use EnumMap;
use Internal;

use core::iter::Enumerate;
use core::marker::PhantomData;
use core::mem::ManuallyDrop;
use core::ptr;
use core::slice;

/// Immutable enum map iterator
///
/// This struct is created by `iter` method or `into_iter` on a reference
/// to `EnumMap`.
///
/// # Examples
///
/// ```
/// #[macro_use]
/// extern crate enum_map;
///
/// #[derive(EnumMap)]
/// enum Example {
///     A,
///     B,
///     C,
/// }
///
/// fn main() {
///     let mut map = enum_map! { Example::A => 3, _ => 0 };
///     assert_eq!(map[Example::A], 3);
///     for (key, &value) in &map {
///         assert_eq!(value, match key {
///             Example::A => 3,
///             _ => 0,
///         });
///     }
/// }
/// ```
#[derive(Debug)]
pub struct Iter<'a, K, V: 'a> {
    _phantom: PhantomData<fn() -> K>,
    iterator: Enumerate<slice::Iter<'a, V>>,
}

impl<'a, K: Internal<V>, V> Iterator for Iter<'a, K, V> {
    type Item = (K, &'a V);
    fn next(&mut self) -> Option<Self::Item> {
        self.iterator
            .next()
            .map(|(index, item)| (K::from_usize(index), item))
    }

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

impl<'a, K: Internal<V>, V> DoubleEndedIterator for Iter<'a, K, V> {
    fn next_back(&mut self) -> Option<Self::Item> {
        self.iterator
            .next_back()
            .map(|(index, item)| (K::from_usize(index), item))
    }
}

impl<'a, K: Internal<V>, V> ExactSizeIterator for Iter<'a, K, V> {}

impl<'a, K: Internal<V>, V> IntoIterator for &'a EnumMap<K, V> {
    type Item = (K, &'a V);
    type IntoIter = Iter<'a, K, V>;
    fn into_iter(self) -> Self::IntoIter {
        Iter {
            _phantom: PhantomData,
            iterator: self.as_slice().iter().enumerate(),
        }
    }
}

/// Mutable map iterator
///
/// This struct is created by `iter_mut` method or `into_iter` on a mutable
/// reference to `EnumMap`.
///
/// # Examples
///
/// ```
/// #[macro_use]
/// extern crate enum_map;
///
/// #[derive(Debug, EnumMap)]
/// enum Example {
///     A,
///     B,
///     C,
/// }
///
/// fn main() {
///     let mut map = enum_map! { Example::A => 3, _ => 0 };
///     for (_, value) in &mut map {
///         *value += 1;
///     }
///     assert_eq!(map, enum_map! { Example::A => 4, _ => 1 });
/// }
/// ```
#[derive(Debug)]
pub struct IterMut<'a, K, V: 'a> {
    _phantom: PhantomData<fn() -> K>,
    iterator: Enumerate<slice::IterMut<'a, V>>,
}

impl<'a, K: Internal<V>, V> Iterator for IterMut<'a, K, V> {
    type Item = (K, &'a mut V);
    fn next(&mut self) -> Option<Self::Item> {
        self.iterator
            .next()
            .map(|(index, item)| (K::from_usize(index), item))
    }

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

impl<'a, K: Internal<V>, V> DoubleEndedIterator for IterMut<'a, K, V> {
    fn next_back(&mut self) -> Option<Self::Item> {
        self.iterator
            .next_back()
            .map(|(index, item)| (K::from_usize(index), item))
    }
}

impl<'a, K: Internal<V>, V> ExactSizeIterator for IterMut<'a, K, V> {}

impl<'a, K: Internal<V>, V> IntoIterator for &'a mut EnumMap<K, V> {
    type Item = (K, &'a mut V);
    type IntoIter = IterMut<'a, K, V>;
    fn into_iter(self) -> Self::IntoIter {
        IterMut {
            _phantom: PhantomData,
            iterator: self.as_mut_slice().iter_mut().enumerate(),
        }
    }
}

/// A map iterator that moves out of map.
///
/// This struct is created by `into_iter` on `EnumMap`.
///
/// # Examples
///
/// ```
/// #[macro_use]
/// extern crate enum_map;
///
/// #[derive(Debug, EnumMap)]
/// enum Example {
///     A,
///     B,
/// }
///
/// fn main() {
///     let map = enum_map! { Example::A | Example::B => String::from("123") };
///     for (_, value) in map {
///         assert_eq!(value + "4", "1234");
///     }
/// }
/// ```
pub struct IntoIter<K: Internal<V>, V> {
    map: ManuallyDrop<EnumMap<K, V>>,
    position: usize,
}

impl<K: Internal<V>, V> Iterator for IntoIter<K, V> {
    type Item = (K, V);
    fn next(&mut self) -> Option<(K, V)> {
        let slice = self.map.as_slice();
        if self.position < slice.len() {
            let key = K::from_usize(self.position);
            let result = Some((key, unsafe { ptr::read(&slice[self.position]) }));
            self.position += 1;
            result
        } else {
            None
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let slice = self.map.as_slice();
        let diff = slice.len() - self.position;
        (diff, Some(diff))
    }
}

impl<K: Internal<V>, V> ExactSizeIterator for IntoIter<K, V> {}

impl<K: Internal<V>, V> Drop for IntoIter<K, V> {
    fn drop(&mut self) {
        for _item in self {}
    }
}

impl<K: Internal<V>, V> IntoIterator for EnumMap<K, V> {
    type Item = (K, V);
    type IntoIter = IntoIter<K, V>;
    fn into_iter(self) -> Self::IntoIter {
        IntoIter {
            map: ManuallyDrop::new(self),
            position: 0,
        }
    }
}