//! Trivially-copyable, easily comparable typed [indices](MapIndex),
//! and an [IndexMap] to contain them.
//!
//! # Examples
//!
//! ```rust
//! # use cl_structures::index_map::*;
//! // first, create a new MapIndex type (this ensures type safety)
//! make_index! {
//!     Number
//! }
//!
//! // then, create a map with that type
//! let mut numbers: IndexMap<Number, i32> = IndexMap::new();
//! let first = numbers.insert(1);
//! let second = numbers.insert(2);
//! let third = numbers.insert(3);
//!
//! // You can access elements immutably with `get`
//! assert_eq!(Some(&3), numbers.get(third));
//! assert_eq!(Some(&2), numbers.get(second));
//! // or by indexing
//! assert_eq!(1, numbers[first]);
//!
//! // Or mutably
//! *numbers.get_mut(first).unwrap() = 100000;
//!
//! assert_eq!(Some(&100000), numbers.get(first));
//! ```

/// Creates newtype indices over [`usize`] for use as [IndexMap] keys.
///
/// Generated key types implement [Clone], [Copy],
/// [Debug](core::fmt::Debug), [PartialEq], [Eq], [PartialOrd], [Ord], [Hash](core::hash::Hash),
/// and [MapIndex].
#[macro_export]
macro_rules! make_index {($($(#[$meta:meta])* $name:ident),*$(,)?) => {$(
    $(#[$meta])*
    #[repr(transparent)]
    #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
    pub struct $name(usize);

    impl $crate::index_map::MapIndex for $name {
        #[doc = concat!("Constructs a [`", stringify!($name), "`] from a [`usize`] without checking bounds.\n")]
        /// The provided value should be within the bounds of its associated container
        #[inline]
        fn from_usize(value: usize) -> Self {
            Self(value)
        }
        #[inline]
        fn get(&self) -> usize {
            self.0
        }
    }

    impl From< $name > for usize {
        fn from(value: $name) -> Self {
            value.0
        }
    }
)*}}

use self::iter::MapIndexIter;
use core::slice::GetManyMutError;
use std::ops::{Index, IndexMut};

pub use make_index;

/// An index into a [IndexMap]. For full type-safety,
/// there should be a unique [MapIndex] for each [IndexMap].
pub trait MapIndex: std::fmt::Debug {
    /// Constructs an [`MapIndex`] from a [`usize`] without checking bounds.
    ///
    /// The provided value should be within the bounds of its associated container.
    fn from_usize(value: usize) -> Self;
    /// Gets the index of the [`MapIndex`] by value
    fn get(&self) -> usize;
}

/// It's an array. Lmao.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct IndexMap<K: MapIndex, V> {
    map: Vec<V>,
    id_type: std::marker::PhantomData<K>,
}

impl<V, K: MapIndex> IndexMap<K, V> {
    /// Constructs an empty IndexMap.
    pub fn new() -> Self {
        Self::default()
    }

    /// Gets a reference to the value in slot `index`.
    pub fn get(&self, index: K) -> Option<&V> {
        self.map.get(index.get())
    }

    /// Gets a mutable reference to the value in slot `index`.
    pub fn get_mut(&mut self, index: K) -> Option<&mut V> {
        self.map.get_mut(index.get())
    }

    /// Returns mutable references to many indices at once.
    ///
    /// Returns an error if any index is out of bounds, or if the same index was passed twice.
    pub fn get_many_mut<const N: usize>(
        &mut self,
        indices: [K; N],
    ) -> Result<[&mut V; N], GetManyMutError> {
        self.map.get_many_mut(indices.map(|id| id.get()))
    }

    /// Returns an iterator over the IndexMap.
    pub fn values(&self) -> impl Iterator<Item = &V> {
        self.map.iter()
    }

    /// Returns an iterator that allows modifying each value.
    pub fn values_mut(&mut self) -> impl Iterator<Item = &mut V> {
        self.map.iter_mut()
    }

    /// Returns an iterator over all keys in the IndexMap.
    pub fn keys(&self) -> iter::MapIndexIter<K> {
        // Safety: IndexMap currently has map.len() entries, and data cannot be removed
        MapIndexIter::new(0..self.map.len())
    }

    /// Constructs an [ID](MapIndex) from a [usize], if it's within bounds
    #[doc(hidden)]
    pub fn try_key_from(&self, value: usize) -> Option<K> {
        (value < self.map.len()).then(|| K::from_usize(value))
    }

    /// Inserts a new item into the IndexMap, returning the key associated with it.
    pub fn insert(&mut self, value: V) -> K {
        let id = self.map.len();
        self.map.push(value);

        // Safety: value was pushed to `self.map[id]`
        K::from_usize(id)
    }

    /// Replaces a value in the IndexMap, returning the old value.
    pub fn replace(&mut self, key: K, value: V) -> V {
        std::mem::replace(&mut self[key], value)
    }
}

impl<K: MapIndex, V> Default for IndexMap<K, V> {
    fn default() -> Self {
        Self { map: vec![], id_type: std::marker::PhantomData }
    }
}

impl<K: MapIndex, V> Index<K> for IndexMap<K, V> {
    type Output = V;

    fn index(&self, index: K) -> &Self::Output {
        match self.map.get(index.get()) {
            None => panic!("Index {:?} out of bounds in IndexMap!", index),
            Some(value) => value,
        }
    }
}

impl<K: MapIndex, V> IndexMut<K> for IndexMap<K, V> {
    fn index_mut(&mut self, index: K) -> &mut Self::Output {
        match self.map.get_mut(index.get()) {
            None => panic!("Index {:?} out of bounds in IndexMap!", index),
            Some(value) => value,
        }
    }
}

mod iter {
    //! Iterators for [IndexMap](super::IndexMap)
    use super::MapIndex;
    use std::{marker::PhantomData, ops::Range};

    /// Iterates over the keys of an [IndexMap](super::IndexMap), independently of the map.
    ///
    /// This is guaranteed to never overrun the length of the map, but is *NOT* guaranteed
    /// to iterate over all elements of the map if the map is extended during iteration.
    #[derive(Clone, Debug, PartialEq, Eq, Hash)]
    pub struct MapIndexIter<K: MapIndex> {
        range: Range<usize>,
        _id: PhantomData<K>,
    }

    impl<K: MapIndex> MapIndexIter<K> {
        /// Creates a new [MapIndexIter] producing the given [MapIndex]
        pub(super) fn new(range: Range<usize>) -> Self {
            Self { range, _id: PhantomData }
        }
    }

    impl<ID: MapIndex> Iterator for MapIndexIter<ID> {
        type Item = ID;

        fn next(&mut self) -> Option<Self::Item> {
            Some(ID::from_usize(self.range.next()?))
        }
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.range.size_hint()
        }
    }

    impl<ID: MapIndex> DoubleEndedIterator for MapIndexIter<ID> {
        fn next_back(&mut self) -> Option<Self::Item> {
            // Safety: see above
            Some(ID::from_usize(self.range.next_back()?))
        }
    }

    impl<ID: MapIndex> ExactSizeIterator for MapIndexIter<ID> {}
}