()
        .upcast_mut::<dyn Sequence<'src, E> + 'r>()
    {
        // Allow the visitor to walk the sequence scope.
        object.visit(scope)
    } else {
        // If the visitor doesn't support sequence then we continue.
        E::value(VisitResult::Skipped(())).cast()
    }
}