Experimental DODB::DirectedGraph feature.

src/dodb.cr

@@ -159,6 +159,12 @@ abstract class DODB::Storage(V)
 		partition.not_nil!.as(DODB::Tags).get name, key
 	end
 
+	def new_directed_graph(name : String, index : DODB::Index(V), &block : Proc(V, Array(String))) : DirectedGraph(V)
+		DirectedGraph(V).new(self, @directory_name, index, name, block).tap do |table|
+			@indexers << table
+		end
+	end
+
 	def check_collisions!(key : Int32, value : V, old_value : V?)
 		@indexers.each &.check!(stringify_key(key), value, old_value)
 	end

src/dodb/directed_graph.cr

@@ -0,0 +1,174 @@
+require "file_utils"
+require "json"
+
+require "./indexer.cr"
+
+class DODB::DirectedGraph(V) < DODB::Indexer(V)
+	property name         : String
+	property key_proc     : Proc(V, Array(String))
+	getter   storage_root : String
+
+	getter index : Index(V)
+
+	@storage : DODB::Storage(V)
+
+	def initialize(@storage, @storage_root, @index, @name, @key_proc)
+		::Dir.mkdir_p indexing_directory
+	end
+
+	def check!(key, value, old_value)
+		return true # Graphs don’t have collisions or overloads.
+	end
+
+	def index(key, value)
+		outgoing_nodes = key_proc.call value
+		current_node = @index.key_proc.call value
+
+		# FIXME: Not 100% completely sure what to do with those.
+		#        Let’s ignore them for now and assume they’re undefined
+		#        behavior.
+		return if current_node.is_a? NoIndex
+
+		outgoing_links_directory = get_outgoing_links_directory current_node
+
+		# TODO: Update old incoming links, if any, before removing?
+		::FileUtils.rm_r outgoing_links_directory if ::Dir.exists? outgoing_links_directory
+
+		::Dir.mkdir_p outgoing_links_directory
+
+		outgoing_nodes.each do |node|
+			outgoing_symlink = get_outgoing_symlink current_node, node
+			incoming_symlink = get_incoming_symlink current_node, node
+
+			# FIXME: How necessary is this?
+			::File.delete outgoing_symlink if ::File.exists? outgoing_symlink
+			::File.delete incoming_symlink if ::File.exists? incoming_symlink
+
+			# Updates outgoing links.
+			::File.symlink get_cross_index_data_symlink(node), outgoing_symlink
+
+			# Updates incoming links.
+			::Dir.mkdir_p get_incoming_links_directory node
+			::File.symlink get_data_symlink(key), incoming_symlink
+		end
+	end
+
+	def deindex(key, value)
+		outgoing_nodes = key_proc.call value
+		current_node = @index.key_proc.call value
+
+		::FileUtils.rm_r get_outgoing_links_directory current_node
+
+		outgoing_nodes.each do |node|
+			symlink = get_incoming_symlink current_node, node
+
+			::File.delete symlink if ::File.exists? symlink
+		end
+
+		::FileUtils.rm_r indexing_directory current_node
+	end
+
+	# FIXME: Heavy duplication down below.
+
+	# FIXME: references to missing (eg. removed or never added) nodes will
+	#        raise File::NotFoundError. Should be caught and handled.
+	def get_incoming_values(node)
+		r_value = Array(V).new
+
+		incoming_links_directory = get_incoming_links_directory node
+
+		return r_value unless Dir.exists? incoming_links_directory
+
+		Dir.each_child incoming_links_directory do |child|
+			r_value << V.from_json ::File.read "#{incoming_links_directory}/#{child}"
+		end
+
+		r_value
+	end
+	def get_incoming_keys(node)
+		r_value = Array(String).new
+
+		incoming_links_directory = get_incoming_links_directory node
+
+		return r_value unless Dir.exists? incoming_links_directory
+
+		Dir.each_child incoming_links_directory do |child|
+			r_value << child.sub /.json$/, ""
+		end
+
+		r_value
+	end
+
+	# FIXME: references to missing (eg. removed or never added) nodes will
+	#        raise File::NotFoundError. Should be caught and handled.
+	def get_outgoing_values(node)
+		r_value = Array(V).new
+
+		outgoing_links_directory = get_outgoing_links_directory node
+
+		return r_value unless Dir.exists? outgoing_links_directory
+
+		Dir.each_child outgoing_links_directory do |child|
+			r_value << V.from_json ::File.read "#{outgoing_links_directory}/#{child}"
+		end
+
+		r_value
+	end
+	def get_outgoing_keys(node)
+		r_value = Array(String).new
+
+		outgoing_links_directory = get_outgoing_links_directory node
+
+		return r_value unless Dir.exists? outgoing_links_directory
+
+		Dir.each_child outgoing_links_directory do |child|
+			r_value << child.sub /.json$/, ""
+		end
+
+		r_value
+	end
+
+	def indexing_directory : String
+		"#{@storage_root}/graphs/by_#{@name}"
+	end
+
+	private def get_key(path : String) : Int32
+		::File.readlink(path)
+			.sub(/\.json$/, "")
+			.sub(/^.*\//,   "")
+			.to_i
+	end
+
+	private def indexing_directory(node)
+		"#{indexing_directory}/#{node}"
+	end
+
+	private def get_node_symlink(node : String, key : String)
+		"#{indexing_directory node}/#{key}.json"
+	end
+
+	private def get_outgoing_links_directory(node)
+		"#{indexing_directory node}/outgoing"
+	end
+
+	private def get_outgoing_symlink(node, link)
+		"#{get_outgoing_links_directory node}/#{link}"
+	end
+
+	private def get_incoming_links_directory(node)
+		"#{indexing_directory node}/incoming"
+	end
+
+	private def get_incoming_symlink(node, link)
+		"#{get_incoming_links_directory link}/#{node}"
+	end
+
+	private def get_data_symlink(key : String)
+		"../../../../data/#{key}.json"
+	end
+
+	private def get_cross_index_data_symlink(node : String)
+		"../../../../../#{@index.file_path_index node}"
+	end
+end
+

src/dodb/index.cr

@@ -140,7 +140,8 @@ class DODB::Index(V) < DODB::Indexer(V)
 		"#{@storage_root}/indices/by_#{@name}"
 	end
 
-	private def file_path_index(index_key : String)
+	# FIXME: Now that it’s being used outside of this class, name it properly.
+	def file_path_index(index_key : String)
 		"#{indexing_directory}/#{index_key}.json"
 	end