use smallvec::SmallVec;
use std::fmt::Debug;
use std::hash::Hash;
use std::ops::Deref;

use crate::inherent::*;
use crate::ir_print::IrPrint;
use crate::solve::inspect::GoalEvaluationStep;
use crate::visit::{Flags, TypeSuperVisitable, TypeVisitable};
use crate::{
    AliasTerm, AliasTermKind, AliasTy, AliasTyKind, CanonicalVarInfo, CoercePredicate,
    DebugWithInfcx, ExistentialProjection, ExistentialTraitRef, FnSig, GenericArgKind,
    NormalizesTo, ProjectionPredicate, SubtypePredicate, TraitPredicate, TraitRef,
};

pub trait Interner:
    Sized
    + Copy
    + IrPrint<AliasTy<Self>>
    + IrPrint<AliasTerm<Self>>
    + IrPrint<TraitRef<Self>>
    + IrPrint<TraitPredicate<Self>>
    + IrPrint<ExistentialTraitRef<Self>>
    + IrPrint<ExistentialProjection<Self>>
    + IrPrint<ProjectionPredicate<Self>>
    + IrPrint<NormalizesTo<Self>>
    + IrPrint<SubtypePredicate<Self>>
    + IrPrint<CoercePredicate<Self>>
    + IrPrint<FnSig<Self>>
{
    type DefId: Copy + Debug + Hash + Eq;
    type AdtDef: Copy + Debug + Hash + Eq;

    type GenericArgs: GenericArgs<Self>;
    /// The slice of args for a specific item. For a GAT like `type Foo<'a>`, it will be `['a]`,
    /// not including the args from the parent item (trait or impl).
    type OwnItemArgs: Copy + Debug + Hash + Eq;
    type GenericArg: Copy + DebugWithInfcx<Self> + Hash + Eq + IntoKind<Kind = GenericArgKind<Self>>;
    type Term: Copy + Debug + Hash + Eq;

    type Binder<T: TypeVisitable<Self>>: BoundVars<Self> + TypeSuperVisitable<Self>;
    type BoundVars: IntoIterator<Item = Self::BoundVar>;
    type BoundVar;

    type CanonicalVars: Copy + Debug + Hash + Eq + IntoIterator<Item = CanonicalVarInfo<Self>>;
    type PredefinedOpaques: Copy + Debug + Hash + Eq;
    type DefiningOpaqueTypes: Copy + Debug + Hash + Default + Eq + TypeVisitable<Self>;
    type ExternalConstraints: Copy + Debug + Hash + Eq;
    type GoalEvaluationSteps: Copy + Debug + Hash + Eq + Deref<Target = [GoalEvaluationStep<Self>]>;

    // Kinds of tys
    type Ty: Ty<Self>;
    type Tys: Tys<Self>;
    type FnInputTys: Copy + Debug + Hash + Eq + Deref<Target = [Self::Ty]>;
    type ParamTy: Copy + Debug + Hash + Eq;
    type BoundTy: Copy + Debug + Hash + Eq + BoundVarLike<Self>;
    type PlaceholderTy: PlaceholderLike;

    // Things stored inside of tys
    type ErrorGuaranteed: Copy + Debug + Hash + Eq;
    type BoundExistentialPredicates: Copy + DebugWithInfcx<Self> + Hash + Eq;
    type PolyFnSig: Copy + DebugWithInfcx<Self> + Hash + Eq;
    type AllocId: Copy + Debug + Hash + Eq;
    type Pat: Copy + Debug + Hash + Eq + DebugWithInfcx<Self>;
    type Safety: Safety<Self>;
    type Abi: Abi<Self>;

    // Kinds of consts
    type Const: Const<Self>;
    type AliasConst: Copy + DebugWithInfcx<Self> + Hash + Eq;
    type PlaceholderConst: PlaceholderLike;
    type ParamConst: Copy + Debug + Hash + Eq;
    type BoundConst: Copy + Debug + Hash + Eq + BoundVarLike<Self>;
    type ValueConst: Copy + Debug + Hash + Eq;
    type ExprConst: Copy + DebugWithInfcx<Self> + Hash + Eq;

    // Kinds of regions
    type Region: Region<Self>;
    type EarlyParamRegion: Copy + Debug + Hash + Eq;
    type LateParamRegion: Copy + Debug + Hash + Eq;
    type BoundRegion: Copy + Debug + Hash + Eq + BoundVarLike<Self>;
    type InferRegion: Copy + DebugWithInfcx<Self> + Hash + Eq;
    type PlaceholderRegion: PlaceholderLike;

    // Predicates
    type ParamEnv: Copy + Debug + Hash + Eq;
    type Predicate: Predicate<Self>;
    type TraitPredicate: Copy + Debug + Hash + Eq;
    type RegionOutlivesPredicate: Copy + Debug + Hash + Eq;
    type TypeOutlivesPredicate: Copy + Debug + Hash + Eq;
    type ProjectionPredicate: Copy + Debug + Hash + Eq;
    type NormalizesTo: Copy + Debug + Hash + Eq;
    type SubtypePredicate: Copy + Debug + Hash + Eq;
    type CoercePredicate: Copy + Debug + Hash + Eq;
    type ClosureKind: Copy + Debug + Hash + Eq;
    type Clauses: Copy + Debug + Hash + Eq + TypeSuperVisitable<Self> + Flags;

    fn mk_canonical_var_infos(self, infos: &[CanonicalVarInfo<Self>]) -> Self::CanonicalVars;

    type GenericsOf: GenericsOf<Self>;
    fn generics_of(self, def_id: Self::DefId) -> Self::GenericsOf;

    // FIXME: Remove after uplifting `EarlyBinder`
    fn type_of_instantiated(self, def_id: Self::DefId, args: Self::GenericArgs) -> Self::Ty;

    fn alias_ty_kind(self, alias: AliasTy<Self>) -> AliasTyKind;

    fn alias_term_kind(self, alias: AliasTerm<Self>) -> AliasTermKind;

    fn trait_ref_and_own_args_for_alias(
        self,
        def_id: Self::DefId,
        args: Self::GenericArgs,
    ) -> (TraitRef<Self>, Self::OwnItemArgs);

    fn mk_args(self, args: &[Self::GenericArg]) -> Self::GenericArgs;

    fn mk_args_from_iter(self, args: impl Iterator<Item = Self::GenericArg>) -> Self::GenericArgs;

    fn check_and_mk_args(
        self,
        def_id: Self::DefId,
        args: impl IntoIterator<Item: Into<Self::GenericArg>>,
    ) -> Self::GenericArgs;

    fn parent(self, def_id: Self::DefId) -> Self::DefId;

    fn recursion_limit(self) -> usize;
}

/// Imagine you have a function `F: FnOnce(&[T]) -> R`, plus an iterator `iter`
/// that produces `T` items. You could combine them with
/// `f(&iter.collect::<Vec<_>>())`, but this requires allocating memory for the
/// `Vec`.
///
/// This trait allows for faster implementations, intended for cases where the
/// number of items produced by the iterator is small. There is a blanket impl
/// for `T` items, but there is also a fallible impl for `Result<T, E>` items.
pub trait CollectAndApply<T, R>: Sized {
    type Output;

    /// Produce a result of type `Self::Output` from `iter`. The result will
    /// typically be produced by applying `f` on the elements produced by
    /// `iter`, though this may not happen in some impls, e.g. if an error
    /// occurred during iteration.
    fn collect_and_apply<I, F>(iter: I, f: F) -> Self::Output
    where
        I: Iterator<Item = Self>,
        F: FnOnce(&[T]) -> R;
}

/// The blanket impl that always collects all elements and applies `f`.
impl<T, R> CollectAndApply<T, R> for T {
    type Output = R;

    /// Equivalent to `f(&iter.collect::<Vec<_>>())`.
    fn collect_and_apply<I, F>(mut iter: I, f: F) -> R
    where
        I: Iterator<Item = T>,
        F: FnOnce(&[T]) -> R,
    {
        // This code is hot enough that it's worth specializing for the most
        // common length lists, to avoid the overhead of `SmallVec` creation.
        // Lengths 0, 1, and 2 typically account for ~95% of cases. If
        // `size_hint` is incorrect a panic will occur via an `unwrap` or an
        // `assert`.
        match iter.size_hint() {
            (0, Some(0)) => {
                assert!(iter.next().is_none());
                f(&[])
            }
            (1, Some(1)) => {
                let t0 = iter.next().unwrap();
                assert!(iter.next().is_none());
                f(&[t0])
            }
            (2, Some(2)) => {
                let t0 = iter.next().unwrap();
                let t1 = iter.next().unwrap();
                assert!(iter.next().is_none());
                f(&[t0, t1])
            }
            _ => f(&iter.collect::<SmallVec<[_; 8]>>()),
        }
    }
}

/// A fallible impl that will fail, without calling `f`, if there are any
/// errors during collection.
impl<T, R, E> CollectAndApply<T, R> for Result<T, E> {
    type Output = Result<R, E>;

    /// Equivalent to `Ok(f(&iter.collect::<Result<Vec<_>>>()?))`.
    fn collect_and_apply<I, F>(mut iter: I, f: F) -> Result<R, E>
    where
        I: Iterator<Item = Result<T, E>>,
        F: FnOnce(&[T]) -> R,
    {
        // This code is hot enough that it's worth specializing for the most
        // common length lists, to avoid the overhead of `SmallVec` creation.
        // Lengths 0, 1, and 2 typically account for ~95% of cases. If
        // `size_hint` is incorrect a panic will occur via an `unwrap` or an
        // `assert`, unless a failure happens first, in which case the result
        // will be an error anyway.
        Ok(match iter.size_hint() {
            (0, Some(0)) => {
                assert!(iter.next().is_none());
                f(&[])
            }
            (1, Some(1)) => {
                let t0 = iter.next().unwrap()?;
                assert!(iter.next().is_none());
                f(&[t0])
            }
            (2, Some(2)) => {
                let t0 = iter.next().unwrap()?;
                let t1 = iter.next().unwrap()?;
                assert!(iter.next().is_none());
                f(&[t0, t1])
            }
            _ => f(&iter.collect::<Result<SmallVec<[_; 8]>, _>>()?),
        })
    }
}