Readme update to include a few words on tags.

README.md

@@ -162,25 +162,16 @@ $ tree storage/
 ...
 └── tags
     └── by_keyword
-        └── other-tags
-            ├── average
-            │   ├── data
-            │   │   └── 0000000004.json -> ../../../../..//data/0000000004.json
-...
-            ├── dirty
-            │   ├── data
-            │   │   └── 0000000005.json -> ../../../../..//data/0000000005.json
-...
-            ├── elegant
-            │   ├── data
-            │   │   ├── 0000000000.json -> ../../../../..//data/0000000000.json
-            │   │   └── 0000000003.json -> ../../../../..//data/0000000003.json
+        ├── elegant
+        │   ├── 0000000000.json -> ../../../data/0000000000.json
+        │   └── 0000000003.json -> ../../../data/0000000003.json
+        ├── impressive
+        │   ├── 0000000000.json -> ../../../data/0000000000.json
+        │   ├── 0000000001.json -> ../../../data/0000000001.json
+        │   └── 0000000003.json -> ../../../data/0000000003.json
 ...
 ```
-This is very similar to partitions, but there is a bit more complexity here since we eventually search for a car matching a combination of keywords.
-
-**TODO**: explanations about our tag-based search and an example.
-
+Tags are very similar to partitions and are used the exact same way for search, update and deletion.
 
 ## Updating an object
 
@@ -204,23 +195,41 @@ cars_by_id.update "86a07924-ab3a-4f46-a975-e9803acba22d", car
 Or, in the case the object may not yet exist:
 ```Crystal
 cars_by_id.update_or_create car.id, car
+
+# Search by partitions: all blue cars.
+pp! cars_by_color.get "blue"
+
+# Search by tags: all elegant cars.
+pp! cars_by_keyword.get "elegant"
 ```
 
+Changing a value that is related to a partition or a tag will automatically do what you would expect: de-index then re-index.
+You won't find yourself with a bunch of invalid symbolic links all over the place.
+
 ## Removing an object
 
 ```Crystal
+# Remove a value based on an index.
 cars_by_id.delete "86a07924-ab3a-4f46-a975-e9803acba22d"
 
+# Remove a value based on a partition.
 cars_by_color.delete "red"
-cars_by_color.delete "red", do |car|
+cars_by_color.delete "blue", do |car|
 	car.keywords.empty
 end
+
+# Remove a value based on a tag.
+cars_by_keyword.delete "shiny"
+cars_by_keyword.delete "elegant", do |car|
+	car.name == "GTI"
+end
 ```
 
-In this last example, we apply the function on red cars only.
+In this code snippet, we apply a function on blue cars only;
+and blue cars are only removed if they don't have any associated keywords.
+Same thing for elegant cars.
 This represents a performance boost compared to applying the function on all the cars.
 
-
 # Complete example
 
 ```Crystal
@@ -292,11 +301,10 @@ pp! cars_by_name.get "Corvet"
 # based on a partition (print all red cars)
 pp! cars_by_color.get "red"
 
-# based on a tag
+# based on a tag (print all fast cars)
 pp! cars_by_keyword.get "fast"
 
 
-
 ############
 # Updating #
 ############
@@ -314,7 +322,11 @@ cars_by_name.update "Bullet-GT", car # the name changed
 car = Car.new "Mustang", "red", [] of String
 cars_by_name.update_or_create car.name, car
 
-
+# We all know it, elegant cars are also expensive.
+cars_by_keyword.get("elegant").each do |car|
+	car.keywords << "expensive"
+	cars_by_name.update car.name, car
+end
 
 ###############
 # Deleting... #
@@ -328,9 +340,8 @@ cars_by_color.delete "red"
 # based on a color (but not only)
 cars_by_color.delete "blue", &.name.==("GTI")
 
-## TAG-based deletion, soon.
-# # based on a keyword
-# cars_by_keyword.delete "solid"
-# # based on a keyword (but not only)
-# cars_by_keyword.delete "fast", &.name.==("Corvet")
+# based on a keyword
+cars_by_keyword.delete "solid"
+# based on a keyword (but not only)
+cars_by_keyword.delete "fast", &.name.==("Corvet")
 ```

spec/test.cr

@@ -277,7 +277,7 @@ describe "DODB::DataBase" do
 			end
 
 			# Removing the “flagship” tag, brace for impact.
-			flagship, index = db_ships_by_tags.get_with_indices("flagship")[0]
+			flagship, index = db_ships_by_tags.get_with_indice("flagship")[0]
 			flagship.tags = [] of String
 			db[index] = flagship
 

src/dodb.cr

@@ -148,15 +148,15 @@ abstract class DODB::Storage(V)
 	end
 
 	def new_tags(name : String, &block : Proc(V, Array(String)))
-		Tags(V).new(@directory_name, name, block).tap do |tags|
+		Tags(V).new(self, @directory_name, name, block).tap do |tags|
 			@indexers << tags
 		end
 	end
 
 	def get_tags(name, key : String)
-		partition = @indexers.find &.name.==(name)
+		tag = @indexers.find &.name.==(name)
 
-		partition.not_nil!.as(DODB::Tags).get name, key
+		tag.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)

src/dodb/partition.cr

@@ -8,6 +8,7 @@ class DODB::Partition(V) < DODB::Indexer(V)
 	property key_proc     : Proc(V, String)
 	getter   storage_root : String
 
+	# Required to remove an entry in the DB.
 	@storage : DODB::Storage(V)
 
 	def initialize(@storage, @storage_root, @name, @key_proc)

src/dodb/tags.cr

@@ -6,77 +6,48 @@ class DODB::Tags(V) < DODB::Indexer(V)
 	property key_proc     : Proc(V, Array(String))
 	getter   storage_root : String
 
-	def initialize(@storage_root, @name, @key_proc)
+	# Required to remove an entry in the DB.
+	@storage : DODB::Storage(V)
+
+	def initialize(@storage, @storage_root, @name, @key_proc)
 		::Dir.mkdir_p indexing_directory
 	end
 
-	# FIXME: The slow is damn too high.
-	def tag_combinations(tags)
-		combinations = [] of Array(String)
-
-		tags.size.times do |i|
-			combinations.concat tags.permutations (i+1)
-		end
-
-		return combinations
-	end
-
-	def index(key, value)
-		indices = key_proc.call(value).sort
-
-		tag_combinations(indices).each do |previous_indices|
-			# FIXME: Not on `index`, but on the list of all previous indices.
-			symdir = symlinks_directory previous_indices
-			otdir  = other_tags_directory previous_indices
-
-			::Dir.mkdir_p symdir
-			::Dir.mkdir_p otdir
-
-			symlink = get_tagged_entry_path(key, previous_indices)
-
-			::File.delete symlink if ::File.exists? symlink
-
-			::File.symlink get_data_symlink(key, previous_indices), symlink
-		end
-	end
-
-	def deindex(key, value)
-		indices = key_proc.call(value).sort
-
-		tag_combinations(indices).each do |previous_indices|
-			# FIXME: Not on `index`, but on the list of all previous indices.
-			symdir = symlinks_directory previous_indices
-			otdir  = other_tags_directory previous_indices
-
-			::Dir.mkdir_p symdir
-			::Dir.mkdir_p otdir
-
-			symlink = get_tagged_entry_path(key, previous_indices)
-
-			::File.delete symlink if ::File.exists? symlink
-
-			# FIXME: Remove directories if empty?
-		end
-	end
-
 	def check!(key, value, old_value)
 		return true # Tags don’t have collisions or overloads.
 	end
 
-	def get_with_indices(key : String) : Array(Tuple(V, Int32))
-		get_with_indices [key]
+	def index(key, value)
+		indices = key_proc.call(value)
+
+		indices.each do |i|
+			symlink = get_tagged_entry_path(i, key)
+			Dir.mkdir_p ::File.dirname symlink
+			# FIXME: Should not happen anymore. Should we remove this?
+			::File.delete symlink if ::File.exists? symlink
+			::File.symlink get_data_symlink(key), symlink
+		end
 	end
 
-	def get_with_indices(keys : Array(String)) : Array(Tuple(V, Int32))
+	def deindex(key, value)
+		indices = key_proc.call(value)
+
+		indices.each do |i|
+			symlink = get_tagged_entry_path(i, key)
+			::File.delete symlink
+		end
+	end
+
+	def get_with_indice(tag : String) : Array(Tuple(V, Int32))
 		r_value = Array(Tuple(V, Int32)).new
 
-		partition_directory = symlinks_directory keys
+		tag_directory = indexing_directory tag
 
-		return r_value unless Dir.exists? partition_directory
+		return r_value unless Dir.exists? tag_directory
 
-		Dir.each_child partition_directory do |child|
+		Dir.each_child tag_directory do |child|
 			r_value << {
-				V.from_json(::File.read("#{partition_directory}/#{child}")),
+				V.from_json(::File.read("#{tag_directory}/#{child}")),
 				File.basename(child).gsub(/\.json$/, "").to_i
 			}
 		end
@@ -84,30 +55,62 @@ class DODB::Tags(V) < DODB::Indexer(V)
 		r_value
 	end
 
-	def get(key : String) : Array(V)
-		get_with_indices(key).map &.[0]
+	def get_with_indices(keys : Array(String)) : Array(Tuple(V, Int32))
+		r_value = Array(Tuple(V, Int32)).new
+		keys.each do |tag|
+			r_value.concat get_with_indice tag
+		end
+		r_value
+	end
+
+	def get(tag : String) : Array(V)
+		get_with_indice(tag).map &.[0]
 	end
 
 	def get(keys : Array(String)) : Array(V)
 		get_with_indices(keys.sort).map &.[0]
 	end
 
+	def delete(tag)
+		delete tag, do true end
+	end
+
+	def delete(tag, &matcher)
+		tag_directory = indexing_directory tag
+
+		return unless Dir.exists? tag_directory
+
+		Dir.each_child tag_directory do |child|
+			path = "#{tag_directory}/#{child}"
+			item = V.from_json ::File.read path
+
+			if yield item
+				key = get_key path
+				@storage.delete key
+			end
+		end
+	end
+
+	private def get_key(path : String) : Int32
+		::File.readlink(path)
+			.sub(/\.json$/, "")
+			.sub(/^.*\//,   "")
+			.to_i
+	end
+
 	def indexing_directory : String
 		"#{@storage_root}/tags/by_#{@name}"
 	end
 
-	private def symlinks_directory(previous_indices : Array(String))
-		"#{indexing_directory}#{previous_indices.map { |i| "/other-tags/#{i}" }.join}/data"
-	end
-	private def other_tags_directory(previous_indices : Array(String))
-		"#{indexing_directory}#{previous_indices.map { |i| "/other-tags/#{i}" }.join}/other-tags"
+	private def indexing_directory(tag)
+		"#{indexing_directory}/#{tag}"
 	end
 
-	private def get_tagged_entry_path(key : String, indices : Array(String))
-		"#{indexing_directory}#{indices.map { |i| "/other-tags/#{i}" }.join}/data/#{key}.json"
+	private def get_tagged_entry_path(tag : String, key : String)
+		"#{indexing_directory}/#{tag}/#{key}.json"
 	end
-	private def get_data_symlink(key : String, indices : Array(String))
-		"../../../#{indices.map { "../../" }.join}/data/#{key}.json"
+
+	private def get_data_symlink(key : String)
+		"../../../data/#{key}.json"
 	end
 end
-