use effectful::{
    bound::Dynamic,
    effective::{Effective, Canonical},
    environment::{Environment},
    DynBind,
    SendSync,
};

use crate::{
    any::{BorrowedStatic, OwnedStatic, TempBorrowedStatic},
    protocol::{
        visitor::{visit_value, EffectiveVisitExt as _, VisitResult},
        DynVisitor,
    },
    Never,
};

/// A very basic walker that uses the [`Value`][crate::protocol::visitor::value::Value] protocol.
///
/// Primitive types use this walker as their main walker.
/// This walker doesn't consider it an error if the visitor doesn't have the protocol.
#[derive(Debug, SendSync)]
pub struct ValueWalker<T>(Dynamic<T>);

impl<T> ValueWalker<T> {
    /// Create walker from a value.
    #[inline(always)]
    pub fn new(value: T) -> Self {
        Self(Dynamic(value))
    }
}

impl<T> From<T> for ValueWalker<T> {
    #[inline(always)]
    fn from(value: T) -> Self {
        Self::new(value)
    }
}

impl<T: Copy> From<&T> for ValueWalker<T> {
    #[inline(always)]
    fn from(value: &T) -> Self {
        Self::new(*value)
    }
}

impl<'ctx, T: 'static, E: Environment> crate::Walker<'ctx, E> for ValueWalker<T>
where
    Dynamic<T>: DynBind<E>,
    Dynamic<OwnedStatic<T>>: DynBind<E>,
{
    type Error = Never;

    type Output = ();

    #[inline(always)]
    fn walk<'b: 'c, 'd: 'c, 'c>(
        self,
        visitor: DynVisitor<'b, 'd, 'ctx, E>,
    ) -> Canonical<'c, Result<Self::Output, Self::Error>, E> {
        // Attempt to visit using the value protocol.
        visit_value::<OwnedStatic<T>, E>(visitor, OwnedStatic(self.0 .0))
            .map((), |_, _| Ok(()))
            .cast()
    }
}

/// Borrowed form of [`ValueWalker`].
///
/// This walker supports values borrowed for `'ctx` or longer.
#[derive(SendSync)]
pub struct BorrowWalker<'ctx, T: ?Sized>(Dynamic<&'ctx T>);

impl<'ctx, T: ?Sized> BorrowWalker<'ctx, T> {
    /// Create walker from a value.
    #[inline(always)]
    pub fn new(value: &'ctx T) -> Self {
        Self(Dynamic(value))
    }
}

impl<'ctx, T: ?Sized + 'static, E: Environment> crate::Walker<'ctx, E> for BorrowWalker<'ctx, T>
where
    Dynamic<&'ctx T>: DynBind<E>,
    Dynamic<BorrowedStatic<'ctx, T>>: DynBind<E>,
    for<'a> Dynamic<TempBorrowedStatic<'a, T>>: DynBind<E>,
{
    type Error = Never;

    type Output = Dynamic<&'ctx T>;

    #[inline(always)]
    fn walk<'b: 'c, 'd: 'c, 'c>(
        self,
        visitor: DynVisitor<'b, 'd, 'ctx, E>,
    ) -> Canonical<'c, Result<Self::Output, Self::Error>, E> {
        // Attempt to visit using the value protocol.
        E::value((self, visitor))
            .update_map((), |_, (this, visitor)| {
                visit_value::<_, E>(visitor.cast(), BorrowedStatic(this.0 .0))
                    .map((), |_, x| VisitResult::unit_skipped(x))
                    .cast()
            })
            .if_skipped((), |_, (this, visitor)| {
                visit_value::<_, E>(visitor.cast(), TempBorrowedStatic(this.0 .0))
                    .map((), |_, x| VisitResult::unit_skipped(x))
                    .cast()
            })
            .map((), |_, ((this, _), _)| Ok(this.0))
            .cast()
    }
}