##   RSence
 #   Copyright 2006 Riassence Inc.
 #   http://riassence.com/
 #
 #   You should have received a copy of the GNU General Public License along
 #   with this software package. If not, contact licensing@riassence.com
 ##

module ::RSence
  module Plugins
    
    ## = Abstract
    ##
    ## The PluginTemplate is used to create a Plugin mimic class in
    ## Plugins.bundle_loader using the Plugins.PluginWrapper mimic.
    ##
    ## The Plugin class is the base class for extending server logic.
    ## A single Plugin instance serves the requests of all sessions,
    ## which makes them very cpu and memory efficient compared to systems,
    ## where the server classes are constructed and destructed for each
    ## request.
    ##
    ## Plugins are designed to be contained in a plugin directory bundle and
    ## to be loaded by the +PluginManager+, which is also responsible for
    ## delegating the events and other calls throughout the system.
    ##
    ## == Anatomy of a plugin bundle
    ## The plugin bundle contains all data needed to run the plugin. Design
    ## your plugin without any hard-coded paths, remember that it's intended
    ## to be deployed by "dropping" the whole plugin into one of the server's
    ## plugins directories.
    ##
    ## The +PluginManager+ looks for such bundles and evaluates them into an
    ## anonymous +Module+ namespace. The content of the ruby source file
    ## is then responsible for including its libraries, constructing an
    ## instance of itself and registering itself as a part of the system.
    ##
    ## It's advised to use the +GUIPlugin+ class for plugins that handle
    ## user interfaces. Usage of the +Plugin+ bundle is advised to use
    ## for plugins that provide extra functionality, value responders
    ## and other utilities that supplement the user interface.
    ##
    ## You must call the +#register+ method after the class is constructed.
    ## Otherwise, the class is not connected to the system and just discarded
    ## and then garbage collected.
    ##
    ## == Messages
    ## As a side effect of having single instances of plugins serve the requests
    ## of all sessions, the request/response/session messaging is implemented
    ## as messaging objects. These objects contain or delegate all the necessary
    ## hooks required by the complete request/response cycle.
    ##
    ## The naming convention of the +Message+ instance is +msg+ and it's
    ## given as the first parameter of methods needing it.
    ##
    ## Use +msg.ses_id+ to identify the session's serial number and +msg.user_id+
    ## to identify the user's identity.
    ##
    ## Use the +msg.session+ +Hash+ to store any persistent data
    ## associated with the user's session, preferably using the name of the
    ## plugin or its registered name as the primary key entry in the Hash.
    ## The session data is persistent; it's stored in the session database
    ## by +SessionStorage+ automatically.
    ##
    ## The +msg+ instance also provides access to the +Request+ and +Response+
    ## objects as +msg.request+ and +msg.response+, respectively.
    ##
    ## Use the +msg.run+ method to call other plugins.
    ##
    ## To append js source code to be evaluated in the client, use the +msg.reply+
    ## call. The +msg.console+ call appends messages to the browser's js console.
    ##
    ##
    ## == Session -related event methods
    ## The +#get_ses+ method returns (or creates and returns) the entry in
    ## the session based on the name your plugin is registered as. It's advised
    ## to use this call instead of manually managing +msg.session+ in most cases.
    ##
    ## The +#idle+ method is called each time a client performs a data
    ## synchronization or "idle poll" request.
    ##
    ## The +#init_ses+ method is called once in the same request a new session
    ## is created. A new session is created, when a user enters accesses the
    ## server the first time, or the first time after the previous session is 
    ## expired.
    ##
    ## The +#init_ui+ method is called by the "main" plugin after the client has
    ## booted successfully. The +GUIPlugin+ class extends this method to
    ## automatically load and initialize the user interface from a data structure.
    ##
    ## The +#restore_ses+ method is called once in the same request an old
    ## session is restored. A session is restored, when the user returns to
    ## the page or reloads the page before the session is expired.
    ##
    ## === When the server is configured to restore previous sessions (default):
    ## If the user accesses the same page using the same browser (in different
    ## tabs or windows), only the most recently restored one is valid, while 
    ## the previous ones are immediately invalidated.
    ## If your application is intended to support several sessions per browser,
    ## enable session cloning in the configuration file.
    ##
    ## === When the server is configured to restore and clone previous sessions:
    ## When sessions are cloned, the previous session is not invalidated and
    ## exists until timing out as a result of the web browser window being closed
    ## or client computer losing network connectivity for a certain (configurable)
    ## time frame.
    ##
    ## The +#cloned_target+ method is like +#restore_ses+, but called when 
    ## the session is a clone of a previous session.
    ##
    ## The +#cloned_source+ method is called on the next request of the previous
    ## session after it has been cloned.
    ##
    ## == Server event methods
    ## Extend the +#init+ method to invoke constructor functionality that
    ## depends on the plugin to be constructed and registered as a part of
    ## the system.
    ##
    ## Extend the +#open+, +#flush+ and +#close+ methods to open, flush and close
    ## streams or other similar functionality.
    ##
    ## == Data handling
    ## The data exchange system exists to support bi-directional
    ## data synchronization between the browser and the plugin. The values
    ## are stored in the session as +HValue+ instances.
    ##
    ## Values support Hashes, Arrays, Strings, Numbers, Booleans and
    ## combinations of them. The data is automatically converted between
    ## ruby objects (server) and json objects (client).
    ##
    ## Each instance may be bound to plugin methods that are used as
    ## value change notification responders.
    ##
    ## When a method is bound to the value, the method is called as an
    ## event notification whenever the client has changed the value and
    ## synchronizes it to the server. The responders act as validators
    ## by default.
    ##
    ## Values are also bound in the client to classes implementing the
    ## HValueResponder interface, like any derivate of HControl. See the
    ## client documentation for instructions about using them.
    ##
    ## To define a value responder method, it needs to respond to exactly
    ## two parameters: the +Message+ instance +msg+ and the HValue object
    ## (in that order). The method's return value must be either +true+
    ## or +false+. When the method returns +false+, the change is discarded
    ## and the previously server-set value is sent back to the client.
    ##
    ## A minimal value responder method is defined like this:
    ##
    ##    def my_value_responder( msg, my_value )
    ##      return true
    ##    end
    ##
    ## To access the content of the value, use the +HValue#data+ attribute.
    ##
    ##    def int_between_100_and_200( msg, value )
    ##      data = value.data.to_i
    ##      return ( data >= 100 and data <= 200 )
    ##    end
    ##
    ## To change the content of the value, use the +HValue#set+ method.
    ##
    ##    def int_between_100_and_200( msg, value )
    ##      data = value.data.to_i
    ##      value.set( msg, 100 ) if data < 100
    ##      value.set( msg, 200 ) if data > 200
    ##      return true
    ##    end
    ##
    ## == Defining values
    ## The simplest and recommended way of defining the values is to define
    ## the value configuration file +values.yaml+. Its configuration is then
    ## applied to sessions automatically.
    ##
    ## 
    ## === Syntax reference of the contents of a +values.yaml+ file:
    ##
    ##    # The name of the value (:value_name).
    ##    # A hash key in the yaml syntax
    ##    :value_name:
    ##      
    ##      # All of these keys are optional!
    ##      
    ##      # Default value, a string "Foo" here.
    ##      # Defaults to 0
    ##      :value: Foo
    ##      
    ##      # A plugin method to call to define the default value
    ##      # instead of the one defined in :value
    ##      :value_call:
    ##        :plugin: plugin_name # defaults to the plugin where defined
    ##        
    ##        # Mandatory; name of the method to call
    ##        :method: method_name
    ##        
    ##        # Optional, list of parameter values for the :method
    ##        :args:
    ##          # three parameters: 1, 'foo', 3
    ##          - 1
    ##          - foo
    ##          - 3
    ##        
    ##        # When false, doesn't pass the msg as the first parameter.
    ##        # Defaults to true
    ##        :uses_msg: true
    ##      
    ##      # Restore the default, when the session is restored; defaults to false
    ##      :restore_default: false
    ##      
    ##      # List of value responder methods to bind.
    ##      :responders:
    ##        - 
    ##          # name of plugin to call, defaults to the plugin where defined:
    ##          :plugin: plugin_name
    ##          
    ##          # mandatory, name of the method to call
    ##          :method: method_name
    ##        
    ##        # Another responder, this one using the same plugin where defined:
    ##        - :method: another_method
    ##    
    ##    # Another value, this one just defining the defaults
    ##    # by supplying an empty Hash:
    ##    # (value: 0, default restored, no responders or calls)
    ##    :value_with_defaults: {}
    ##    
    ##    # This value defines a Number (123) and doesn't restore
    ##    # the default, when restoring the session.
    ##    :one_two_three:
    ##      :value: 123
    ##      :restore_default: false
    ##    
    ##    # This value gets a random string and specifies a responder,
    ##    # that ensures it's unique, if changed in the client.
    ##    :random_unique_string:
    ##      :value_call:
    ##        :method:   get_unique_random_string
    ##        :uses_msg: false
    ##      :responders:
    ##        - :method: ensure_unique_random_string
    ##
    ## = Examples
    ## More examples are available in the repository;
    ## http://svn.rsence.org/contrib/plugins
    ## ..as well as the standard "main" plugin in the "plugins" directory.
    ## 
    ## 
    ## == A minimal Plugin bundle
    ## The minimal active plugin bundle (named "name_of_plugin")
    ## is defined like this:
    ##
    ##    [dir] name_of_plugin
    ##      |
    ##      +---[file] name_of_plugin.rb
    ##
    ## This sample Plugin doesn't do anything except construct itself and
    ## respond as 'name_of_plugin'.
    ##
    ##    Plugin.new.register('name_of_plugin')
    ##
    ## However, this is not very useful in itself, so you'll need to extend
    ## its functionality to do anything useful.
    ##
    ## == A simple Plugin extension
    ## This plugin logs session events to the logs/session_log file.
    ##
    ##    [dir] ses_logger
    ##      |
    ##      +---[file] ses_logger.rb
    ##      |
    ##      +---[dir] logs
    ##            |
    ##            +---[file] session_log
    ##
    ## == Contents of "ses_logger.rb"
    ##
    ##    class SessionLogger < Plugin
    ##      def init
    ##        super
    ##        @logfile = false
    ##      end
    ##      def open
    ##        log_path = bundle_path( 'session_log', 'logs' )
    ##        @logfile = File.open( log_path, 'a' )
    ##      end
    ##      def close
    ##        @logfile.close if @logfile
    ##        @logfile = false
    ##      end
    ##      def flush
    ##        @logfile.flush if @logfile
    ##      end
    ##      def init_ses( msg )
    ##        super
    ##        @logfile.write( "#{Time.new} -- Session id #{msg.ses_id} was created.\n" )
    ##      end
    ##      def restore_ses( msg )
    ##        super
    ##        @logfile.write( "#{Time.new} -- Session id #{msg.ses_id} was restored.\n" )
    ##      end
    ##      def idle( msg )
    ##        @logfile.write( "#{Time.new} -- Client of session id #{msg.ses_id} connected.\n" )
    ##      end
    ##    end
    ##    SessionLogger.new.register( 'ses_logger' )
    ##
    class PluginTemplate
      include PluginUtil
      def self.bundle_type; :Plugin; end
  
      # The +names+ is a list of (usually just one) names the plugin is registered under.
      attr_reader :name, :path, :info, :inited
  
      # The constructor should not take any parameters. In most cases, it's better
      # to extend the +#init+ method, because it's called after the plugin is set up.
      def initialize( bundle_name, bundle_info, bundle_path, plugin_manager )
        @inited  = false
        @info    = bundle_info
        @name    = bundle_name
        @path    = bundle_path
        @plugins = plugin_manager
        register unless @info[:inits_self]
      end
  
      # Extend this method to do any initial tasks before other methods are called.
      # By default init_values is called to load the +values.yaml+ configuration file.
      def init
        @values = init_values
      end
  
      # Extend this method to do any tasks every time the client makes a request.
      def idle( msg )
      end
  
      # Extend this method to invoke actions, when a new session is created.
      # By default +#init_ses_values+ is called to initialize values defined in the 
      # +values.yaml+ configuration file.
      def init_ses( msg )
        init_ses_values( msg )
      end
  
      # Extend this method to invoke actions, when a previous session is restored.
      # By default +#restore_ses_values+ is called to perform actions on values as
      # defined in the +values.yaml+ configuration file.
      def restore_ses( msg )
        restore_ses_values( msg )
      end
  
      # Extend this method to invoke actions, when the session
      # is a clone of another session. It's called once, just
      # before +#restore_ses+ is called.
      #
      # A session is cloned, when a user opens a another browser
      # window or tab, while the previous session is still active.
      #
      # The +source_ses+ is the actual previous session object, which
      # was used as the source of the clone.
      def cloned_target( msg, source_session )
      end
  
      # Extend this method to invoke actions, when the session
      # has been cloned to another session. It's called once, just
      # before +#restore_ses+ is called on the first request after
      # the cloning happened.
      #
      # A session is cloned, when a user opens a another browser
      # window or tab, while the previous session is still active.
      #
      # The +target_ses+ is the actual cloned session object, which
      # is a copy of the current session.
      def cloned_source( msg, target_sessions )
      end
  
      # This method must be called to register the plugin instance
      # into the system. Otherwise, it's subject to destruction
      # and garbage collection. Use the +name+ parameter to 
      # give the (unique) name of your plugin.
      def register( name=false )
        if @inited
          @plugins.register_alias( @name, name )
        else
          if name
            name = name.to_s
          else
            name = @name
          end
          @plugins.register_bundle( self, name )
          @inited = true
        end
      end
  
    private
  
      # This method looks looks for a file called "values.yaml"
      # in the plugin's bundle directory
      #.
      # If this file is found, it loads it for initial value definitions.
      #
      # These definitions are accessible as the +@values+ attribute.
      def init_values
        values_path = bundle_path( 'values.yaml' )
        return yaml_read( values_path )
      end
  
      # Returns all the names your plugin respond to.
      # def name
      #   return @names.first
      # end
  
  
      # Returns or creates a new session hash for the plugin.
      #
      # Uses the first name registered for the plugin and converts it to a symbol.
      def get_ses( msg )
        name_sym = name.to_sym
        unless msg.session.has_key?( name_sym )
          msg.session[ name_sym ] = {}
        end
        return msg.session[ name_sym ]
      end
  
      # Returns the source code of the javascript file +name+ in the 'js'
      # subdirectory of the plugin bundle.
      def read_js( js_name )
        file_read( bundle_path( js_name, 'js', '.js' ) )
      end
  
      # Deprecated name of +#read_js+
      alias require_js read_js
  
      # Like +#read_js+, but reads the file only once per session.
      #
      # Returns the contents of the file on the first call,
      # an empty string on the subsequent calls.
      #
      # Returns false otherwise.
      def read_js_once( msg, js_name )
        ses = msg.session
        if not ses.has_key?(:deps)
          ses[:deps] = []
        end
        path = bundle_path( js_name, 'js', '.js' )
        unless ses[:deps].include?( path )
          ses[:deps].push( path )
          return file_read( path )
        else
          return ''
        end
      end
  
      # Deprecated name of +#read_js_once+
      alias require_js_once read_js_once
  
      # Creates a new instance of HValue, assigns it as +value_name+ into the
      # session and uses the +value_properties+ Hash to define the default
      # value and value responders.
      #
      # This method is invoked automatically, when handling the properties
      # of the +values.yaml+ configuration file of a new session.
      #
      # It's invoked by +#init_ses+ via +#init_ses_values+.
      #
      # Structure of +value_properties+, all top-level items are optional:
      #
      #   {
      #     # Default value; defaults to 0
      #     :value => 'foo',
      #     
      #     # A plugin method to call to define the default value instead of the one defined in :value
      #     :value_call => {
      #       :plugin => 'plugin_name', # defaults to the plugin where defined
      #       :method => 'method_name', # mandatory; name of the method to call
      #       :args => [ 1, 'foo', 3 ], # optional, list of parameter values for the :method
      #       :uses_msg => true         # defaults to true; when false, doesn't pass the msg as the first parameter
      #     },
      #     
      #     # Restore the default, when the session is restored; defaults to false
      #     :restore_default => false,
      #     
      #     # List of value responder methods to bind.
      #     :responders => [
      #        {
      #          :plugin => 'plugin_name', # defaults to the plugin where defined
      #          :method => 'method_name'  # mandatory, name of the method to call
      #        },
      #        # You can supply as many responders as you like:
      #        { :plugin => 'another_plugin', :method => 'another_method' }
      #     ]
      #   }
      #
      def init_ses_value( msg, value_name, value_properties )
        ses = get_ses( msg )
        if value_properties.has_key?(:value_call)
          default_value = init_value_call( msg, value_properties[:value_call] )
        elsif value_properties.has_key?(:value)
          default_value = value_properties[:value]
        else
          default_value = 0
        end
        ses[value_name] = HValue.new( msg, default_value, { :name => "#{@name}.#{value_name}" } )
        if value_properties.has_key?(:responders)
          value_properties[:responders].each do |responder|
            if responder.has_key?(:plugin)
              responder_plugin = responder[:plugin]
            else
              responder_plugin = @name
            end
            if responder.has_key?(:method)
              ses[value_name].bind( responder_plugin, responder[:method] )
            end
          end
        end
      end
  
      # Initializes session values, if the contents of the +values.yaml+ 
      # file is defined in the bundle directory and loaded in +#init_values+.
      def init_ses_values( msg )
        return unless @values
        @values.each do | value_name, value_properties |
          init_ses_value( msg, value_name, value_properties )
        end
      end
  
      # Returns a value based on the :method and :plugin members of the
      # +value_call+ hash.
      #
      # The call is made via msg.run if the method is not defined in
      # the local plugin bundle.
      #
      # This method is called from +#init_ses_value+.
      #
      # Structure of the +value_call+ Hash:
      #   { :plugin => 'plugin_name', # defaults to the plugin where defined
      #     :method => 'method_name', # mandatory; name of the method to call
      #     :args => [ 1, 'foo', 3 ], # optional, list of parameter values for the :method
      #     :uses_msg => true         # defaults to true; when false, doesn't pass the msg as the first parameter
      #   }
      def init_value_call( msg, value_call )
        value_call_method = value_call[:method]
        if value_call.has_key?(:plugin)
          value_call_plugin = value_call[:plugin]
        else
          value_call_plugin = false
        end
        if value_call.has_key?(:args)
          if value_call.has_key?(:uses_msg) and value_call[:uses_msg] != false
            if value_call_plugin
              return msg.run( value_call_plugin, value_call_method, msg, *value_call[:args] )
            else
              return self.method( value_call_method ).call( msg, *value_call[:args] )
            end
          else
            if value_call_plugin
              return msg.run( value_call_plugin, value_call_method, *value_call[:args] )
            else
              return self.method( value_call_method ).call( *value_call[:args] )
            end
          end
        else
          if value_call.has_key?(:uses_msg) and value_call[:uses_msg] != false
            if value_call_plugin
              return msg.run( value_call_plugin, value_call_method, msg )
            else
              return self.method( value_call_method ).call( msg )
            end
          else
            if value_call_plugin
              return msg.run( value_call_plugin, value_call_method )
            else
              return self.method( value_call_method ).call( )
            end
          end
        end
      end
  
      # Restores session values to default, unless specified otherwise.
      #
      # Called from +#restore_ses+
      def restore_ses_values( msg )
        return unless @values
        ses = get_ses( msg )
        @values.each do | value_name, value_properties |
          if ses.has_key?( value_name ) and ses[ value_name ].class == HValue
            unless value_properties[:restore_default] == false
              if value_properties.has_key?(:value_call)
                default_value = init_value_call( msg, value_properties[:value_call] )
              elsif value_properties.has_key?(:value)
                default_value = value_properties[:value]
              else
                default_value = 0
              end
              ses[value_name].set( msg, default_value )
            end
          else
            init_ses_value( msg, value_name, value_properties )
          end
        end
      end
  
      # Extracts +HValue+ references as javascript from the session Hash.
      # The +ses+ parameter is used for supplying a hash with the +HValue+
      # instances. It's optional and defaults to the current plugin node in
      # the active session.
      # 
      # The return value is a string representing a js object similar to
      # the ruby Hash +ses+.
      # 
      # Sample usage:
      #
      #   values_js( msg, msg.session[:main] )
      #
      def values_js( msg, ses=false )
        # backwards-compatible with pre-1.3 behaviour
        ses = msg if msg.class == Hash
        # gets the session automatically, if false
        ses = get_ses( msg ) unless ses
        js_references = []
        ses.each_key do |key_name|
          if ses[key_name].class == HValue
            js_references.push( "#{key_name.to_s}:HVM.values['#{ses[key_name].val_id}']" )
          end
        end
        return "{#{js_references.join(',')}}"
      end
  
      # Deprecated name of +#values_js+
      alias extract_hvalues_from_hash values_js
  
      # Tells the js client framework to load a list of dependency packages.
      # It keeps track of what's loaded, so nothing library loaded twice.
      #
      # The +dependencies+ parameter is an Array of dependencies.
      #
      # Sample usage:
      #
      #   include_js( msg, [ 'default_theme', 'controls', 'lists', 'datetime' ] )
      #
      def include_js( msg, dependencies=[] )
        ses = msg.session
        # check, if the session has a dependency array
        if not ses.has_key?( :deps )
          # make an array of dependencies for this session, if not already done
          ses[:deps] = []
        end
        dependencies = [dependencies] if dependencies.class == String
        # Check the required dependencies until everything is loaded.
        dependencies.each do |dependency|
          unless ses[:deps].include?( dependency )
            ses[:deps].push( dependency )
            msg.reply(%{jsLoader.load("#{dependency}");})
          end
        end
      end
    end
  end
end