# -*- ruby -*-
# vim: set nosta noet ts=4 sw=4 ft=ruby:
# encoding: utf-8

require 'mdbx' unless defined?( MDBX )


# The primary class for interacting with an MDBX database.
#
class MDBX::Database
	extend Loggability

	log_to :mdbx

	### call-seq:
	###    MDBX::Database.open( path ) => db
	###    MDBX::Database.open( path, options ) => db
	###
	### Open an existing (or create a new) mdbx database at filesystem
	### +path+.  In block form, the database is automatically closed
	### when the block exits.
	###
	###    MDBX::Database.open( path, options ) do |db|
	###        db[ 'key' ] = value
	###    end # closed!
	###
	### Passing options modify various database behaviors.  See the libmdbx
	### documentation for detailed information.
	###
	### ==== Options
	###
	### Unless otherwise mentioned, option keys are symbols, and values
	### are boolean.
	###
	### [:coalesce]
	###   Attempt to coalesce items for the garbage collector,
	###   potentialy increasing the chance of unallocating storage
	###   earlier.
	###
	### [:compatible]
	###   Skip compatibility checks when opening an in-use database with
	###   unknown or mismatched flag values.
	###
	### [:exclusive]
	###   Access is restricted to the first opening process. Other attempts
	###   to use this database (even in readonly mode) are denied.
	###
	### [:lifo_reclaim]
	###   Recycle garbage collected items via LIFO, instead of FIFO.
	###   Depending on underlying hardware (disk write-back cache), this
	###   could increase write performance.
	###
	### [:max_collections]
	###   Set the maximum number of "subdatabase" collections allowed. By
	###   default, collection support is disabled.
	###
	### [:max_readers]
	###   Set the maximum number of allocated simultaneous reader slots.
	###
	### [:max_size]
	###   Set an upper boundary (in bytes) for the database map size.
	###   The default is 10485760 bytes.
	###
	### [:mode]
	###   Whe creating a new database, set permissions to this 4 digit
	###   octal number.  Defaults to `0644`.  Set to `0` to never automatically
	###   create a new file, only opening existing databases.
	###
	### [:no_memory_init]
	###   Skip initializing malloc'ed memory to zeroes before writing.
	###
	### [:no_metasync]
	###   A system crash may sacrifice the last commit for a potentially
	###   large write performance increase.  Database integrity is
	###   maintained.
	###
	### [:no_subdir]
	###   When creating a new database, don't put the data and lock file
	###   under a dedicated subdirectory.
	###
	### [:no_readahead]
	###   Disable all use of OS readahead.  Potentially useful for
	###   random reads wunder low memory conditions.  Default behavior
	###   is to dynamically choose when to use or omit readahead.
	###
	### [:no_threadlocal]
	###   Parallelize read-only transactions across threads.  Writes are
	###   always thread local. (See MDBX documentation for details.)
	###
	### [:readonly]
	###   Reject any write attempts while using this database handle.
	###
	### [:writemap]
	###   Trade safety for speed for databases that fit within available
	###   memory. (See MDBX documentation for details.)
	###
	def self::open( *args, &block )
		db = new( *args )

		db.serializer   = ->( v ) { Marshal.dump( v ) }
		db.deserializer = ->( v ) { Marshal.load( v ) }

		if block_given?
			begin
				yield db
			ensure
				db.close
			end
		end

		return db
	end


	# Only instantiate Database objects via #open.
	private_class_method :new


	# Options used when instantiating this database handle.
	attr_reader :options

	# The path on disk of the database.
	attr_reader :path

	# A Proc for automatically serializing values.
	# Defaults to +Marshal.dump+.
	attr_accessor :serializer

	# A Proc for automatically deserializing values.
	# Defaults to +Marshal.load+.
	attr_accessor :deserializer


	alias_method :size, :length
	alias_method :each, :each_pair
	alias_method :has_key?, :include?


	### Gets or sets the sub-database "collection" that read/write
	### operations apply to. If a block is passed, the collection
	### automatically reverts to the prior collection when it exits.
	###
	###  db.collection #=> (collection name, or nil if in main)
	###  db.collection( 'collection_name' ) #=> db
	###
	###  db.collection( 'collection_name' ) do
	###      [ ... ]
	###  end # reverts to the previous collection name
	###
	def collection( name=nil )
		current = self.get_subdb
		return current unless name

		self.set_subdb( name.to_s )
		yield( self ) if block_given?

		return self

	ensure
		self.set_subdb( current ) if name && block_given?
	end
	alias_method :namespace, :collection


	### Switch to the top-level collection.
	###
	def main
		return self.set_subdb( nil )
	end


	#
	# Transaction methods
	#

	### Open a new mdbx read/write transaction.  In block form,
	### the transaction is automatically committed when the block ends.
	###
	### Raising a MDBX::Rollback exception from within the block
	### automatically rolls the transaction back.
	###
	def transaction( commit: true, &block )
		self.open_transaction( commit )
		yield self if block_given?

		return self

	rescue MDBX::Rollback
		commit = false
		self.rollback
	rescue
		commit = false
		self.rollback
		raise
	ensure
		if block_given?
			commit ? self.commit : self.rollback
		end
	end


	### Open a new mdbx read only snapshot.  In block form,
	### the snapshot is automatically closed when the block ends.
	###
	def snapshot( &block )
		self.transaction( commit: false, &block )
	end


	### Close any open transaction, abandoning all changes.
	###
	def rollback
		return self.close_transaction( false )
	end
	alias_method :abort, :rollback


	### Close any open transaction, writing all changes.
	###
	def commit
		return self.close_transaction( true )
	end
	alias_method :save, :commit


	#
	# Hash-alike methods
	#

	### Return the entirety of database contents as an Array of array
	### pairs.
	###
	def to_a
		return self.conditional_snapshot do
			self.each_pair.to_a
		end
	end


	### Return the entirety of database contents as a Hash.
	###
	def to_h
		return self.conditional_snapshot do
			self.each_pair.to_h
		end
	end


	### Returns +true+ if the current collection has no data.
	###
	def empty?
		return self.size.zero?
	end


	### Returns the value for the given key, if found.
	### If key is not found and no block was given, returns nil.
	### If key is not found and a block was given, yields key to the
	### block and returns the block's return value.
	###
	def fetch( key, &block )
		val = self[ key ]
		if block_given?
			return block.call( key ) if val.nil?
		else
			return val if val
			raise KeyError, "key not found: %p" % [ key ]
		end
	end


	### Deletes the entry for the given key and returns its associated
	### value.  If no block is given and key is found, deletes the entry
	### and returns the associated value.  If no block given and key is
	### not found, returns nil.
	###
	### If a block is given and key is found, ignores the block, deletes
	### the entry, and returns the associated value.  If a block is given
	### and key is not found, calls the block and returns the block's
	### return value.
	###
	def delete( key, &block )
		val = self[ key ]
		return block.call( key ) if block_given? && val.nil?

		self[ key ] = nil
		return val
	end


	### Returns a new Array containing all keys in the collection.
	###
	def keys
		return self.conditional_snapshot do
			self.each_key.to_a
		end
	end


	### Returns a new Hash object containing the entries for the given
	### keys.  Any given keys that are not found are ignored.
	###
	def slice( *keys )
		return self.conditional_snapshot do
			keys.each_with_object( {} ) do |key, acc|
				val = self[ key ]
				acc[ key ] = val if val
			end
		end
	end


	### Returns a new Array containing all values in the collection.
	###
	def values
		return self.conditional_snapshot do
			self.each_value.to_a
		end
	end


	### Returns a new Array containing values for the given +keys+.
	###
	def values_at( *keys )
		return self.conditional_snapshot do
			keys.each_with_object( [] ) do |key, acc|
				acc << self[ key ]
			end
		end
	end


	#
	# Utility methods
	#

	### Return a hash of various metadata for the current database.
	###
	def statistics
		raw = self.raw_stats

		# Place build options in their own hash.
		#
		build_opts = raw.delete( :build_options ).split.each_with_object( {} ) do |opt, acc|
			key, val = opt.split( '=' )
			acc[ key.to_sym ] = Integer( val ) rescue val
		end

		stats = {
			build: {
				compiler: raw.delete( :build_compiler ),
				flags:    raw.delete( :build_flags ),
				options:  build_opts,
				target:   raw.delete( :build_target )
			}
		}
		stats.merge!( raw )

		return stats
	end


	#########
	protected
	#########

	### Safely serialize a value, closing any open transaction and re-raising
	### if necessary.
	###
	def serialize( val )
		return val unless self.serializer
		return self.serializer.call( val )

	rescue => err
		self.close_transaction( false )
		raise err
	end


	### Safely deserialize a value, closing any open transaction and re-raising
	### if necessary.
	###
	def deserialize( val )
		return val unless self.deserializer
		return self.deserializer.call( val )

	rescue => err
		self.close_transaction( false )
		raise err
	end


	### Yield and return the block, opening a snapshot first if
	### there isn't already a transaction in progress.  Closes
	### the snapshot if this method opened it.
	###
	def conditional_snapshot
		in_txn = self.in_transaction?
		self.snapshot unless in_txn

		return yield
	ensure
		self.abort unless in_txn
	end

end # class MDBX::Database