# Binary Tree Map
#
# Properties:
#  * unique root
#  * node.left.key < node.key
#  * node.right.key > node.key
#  * no duplicates allowed
#
# Operations:
#  * search average O(lg n) worst O(n)
#  * insert average O(lg n) worst O(n)
#  * delete average O(lg n) worst O(n)
#
# Usage:
#
#     var tree = new BinTreeMap[Int, String]
#     tree[1] = "n1"
#     assert tree.min == "n1"
class BinTreeMap[K: Comparable, E]
	super TreeMap[K, E]

	redef type N: BinTreeNode[K, E]

	private var len = 0
	private var first_node: nullable BinTreeNode[K, E] = null
	private var last_node: nullable BinTreeNode[K, E] = null

	# O(n) in worst case, average is O(h) with h: tree height
	#
	#     var tree = new BinTreeMap[Int, String]
	#     assert tree.is_empty
	#     tree[1] = "n1"
	#     assert not tree.is_empty
	redef fun is_empty do return root == null

	# O(n) in worst case, average is O(h) with h: tree height
	#
	#     var tree = new BinTreeMap[Int, String]
	#     assert not tree.has_key(1)
	#     for i in [4, 2, 1, 5, 3] do tree[i] = "n{i}"
	#     assert not tree.has_key(0)
	#     assert tree.has_key(2)
	#     assert not tree.has_key(6)
	redef fun has_key(key) do
		if is_empty then return false
		var res = search_down(root.as(not null), key)
		if res != null then
			cache_node = res
			return true
		end
		return false
	end

	private var cache_node: nullable N = null

	# Get the node value associated to `key`
	# O(n) in worst case, average is O(h) with h: tree height
	#
	#     var tree = new BinTreeMap[Int, String]
	#     for i in [4, 2, 1, 5, 3] do tree[i] = "n{i}"
	#     assert tree.has_key(1)
	#     assert tree[1] == "n1"
	#     assert tree.has_key(1)
	#     assert tree[2] == "n2"
	redef fun [](key) do
		assert not_empty: not is_empty
		if cache_node != null and cache_node.key == key then return cache_node.value
		var res = search_down(root.as(not null), key)
		assert has_key: res != null
		return res.value
	end

	# Search `key` in `from` and its children nodes.
	protected fun search_down(from: N, key: nullable Object): nullable N do
		if not key isa Comparable then return null
		var cmp = key <=> from.key
		if cmp == 0 then return from
		if from.left != null and cmp < 0 then
			return search_down(from.left.as(not null), key)
		else if from.right != null then
			return search_down(from.right.as(not null), key)
		end
		return null
	end

	# Get the node with the minimum key
	# O(n) in worst case, average is O(h) with h: tree height
	#
	#     var tree = new BinTreeMap[Int, String]
	#     for i in [4, 2, 1, 5, 3] do tree[i] = "n{i}"
	#     assert tree.min == "n1"
	fun min: E do
		assert not_empty: root != null
		return min_from(root.as(not null)).value
	end

	# Get the left-most child from `node`.
	protected fun min_from(node: N): N do
		if node.left == null then return node
		return min_from(node.left.as(not null))
	end

	# Get the node with the maximum key
	# O(n) in worst case, average is O(h) with h: tree height
	#
	#     var tree = new BinTreeMap[Int, String]
	#     for i in [4, 2, 1, 5, 3, 6, 7, 8] do tree[i] = "n{i}"
	#     assert tree.max == "n8"
	fun max: E do
		assert not_empty: root != null
		return max_from(root.as(not null)).value
	end

	# Get the right-most child from `node`.
	protected fun max_from(node: N): N do
		if node.right == null then return node
		return max_from(node.right.as(not null))
	end

	# Insert a new node in tree using `key` and `item`
	# O(n) in worst case, average is O(h) with h: tree height
	#
	#     var tree = new BinTreeMap[Int, String]
	#     tree[1] = "n1"
	#     assert tree.max == "n1"
	#     tree[3] = "n3"
	#     assert tree.max == "n3"
	redef fun []=(key, item) do
		insert_node(new BinTreeNode[K, E](key, item))
	end

	# Add `node` in the tree.
	protected fun insert_node(node: N) do
		len += 1
		if root == null then
			root = node
		else
			shift_down(root.as(not null), node)
		end
		if first_node == null then
			first_node = node
		end
		if last_node != null then
			last_node.next = node
			node.prev = last_node
		end
		last_node = node
	end

	# Push down the `node` in tree from a specified `from` index
	protected fun shift_down(from, node: N) do
		var cmp = node.key <=> from.key
		if cmp < 0 then
			if from.left == null then
				from.left = node
				node.parent = from
			else
				shift_down(from.left.as(not null), node)
			end
		else if cmp > 0 then
			if from.right == null then
				from.right = node
				node.parent = from
			else
				shift_down(from.right.as(not null), node)
			end
		end
	end

	# Delete node at `key` (also return the deleted node value)
	# O(n) in worst case, average is O(h) with h: tree height
	#
	#     var tree = new BinTreeMap[Int, String]
	#     tree[1] = "n1"
	#     assert tree.max == "n1"
	#     tree[3] = "n3"
	#     assert tree.max == "n3"
	#     tree.delete(3)
	#     assert tree.max == "n1"
	fun delete(key: K): nullable E do
		assert is_empty: root != null
		len -= 1
		var node = search_down(root.as(not null), key)
		if node == null then return null
		if node.left == null then
			transplant(node, node.right)
		else if node.right == null then
			transplant(node, node.left)
		else
			var min = min_from(node.right.as(not null))
			if min.parent != node then
				transplant(min, min.right)
				min.right = node.right
				min.right.parent = min
			end
			transplant(node, min)
			min.left = node.left
			min.left.parent = min
		end
		if first_node == node then
			first_node = null
		end
		if last_node == node then
			last_node = node.prev
			last_node.next = null
		else
			node.prev.next = node.next
			node.next.prev = node.prev
		end
		return node.value
	end

	# Swap a `node` with the `other` in this Tree
	# note: Nodes parents are updated, children still untouched
	protected fun transplant(node, other: nullable N) do
		if node == null then return
		if node.parent == null then
			root = other
		else if node == node.parent.left then
			node.parent.left = other
		else
			node.parent.right = other
		end
		if other != null then other.parent = node.parent
	end

	# Perform left rotation on `node`
	#
	# ~~~raw
	#     N             Y
	#    / \     >     / \
	#   a   Y         N   c
	#      / \   <   / \
	#     b   c     a   b
	# ~~~
	#
	protected fun rotate_left(node: N) do
		var y = node.right
		node.right = y.left
		if y.left != null then
			y.left.parent = node
		end
		y.parent = node.parent
		if node.parent == null then
			root = y
		else if node == node.parent.left then
			node.parent.left = y
		else
			node.parent.right = y
		end
		y.left = node
		node.parent = y
	end

	# Perform right rotation on `node`
	#
	# ~~~raw
	#     N             Y
	#    / \     >     / \
	#   a   Y         N   c
	#      / \   <   / \
	#     b   c     a   b
	# ~~~
	#
	protected fun rotate_right(node: N) do
		var y = node.left
		node.left = y.right
		if y.right != null then
			y.right.parent = node
		end
		y.parent = node.parent
		if node.parent == null then
			root = y
		else if node == node.parent.right then
			node.parent.right = y
		else
			node.parent.left = y
		end
		y.right = node
		node.parent = y
	end

	# Sort the tree into an array
	# O(n)
	#
	#     var tree = new BinTreeMap[Int, String]
	#     for i in [4, 2, 1, 5, 3] do tree[i] = "n{i}"
	#     assert tree.sort == ["n1", "n2", "n3", "n4", "n5"]
	fun sort: Array[E] do
		var sorted = new Array[E]
		if root == null then return sorted
		sort_down(root.as(not null), sorted)
		return sorted
	end

	# Sort the tree from `node` and place results in `sorted`.
	protected fun sort_down(node: N, sorted: Array[E]) do
		if node.left != null then sort_down(node.left.as(not null), sorted)
		sorted.add(node.value)
		if node.right != null then sort_down(node.right.as(not null), sorted)
	end

	redef fun to_s do
		var root = self.root
		if root == null then return "[]"
		return "[{print_tree(root)}]"
	end

	# Print the tree starting from `node`.
	protected fun print_tree(node: N): String do
		var s = new FlatBuffer
		s.append(node.to_s)
		if node.left != null then s.append(print_tree(node.left.as(not null)))
		if node.right != null then s.append(print_tree(node.right.as(not null)))
		return s.to_s
	end

	redef fun show_dot do
		assert not_empty: root != null
		var f = new ProcessWriter("dot", "-Txlib")
		f.write "digraph \{\n"
		dot_down(root.as(not null), f)
		f.write "\}\n"
		f.close
	end

	# Translate the tree in dot format starting from `node`.
	protected fun dot_down(node: N, f: ProcessWriter) do
		if node.left != null then dot_down(node.left.as(not null), f)
		f.write node.to_dot
		if node.right != null then dot_down(node.right.as(not null), f)
	end

	# O(n)
	#
	#     var tree = new BinTreeMap[Int, String]
	#     assert tree.length == 0
	#     for i in [4, 2, 1, 5, 3] do tree[i] = "n{i}"
	#     assert tree.length == 5
	redef fun length do return len

	# Nodes are iterated in the same order in which they were added to the tree.
	# O(n)
	#
	#     var tree = new BinTreeMap[Int, String]
	#     for i in [4, 2, 1, 5, 3] do tree[i] = "n{i}"
	#     var keys = new Array[Int]
	#     for k, v in tree do
	#         keys.add k
	#     end
	#     assert keys == [4, 2, 1, 5, 3]
	redef fun iterator do return new BinTreeMapIterator[K, E](self)
end