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

module Og; 

require 'glue/property'
require 'glue/array'
require 'glue/time'

# A Connection to the Database. This file defines the skeleton 
# functionality. A backend specific implementation file (driver) 
# implements all methods.
#
# === Future 
#
# - support caching.
# - support prepared statements.

class Connection

	# The Og database object. 
	
	attr_reader :db

	# The actual connection to the backend store.

	attr_accessor :store

	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
	# :section: Backend connection methods.
	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

	# Initialize a connection to the database.
	
	def initialize(db)
		@db = db
		Logger.debug "Created DB connection." if $DBG 
	end
	
	# Close the connection to the database.
	
	def close
		Logger.debug "Closed DB connection." if $DBG
	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
	
	# Drop the managed object table.
	
	def drop_table(klass)
		exec "DROP TABLE #{klass::DBTABLE}"
	end

	# Prepare an sql statement.

	def prepare(sql)
		raise 'Not implemented!'		
	end
	
	# Execute an SQL query and return the result.
	
	def query(sql)
		raise 'Not implemented!'
	end
	
	# Execute an SQL query, no result returned.
	
	def exec(sql)
		raise 'Not implemented!'
	end
	alias_method :execute, :exec

	# Start a new transaction.
	
	def start
		exec 'START TRANSACTION'
	end
	
	# Commit a transaction.
	
	def commit
		exec 'COMMIT'
	end
	
	# Rollback a transaction.
	
	def rollback
		exec 'ROLLBACK'
	end
	
	# Transaction helper. In the transaction block use
	# the db pointer to the backend.
	
	def transaction(&block)
		begin
			start
			yield(self) 
			commit
		rescue => ex
			Logger.error "DB Error: ERROR IN TRANSACTION"
			Logger.error "#{ex}"
			Logger.error "#{ex.backtrace}"
			rollback
		end
	end
		
	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
	# :section: Deserialization methods.
	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

	# Is the given resultset valid?

	def valid_res?(res)
		return !(res.nil?)
	end
	
	# Read (deserialize) one row of the resultset.
	
	def read_one(res, klass)
		raise 'Not implemented!'
	end

	# Read (deserialize) all rows of the resultset.

	def read_all(res, klass)
		raise 'Not implemented!'
	end

	# Read the first column of the resultset as an Integer.

	def read_int(res, idx = 0)
		raise 'Not implemented!'
	end

	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
	# :section: Managed object methods.
	# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

	# Save an object to the database. Insert if this is a new object or
	# update if this is already stored in the database.
		
	def save(obj)
		if obj.oid
			# object allready inserted, update!
			obj.og_update(self)
		else
			# not in the database, insert!
			obj.og_insert(self)
		end
	end
	alias_method :<<, :save
	alias_method :put, :save
	
	# Force insertion of managed object.
	
	def insert(obj)
		obj.og_insert(self)
	end

	# Force update of managed object.
	
	def update(obj)
		obj.og_update(self)
	end

	# Update only specific fields of the managed object.
	# 
	# Input:
	# sql = the sql code to updated the properties.
	#
	# WARNING: the object in memory is not updated.
	#--
	# TODO: should update the object in memory.
	#++
	
	def update_properties(update_sql, obj_or_oid, klass = nil)
		oid = obj_or_oid.to_i
		klass = obj_or_oid.class unless klass
		
		exec "UPDATE #{klass::DBTABLE} SET #{update_sql} WHERE oid=#{oid}"
	end
	alias_method :pupdate, :update_properties

	# Load an object from the database.
	#
	# Input:
	# oid = the object oid, OR the object name.
	
	def load(oid, klass)
		if oid.to_i > 0 # a valid Fixnum ?
			load_by_oid(oid, klass)
		else
			load_by_name(oid, klass)
		end
	end
	alias_method :get, :load
	
	# Load an object by oid.
	
	def load_by_oid(oid, klass)
		res = query "SELECT * FROM #{klass::DBTABLE} WHERE oid=#{oid}"
		read_one(res, klass)
	end
	alias_method :get_by_oid, :load_by_oid
	
	# Load an object by name.
	
	def load_by_name(name, klass)
		res = query "SELECT * FROM #{klass::DBTABLE} WHERE name='#{name}'"
		read_one(res, klass)
	end
	alias_method :get_by_name, :load_by_name
	
	# Load all objects of the given klass.
	# Used to be called 'collect' in an earlier version.
	
	def load_all(klass, extrasql = nil)
		res = query "SELECT * FROM #{klass::DBTABLE} #{extrasql}"
		read_all(res, klass)
	end
	alias_method :get_all, :load_all
	
	# Perform a standard SQL query to the database. Deserializes the
	# results.
	
	def select(sql, klass)
		unless sql =~ /SELECT/i
			sql = "SELECT * FROM #{klass::DBTABLE} WHERE #{sql}"
		end
		
		res = query(sql)
		read_all(res, klass)
	end
	
	# Optimized for one result.
	
	def select_one(sql, klass)
		unless sql =~ /SELECT/i
			sql = "SELECT * FROM #{klass::DBTABLE} WHERE #{sql}"
		end
		
		res = query(sql)
		read_one(res, klass)
	end	

	# Perform a count query.
		
	def count(sql, klass = nil)
		unless sql =~ /SELECT/i
			sql = "SELECT COUNT(*) FROM #{klass::DBTABLE} WHERE #{sql}"
		end
		
		res =	query(sql)
		return read_int(res)
	end
	
	# Delete an object from the database. Allways perform a deep delete.
	#
	# No need to optimize here with pregenerated code. Deletes are
	# not used as much as reads or writes.
	#
	# Input:
	#
	# obj_or_oid = Object or oid to delete.
	# klass = Class of object (can be nil if an object is passed)
	#
	#--
	# TODO: pre evaluate for symmetry to the other methods
	#++
	
	def delete(obj_or_oid, klass = nil, cascade = true)
		oid = obj_or_oid.to_i
		klass = obj_or_oid.class unless klass

		# this is a class callback!
		
		if klass.respond_to?(:og_pre_delete)
			klass.og_pre_delete(self, oid)
		end
		
		# TODO: implement this as stored procedure? naaah.
		# TODO: also handle many_to_many relations.

		transaction do |tx|
			tx.exec "DELETE FROM #{klass::DBTABLE} WHERE oid=#{oid}"
			if cascade and klass.__meta.include?(:descendants)
				klass.__meta[:descendants].each do |dclass, linkback|
					tx.exec "DELETE FROM #{dclass::DBTABLE} WHERE #{linkback}=#{oid}"
				end
			end
		end
	end
	alias_method :delete!, :delete
		
end

end