#![warn(missing_docs)]
#![doc = include_str!("../README.md")]

use std::cmp::Ordering::{self, *};

pub use cc_traits;
use sealed::sealed;

/// Module for definiting algebraic structures and properties.
pub mod algebra;
pub mod collections;
mod conflict;
mod dom_pair;
pub mod map_union;
pub mod map_union_with_tombstones;
mod ord;
mod pair;
mod point;
pub mod set_union;
pub mod set_union_with_tombstones;
pub mod test;
pub mod union_find;
mod unit;
mod vec_union;
mod with_bot;
mod with_top;

pub use conflict::Conflict;
pub use dom_pair::DomPair;
pub use ord::{Max, Min};
pub use pair::Pair;
pub use point::Point;
pub use vec_union::VecUnion;
pub use with_bot::WithBot;
pub use with_top::WithTop;

/// Alias trait for lattice types.
#[sealed]
pub trait Lattice: Sized + Merge<Self> + LatticeOrd + NaiveLatticeOrd + IsBot + IsTop {}
#[sealed]
impl<T> Lattice for T where T: Sized + Merge<Self> + LatticeOrd + NaiveLatticeOrd + IsBot + IsTop {}

/// Trait for lattice merge (AKA "join" or "least upper bound").
pub trait Merge<Other> {
    /// Merge `other` into the `self` lattice.
    ///
    /// This operation must be associative, commutative, and idempotent.
    ///
    /// Returns `true` if `self` changed, `false` otherwise.
    /// Returning `true` implies that the new value for `self` is later in the lattice order than
    /// the old value. Returning `false` means that `self` was unchanged and therefore `other` came
    /// before `self` (or the two are equal) in the lattice order.
    fn merge(&mut self, other: Other) -> bool;

    /// Merge `this` and `delta` together, returning the new value.
    fn merge_owned(mut this: Self, delta: Other) -> Self
    where
        Self: Sized,
    {
        Self::merge(&mut this, delta);
        this
    }
}

/// Trait for lattice partial order comparison
/// PartialOrd is implemented for many things, this trait can be used to require the type be a lattice.
pub trait LatticeOrd<Rhs = Self>: PartialOrd<Rhs> {}

/// Naive lattice compare, based on the [`Merge::merge`] function.
#[sealed]
pub trait NaiveLatticeOrd<Rhs = Self>
where
    Self: Clone + Merge<Rhs> + Sized,
    Rhs: Clone + Merge<Self>,
{
    /// Naive compare based on the [`Merge::merge`] method. This method can be very inefficient;
    /// use [`PartialOrd::partial_cmp`] instead.
    ///
    /// This method should not be overridden.
    fn naive_cmp(&self, other: &Rhs) -> Option<Ordering> {
        let mut self_a = self.clone();
        let other_a = other.clone();
        let self_b = self.clone();
        let mut other_b = other.clone();
        match (self_a.merge(other_a), other_b.merge(self_b)) {
            (true, true) => None,
            (true, false) => Some(Less),
            (false, true) => Some(Greater),
            (false, false) => Some(Equal),
        }
    }
}
#[sealed]
impl<This, Other> NaiveLatticeOrd<Other> for This
where
    Self: Clone + Merge<Other>,
    Other: Clone + Merge<Self>,
{
}

/// Same as `From` but for lattices.
///
/// This should only be implemented between different representations of the same lattice type.
/// This should recursively convert nested lattice types, but not non-lattice ("scalar") types.
pub trait LatticeFrom<Other> {
    /// Convert from the `Other` lattice into `Self`.
    fn lattice_from(other: Other) -> Self;
}

/// Trait to check if a lattice instance is bottom (⊥).
pub trait IsBot {
    /// Returns if `self` is lattice bottom (⊥).
    ///
    /// Must be consistent with equality, any element equal to bottom is also considered to be bottom.
    fn is_bot(&self) -> bool;
}

/// Trait to check if a lattice instance is top (⊤) and therefore cannot change any futher.
pub trait IsTop {
    /// Returns if `self` is lattice top (⊤).
    ///
    /// Must be consistent with equality, any element equal to top is also considered to be top.
    fn is_top(&self) -> bool;
}

/// Trait to atomize a lattice into individual elements. For example, a [`set_union::SetUnion`]
/// will be broken up into individual singleton elements.
///
/// Formally, breaks up `Self` into an set of lattice points forming a (strong) [antichain](https://en.wikipedia.org/wiki/Antichain).
/// "Strong" in the sense that any pair of lattice points in the antichain should have a greatest
/// lower bound (GLB or "meet") of bottom.
pub trait Atomize: Merge<Self::Atom> {
    /// The type of atoms for this lattice.
    type Atom: 'static + IsBot;

    /// The iter type iterating the antichain atoms.
    type AtomIter: 'static + Iterator<Item = Self::Atom>;

    /// Atomize self: convert into an iter of atoms.
    ///
    /// The returned iterator should be empty if and only if `self.is_bot()` is true.
    /// All atoms in the returned iterator should have `self.is_bot()` be false.
    ///
    /// Returned values must merge to reform a value equal to the original `self`.
    fn atomize(self) -> Self::AtomIter;
}

/// Trait for recursively revealing the underlying types within lattice types.
pub trait DeepReveal {
    /// The underlying type when revealed.
    type Revealed;

    /// Reveals the underlying lattice types recursively.
    fn deep_reveal(self) -> Self::Revealed;
}

/// Semilattice morphism. Lattice merge must distribute over this unary function.
///
/// Use [`crate::test::check_lattice_morphism`] to spot-test an implementation.
///
/// See the [lattice math doc's lattice morphism section](https://hydro.run/docs/hydroflow/lattices_crate/lattice_math/#lattice-morphism).
pub trait LatticeMorphism<LatIn> {
    /// The output lattice type.
    type Output;
    /// Executes the function.
    fn call(&mut self, lat_in: LatIn) -> Self::Output;
}

/// Semilattice bimorphism. Lattice merge must distribute over this binary function, in both arguments.
///
/// Use [`crate::test::check_lattice_bimorphism`] to spot-test an implementation.
///
/// See the [lattice math doc's lattice bimorphism section](https://hydro.run/docs/hydroflow/lattices_crate/lattice_math/#lattice-bimorphism).
pub trait LatticeBimorphism<LatA, LatB> {
    /// The output lattice type.
    type Output;
    /// Executes the function.
    fn call(&mut self, lat_a: LatA, lat_b: LatB) -> Self::Output;
}

/// Converts a closure to a morphism. Does not check for correctness.
pub fn closure_to_morphism<LatIn, LatOut, F>(
    func: F,
) -> impl LatticeMorphism<LatIn, Output = LatOut>
where
    F: FnMut(LatIn) -> LatOut,
{
    struct FnMorphism<F>(F);
    impl<F, LatIn, LatOut> LatticeMorphism<LatIn> for FnMorphism<F>
    where
        F: FnMut(LatIn) -> LatOut,
    {
        type Output = LatOut;

        fn call(&mut self, lat_in: LatIn) -> Self::Output {
            (self.0)(lat_in)
        }
    }
    FnMorphism(func)
}

/// Converts a closure to a bimorphism. Does not check for correctness.
pub fn closure_to_bimorphism<LatA, LatB, LatOut, F>(
    func: F,
) -> impl LatticeBimorphism<LatA, LatB, Output = LatOut>
where
    F: FnMut(LatA, LatB) -> LatOut,
{
    struct FnBimorphism<F>(F);
    impl<F, LatA, LatB, LatOut> LatticeBimorphism<LatA, LatB> for FnBimorphism<F>
    where
        F: FnMut(LatA, LatB) -> LatOut,
    {
        type Output = LatOut;

        fn call(&mut self, lat_a: LatA, lat_b: LatB) -> Self::Output {
            (self.0)(lat_a, lat_b)
        }
    }
    FnBimorphism(func)
}