# Copyright, 2017, by Samuel G. D. Williams. <http://www.codeotaku.com>
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

require 'set'

module Async
	# Represents a node in a tree, used for nested {Task} instances.
	class Node
		# Create a new node in the tree.
		# @param parent [Node, nil] This node will attach to the given parent.
		def initialize(parent = nil)
			@children = nil
			@parent = nil
			
			@annotation = nil
			@object_name = nil
			
			if parent
				self.parent = parent
			end
		end
		
		# @attr parent [Node, nil]
		attr :parent
		
		# @attr children [Set<Node>] Optional list of children.
		attr :children
		
		# A useful identifier for the current node.
		attr :annotation
		
		def annotate(annotation)
			if block_given?
				previous_annotation = @annotation
				@annotation = annotation
				yield
				@annotation = previous_annotation
			else
				@annotation = annotation
			end
		end
		
		def description
			@object_name ||= "#{self.class}:0x#{object_id.to_s(16)}"
			
			if @annotation
				"#{@object_name} #{@annotation}"
			else
				@object_name
			end
		end
		
		def to_s
			"\#<#{description}>"
		end
		
		# Change the parent of this node.
		# @param parent [Node, nil] the parent to attach to, or nil to detach.
		# @return [self]
		def parent=(parent)
			return if @parent.equal?(parent)
			
			if @parent
				@parent.reap(self)
				@parent = nil
			end
			
			if parent
				@parent = parent
				@parent.add_child(self)
			end
			
			return self
		end
		
		protected def add_child child
			@children ||= Set.new
			@children << child
		end
		
		# Whether the node can be consumed safely. By default, checks if the
		# children set is empty.
		# @return [Boolean]
		def finished?
			@children.nil? or @children.empty?
		end
		
		# If the node has a parent, and is {finished?}, then remove this node from
		# the parent.
		def consume
			if @parent and finished?
				@parent.reap(self)
				@parent.consume
				@parent = nil
			end
		end
		
		# Remove a given child node.
		# @param child [Node]
		def reap(child)
			@children.delete(child)
		end
		
		# Traverse the tree.
		# @yield [node, level] The node and the level relative to the given root.
		def traverse(level = 0, &block)
			yield self, level
			
			@children&.each do |child|
				child.traverse(level + 1, &block)
			end
		end
		
		def print_hierarchy(out = $stdout)
			self.traverse do |node, level|
				out.puts "#{"\t" * level}#{node}"
			end
		end
	end
end