From 5d662e4225dbeb9646476223cb12857b5f4cdca7 Mon Sep 17 00:00:00 2001
From: Karchnu <karchnu@karchnu.fr>
Date: Thu, 16 Jul 2020 18:40:11 +0200
Subject: [PATCH] Adding cached.cr to the repository.

---
 src/cached.cr | 304 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 304 insertions(+)
 create mode 100644 src/cached.cr

diff --git a/src/cached.cr b/src/cached.cr
new file mode 100644
index 0000000..2d961f5
--- /dev/null
+++ b/src/cached.cr
@@ -0,0 +1,304 @@
+
+#class Hash(K,V)
+#	def reverse
+#		rev = Array(Tuple(K,V)).new
+#		keys = Array(K).new
+#		each_key do |k|
+#			keys << k
+#		end
+#		keys.reverse.each do |k|
+#			rev << {k, self.[k]}
+#		end
+#
+#		rev
+#	end
+#end
+
+class DODB::DataBase::Cached(V)
+	@indexers = [] of Indexer(V)
+	property data = Hash(Int32, V).new
+
+	def initialize(@directory_name : String)
+		Dir.mkdir_p data_path
+		Dir.mkdir_p locks_directory
+
+		begin
+			self.last_index
+		rescue
+			self.last_index = -1
+		end
+
+		# TODO: load the database in RAM at start-up
+	end
+
+	# Data should be written on disk AND in RAM.
+	def <<(item : V)
+		index = last_index + 1
+		self[index] = item
+		self.last_index = index
+		@data[self.last_index] = item
+	end
+
+	# Getting data from the hash in RAM.
+	def []?(key : Int32) : V?
+		@data[key]
+	rescue e
+		# FIXME: rescues any error the same way.
+		return nil
+	end
+	def [](key : Int32) : V
+		# raise MissingEntry.new(key) unless ::File.exists? file_path key
+		# read file_path key
+		@data[key]
+	end
+
+	def []=(index : Int32, value : V)
+		old_value = self.[index]?
+
+		check_collisions! index, value, old_value
+
+		# Removes any old indices or partitions pointing to a value about
+		# to be replaced.
+		if old_value
+			remove_partitions index, old_value
+		end
+
+		# Avoids corruption in case the application crashes while writing.
+		file_path(index).tap do |path|
+			::File.write "#{path}.new", value.to_json
+			::FileUtils.mv "#{path}.new", path
+		end
+
+		write_partitions index, value
+
+		if index > last_index
+			self.last_index = index
+		end
+
+		@data[index] = value
+	end
+
+	##
+	# CAUTION: Very slow. Try not to use.
+	# Can be useful for making dumps or to restore a database, however.
+	def each_with_index(reversed : Bool = false, start_offset = 0, end_offset : Int32? = nil)
+		i = -1 # do not trust key to be the right index
+		#(reversed ? @data.reverse : @data).each do |index, v|
+		@data.each do |index, v|
+			i += 1
+			next if start_offset > i
+			break unless end_offset.nil? || i < end_offset
+
+			yield v, index
+		end
+	end
+	def each(reversed : Bool = false, start_offset = 0, end_offset : Int32? = nil)
+		each_with_index(
+			reversed: reversed,
+			start_offset: start_offset,
+			end_offset: end_offset
+		) do |item, index|
+			yield item
+		end
+	end
+
+	def to_a(reversed : Bool = false, start_offset = 0, end_offset : Int32? = nil)
+		@data.values
+	end
+
+	def to_h(reversed : Bool = false, start_offset = 0, end_offset : Int32? = nil)
+		res = Hash(Int32, V).new
+
+		# (reversed ? @data.reverse : @data).each do |index, v|
+		@data.each do |index, v|
+			next if start_offset > index
+			break unless end_offset.nil? || index < end_offset
+
+			res[index] = v
+		end
+
+		res
+	end
+
+	private def index_file
+		"#{@directory_name}/last-index"
+	end
+	def last_index : Int32
+		File.read(index_file).to_i
+	end
+	def last_index=(x : Int32)
+		file = File.open(index_file, "w")
+
+		file << x.to_s
+
+		file.close
+
+		x
+	rescue
+		raise Exception.new "could not update index file"
+	end
+
+	def stringify_key(key : Int32)
+		# Negative numbers give strange results with Crystal’s printf.
+		if key >= 0
+			"%010i" % key
+		else
+			key.to_s
+		end
+	end
+
+	def request_lock(name)
+		r = -1
+		file_path = get_lock_file_path name
+		file_perms = 0o644
+
+		flags = LibC::O_EXCL | LibC::O_CREAT
+		while (r = LibC.open file_path, flags, file_perms) == -1
+			sleep 1.milliseconds
+		end
+
+		LibC.close r
+	end
+	def release_lock(name)
+		File.delete get_lock_file_path name
+	end
+
+	##
+	# name is the name that will be used on the file system.
+	def new_partition(name : String, &block : Proc(V, String))
+		Partition(V).new(self, @directory_name, name, block).tap do |table|
+			@indexers << table
+		end
+	end
+
+	##
+	# name is the name that will be used on the file system.
+	def new_index(name : String, &block : Proc(V, String))
+		Index(V).new(self, @directory_name, name, block).tap do |indexer|
+			@indexers << indexer
+		end
+	end
+
+	def new_tags(name : String, &block : Proc(V, Array(String)))
+		Tags(V).new(@directory_name, name, block).tap do |tags|
+			@indexers << tags
+		end
+	end
+
+	def get_index(name : String, key)
+		index = @indexers.find &.name.==(name)
+
+		index.not_nil!.as(DODB::Index).get key
+	end
+
+	def get_partition(table_name : String, partition_name : String)
+		partition = @indexers.find &.name.==(table_name)
+
+		partition.not_nil!.as(DODB::Partition).get partition_name
+	end
+
+	def get_tags(name, key : String)
+		partition = @indexers.find &.name.==(name)
+
+		partition.not_nil!.as(DODB::Tags).get name, key
+	end
+
+	def check_collisions!(key : Int32, value : V, old_value : V?)
+		@indexers.each &.check!(stringify_key(key), value, old_value)
+	end
+
+	def write_partitions(key : Int32, value : V)
+		@indexers.each &.index(stringify_key(key), value)
+	end
+
+	def pop
+		index = last_index
+
+		# Some entries may have been removed. We’ll skip over those.
+		# Not the most efficient if a large number of indices are empty.
+		while index >= 0 && self[index]?.nil?
+			index = index - 1
+		end
+
+		if index < 0
+			return nil
+		end
+
+		poped = self[index]
+
+		self.delete index
+
+		last_index = index - 1
+
+		poped
+	end
+
+	def delete(key : Int32)
+		value = self[key]?
+
+		return if value.nil?
+
+		begin
+			::File.delete file_path key
+		rescue
+			# FIXME: Only intercept “no such file" errors
+		end
+
+		remove_partitions key, value
+
+		@data.delete key
+		value
+	end
+
+	def remove_partitions(key : Int32, value : V)
+		@indexers.each &.deindex(stringify_key(key), value)
+	end
+
+	private def data_path
+		"#{@directory_name}/data"
+	end
+
+	private def file_path(key : Int32)
+		"#{data_path}/%010i.json" % key
+	end
+
+	private def locks_directory : String
+		"#{@directory_name}/locks"
+	end
+
+	private def get_lock_file_path(name : String)
+		"#{locks_directory}/#{name}.lock"
+	end
+
+	private def read(file_path : String)
+		V.from_json ::File.read file_path
+	end
+
+	private def remove_data!
+		FileUtils.rm_rf data_path
+		Dir.mkdir_p data_path
+	end
+
+	private def remove_indexing!
+		@indexers.each do |indexer|
+			FileUtils.rm_rf indexer.indexing_directory
+		end
+	end
+
+	# A very slow operation that removes all indices and then rewrites
+	# them all.
+	# FIXME: Is this really useful in its current form? We should remove the
+	#        index directories, not the indices based on our current (and
+	#        possiblly different from what’s stored) data.
+	def reindex_everything!
+		old_data = to_h
+
+		remove_indexing!
+		remove_data!
+
+		old_data.each do |index, item|
+			self[index] = item
+		end
+	end
+end
+