use std::borrow::Borrow;
use std::cmp::Ordering;
use std::iter::FromIterator;
use std::mem;
use std::ops::{RangeBounds, Bound, Index, IndexMut};

/// `SortedMap` is a data structure with similar characteristics as BTreeMap but
/// slightly different trade-offs: lookup, insertion, and removal are O(log(N))
/// and elements can be iterated in order cheaply.
///
/// `SortedMap` can be faster than a `BTreeMap` for small sizes (<50) since it
/// stores data in a more compact way. It also supports accessing contiguous
/// ranges of elements as a slice, and slices of already sorted elements can be
/// inserted efficiently.
#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Default, Debug, RustcEncodable,
         RustcDecodable)]
pub struct SortedMap<K: Ord, V> {
    data: Vec<(K, V)>
}

impl<K: Ord, V> SortedMap<K, V> {
    #[inline]
    pub fn new() -> SortedMap<K, V> {
        SortedMap {
            data: vec![]
        }
    }

    /// Construct a `SortedMap` from a presorted set of elements. This is faster
    /// than creating an empty map and then inserting the elements individually.
    ///
    /// It is up to the caller to make sure that the elements are sorted by key
    /// and that there are no duplicates.
    #[inline]
    pub fn from_presorted_elements(elements: Vec<(K, V)>) -> SortedMap<K, V>
    {
        debug_assert!(elements.windows(2).all(|w| w[0].0 < w[1].0));

        SortedMap {
            data: elements
        }
    }

    #[inline]
    pub fn insert(&mut self, key: K, mut value: V) -> Option<V> {
        match self.lookup_index_for(&key) {
            Ok(index) => {
                let slot = unsafe {
                    self.data.get_unchecked_mut(index)
                };
                mem::swap(&mut slot.1, &mut value);
                Some(value)
            }
            Err(index) => {
                self.data.insert(index, (key, value));
                None
            }
        }
    }

    #[inline]
    pub fn remove(&mut self, key: &K) -> Option<V> {
        match self.lookup_index_for(key) {
            Ok(index) => {
                Some(self.data.remove(index).1)
            }
            Err(_) => {
                None
            }
        }
    }

    #[inline]
    pub fn get<Q>(&self, key: &Q) -> Option<&V>
        where K: Borrow<Q>,
              Q: Ord + ?Sized
    {
        match self.lookup_index_for(key) {
            Ok(index) => {
                unsafe {
                    Some(&self.data.get_unchecked(index).1)
                }
            }
            Err(_) => {
                None
            }
        }
    }

    #[inline]
    pub fn get_mut<Q>(&mut self, key: &Q) -> Option<&mut V>
        where K: Borrow<Q>,
              Q: Ord + ?Sized
    {
        match self.lookup_index_for(key) {
            Ok(index) => {
                unsafe {
                    Some(&mut self.data.get_unchecked_mut(index).1)
                }
            }
            Err(_) => {
                None
            }
        }
    }

    #[inline]
    pub fn clear(&mut self) {
        self.data.clear();
    }

    /// Iterate over elements, sorted by key
    #[inline]
    pub fn iter(&self) -> ::std::slice::Iter<'_, (K, V)> {
        self.data.iter()
    }

    /// Iterate over the keys, sorted
    #[inline]
    pub fn keys(&self) -> impl Iterator<Item = &K> + ExactSizeIterator {
        self.data.iter().map(|&(ref k, _)| k)
    }

    /// Iterate over values, sorted by key
    #[inline]
    pub fn values(&self) -> impl Iterator<Item = &V> + ExactSizeIterator {
        self.data.iter().map(|&(_, ref v)| v)
    }

    #[inline]
    pub fn len(&self) -> usize {
        self.data.len()
    }

    #[inline]
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    #[inline]
    pub fn range<R>(&self, range: R) -> &[(K, V)]
        where R: RangeBounds<K>
    {
        let (start, end) = self.range_slice_indices(range);
        (&self.data[start .. end])
    }

    #[inline]
    pub fn remove_range<R>(&mut self, range: R)
        where R: RangeBounds<K>
    {
        let (start, end) = self.range_slice_indices(range);
        self.data.splice(start .. end, ::std::iter::empty());
    }

    /// Mutate all keys with the given function `f`. This mutation must not
    /// change the sort-order of keys.
    #[inline]
    pub fn offset_keys<F>(&mut self, f: F)
        where F: Fn(&mut K)
    {
        self.data.iter_mut().map(|&mut (ref mut k, _)| k).for_each(f);
    }

    /// Inserts a presorted range of elements into the map. If the range can be
    /// inserted as a whole in between to existing elements of the map, this
    /// will be faster than inserting the elements individually.
    ///
    /// It is up to the caller to make sure that the elements are sorted by key
    /// and that there are no duplicates.
    #[inline]
    pub fn insert_presorted(&mut self, mut elements: Vec<(K, V)>) {
        if elements.is_empty() {
            return
        }

        debug_assert!(elements.windows(2).all(|w| w[0].0 < w[1].0));

        let start_index = self.lookup_index_for(&elements[0].0);

        let drain = match start_index {
            Ok(index) => {
                let mut drain = elements.drain(..);
                self.data[index] = drain.next().unwrap();
                drain
            }
            Err(index) => {
                if index == self.data.len() ||
                   elements.last().unwrap().0 < self.data[index].0 {
                    // We can copy the whole range without having to mix with
                    // existing elements.
                    self.data.splice(index .. index, elements.drain(..));
                    return
                }

                let mut drain = elements.drain(..);
                self.data.insert(index, drain.next().unwrap());
                drain
            }
        };

        // Insert the rest
        for (k, v) in drain {
            self.insert(k, v);
        }
    }

    /// Looks up the key in `self.data` via `slice::binary_search()`.
    #[inline(always)]
    fn lookup_index_for<Q>(&self, key: &Q) -> Result<usize, usize>
        where K: Borrow<Q>,
              Q: Ord + ?Sized
    {
        self.data.binary_search_by(|&(ref x, _)| x.borrow().cmp(key))
    }

    #[inline]
    fn range_slice_indices<R>(&self, range: R) -> (usize, usize)
        where R: RangeBounds<K>
    {
        let start = match range.start_bound() {
            Bound::Included(ref k) => {
                match self.lookup_index_for(k) {
                    Ok(index) | Err(index) => index
                }
            }
            Bound::Excluded(ref k) => {
                match self.lookup_index_for(k) {
                    Ok(index) => index + 1,
                    Err(index) => index,
                }
            }
            Bound::Unbounded => 0,
        };

        let end = match range.end_bound() {
            Bound::Included(ref k) => {
                match self.lookup_index_for(k) {
                    Ok(index) => index + 1,
                    Err(index) => index,
                }
            }
            Bound::Excluded(ref k) => {
                match self.lookup_index_for(k) {
                    Ok(index) | Err(index) => index,
                }
            }
            Bound::Unbounded => self.data.len(),
        };

        (start, end)
    }

    #[inline]
    pub fn contains_key<Q>(&self, key: &Q) -> bool
        where K: Borrow<Q>,
              Q: Ord + ?Sized
    {
        self.get(key).is_some()
    }
}

impl<K: Ord, V> IntoIterator for SortedMap<K, V> {
    type Item = (K, V);
    type IntoIter = ::std::vec::IntoIter<(K, V)>;

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

impl<'a, K, Q, V> Index<&'a Q> for SortedMap<K, V>
    where K: Ord + Borrow<Q>,
          Q: Ord + ?Sized
{
    type Output = V;

    fn index(&self, key: &Q) -> &Self::Output {
        self.get(key).expect("no entry found for key")
    }
}

impl<'a, K, Q, V> IndexMut<&'a Q> for SortedMap<K, V>
    where K: Ord + Borrow<Q>,
          Q: Ord + ?Sized
{
    fn index_mut(&mut self, key: &Q) -> &mut Self::Output {
        self.get_mut(key).expect("no entry found for key")
    }
}

impl<K: Ord, V> FromIterator<(K, V)> for SortedMap<K, V> {
    fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> Self {
        let mut data: Vec<(K, V)> = iter.into_iter().collect();

        data.sort_unstable_by(|&(ref k1, _), &(ref k2, _)| k1.cmp(k2));
        data.dedup_by(|&mut (ref k1, _), &mut (ref k2, _)| {
            k1.cmp(k2) == Ordering::Equal
        });

        SortedMap {
            data
        }
    }
}

#[cfg(test)]
mod tests;