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use super::BoneKind;

use core::ops::{Index, IndexMut};
use derive_more::From;
use stackvec::{error::IncompleteArrayError, TryCollect, TryFromIterator};
use std::collections::HashMap;
use std::iter::{Enumerate, Map};

/// Provides a map of `BoneKind` -> `T`. Every possible `BoneKind` must have a
/// corresponding value.
///
/// This is more efficient than a `HashMap`, because it is done without allocation
/// inline, and the `BoneKind`s don't need to be hashed.
///
/// # Example
///
/// ```
/// # use skeletal_model::bone::{BoneMap, BoneKind};
/// let mut m = BoneMap::default();
/// for b in BoneKind::iter() {
///     m[b] = format!("this is a {b:?}");
/// }
///
/// assert_eq!(m[BoneKind::Chest], format!("this is a {:?}", BoneKind::Chest))
/// ```
#[derive(Debug, Default, Clone, Copy, From, Eq, PartialEq)]
pub struct BoneMap<T>([T; BoneKind::num_types()]);
impl<T> BoneMap<T> {
	pub fn new(map: [T; BoneKind::num_types()]) -> Self {
		Self(map)
	}

	/// Gets an iterator over the (key, value) pairs of the `BoneMap`.
	///
	/// Iteration is guaranteed to start at [`BoneKind::root()`] but beyond that,
	/// iteration order is not guaranteed. However, iteration *is* exhaustive over
	/// the various kinds of bones.
	pub fn iter(&self) -> Iter<'_, T> {
		self.into_iter()
	}

	/// Gets a mutable iterator over the `(key, value)` pairs of the `BoneMap`.
	///
	/// See also: [`Self::iter()`]
	pub fn iter_mut(&mut self) -> IterMut<'_, T> {
		self.into_iter()
	}

	/// Applies a function to each element of the `BoneMap`, mapping it from `T` to `U`.
	pub fn map<U>(self, mut f: impl FnMut(BoneKind, T) -> U) -> BoneMap<U> {
		let it = self.into_iter().map(|(kind, item)| (kind, f(kind, item)));
		it.try_collect().unwrap()
	}
}

// ---- Type conversion stuff ----
impl<T> TryFrom<HashMap<BoneKind, T>> for BoneMap<T> {
	type Error = IncompleteArrayError;

	fn try_from(other: HashMap<BoneKind, T>) -> Result<Self, Self::Error> {
		other.into_iter().try_collect()
	}
}

impl<T> TryFromIterator<(BoneKind, T)> for BoneMap<T> {
	type Error = IncompleteArrayError;

	fn try_from_iter<I>(iter: I) -> Result<Self, Self::Error>
	where
		I: IntoIterator<Item = (BoneKind, T)>,
	{
		let mut bmap: BoneMap<Option<T>> = BoneMap::default();
		for (kind, item) in iter.into_iter().take(BoneKind::NUM_TYPES) {
			bmap[kind] = Some(item);
		}
		if bmap.iter().any(|(_kind, item)| item.is_none()) {
			return Err(IncompleteArrayError);
		}
		Ok(BoneMap::new(bmap.0.map(|item| item.unwrap())))
	}
}

// ---- Index stuff ----
impl<T> Index<BoneKind> for BoneMap<T> {
	type Output = T;

	fn index(&self, index: BoneKind) -> &Self::Output {
		// I *could* do get_unchecked, but meh, why introduce more unsafe. Maybe the
		// compiler will optimize it.
		&self.0[usize::from(index)]
	}
}
impl<T> IndexMut<BoneKind> for BoneMap<T> {
	fn index_mut(&mut self, index: BoneKind) -> &mut Self::Output {
		&mut self.0[usize::from(index)]
	}
}

// ---- Iterator stuff ----

type MapIdxFnType<T> = fn((usize, T)) -> (BoneKind, T);

pub type Iter<'a, T> = Map<Enumerate<std::slice::Iter<'a, T>>, MapIdxFnType<&'a T>>;

pub type IterMut<'a, T> =
	Map<Enumerate<std::slice::IterMut<'a, T>>, MapIdxFnType<&'a mut T>>;

pub type IntoIter<T> =
	Map<Enumerate<std::array::IntoIter<T, { BoneKind::NUM_TYPES }>>, MapIdxFnType<T>>;

impl<T> IntoIterator for BoneMap<T> {
	type Item = (BoneKind, T);

	type IntoIter = IntoIter<T>;

	fn into_iter(self) -> Self::IntoIter {
		self.0.into_iter().enumerate().map(map_idx)
	}
}

impl<'a, T> IntoIterator for &'a BoneMap<T> {
	type Item = (BoneKind, &'a T);

	type IntoIter = Iter<'a, T>;

	fn into_iter(self) -> Self::IntoIter {
		self.0.iter().enumerate().map(map_idx)
	}
}

impl<'a, T> IntoIterator for &'a mut BoneMap<T> {
	type Item = (BoneKind, &'a mut T);

	type IntoIter = IterMut<'a, T>;

	fn into_iter(self) -> Self::IntoIter {
		self.0.iter_mut().enumerate().map(map_idx)
	}
}

fn map_idx<T>(item: (usize, T)) -> (BoneKind, T) {
	(BoneKind::try_from(item.0).unwrap(), item.1)
}

#[cfg(test)]
mod tests {
	use super::*;

	#[test]
	fn test_default() {
		let zeros = BoneMap::new([0u8; BoneKind::NUM_TYPES]);
		let ones = BoneMap::new([1u8; BoneKind::NUM_TYPES]);
		assert_eq!(zeros, BoneMap::default());
		assert_ne!(ones, BoneMap::default());

		#[derive(Copy, Clone, Eq, PartialEq, Debug)]
		struct Foo;
		let nones: BoneMap<Option<Foo>> = BoneMap::new([None; BoneKind::NUM_TYPES]);
		assert_eq!(nones, BoneMap::default())
	}

	#[test]
	fn test_map() {
		let zeros = BoneMap::new([0u8; BoneKind::NUM_TYPES]);

		let as_u8 = zeros.map(|kind, _| kind as u8);
		for (kind, _) in zeros.iter() {
			assert_eq!(kind as u8, as_u8[kind]);
		}
	}
}