use crate::keys::*;
use crate::{SubTrie, SubTrieMut, BRANCH_FACTOR};
use std::borrow::Borrow;
use std::default::Default;

use nibble_vec::Nibblet;

#[derive(Debug, Clone)]
pub struct TrieNode<K, V> {
    /// Key fragments/bits associated with this node, such that joining the keys from all
    /// parent nodes and this node is equal to the bit-encoding of this node's key.
    pub key: Nibblet,

    /// The key and value stored at this node.
    pub key_value: Option<Box<KeyValue<K, V>>>,

    /// The number of children which are Some rather than None.
    pub child_count: usize,

    /// The children of this node stored such that the first nibble of each child key
    /// dictates the child's bucket.
    pub children: [Option<Box<TrieNode<K, V>>>; BRANCH_FACTOR],
}

#[derive(Debug, Clone)]
pub struct KeyValue<K, V> {
    pub key: K,
    pub value: V,
}

impl<K, V> TrieNode<K, V>
where
    K: TrieKey,
{
    /// Create a value-less, child-less TrieNode.
    #[inline]
    pub fn new() -> TrieNode<K, V> {
        TrieNode {
            key: Nibblet::new(),
            key_value: None,
            children: Default::default(),
            child_count: 0,
        }
    }

    /// Create a TrieNode with no children.
    #[inline]
    pub fn with_key_value(key_fragments: Nibblet, key: K, value: V) -> TrieNode<K, V> {
        TrieNode {
            key: key_fragments,
            key_value: Some(Box::new(KeyValue {
                key: key,
                value: value,
            })),
            children: Default::default(),
            child_count: 0,
        }
    }

    /// Get the key stored at this node, if any.
    #[inline]
    pub fn key(&self) -> Option<&K> {
        self.key_value.as_ref().map(|kv| &kv.key)
    }

    /// Get the value stored at this node, if any.
    #[inline]
    pub fn value(&self) -> Option<&V> {
        self.key_value.as_ref().map(|kv| &kv.value)
    }

    /// Get a mutable reference to the value stored at this node, if any.
    #[inline]
    pub fn value_mut(&mut self) -> Option<&mut V> {
        self.key_value.as_mut().map(|kv| &mut kv.value)
    }

    /// Get the value whilst checking a key match.
    ///
    /// The key may be any borrowed form of the trie's key type, but TrieKey on the borrowed
    /// form *must* match those for the key type.
    #[inline]
    pub fn value_checked<Q: ?Sized>(&self, key: &Q) -> Option<&V>
    where
        K: Borrow<Q>,
        Q: TrieKey,
    {
        self.key_value.as_ref().map(|kv| {
            check_keys(kv.key.borrow(), key);
            &kv.value
        })
    }

    /// Get a mutable value whilst checking a key match.
    ///
    /// The key may be any borrowed form of the trie's key type, but TrieKey on the borrowed
    /// form *must* match those for the key type.
    #[inline]
    pub fn value_checked_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut V>
    where
        K: Borrow<Q>,
        Q: TrieKey,
    {
        self.key_value.as_mut().map(|kv| {
            check_keys(kv.key.borrow(), key);
            &mut kv.value
        })
    }

    /// Compute the number of keys and values in this node's subtrie.
    #[inline]
    pub fn compute_size(&self) -> usize {
        let mut size = self.key_value.is_some() as usize;

        for child in &self.children {
            if let Some(ref child) = *child {
                // TODO: could unroll this recursion
                size += child.compute_size();
            }
        }

        size
    }

    /// Add a child at the given index, given that none exists there already.
    #[inline]
    pub fn add_child(&mut self, idx: usize, node: Box<TrieNode<K, V>>) {
        debug_assert!(self.children[idx].is_none());
        self.child_count += 1;
        self.children[idx] = Some(node);
    }

    /// Remove a child at the given index, if it exists.
    #[inline]
    pub fn take_child(&mut self, idx: usize) -> Option<Box<TrieNode<K, V>>> {
        self.children[idx].take().map(|node| {
            self.child_count -= 1;
            node
        })
    }

    /// Helper function for removing the single child of a node.
    #[inline]
    pub fn take_only_child(&mut self) -> Box<TrieNode<K, V>> {
        debug_assert_eq!(self.child_count, 1);
        for i in 0..BRANCH_FACTOR {
            if let Some(child) = self.take_child(i) {
                return child;
            }
        }
        unreachable!("node with child_count 1 has no actual children");
    }

    /// Set the key and value of a node, given that it currently lacks one.
    #[inline]
    pub fn add_key_value(&mut self, key: K, value: V) {
        debug_assert!(self.key_value.is_none());
        self.key_value = Some(Box::new(KeyValue { key, value }));
    }

    /// Move the value out of a node, whilst checking that its key is as expected.
    /// Can panic (see check_keys).
    ///
    /// The key may be any borrowed form of the trie's key type, but TrieKey on the borrowed
    /// form *must* match those for the key type
    #[inline]
    pub fn take_value<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
    where
        K: Borrow<Q>,
        Q: TrieKey,
    {
        self.key_value.take().map(|kv| {
            check_keys(kv.key.borrow(), key);
            kv.value
        })
    }

    /// Replace a value, returning the previous value if there was one.
    #[inline]
    pub fn replace_value(&mut self, key: K, value: V) -> Option<V> {
        // TODO: optimise this?
        let previous = self.take_value(&key);
        self.add_key_value(key, value);
        previous
    }

    /// Get a reference to this node if it has a value.
    #[inline]
    pub fn as_value_node(&self) -> Option<&TrieNode<K, V>> {
        self.key_value.as_ref().map(|_| self)
    }

    /// Split a node at a given index in its key, transforming it into a prefix node of its
    /// previous self.
    #[inline]
    pub fn split(&mut self, idx: usize) {
        // Extract all the parts of the suffix node, starting with the key.
        let key = self.key.split(idx);

        // Key-value.
        let key_value = self.key_value.take();

        // Children.
        let mut children: [Option<Box<TrieNode<K, V>>>; BRANCH_FACTOR] = Default::default();

        for (i, child) in self.children.iter_mut().enumerate() {
            if child.is_some() {
                children[i] = child.take();
            }
        }

        // Child count.
        let child_count = self.child_count;
        self.child_count = 1;

        // Insert the collected items below what is now an empty prefix node.
        let bucket = key.get(0) as usize;
        self.children[bucket] = Some(Box::new(TrieNode {
            key: key,
            key_value,
            children,
            child_count,
        }));
    }
    #[inline]
    pub fn as_subtrie(&self, prefix: Nibblet) -> SubTrie<K, V> {
        SubTrie {
            prefix: prefix,
            node: self,
        }
    }
    #[inline]
    pub fn as_subtrie_mut<'a>(
        &'a mut self,
        prefix: Nibblet,
        length: &'a mut usize,
    ) -> SubTrieMut<'a, K, V> {
        SubTrieMut {
            prefix: prefix,
            length: length,
            node: self,
        }
    }

    /// Check the integrity of a trie subtree (quite costly).
    /// Return true and the size of the subtree if all checks are successful,
    /// or false and a junk value if any test fails.
    pub fn check_integrity_recursive(&self, prefix: &Nibblet) -> (bool, usize) {
        let mut sub_tree_size = 0;
        let is_root = prefix.len() == 0;

        // Check that no value-less, non-root nodes have only 1 child.
        if !is_root && self.child_count == 1 && self.key_value.is_none() {
            println!("Value-less node with a single child.");
            return (false, sub_tree_size);
        }

        // Check that all non-root key vector's have length > 1.
        if !is_root && self.key.len() == 0 {
            println!("Key length is 0 at non-root node.");
            return (false, sub_tree_size);
        }

        // Check that the child count matches the actual number of children.
        let child_count = self
            .children
            .iter()
            .fold(0, |acc, e| acc + (e.is_some() as usize));

        if child_count != self.child_count {
            println!(
                "Child count error, recorded: {}, actual: {}",
                self.child_count, child_count
            );
            return (false, sub_tree_size);
        }

        // Compute the key fragments for this node, according to the trie.
        let trie_key = prefix.clone().join(&self.key);

        // Account for this node in the size check, and check its key.
        if let Some(ref kv) = self.key_value {
            sub_tree_size += 1;

            let actual_key = kv.key.encode();

            if trie_key != actual_key {
                return (false, sub_tree_size);
            }
        }

        // Recursively check children.
        for i in 0..BRANCH_FACTOR {
            if let Some(ref child) = self.children[i] {
                match child.check_integrity_recursive(&trie_key) {
                    (false, _) => return (false, sub_tree_size),
                    (true, child_size) => sub_tree_size += child_size,
                }
            }
        }

        (true, sub_tree_size)
    }
}

impl<K: TrieKey, V> Default for TrieNode<K, V> {
    fn default() -> Self {
        Self::new()
    }
}