treaty -


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use core::any::Any;

use crate::{
    build::{Build, Builder},
    protocol::{
        lookup_hint, lookup_visit, AnyVisit, ProtocolId, Visit, VisitorMissingProtocol,
        WalkerMissingProtocol,
    },
    protocols::reference,
    walk::{Walk, WalkMut, WalkOnce},
    ControlFlow, Visitor, Walker,
};

impl<'borrow, 'ctx, T> WalkOnce<'ctx> for &'borrow mut T
where
    T: WalkMut<'borrow, 'ctx>,
{
    type Error = T::Error;

    type Value = T::Value;

    fn walk_once(self, visitor: &mut dyn Visitor<'ctx>) -> Result<Self::Value, Self::Error> {
        T::walk_mut(self, visitor)
    }
}

impl<'borrow, 'ctx, T> WalkMut<'borrow, 'ctx> for &'borrow mut T
where
    T: WalkMut<'borrow, 'ctx>,
{
    fn walk_mut(
        &'borrow mut self,
        visitor: &mut dyn Visitor<'ctx>,
    ) -> Result<Self::Value, Self::Error> {
        T::walk_mut(self, visitor)
    }
}

impl<'borrow, 'ctx, T> Walk<'borrow, 'ctx> for &'borrow mut T
where
    T: Walk<'borrow, 'ctx>,
{
    fn walk(&'borrow self, visitor: &mut dyn Visitor<'ctx>) -> Result<Self::Value, Self::Error> {
        T::walk(self, visitor)
    }
}

impl<'ctx, T: ?Sized + Any> Build<'ctx> for &'ctx mut T {
    type Builder = MutBuilder<'ctx, T>;
}

pub struct MutWalker<'ctx, T: ?Sized> {
    value: Option<&'ctx mut T>,
}

impl<'ctx, T: ?Sized> MutWalker<'ctx, T> {
    pub fn new(value: &'ctx mut T) -> Self {
        Self {
            value: Some(value),
        }
    }
}

impl<'ctx, T: ?Sized + Any> WalkOnce<'ctx> for MutWalker<'ctx, T> {
    type Error = VisitorMissingProtocol;

    type Value = ();

    fn walk_once(mut self, visitor: &mut dyn Visitor<'ctx>) -> Result<Self::Value, Self::Error> {
        if let Some(value) = self.value.take() {
            let visit = lookup_visit::<reference::ReferenceMut<T>, _>(visitor)?;
            visit.visit(reference::Mut::Context(value));
        }
        Ok(())
    }
}

#[derive(thiserror::Error, Debug)]
pub enum Error {
    #[error("Missing value after walk.")]
    MissingValue,

    #[error("A value with a lifetime to short was given.")]
    ShortLifetime,

    #[error(transparent)]
    MissingProtocol(#[from] WalkerMissingProtocol),
}

pub struct MutBuilder<'ctx, T: ?Sized> {
    value: Option<Result<&'ctx mut T, Error>>,
}

impl<'ctx, T: ?Sized> Default for MutBuilder<'ctx, T> {
    fn default() -> Self {
        Self { value: None }
    }
}

impl<'ctx, T: ?Sized + Any> Builder<'ctx> for MutBuilder<'ctx, T> {
    type Error = Error;

    type Value = &'ctx mut T;

    fn as_visitor(&mut self) -> &mut dyn Visitor<'ctx> {
        self
    }

    fn build(self) -> Result<Self::Value, Self::Error> {
        match self.value {
            Some(Ok(value)) => Ok(value),
            Some(Err(err)) => Err(err.into()),
            None => Err(Error::MissingValue),
        }
    }
}

impl<'ctx, T: ?Sized + Any> Visitor<'ctx> for MutBuilder<'ctx, T> {
    fn request_hint(
        &mut self,
        hints: &mut dyn crate::Walker<'ctx>,
        _need_hint: bool,
    ) -> ControlFlow {
        match lookup_hint::<reference::Reference<T>, _>(hints) {
            Ok(hint) => hint.hint(
                self,
                reference::Hint {
                    kind: Some(reference::Kind::Context),
                    min_len: None,
                    max_len: None,
                },
            ),
            Err(err) => {
                self.value = Some(Err(err.into()));
                ControlFlow::Error
            }
        }
    }

    fn protocol(&mut self, id: crate::protocol::ProtocolId) -> Option<AnyVisit<'_, 'ctx>> {
        if id == ProtocolId::of::<reference::ReferenceMut<T>>() {
            Some(AnyVisit::new(self))
        } else {
            None
        }
    }
}

impl<'ctx, T: ?Sized + Any> Visit<'ctx, reference::ReferenceMut<T>> for MutBuilder<'ctx, T> {
    fn visit(&mut self, accessor: reference::Mut<'_, 'ctx, T>) -> ControlFlow {
        match accessor {
            reference::Mut::Walking(_) => {
                self.value = Some(Err(Error::ShortLifetime));
                ControlFlow::Continue
            }
            reference::Mut::Context(value) | reference::Mut::Static(value) => {
                self.value = Some(Ok(value));
                ControlFlow::Done
            }
        }
    }
}