// Traits:

pub trait Alpha {
    fn alpha(self) -> usize;
}

pub trait Beta {
    type Gamma;
    fn gamma(&self) -> Self::Gamma;
}

pub trait Delta {
    fn delta(self) -> usize;
}

pub trait Epsilon<'a> {
    type Zeta;
    fn zeta(&'a self) -> Self::Zeta;

    fn epsilon(&'a self) -> usize;
}

pub trait Eta {
    fn eta(self) -> usize;
}

// Assertions:

pub fn assert_alpha<T: Alpha>(x: T) -> usize { x.alpha() }
pub fn assert_static<T: 'static>(_: T) -> usize { 24 }
pub fn assert_delta<T: Delta>(x: T) -> usize { x.delta() }
pub fn assert_epsilon_specific<'a, T: 'a + Epsilon<'a>>(x: &'a T) -> usize { x.epsilon() }
pub fn assert_epsilon_forall<T: for<'a> Epsilon<'a>>() {}
pub fn assert_forall_epsilon_zeta_satisfies_eta<T>(x: T) -> usize
where
    T: for<'a> Epsilon<'a>,
    for<'a> <T as Epsilon<'a>>::Zeta: Eta,
{
    x.epsilon() + x.zeta().eta()
}

// Implementations and types:

#[derive(Copy, Clone)]
pub struct BetaType;

#[derive(Copy, Clone)]
pub struct GammaType;

#[derive(Copy, Clone)]
pub struct ZetaType;

impl<T> Beta for &(dyn Beta<Gamma = T> + Send) {
    type Gamma = T;
    fn gamma(&self) -> Self::Gamma { (*self).gamma() }
}

impl Beta for BetaType {
    type Gamma = GammaType;
    fn gamma(&self) -> Self::Gamma { GammaType }
}

impl<'a> Beta for &'a BetaType {
    type Gamma = GammaType;
    fn gamma(&self) -> Self::Gamma { GammaType }
}

impl Beta for GammaType {
    type Gamma = Self;
    fn gamma(&self) -> Self::Gamma { Self }
}

impl Alpha for GammaType {
    fn alpha(self) -> usize { 42 }
}

impl Delta for GammaType {
    fn delta(self) -> usize { 1337 }
}

impl<'a> Epsilon<'a> for GammaType {
    type Zeta = ZetaType;
    fn zeta(&'a self) -> Self::Zeta { ZetaType }

    fn epsilon(&'a self) -> usize { 7331 }
}

impl Eta for ZetaType {
    fn eta(self) -> usize { 7 }
}

// Desugared forms to check against:

pub fn desugared_bound<B: ?Sized>(beta: &B) -> usize
where
    B: Beta,
    B::Gamma: Alpha
{
    let gamma: B::Gamma = beta.gamma();
    assert_alpha::<B::Gamma>(gamma)
}

pub fn desugared_bound_region<B: ?Sized>(beta: &B) -> usize
where
    B: Beta,
    B::Gamma: 'static,
{
    assert_static::<B::Gamma>(beta.gamma())
}

pub fn desugared_bound_multi<B: ?Sized>(beta: B) -> usize
where
    B: Copy + Beta,
    B::Gamma: Alpha + 'static + Delta,
{
    assert_alpha::<B::Gamma>(beta.gamma()) +
    assert_static::<B::Gamma>(beta.gamma()) +
    assert_delta::<B::Gamma>(beta.gamma())
}

pub fn desugared_bound_region_specific<'a, B: ?Sized>(gamma: &'a B::Gamma) -> usize
where
    B: Beta,
    B::Gamma: 'a + Epsilon<'a>,
{
    assert_epsilon_specific::<B::Gamma>(gamma)
}

pub fn desugared_bound_region_forall<B: ?Sized>(beta: &B) -> usize
where
    B: Beta,
    B::Gamma: Copy + for<'a> Epsilon<'a>,
{
    assert_epsilon_forall::<B::Gamma>();
    let g1: B::Gamma = beta.gamma();
    let g2: B::Gamma = g1;
    assert_epsilon_specific::<B::Gamma>(&g1) +
    assert_epsilon_specific::<B::Gamma>(&g2)
}

pub fn desugared_bound_region_forall2<B: ?Sized>(beta: &B) -> usize
where
    B: Beta,
    B::Gamma: Copy + for<'a> Epsilon<'a>,
    for<'a> <B::Gamma as Epsilon<'a>>::Zeta: Eta,
{
    let gamma = beta.gamma();
    assert_forall_epsilon_zeta_satisfies_eta::<B::Gamma>(gamma)
}

pub fn desugared_contraint_region_forall<B: ?Sized>(beta: &B) -> usize
where
    for<'a> &'a B: Beta,
    for<'a> <&'a B as Beta>::Gamma: Alpha,
{
    let g1 = beta.gamma();
    let g2 = beta.gamma();
    assert_alpha(g1) + assert_alpha(g2)
}

pub fn desugared_bound_nested<B: ?Sized>(beta: &B) -> usize
where
    B: Beta,
    B::Gamma: Copy + Alpha + Beta,
    <B::Gamma as Beta>::Gamma: Delta,
{
    let go = beta.gamma();
    let gi = go.gamma();
    go.alpha() + gi.delta()
}

pub fn desugared() {
    let beta = BetaType;
    let gamma = beta.gamma();

    assert_eq!(42, desugared_bound(&beta));
    assert_eq!(24, desugared_bound_region(&beta));
    assert_eq!(42 + 24 + 1337, desugared_bound_multi(beta));
    assert_eq!(7331, desugared_bound_region_specific::<BetaType>(&gamma));
    assert_eq!(7331 * 2, desugared_bound_region_forall(&beta));
    assert_eq!(42 + 1337, desugared_bound_nested(&beta));
}