// SPDX-License-Identifier: LGPL-3.0-or-later
// See Notices.txt for copyright information
#![allow(clippy::type_complexity)]
use crate::{intern::type_map::TypeIdMap, util::DefaultBuildHasher};
use bitvec::{ptr::BitPtr, slice::BitSlice, vec::BitVec};
use hashbrown::HashTable;
use once_cell::race::OnceRef;
use serde::{Deserialize, Serialize};
use std::{
    any::{Any, TypeId},
    borrow::{Borrow, Cow},
    cell::RefCell,
    cmp::Ordering,
    ffi::{OsStr, OsString},
    fmt,
    hash::{BuildHasher, Hash, Hasher},
    iter::FusedIterator,
    ops::Deref,
    path::{Path, PathBuf},
    sync::RwLock,
};

mod interner;
mod type_map;

/// invariant: T must be zero-sized, `type_id` is unique for every possible T value.
struct LazyInternedLazyInner<T: ?Sized + 'static> {
    type_id: TypeId,
    value: T,
}

impl<T: ?Sized + 'static> Hash for LazyInternedLazyInner<T> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        let Self { type_id, value: _ } = self;
        type_id.hash(state);
    }
}

impl<T: ?Sized + 'static> PartialEq for LazyInternedLazyInner<T> {
    fn eq(&self, other: &Self) -> bool {
        let Self { type_id, value: _ } = self;
        *type_id == other.type_id
    }
}

impl<T: ?Sized + 'static> Eq for LazyInternedLazyInner<T> {}

impl<T: ?Sized + 'static> fmt::Debug for LazyInternedLazyInner<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("LazyInternedLazyInner")
            .finish_non_exhaustive()
    }
}

impl<T: ?Sized + 'static> LazyInternedLazyInner<T> {
    const fn new(value: T) -> Self
    where
        T: Sized,
    {
        const { assert!(size_of::<T>() == 0) };
        Self {
            type_id: TypeId::of::<T>(),
            value,
        }
    }
}

pub struct LazyInternedLazy<T: ?Sized + Send + Sync + 'static>(
    &'static LazyInternedLazyInner<dyn Fn() -> Interned<T> + Send + Sync>,
);

impl<T: ?Sized + Send + Sync + 'static> LazyInternedLazy<T> {
    pub const fn new_const<V: Default + Into<Interned<T>>>() -> Self {
        Self(&const { LazyInternedLazyInner::new(|| V::default().into()) })
    }
    pub const fn new_const_default() -> Self
    where
        Interned<T>: Default,
    {
        Self::new_const::<Interned<T>>()
    }
    pub fn interned(self) -> Interned<T> {
        struct Map(hashbrown::HashTable<(TypeId, &'static (dyn Any + Send + Sync))>);
        impl Map {
            const EMPTY: Self = Self(hashbrown::HashTable::new());
            fn get<T: ?Sized + Send + Sync + 'static>(
                &self,
                lazy_interned_lazy: LazyInternedLazy<T>,
                hash: u64,
            ) -> Option<&'static Interned<T>> {
                let &(_, v) = self.0.find(hash, |v| v.0 == lazy_interned_lazy.0.type_id)?;
                let Some(retval) = v.downcast_ref::<Interned<T>>() else {
                    unreachable!();
                };
                Some(retval)
            }
            fn get_or_insert<T: ?Sized + Send + Sync + 'static>(
                &mut self,
                lazy_interned_lazy: LazyInternedLazy<T>,
                hash: u64,
                v: &'static Interned<T>,
            ) -> &'static Interned<T> {
                let entry = self
                    .0
                    .entry(
                        hash,
                        |&(k, _)| k == lazy_interned_lazy.0.type_id,
                        |&(k, _)| type_map::TypeIdBuildHasher.hash_one(k),
                    )
                    .or_insert_with(|| (lazy_interned_lazy.0.type_id, v));
                let &(_, v) = entry.get();
                let Some(retval) = v.downcast_ref::<Interned<T>>() else {
                    unreachable!();
                };
                retval
            }
        }
        static GLOBAL_CACHE: RwLock<Map> = RwLock::new(Map::EMPTY);
        #[cold]
        fn insert_in_thread_local_cache<T: ?Sized + Send + Sync + 'static>(
            cache: &RefCell<Map>,
            this: LazyInternedLazy<T>,
            hash: u64,
        ) -> Interned<T> {
            let read_lock = GLOBAL_CACHE.read().unwrap();
            let v = read_lock.get(this, hash);
            drop(read_lock);
            let v = v.unwrap_or_else(|| {
                let v = Box::leak(Box::new((this.0.value)()));
                GLOBAL_CACHE.write().unwrap().get_or_insert(this, hash, v)
            });
            *cache.borrow_mut().get_or_insert(this, hash, v)
        }
        thread_local! {
            static THREAD_LOCAL_CACHE: RefCell<Map> = const { RefCell::new(Map::EMPTY) };
        }
        let hash = type_map::TypeIdBuildHasher.hash_one(self.0.type_id);
        THREAD_LOCAL_CACHE.with(|cache| {
            let borrow = cache.borrow();
            if let Some(v) = borrow.get(self, hash) {
                *v
            } else {
                drop(borrow);
                insert_in_thread_local_cache(cache, self, hash)
            }
        })
    }
}

impl<T: ?Sized + Send + Sync + 'static> Copy for LazyInternedLazy<T> {}

impl<T: ?Sized + Send + Sync + 'static> Clone for LazyInternedLazy<T> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<T: ?Sized + Send + Sync + 'static> Hash for LazyInternedLazy<T> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.0.hash(state);
    }
}

impl<T: ?Sized + Send + Sync + 'static> Eq for LazyInternedLazy<T> {}

impl<T: ?Sized + Send + Sync + 'static> PartialEq for LazyInternedLazy<T> {
    fn eq(&self, other: &Self) -> bool {
        self.0 == other.0
    }
}

pub enum LazyInterned<T: ?Sized + Send + Sync + 'static> {
    Interned(Interned<T>),
    Lazy(LazyInternedLazy<T>),
}

impl<T: ?Sized + Send + Sync + 'static> LazyInterned<T> {
    pub const fn new_const<V: Default + Into<Interned<T>>>() -> Self {
        Self::Lazy(LazyInternedLazy::new_const::<V>())
    }
    pub const fn new_const_default() -> Self
    where
        Interned<T>: Default,
    {
        Self::new_const::<Interned<T>>()
    }
    pub fn interned(self) -> Interned<T> {
        match self {
            Self::Interned(retval) => retval,
            Self::Lazy(retval) => retval.interned(),
        }
    }
}

impl<T: ?Sized + Sync + Send + 'static> Clone for LazyInterned<T> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<T: ?Sized + Sync + Send + 'static> Copy for LazyInterned<T> {}

impl<T: ?Sized + Sync + Send + 'static> Deref for LazyInterned<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        Interned::into_inner(self.interned())
    }
}

impl<T: ?Sized + Sync + Send + 'static> Eq for LazyInterned<T> where Interned<T>: Eq {}

impl<T: ?Sized + Sync + Send + 'static> PartialEq for LazyInterned<T>
where
    Interned<T>: PartialEq,
{
    fn eq(&self, other: &Self) -> bool {
        self.interned() == other.interned()
    }
}

impl<T: ?Sized + Sync + Send + 'static> Ord for LazyInterned<T>
where
    Interned<T>: Ord,
{
    fn cmp(&self, other: &Self) -> Ordering {
        self.interned().cmp(&other.interned())
    }
}

impl<T: ?Sized + Sync + Send + 'static> PartialOrd for LazyInterned<T>
where
    Interned<T>: PartialOrd,
{
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        self.interned().partial_cmp(&other.interned())
    }
}

impl<T: ?Sized + Sync + Send + 'static> Hash for LazyInterned<T>
where
    Interned<T>: Hash,
{
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.interned().hash(state);
    }
}

pub trait InternedCompare {
    type InternedCompareKey: Ord + Hash;
    fn interned_compare_key_ref(this: &Self) -> Self::InternedCompareKey;
}

/// Warning: doesn't do what you want with `T = dyn Trait`,
/// since it compares pointers, but pointers can be unequal due do
/// different copies of the same vtable
pub struct PtrEqWithMetadata<T: ?Sized>(pub *const T);

impl<T: ?Sized> Copy for PtrEqWithMetadata<T> {}

impl<T: ?Sized> Clone for PtrEqWithMetadata<T> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<T: ?Sized> PartialEq for PtrEqWithMetadata<T> {
    fn eq(&self, other: &Self) -> bool {
        std::ptr::eq(self.0, other.0)
    }
}

impl<T: ?Sized> Eq for PtrEqWithMetadata<T> {}

impl<T: ?Sized> PartialOrd for PtrEqWithMetadata<T> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl<T: ?Sized> Ord for PtrEqWithMetadata<T> {
    fn cmp(&self, other: &Self) -> Ordering {
        #[allow(ambiguous_wide_pointer_comparisons)]
        self.0.cmp(&other.0)
    }
}

impl<T: ?Sized> Hash for PtrEqWithMetadata<T> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.0.hash(state);
    }
}

impl<T: ?Sized> fmt::Debug for PtrEqWithMetadata<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("PtrEqWithMetadata").field(&self.0).finish()
    }
}

/// Warning: doesn't do what you want for `[T]` or `str`, since it ignores length
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
pub struct PtrEqWithTypeId(pub *const (), pub TypeId);

mod sealed {
    pub trait SupportsPtrEqWithTypeIdSealed {}
}

pub trait SupportsPtrEqWithTypeId: 'static + sealed::SupportsPtrEqWithTypeIdSealed {
    fn get_ptr_eq_with_type_id(&self) -> PtrEqWithTypeId;
}

impl<T: 'static> sealed::SupportsPtrEqWithTypeIdSealed for T {}

impl<T: 'static> SupportsPtrEqWithTypeId for T {
    fn get_ptr_eq_with_type_id(&self) -> PtrEqWithTypeId {
        PtrEqWithTypeId(self as *const Self as *const (), TypeId::of::<Self>())
    }
}

impl<T> InternedCompare for T {
    type InternedCompareKey = PtrEqWithMetadata<Self>;
    fn interned_compare_key_ref(this: &Self) -> Self::InternedCompareKey {
        PtrEqWithMetadata(this)
    }
}

impl<T> InternedCompare for [T] {
    type InternedCompareKey = PtrEqWithMetadata<Self>;
    fn interned_compare_key_ref(this: &Self) -> Self::InternedCompareKey {
        PtrEqWithMetadata(this)
    }
}

#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct BitSlicePtrEq(BitPtr, usize);

impl InternedCompare for BitSlice {
    type InternedCompareKey = BitSlicePtrEq;
    fn interned_compare_key_ref(this: &Self) -> Self::InternedCompareKey {
        BitSlicePtrEq(this.as_bitptr(), this.len())
    }
}

/// Safety: `as_bytes` and `from_bytes_unchecked` must return the same pointer as the input.
/// all values returned by `as_bytes` must be valid to pass to `from_bytes_unchecked`.
/// `into_bytes` must return the exact same thing as `as_bytes`.
/// `Interned<Self>` must contain the exact same references as `Interned<[u8]>`,
/// so they can be safely interconverted without needing re-interning.
unsafe trait InternStrLike: ToOwned {
    fn as_bytes(this: &Self) -> &[u8];
    fn into_bytes(this: Self::Owned) -> Vec<u8>;
    /// Safety: `bytes` must be a valid sequence of bytes for this type. All UTF-8 sequences are valid.
    unsafe fn from_bytes_unchecked(bytes: &[u8]) -> &Self;
}

macro_rules! impl_intern_str_like {
    ($ty:ty, owned = $Owned:ty) => {
        impl InternedCompare for $ty {
            type InternedCompareKey = PtrEqWithMetadata<[u8]>;
            fn interned_compare_key_ref(this: &Self) -> Self::InternedCompareKey {
                PtrEqWithMetadata(InternStrLike::as_bytes(this))
            }
        }
        impl Intern for $ty {
            fn intern(&self) -> Interned<Self> {
                Self::intern_cow(Cow::Borrowed(self))
            }
            fn intern_cow(this: Cow<'_, Self>) -> Interned<Self> {
                Interned::cast_unchecked(
                    <[u8]>::intern_cow(match this {
                        Cow::Borrowed(v) => Cow::Borrowed(<Self as InternStrLike>::as_bytes(v)),
                        Cow::Owned(v) => {
                            // verify $Owned is correct
                            let v: $Owned = v;
                            Cow::Owned(<Self as InternStrLike>::into_bytes(v))
                        }
                    }),
                    // Safety: guaranteed safe because we got the bytes from `as_bytes`/`into_bytes`
                    |v| unsafe { <Self as InternStrLike>::from_bytes_unchecked(v) },
                )
            }
        }
        impl Default for Interned<$ty> {
            fn default() -> Self {
                // Safety: safe because the empty sequence is valid UTF-8
                unsafe { <$ty as InternStrLike>::from_bytes_unchecked(&[]) }.intern()
            }
        }
        impl<'de> Deserialize<'de> for Interned<$ty> {
            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
            where
                D: serde::Deserializer<'de>,
            {
                Cow::<'de, $ty>::deserialize(deserializer).map(Intern::intern_cow)
            }
        }
        impl From<$Owned> for Interned<$ty> {
            fn from(v: $Owned) -> Self {
                v.intern_deref()
            }
        }
        impl From<Interned<$ty>> for $Owned {
            fn from(v: Interned<$ty>) -> Self {
                Interned::into_inner(v).into()
            }
        }
        impl From<Interned<$ty>> for Box<$ty> {
            fn from(v: Interned<$ty>) -> Self {
                Interned::into_inner(v).into()
            }
        }
    };
}

// Safety: satisfies `InternStrLike`'s requirements where the valid sequences for `from_bytes_unchecked` matches `str`
unsafe impl InternStrLike for str {
    fn as_bytes(this: &Self) -> &[u8] {
        this.as_bytes()
    }
    fn into_bytes(this: Self::Owned) -> Vec<u8> {
        this.into_bytes()
    }
    unsafe fn from_bytes_unchecked(bytes: &[u8]) -> &Self {
        // Safety: `bytes` is guaranteed UTF-8 by the caller
        unsafe { str::from_utf8_unchecked(bytes) }
    }
}

impl_intern_str_like!(str, owned = String);

// Safety: satisfies `InternStrLike`'s requirements where the valid sequences for `from_bytes_unchecked` matches `OsStr`
unsafe impl InternStrLike for OsStr {
    fn as_bytes(this: &Self) -> &[u8] {
        this.as_encoded_bytes()
    }
    fn into_bytes(this: Self::Owned) -> Vec<u8> {
        this.into_encoded_bytes()
    }
    unsafe fn from_bytes_unchecked(bytes: &[u8]) -> &Self {
        // Safety: `bytes` is guaranteed valid for `OsStr` by the caller
        unsafe { OsStr::from_encoded_bytes_unchecked(bytes) }
    }
}

impl_intern_str_like!(OsStr, owned = OsString);

// Safety: satisfies `InternStrLike`'s requirements where the valid sequences for `from_bytes_unchecked` matches `OsStr`
unsafe impl InternStrLike for Path {
    fn as_bytes(this: &Self) -> &[u8] {
        this.as_os_str().as_encoded_bytes()
    }
    fn into_bytes(this: Self::Owned) -> Vec<u8> {
        this.into_os_string().into_encoded_bytes()
    }
    unsafe fn from_bytes_unchecked(bytes: &[u8]) -> &Self {
        // Safety: `bytes` is guaranteed valid for `OsStr` by the caller
        unsafe { Path::new(OsStr::from_encoded_bytes_unchecked(bytes)) }
    }
}

impl_intern_str_like!(Path, owned = PathBuf);

impl Interned<str> {
    pub fn from_utf8(v: Interned<[u8]>) -> Result<Self, std::str::Utf8Error> {
        Interned::try_cast_unchecked(v, str::from_utf8)
    }
    pub fn as_interned_bytes(self) -> Interned<[u8]> {
        Interned::cast_unchecked(self, str::as_bytes)
    }
    pub fn as_interned_os_str(self) -> Interned<OsStr> {
        Interned::cast_unchecked(self, AsRef::as_ref)
    }
    pub fn as_interned_path(self) -> Interned<Path> {
        Interned::cast_unchecked(self, AsRef::as_ref)
    }
}

impl From<Interned<str>> for Interned<OsStr> {
    fn from(value: Interned<str>) -> Self {
        value.as_interned_os_str()
    }
}

impl From<Interned<str>> for Interned<Path> {
    fn from(value: Interned<str>) -> Self {
        value.as_interned_path()
    }
}

impl Interned<OsStr> {
    pub fn as_interned_encoded_bytes(self) -> Interned<[u8]> {
        Interned::cast_unchecked(self, OsStr::as_encoded_bytes)
    }
    pub fn to_interned_str(self) -> Option<Interned<str>> {
        Interned::try_cast_unchecked(self, |v| v.to_str().ok_or(())).ok()
    }
    pub fn display(self) -> std::ffi::os_str::Display<'static> {
        Self::into_inner(self).display()
    }
    pub fn as_interned_path(self) -> Interned<Path> {
        Interned::cast_unchecked(self, AsRef::as_ref)
    }
}

impl From<Interned<OsStr>> for Interned<Path> {
    fn from(value: Interned<OsStr>) -> Self {
        value.as_interned_path()
    }
}

impl Interned<Path> {
    pub fn as_interned_os_str(self) -> Interned<OsStr> {
        Interned::cast_unchecked(self, AsRef::as_ref)
    }
    pub fn to_interned_str(self) -> Option<Interned<str>> {
        Interned::try_cast_unchecked(self, |v| v.to_str().ok_or(())).ok()
    }
    pub fn display(self) -> std::path::Display<'static> {
        Self::into_inner(self).display()
    }
    pub fn interned_file_name(self) -> Option<Interned<OsStr>> {
        Some(self.file_name()?.intern())
    }
}

impl From<Interned<Path>> for Interned<OsStr> {
    fn from(value: Interned<Path>) -> Self {
        value.as_interned_os_str()
    }
}

pub trait InternSlice: Sized {
    type Element: 'static + Send + Sync + Clone + Hash + Eq;
    fn intern_slice(self) -> Interned<[Self::Element]>;
}

impl<T: 'static + Send + Sync + Clone + Hash + Eq> InternSlice for Box<[T]> {
    type Element = T;
    fn intern_slice(self) -> Interned<[Self::Element]> {
        self.into_vec().intern_slice()
    }
}

impl<T: 'static + Send + Sync + Clone + Hash + Eq> InternSlice for Vec<T> {
    type Element = T;
    fn intern_slice(self) -> Interned<[Self::Element]> {
        self.intern_deref()
    }
}

impl<T: 'static + Send + Sync + Clone + Hash + Eq> InternSlice for &'_ [T] {
    type Element = T;
    fn intern_slice(self) -> Interned<[Self::Element]> {
        self.intern()
    }
}

impl<T: 'static + Send + Sync + Clone + Hash + Eq> InternSlice for &'_ mut [T] {
    type Element = T;
    fn intern_slice(self) -> Interned<[Self::Element]> {
        self.intern()
    }
}

impl<T: 'static + Send + Sync + Clone + Hash + Eq, const N: usize> InternSlice for [T; N] {
    type Element = T;
    fn intern_slice(self) -> Interned<[Self::Element]> {
        (&self).intern_slice()
    }
}

impl<T: 'static + Send + Sync + Clone + Hash + Eq, const N: usize> InternSlice for Box<[T; N]> {
    type Element = T;
    fn intern_slice(self) -> Interned<[Self::Element]> {
        let this: Box<[T]> = self;
        this.intern_slice()
    }
}

impl<T: 'static + Send + Sync + Clone + Hash + Eq, const N: usize> InternSlice for &'_ [T; N] {
    type Element = T;
    fn intern_slice(self) -> Interned<[Self::Element]> {
        let this: &[T] = self;
        this.intern()
    }
}

impl<T: 'static + Send + Sync + Clone + Hash + Eq, const N: usize> InternSlice for &'_ mut [T; N] {
    type Element = T;
    fn intern_slice(self) -> Interned<[Self::Element]> {
        let this: &[T] = self;
        this.intern()
    }
}

pub trait Intern: Any + Send + Sync {
    fn intern(&self) -> Interned<Self>;
    fn intern_deref(self) -> Interned<Self::Target>
    where
        Self: Sized + Deref<Target: Intern + ToOwned<Owned = Self>>,
    {
        Self::Target::intern_owned(self)
    }
    fn intern_sized(self) -> Interned<Self>
    where
        Self: Clone,
    {
        Self::intern_owned(self)
    }
    fn intern_owned(this: <Self as ToOwned>::Owned) -> Interned<Self>
    where
        Self: ToOwned,
    {
        Self::intern_cow(Cow::Owned(this))
    }
    fn intern_cow(this: Cow<'_, Self>) -> Interned<Self>
    where
        Self: ToOwned,
    {
        this.intern()
    }
}

impl<T: ?Sized + Intern + ToOwned> From<Cow<'_, T>> for Interned<T> {
    fn from(value: Cow<'_, T>) -> Self {
        Intern::intern_cow(value)
    }
}

impl<T: ?Sized + Intern> From<&'_ T> for Interned<T> {
    fn from(value: &'_ T) -> Self {
        Intern::intern(value)
    }
}

impl<T: Intern + Clone> From<T> for Interned<T> {
    fn from(value: T) -> Self {
        Intern::intern_sized(value)
    }
}

impl<T: ?Sized + 'static + Send + Sync + ToOwned> From<Interned<T>> for Cow<'_, T> {
    fn from(value: Interned<T>) -> Self {
        Cow::Borrowed(Interned::into_inner(value))
    }
}

pub struct Interned<T: ?Sized + 'static + Send + Sync> {
    inner: &'static T,
}

macro_rules! forward_fmt_trait {
    ($Tr:ident) => {
        impl<T: ?Sized + Intern + fmt::$Tr> fmt::$Tr for LazyInterned<T> {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                T::fmt(&**self, f)
            }
        }

        impl<T: ?Sized + 'static + Send + Sync + fmt::$Tr> fmt::$Tr for Interned<T> {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                self.inner.fmt(f)
            }
        }
    };
}

forward_fmt_trait!(Debug);
forward_fmt_trait!(Display);
forward_fmt_trait!(LowerExp);
forward_fmt_trait!(LowerHex);
forward_fmt_trait!(Octal);
forward_fmt_trait!(Pointer);
forward_fmt_trait!(UpperExp);
forward_fmt_trait!(UpperHex);

impl<T: ?Sized + 'static + Send + Sync + AsRef<U>, U: ?Sized> AsRef<U> for Interned<T> {
    fn as_ref(&self) -> &U {
        T::as_ref(self)
    }
}

#[derive(Clone, Debug)]
pub struct InternedSliceIter<T: Clone + 'static + Send + Sync> {
    iter: std::iter::Cloned<std::slice::Iter<'static, T>>,
}

impl<T: Clone + 'static + Send + Sync> Default for InternedSliceIter<T> {
    fn default() -> Self {
        Self {
            iter: [].iter().cloned(),
        }
    }
}

impl<T: Clone + 'static + Send + Sync> Iterator for InternedSliceIter<T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        self.iter.next()
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }

    fn count(self) -> usize {
        self.iter.count()
    }

    fn last(mut self) -> Option<Self::Item> {
        self.next_back()
    }

    fn nth(&mut self, n: usize) -> Option<Self::Item> {
        self.iter.nth(n)
    }

    fn fold<B, F>(self, init: B, f: F) -> B
    where
        F: FnMut(B, Self::Item) -> B,
    {
        self.iter.fold(init, f)
    }
}

impl<T: Clone + 'static + Send + Sync> DoubleEndedIterator for InternedSliceIter<T> {
    fn next_back(&mut self) -> Option<Self::Item> {
        self.iter.next_back()
    }

    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
        self.iter.nth_back(n)
    }

    fn rfold<B, F>(self, init: B, f: F) -> B
    where
        F: FnMut(B, Self::Item) -> B,
    {
        self.iter.rfold(init, f)
    }
}

impl<T: Clone + 'static + Send + Sync> FusedIterator for InternedSliceIter<T> {}

impl<T: Clone + 'static + Send + Sync> ExactSizeIterator for InternedSliceIter<T> {}

impl<T: Clone + 'static + Send + Sync> IntoIterator for Interned<[T]> {
    type Item = T;
    type IntoIter = InternedSliceIter<T>;

    fn into_iter(self) -> Self::IntoIter {
        InternedSliceIter {
            iter: Interned::into_inner(self).iter().cloned(),
        }
    }
}

impl<'a, T: 'static + Send + Sync> IntoIterator for &'a Interned<[T]> {
    type Item = &'a T;
    type IntoIter = std::slice::Iter<'a, T>;

    fn into_iter(self) -> Self::IntoIter {
        self.inner.iter()
    }
}

impl<'a, T: 'static + Send + Sync> IntoIterator for &'a mut Interned<[T]> {
    type Item = &'a T;
    type IntoIter = std::slice::Iter<'a, T>;

    fn into_iter(self) -> Self::IntoIter {
        self.inner.iter()
    }
}

impl<I: Clone> FromIterator<I> for Interned<[I]>
where
    [I]: Intern,
{
    fn from_iter<T: IntoIterator<Item = I>>(iter: T) -> Self {
        Intern::intern_owned(Vec::from_iter(iter))
    }
}

impl<I> FromIterator<I> for Interned<str>
where
    String: FromIterator<I>,
{
    fn from_iter<T: IntoIterator<Item = I>>(iter: T) -> Self {
        String::from_iter(iter).intern_deref()
    }
}

impl<I> FromIterator<I> for Interned<Path>
where
    PathBuf: FromIterator<I>,
{
    fn from_iter<T: IntoIterator<Item = I>>(iter: T) -> Self {
        PathBuf::from_iter(iter).intern_deref()
    }
}

impl<I> FromIterator<I> for Interned<OsStr>
where
    OsString: FromIterator<I>,
{
    fn from_iter<T: IntoIterator<Item = I>>(iter: T) -> Self {
        OsString::from_iter(iter).intern_deref()
    }
}

impl From<Interned<str>> for clap::builder::Str {
    fn from(value: Interned<str>) -> Self {
        Interned::into_inner(value).into()
    }
}

impl From<Interned<str>> for clap::builder::OsStr {
    fn from(value: Interned<str>) -> Self {
        Interned::into_inner(value).into()
    }
}

impl From<Interned<str>> for clap::builder::StyledStr {
    fn from(value: Interned<str>) -> Self {
        Interned::into_inner(value).into()
    }
}

impl From<Interned<str>> for clap::Id {
    fn from(value: Interned<str>) -> Self {
        Interned::into_inner(value).into()
    }
}

impl<T: 'static + Clone + Send + Sync> From<Interned<[T]>> for Vec<T> {
    fn from(value: Interned<[T]>) -> Self {
        Vec::from(&*value)
    }
}

impl<T: 'static + Clone + Send + Sync> From<Interned<[T]>> for Box<[T]> {
    fn from(value: Interned<[T]>) -> Self {
        Box::from(&*value)
    }
}

impl<I> Default for Interned<[I]>
where
    [I]: Intern,
{
    fn default() -> Self {
        Intern::intern(&[])
    }
}

impl Default for Interned<BitSlice> {
    fn default() -> Self {
        <&BitSlice>::default().intern()
    }
}

impl<I: Clone + Default> Default for Interned<I>
where
    I: Intern,
{
    fn default() -> Self {
        I::default().intern()
    }
}

impl<T: ?Sized + 'static + Send + Sync> Interned<T> {
    pub fn cast_unchecked<U: ?Sized + 'static + Send + Sync>(
        this: Self,
        f: impl FnOnce(&'static T) -> &'static U,
    ) -> Interned<U> {
        Interned {
            inner: f(this.inner),
        }
    }
    pub fn try_cast_unchecked<U: ?Sized + 'static + Send + Sync, E>(
        this: Self,
        f: impl FnOnce(&'static T) -> Result<&'static U, E>,
    ) -> Result<Interned<U>, E> {
        Ok(Interned {
            inner: f(this.inner)?,
        })
    }
    pub fn into_inner(this: Self) -> &'static T {
        this.inner
    }
    pub fn get_ref(this: &Self) -> &&'static T {
        &this.inner
    }
}

impl<T: ?Sized + 'static + Send + Sync> Clone for Interned<T> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<T: ?Sized + 'static + Send + Sync> Copy for Interned<T> where &'static T: Copy {}

impl<T: ?Sized + 'static + Send + Sync> Deref for Interned<T>
where
    &'static T: Borrow<T>,
{
    type Target = T;

    fn deref(&self) -> &Self::Target {
        self.inner
    }
}

impl<T: ?Sized + 'static + Send + Sync + InternedCompare> PartialEq for Interned<T> {
    fn eq(&self, other: &Self) -> bool {
        T::interned_compare_key_ref(self.inner) == T::interned_compare_key_ref(other.inner)
    }
}

impl<T: ?Sized + 'static + Send + Sync + InternedCompare> Eq for Interned<T> {}

impl<T: ?Sized + 'static + Send + Sync + InternedCompare> PartialOrd for Interned<T> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl<T: ?Sized + 'static + Send + Sync + InternedCompare> Ord for Interned<T> {
    fn cmp(&self, other: &Self) -> Ordering {
        T::interned_compare_key_ref(self.inner).cmp(&T::interned_compare_key_ref(other.inner))
    }
}

impl<T: ?Sized + 'static + Send + Sync + InternedCompare> Hash for Interned<T> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        T::interned_compare_key_ref(self.inner).hash(state);
    }
}

impl<T: ?Sized + 'static + Send + Sync + Serialize> Serialize for Interned<T> {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        T::serialize(self, serializer)
    }
}

impl<'de, T: 'static + Send + Sync + Deserialize<'de> + Clone + Intern> Deserialize<'de>
    for Interned<T>
{
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        T::deserialize(deserializer).map(Intern::intern_sized)
    }
}

impl<'de, T: 'static + Send + Sync + Clone> Deserialize<'de> for Interned<[T]>
where
    [T]: Intern,
    Vec<T>: Deserialize<'de>,
{
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        Vec::<T>::deserialize(deserializer).map(Intern::intern_owned)
    }
}

impl<'de> Deserialize<'de> for Interned<BitSlice> {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        BitVec::deserialize(deserializer).map(Intern::intern_owned)
    }
}

impl<T: Clone + Send + Sync + 'static + Hash + Eq> Intern for T {
    fn intern(&self) -> Interned<Self> {
        Self::intern_cow(Cow::Borrowed(self))
    }

    fn intern_owned(this: <Self as ToOwned>::Owned) -> Interned<Self>
    where
        Self: ToOwned,
    {
        Self::intern_cow(Cow::Owned(this))
    }

    fn intern_cow(this: Cow<'_, Self>) -> Interned<Self>
    where
        Self: ToOwned,
    {
        interner::Interner::get().intern_sized(this)
    }
}

impl<T: Clone + Send + Sync + 'static + Hash + Eq> Intern for [T] {
    fn intern(&self) -> Interned<Self> {
        Self::intern_cow(Cow::Borrowed(self))
    }

    fn intern_owned(this: <Self as ToOwned>::Owned) -> Interned<Self>
    where
        Self: ToOwned,
    {
        Self::intern_cow(Cow::Owned(this))
    }

    fn intern_cow(this: Cow<'_, Self>) -> Interned<Self>
    where
        Self: ToOwned,
    {
        interner::Interner::get().intern_slice(this)
    }
}

impl Intern for BitSlice {
    fn intern(&self) -> Interned<Self> {
        Self::intern_cow(Cow::Borrowed(self))
    }

    fn intern_owned(this: <Self as ToOwned>::Owned) -> Interned<Self>
    where
        Self: ToOwned,
    {
        Self::intern_cow(Cow::Owned(this))
    }

    fn intern_cow(this: Cow<'_, Self>) -> Interned<Self>
    where
        Self: ToOwned,
    {
        interner::Interner::get().intern_bit_slice(this)
    }
}

pub trait MemoizeGeneric: 'static + Send + Sync + Hash + Eq + Copy {
    type InputRef<'a>: 'a + Send + Sync + Hash + Copy;
    type InputOwned: 'static + Send + Sync;
    type InputCow<'a>: 'a;
    type Output: 'static + Send + Sync + Clone;
    fn input_eq(a: Self::InputRef<'_>, b: Self::InputRef<'_>) -> bool;
    fn input_borrow(input: &Self::InputOwned) -> Self::InputRef<'_>;
    fn input_cow_into_owned(input: Self::InputCow<'_>) -> Self::InputOwned;
    fn input_cow_borrow<'a>(input: &'a Self::InputCow<'_>) -> Self::InputRef<'a>;
    fn input_cow_from_owned<'a>(input: Self::InputOwned) -> Self::InputCow<'a>;
    fn input_cow_from_ref(input: Self::InputRef<'_>) -> Self::InputCow<'_>;
    fn inner(self, input: Self::InputRef<'_>) -> Self::Output;
    fn get_cow(self, input: Self::InputCow<'_>) -> Self::Output {
        static TYPE_ID_MAP: TypeIdMap = TypeIdMap::new();
        thread_local! {
            static TYPE_ID_MAP_CACHE: TypeIdMap = const { TypeIdMap::new() };
        }
        let map: &RwLock<(
            DefaultBuildHasher,
            HashTable<(Self, Self::InputOwned, Self::Output)>,
        )> = TYPE_ID_MAP_CACHE.with(|cache| {
            cache.get_or_insert_with(|| {
                TYPE_ID_MAP.get_or_insert_with(|| Box::leak(Default::default()))
            })
        });
        fn hash_eq_key<'a, 'b, T: MemoizeGeneric>(
            this: &'a T,
            input: T::InputRef<'b>,
        ) -> (&'a T, T::InputRef<'b>) {
            (this, input)
        }
        fn hash_eq_key_eq<T: MemoizeGeneric>(
            key: (&T, T::InputRef<'_>),
            this: &T,
            input: T::InputRef<'_>,
        ) -> bool {
            let other = hash_eq_key(this, input);
            key.0 == other.0 && T::input_eq(key.1, other.1)
        }
        let key = hash_eq_key(&self, Self::input_cow_borrow(&input));
        let hash;
        {
            let read = map.read().unwrap();
            let (hasher, map) = &*read;
            hash = hasher.hash_one(key);
            if let Some((_, _, output)) = map.find(hash, |(this2, input2, _)| {
                hash_eq_key_eq(key, this2, Self::input_borrow(input2))
            }) {
                return output.clone();
            }
            drop(read);
        }
        // make sure to call inner while map isn't locked since inner may call get_cow again
        let output = self.inner(Self::input_cow_borrow(&input));
        let mut write = map.write().unwrap();
        let (hasher, map) = &mut *write;
        map.entry(
            hash,
            |(this2, input2, _)| hash_eq_key_eq(key, this2, Self::input_borrow(input2)),
            |(this2, input2, _)| hasher.hash_one(hash_eq_key(this2, Self::input_borrow(input2))),
        )
        .or_insert_with(|| (self, Self::input_cow_into_owned(input), output))
        .get()
        .2
        .clone()
    }
    fn get_owned(self, input: Self::InputOwned) -> Self::Output {
        self.get_cow(Self::input_cow_from_owned(input))
    }
    fn get(self, input: Self::InputRef<'_>) -> Self::Output {
        self.get_cow(Self::input_cow_from_ref(input))
    }
}

pub trait Memoize: 'static + Send + Sync + Hash + Eq + Copy {
    type Input: ?Sized + 'static + Send + Sync + ToOwned<Owned = Self::InputOwned> + Hash + Eq;
    type InputOwned: 'static + Send + Sync + Borrow<Self::Input>;
    type Output: 'static + Send + Sync + Clone;
    fn inner(self, input: &Self::Input) -> Self::Output;
    fn get_cow(self, input: Cow<'_, Self::Input>) -> Self::Output {
        #[derive(Hash, Eq, PartialEq, Copy, Clone)]
        struct MemoizeGenericWrapper<T: Memoize>(T);
        impl<T: Memoize> MemoizeGeneric for MemoizeGenericWrapper<T> {
            type InputRef<'a> = &'a T::Input;
            type InputOwned = T::InputOwned;
            type InputCow<'a> = Cow<'a, T::Input>;
            type Output = T::Output;

            fn input_borrow(input: &Self::InputOwned) -> Self::InputRef<'_> {
                input.borrow()
            }

            fn input_eq(a: Self::InputRef<'_>, b: Self::InputRef<'_>) -> bool {
                a == b
            }

            fn input_cow_into_owned(input: Self::InputCow<'_>) -> Self::InputOwned {
                input.into_owned()
            }

            fn input_cow_borrow<'a>(input: &'a Self::InputCow<'_>) -> Self::InputRef<'a> {
                &**input
            }

            fn input_cow_from_owned<'a>(input: Self::InputOwned) -> Self::InputCow<'a> {
                Cow::Owned(input)
            }

            fn input_cow_from_ref(input: Self::InputRef<'_>) -> Self::InputCow<'_> {
                Cow::Borrowed(input)
            }

            fn inner(self, input: Self::InputRef<'_>) -> Self::Output {
                self.0.inner(input)
            }
        }

        MemoizeGenericWrapper(self).get_cow(input)
    }
    fn get_owned(self, input: Self::InputOwned) -> Self::Output {
        self.get_cow(Cow::Owned(input))
    }
    fn get(self, input: &Self::Input) -> Self::Output {
        self.get_cow(Cow::Borrowed(input))
    }
}

/// like `once_cell::race::OnceBox` but for `Interned<T>` instead of `Box<T>`
pub struct OnceInterned<T: 'static + Send + Sync>(OnceRef<'static, T>);

impl<T: 'static + Send + Sync + fmt::Debug> fmt::Debug for OnceInterned<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("OnceInterned").field(&self.get()).finish()
    }
}

impl<T: 'static + Send + Sync> Default for OnceInterned<T> {
    fn default() -> Self {
        Self::new()
    }
}

impl<T: 'static + Send + Sync> OnceInterned<T> {
    pub const fn new() -> Self {
        Self(OnceRef::new())
    }
    pub fn set(&self, v: Interned<T>) -> Result<(), ()> {
        self.0.set(v.inner)
    }
    pub fn get(&self) -> Option<Interned<T>> {
        self.0.get().map(|inner| Interned { inner })
    }
    pub fn get_or_init<F: FnOnce() -> Interned<T>>(&self, f: F) -> Interned<T> {
        Interned {
            inner: self.0.get_or_init(|| f().inner),
        }
    }
}