# * George Moschovitis  <gm@navel.gr>
# (c) 2004-2005 Navel, all rights reserved.
# $Id: adapter.rb 281 2005-03-10 12:24:14Z gmosx $

require 'yaml'
require 'singleton'

require 'og/connection'

module Og

# An adapter communicates with the backend datastore. 
# The adapters for all supported datastores extend this 
# class. Typically, an RDBMS is used to implement a
# datastore.

class Adapter 
	include Singleton

	# A mapping between Ruby and backend Datastore types.

	attr_accessor :typemap

	# A map for casting Ruby types to SQL safe textual
	# representations.

	attr_accessor :typecast
	
	# Lookup the adapter instance from the adapter name.

	def self.for_name(name)
		require "og/adapters/#{name}"
		eval %{	return  #{name.capitalize}Adapter.instance }
	end

	def initialize
		# The default mappings, should be valid for most
		# RDBMS.

		@typemap = {
			Integer => 'integer',
			Fixnum => 'integer',
			Float => 'float',
			String => 'text',
			Time => 'timestamp',
			Date => 'date',
			TrueClass => 'boolean',
			Object => 'text',
			Array => 'text',
			Hash => 'text'
		}

		# The :s: is a marker that will be replaced with the
		# actual value to be casted. The default parameter of
		# the Hash handles all other types (Object, Array, etc)

		@typecast = Hash.new("'#\{#{self.class}.escape(:s:.to_yaml)\}'").update(
			Integer => "\#\{:s:\}",
			Float => "\#\{:s:\}",
			String => "'#\{#{self.class}.escape(:s:)\}'",
			Time => "'#\{#{self.class}.timestamp(:s:)\}'",
			Date => "'#\{#{self.class}.date(:s:)\}'",
			TrueClass => "#\{:s: ? \"'t'\" : 'NULL' \}"
		)
	end

	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
	# :section: Utilities
	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

	# Escape an SQL string
	
	def self.escape(str)
		return nil unless str
		return str.gsub( /'/, "''" )
	end

	# Convert a ruby time to an sql timestamp.
	# TODO: Optimize this
	 
	def self.timestamp(time = Time.now)
		return nil unless time
		return time.strftime("%Y-%m-%d %H:%M:%S")
	end
	
	# Output YYY-mm-dd
	# TODO: Optimize this
	
	def self.date(date)
		return nil unless date
		return "#{date.year}-#{date.month}-#{date.mday}" 
	end
	
	# Parse sql datetime
	# TODO: Optimize this
	
	def self.parse_timestamp(str)
		return nil unless str
		return Time.parse(str)		
	end
	
	# Input YYYY-mm-dd
	# TODO: Optimize this
	
	def self.parse_date(str)
		return nil unless str
		return Date.strptime(str)
	end

	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
	# :section: Database methods 
	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

	# Create the database.
	
	def create_db(database, user = nil, password = nil)
		Logger.info "Creating database '#{database}'."
	end
	
	# Drop the database.
	
	def drop_db(database, user = nil, password = nil)
		Logger.info "Dropping database '#{database}'."
	end

	# Create a new connection to the backend.

	def new_connection(db)
		return Connection.new(db)
	end

	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
	# :section: O->R mapping methods and utilities. 
	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

	# Encode the name of the klass as an sql safe string.
	# The Module separators are replaced with _ and NOT stripped 
	# out so that we can convert back to the original notation if 
	# needed. The leading module if available is removed.
	
	def self.encode(klass)
		"#{klass.name.gsub(/^.*::/, "")}".gsub(/::/, "_").downcase
	end

	# The name of the SQL table where objects of this class 
	# are stored. A prefix is needed to avoid colision with
	# reserved prefices (for example User maps to user which
	# is reserved in postgresql). The prefix should start
	# with an alphanumeric character to be compatible with
	# all RDBMS (most notable Oracle).
	#
	# You may want to override this method to map an existing
	# database schema using Og.
	
	def self.table(klass)
		"og_#{Og.table_prefix}#{encode(klass)}"
	end

	# The name of the join table for the two given classes.
	# A prefix is needed to avoid colision with reserved 
	# prefices (for example User maps to user which
	# is reserved in postgresql). The prefix should start
	# with an alphanumeric character to be compatible with
	# all RDBMS (most notable Oracle).
	#
	# You may want to override this method to map an existing
	# database schema using Og.
	
	def self.join_table(klass1, klass2, field)
		"og_#{Og.table_prefix}j_#{encode(klass1)}_#{encode(klass2)}_#{field}"
	end

	# Return an sql string evaluator for the property.
	# No need to optimize this, used only to precalculate code.
	# YAML is used to store general Ruby objects to be more 
	# portable.
	#--
	# FIXME: add extra handling for float.
	#++
	
	def write_prop(p)
		if p.klass.ancestors.include?(Integer)
			return "#\{@#{p.symbol} || 'NULL'\}"
		elsif p.klass.ancestors.include?(Float)
			return "#\{@#{p.symbol} || 'NULL'\}"		
		elsif p.klass.ancestors.include?(String)
			return %|#\{@#{p.symbol} ? "'#\{#{self.class}.escape(@#{p.symbol})\}'" : 'NULL'\}|
		elsif p.klass.ancestors.include?(Time)
			return %|#\{@#{p.symbol} ? "'#\{#{self.class}.timestamp(@#{p.symbol})\}'" : 'NULL'\}|
		elsif p.klass.ancestors.include?(Date)
			return %|#\{@#{p.symbol} ? "'#\{#{self.class}.date(@#{p.symbol})\}'" : 'NULL'\}|
		elsif p.klass.ancestors.include?(TrueClass)
			return "#\{@#{p.symbol} ? \"'t'\" : 'NULL' \}"
		else 
			# gmosx: keep the '' for nil symbols.
			return %|#\{@#{p.symbol} ? "'#\{#{self.class}.escape(@#{p.symbol}.to_yaml)\}'" : "''"\}|
		end
	end		

	# Return an evaluator for reading the property.
	# No need to optimize this, used only to precalculate code.
	
	def read_prop(p, idx)
		if p.klass.ancestors.include?(Integer)
			return "res[#{idx}].to_i"
		elsif p.klass.ancestors.include?(Float)
			return "res[#{idx}].to_f"
		elsif p.klass.ancestors.include?(String)
			return "res[#{idx}]"
		elsif p.klass.ancestors.include?(Time)
			return "#{self.class}.parse_timestamp(res[#{idx}])"
		elsif p.klass.ancestors.include?(Date)
			return "#{self.class}.parse_date(res[#{idx}])"
		elsif p.klass.ancestors.include?(TrueClass)
			return "('0' != res[#{idx}])"
		else 
			return "YAML::load(res[#{idx}])"
		end				
	end

	# Create the fields that correpsond to the klass properties.
	# The generated fields array is used in create_table.
	# If the property has an :sql metadata this overrides the 
	# default mapping. If the property has an :extra_sql metadata 
	# the extra sql is appended after the default mapping.
	
	def create_fields(klass)
		fields = []
		
		klass.__props.each do |p|
			klass.sql_index(p.symbol) if p.meta[:sql_index]
				
			field = "#{p.symbol}"
			
			if p.meta and p.meta[:sql]
				field << " #{p.meta[:sql]}"
			else
				field << " #{@typemap[p.klass]}"
				
				if p.meta
					# set default value (gmosx: not that useful in the
					# current implementation).
					if default = p.meta[:default]
						field << " DEFAULT #{default.inspect} NOT NULL"
					end
				
					# set unique
					field << " UNIQUE" if p.meta[:unique]

					# attach extra sql
					if extra_sql = p.meta[:extra_sql]
						field << " #{extra_sql}"
					end
				end
			end
			
			fields << field 
		end

		return fields
	end

	# Create the managed object table. The properties of the
	# object are mapped to the table columns. Additional sql relations
	# and constrains are created (indicices, sequences, etc).
	
	def create_table(klass)
		raise 'Not implemented!'	
	end

	# Returns the props that will be included in the insert query.
	# For some backends the oid should be stripped.
	
	def props_for_insert(klass)
		klass.__props
	end

	# Returns the code that actually inserts the object into the
	# database. Returns the code as String.
	
	def insert_code(klass, sql, pre_cb, post_cb)
		raise 'Not implemented!'
	end
	
	# Generate the mapping of the database fields to the
	# object properties.
	
	def calc_field_index(klass, og)
		# Implement if needed.
	end

	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
	# :section: Precompile lifecycle methods.
	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

	# Precompile some code that gets executed all the time.
	# Deletion code is not precompiled, because it is not used
	# as frequently.

	def eval_lifecycle_methods(klass, db)
		eval_og_insert(klass, db)
		eval_og_update(klass, db)
		eval_og_read(klass, db)
	end
		
	# Generate the property for oid.

	def eval_og_oid(klass)
		klass.class_eval %{
			prop_accessor :oid, Fixnum, :sql => "integer PRIMARY KEY"
		}
	end

	# Precompile the insert code for the given class.
	# The generated code sets the oid when inserting!
	
	def eval_og_insert(klass, db)

		# Attach object callbacks.
		
		if klass.instance_methods.include?('og_pre_insert')
			pre_cb = 'og_pre_insert(conn);'
		else
			pre_cb = ''
		end

		if klass.instance_methods.include?('og_post_insert')
			post_cb = 'og_post_insert(conn);'
		else
			post_cb = ''
		end

		if klass.instance_methods.include?('og_pre_insert_update')
			pre_cb << 'og_pre_insert_update(conn);'
		end

		if klass.instance_methods.include?('og_post_insert_update')
			post_cb << 'og_post_insert_update(conn);'
		end

		# Attach observers.

		if observers = klass.__meta[:og_observers]
			observers.each_with_index do |o, idx|
				if o.is_a?(Class)
					obs = "#{o}.instance"
					o = o.instance
				else
					obs = "self.class.__meta[:og_observers][#{idx}]" 
				end

				if o.respond_to?(:og_pre_insert)
					pre_cb << "#{obs}.og_pre_insert(conn, self);"
				end

				if o.respond_to?(:og_post_insert)
					post_cb << "#{obs}.og_post_insert(conn, self);"
				end

				if o.respond_to?(:og_pre_insert_update)
					pre_cb << "#{obs}.og_pre_insert_update(conn, self);"
				end
				
				if o.respond_to?(:og_post_insert_update)
					post_cb << "#{obs}.og_post_insert_update(conn, self);"
				end
			end
		end
			
		klass.class_eval %{
			def og_insert(conn)
				#{insert_code(klass, db, pre_cb, post_cb)}
			end
		}
	end

	# Precompile the update code for the given class.
	# Ignore the oid when updating!
	
	def eval_og_update(klass, db)
		props = klass.__props.reject { |p| :oid == p.symbol }
		
		updates = props.collect { |p|
			"#{p.name}=#{write_prop(p)}"
		}

		sql = "UPDATE #{klass::DBTABLE} SET #{updates.join(', ')} WHERE oid=#\{@oid\}"

		# Attach object callbacks.

		if klass.instance_methods.include?('og_pre_update')
			pre_cb = 'og_pre_update(conn);'
		else
			pre_cb = ''
		end

		if klass.instance_methods.include?('og_post_update')
			post_cb = 'og_post_update(conn);'
		else
			post_cb = ''
		end

		if klass.instance_methods.include?('og_pre_insert_update')
			pre_cb << 'og_pre_insert_update(conn);'
		end

		if klass.instance_methods.include?('og_post_insert_update')
			post_cb << 'og_post_insert_update(conn);'
		end
		
		# Attach observers.

		if observers = klass.__meta[:og_observers]
			observers.each_with_index do |o, idx|
				if o.is_a?(Class)
					obs = "#{o}.instance"
					o = o.instance
				else
					obs = "self.class.__meta[:og_observers][#{idx}]" 
				end

				if o.respond_to?(:og_pre_update)
					pre_cb << "#{obs}.og_pre_update(conn, self);"
				end

				if o.respond_to?(:og_post_update)
					post_cb << "#{obs}.og_post_update(conn, self);"
				end

				if o.respond_to?(:og_pre_insert_update)
					pre_cb << "#{obs}.og_pre_insert_update(conn, self);"
				end
				
				if o.respond_to?(:og_post_insert_update)
					post_cb << "#{obs}.og_post_insert_update(conn, self);"
				end
			end
		end

		klass.class_eval %{
			def og_update(conn)
				#{pre_cb}
				conn.exec "#{sql}"
				#{post_cb}
			end
		}
	end

	# Precompile the code to read (deserialize) objects of the 
	# given class from the backend. In order to allow for changing 
	# field/attribute orders we have to use a field mapping hash.
	
	def eval_og_read(klass, db)
		calc_field_index(klass, db)
		
		props = klass.__props 
		code = []

		props.each do |p|
			if idx = db.managed_classes[klass].field_index[p.name]
				# more fault tolerant if a new field is added and it 
				# doesnt exist in the database.
				code << "@#{p.name} = #{read_prop(p, idx)}"
			end
		end
		
		# Attach object callbacks.

		if klass.instance_methods.include?('og_pre_read')
			pre_cb = 'og_pre_read(conn);'
		else
			pre_cb = ''
		end

		if klass.instance_methods.include?('og_post_read')
			post_cb = 'og_post_read(conn);'
		else
			post_cb = ''
		end

		# Attach observers.

		if observers = klass.__meta[:og_observers]
			observers.each_with_index do |o, idx|
				if o.is_a?(Class)
					obs = "#{o}.instance"
					o = o.instance
				else
					obs = "self.class.__meta[:og_observers][#{idx}]" 
				end

				if o.respond_to?(:og_pre_read)
					pre_cb << "#{obs}.og_pre_read(conn, self);"
				end

				if o.respond_to?(:og_post_read)
					post_cb << "#{obs}.og_post_read(conn, self);"
				end
			end
		end

		klass.class_eval %{
	 		def og_read(res, tuple = nil)
				#{pre_cb}
				#{code.join('; ')}
				#{post_cb}
			end
		}
	end				

end

end