module ReactiveRecord
  class Base
  
    # Its all about lazy loading. This prevents us from grabbing enormous association collections, or large attributes
    # unless they are explicitly requested.
  
    # During prerendering we get each attribute as its requested and fill it in both on the javascript side, as well as
    # remember that the attribute needs to be part of the download to client. 
  
    # On the client we fill in the record data with empty values (nil, or one element collections) but only as the attribute
    # is requested.  Each request queues up a request to get the real data from the server.
  
    # The ReactiveRecord class serves two purposes.  First it is the unique data corresponding to the last known state of a 
    # database record.  This means All records matching a specific database record are unique.  This is unlike AR but is 
    # important both for the lazy loading and also so that when values change react can be informed of the change.
  
    # Secondly it serves as name space for all the ReactiveRecord specific methods, so every AR Instance has a ReactiveRecord
  
    # Because there is no point in generating a new ar_instance everytime a search is made we cache the first ar_instance created.
    # Its possible however during loading to create a new ar_instances that will in the end point to the same record.
  
    # VECTORS... are an important concept.  They are the substitute for a primary key before a record is loaded.
    # Vectors have the form [ModelClass, method_call, method_call, method_call...]
  
    # Each method call is either a simple method name or an array in the form [method_name, param, param ...]
    # Example [User, [find, 123], todos, active, [due, "1/1/2016"], title]
    # Roughly corresponds to this query: User.find(123).todos.active.due("1/1/2016").select(:title)
  
    attr_accessor :ar_instance
    attr_accessor :vector
    attr_accessor :model
    
    # While data is being loaded from the server certain internal behaviors need to change
    # for example records all record changes are synced as they happen.
    # This is implemented this way so that the ServerDataCache class can use pure active
    # record methods in its implementation
    
    def self.data_loading?
      @data_loading
    end
    
    def data_loading?
      self.class.data_loading?
    end
    
    def self.load_data(&block)
      current_data_loading, @data_loading = [@data_loading, true]
      yield
      @data_loading = current_data_loading
    end
    
    def self.load_from_json(json, target = nil)
      load_data { ServerDataCache.load_from_json(json, target) }
    end
    
    def self.class_scopes(model)
      @class_scopes[model.base_class]
    end
  
    def self.find(model, attribute, value) 
      # will return the unique record with this attribute-value pair
      # value cannot be an association or aggregation
        
      model = model.base_class
      # already have a record with this attribute-value pair?
      record = @records[model].detect { |record| record.attributes[attribute] == value}
      if !record and attribute == 'id' and !@disabled_debugging
       # `debugger`
      end
      unless record
        # if not, and then the record may be loaded, but not have this attribute set yet,
        # so find the id of of record with the attribute-value pair, and see if that is loaded.
        # find_in_db returns nil if we are not prerendering which will force us to create a new record
        # because there is no way of knowing the id.
        if attribute != model.primary_key and id = find_in_db(model, attribute, value)
          record = @records[model].detect { |record| record.id == id} 
        end
        # if we don't have a record then create one
        (record = new(model)).vector = [model, ["find_by_#{attribute}", value]] unless record
        # and set the value
        record.sync_attribute(attribute, value)
        # and set the primary if we have one
        record.sync_attribute(model.primary_key, id) if id
      end
    
      # finally initialize and return the ar_instance
      record.ar_instance ||= infer_type_from_hash(model, record.attributes).new(record)
    end
  
    def self.new_from_vector(model, aggregate_parent, *vector)
      # this is the equivilent of find but for associations and aggregations
      # because we are not fetching a specific attribute yet, there is NO communication with the 
      # server.  That only happens during find.
    
      model = model.base_class
    
      # do we already have a record with this vector?  If so return it, otherwise make a new one.
    
      record = @records[model].detect { |record| record.vector == vector}
      (record = new(model)).vector = vector unless record
      record.ar_instance ||= infer_type_from_hash(model, record.attributes).new(record)
    
    end
    
    def initialize(model, hash = {}, ar_instance = nil)
      @model = model
      @ar_instance = ar_instance
      @synced_attributes = {}
      @attributes = {}
      records[model] << self
    end
  
    def find(*args)
      self.class.find(*args)
    end
  
    def new_from_vector(*args)
      self.class.new_from_vector(*args)
    end
  
    def primary_key
      @model.primary_key
    end
  
    def id
      attributes[primary_key]
    end
  
    def id=(value)
      # we need to keep the id unique
      existing_record = records[@model].detect { |record| record.attributes[primary_key] == value}
      if existing_record
        @ar_instance.instance_eval { @backing_record = existing_record }
        existing_record.attributes.merge!(attributes) { |key, v1, v2| v1 }
      else
        attributes[primary_key] = value
      end
    end
  
    def attributes
      @last_access_at = Time.now
      @attributes
    end
  
    def reactive_get!(attribute)
      unless @destroyed
        apply_method(attribute) unless @attributes.has_key? attribute 
        React::State.get_state(self, attribute) unless data_loading?
        attributes[attribute]
      end
    end
  
    def reactive_set!(attribute, value)
      unless @destroyed or (!(attributes[attribute].is_a? DummyValue) and attributes.has_key?(attribute) and attributes[attribute] == value)
        if association = @model.reflect_on_association(attribute) 
          if association.collection? 
            collection = Collection.new(association.klass, @ar_instance, association)
            collection.replace(value || [])
            value = collection
          else
            inverse_of = association.inverse_of
            inverse_association = association.klass.reflect_on_association(inverse_of)
            if inverse_association.collection?
              if !value
                attributes[attribute].attributes[inverse_of].delete(@ar_instance) if attributes[attribute]
              elsif value.attributes[inverse_of]
                value.attributes[inverse_of] << @ar_instance
              else
                value.attributes[inverse_of] = Collection.new(@model, value, inverse_association)
                value.attributes[inverse_of].replace [@ar_instance]
              end
            elsif value
              attributes[attribute].attributes[inverse_of] = nil if attributes[attribute]
              value.attributes[inverse_of] = @ar_instance 
              React::State.set_state(value.instance_variable_get(:@backing_record), inverse_of, @ar_instance) unless data_loading?
            elsif attributes[attribute]
              attributes[attribute].attributes[inverse_of] = nil
            end
          end
        end
        was_changed = changed2(@attributes.dup)
        attributes[attribute] = value
        React::State.set_state(self, attribute, value) unless data_loading?
        React::State.set_state(self, self, :changed) unless data_loading? or (was_changed == changed2({attribute => value}))
      end
      value
    end
    
    def changed?(*args)
      changed2(if args.count == 0
        React::State.get_state(self, self)
        @attributes.dup
      else
        React::State.get_state(@attributes, args[0])
        {args[0] => @attributes[args[0]]}
      end)
    end
  
    def changed2(attrs)
      attrs.each do |attribute, value|
        if association = @model.reflect_on_association(attribute) and association.collection? and value
          return true unless value == @synced_attributes[attribute]
        elsif !@synced_attributes.has_key?(attribute)
          return true
        elsif @synced_attributes[attribute] != value
          return true
        end
      end
      false
    end
  
    def sync!(hash = {})
      @attributes.merge! hash
      @synced_attributes = @attributes.dup
      @synced_attributes.each { |key, value| @synced_attributes[key] = value.dup_for_sync if value.is_a? Collection }
      @saving = false
      React::State.set_state(self, self, :synced) unless data_loading?
      self
    end
  
    def sync_attribute(attribute, value)
      @synced_attributes[attribute] = attributes[attribute] = value
      @synced_attributes[attribute] = value.dup if value.is_a? ReactiveRecord::Collection
      value
    end
    
    def revert
      @attributes.each do |attribute, value|
        @ar_instance.send("#{attribute}=", @synced_attributes[attribute])
      end
      @attributes.delete_if { |attribute, value| !@synced_attributes.has_key?(attribute) }
    end
    
    def saving! 
      React::State.set_state(self, self, :saving) unless data_loading?
      @saving = true
    end
    
    def saving?
      React::State.get_state(self, self)
      @saving
    end
  
    def find_association(association, id)
      inverse_of = association.inverse_of
      instance = if id
        find(association.klass, association.klass.primary_key, id)
      else
        new_from_vector(association.klass, nil, *vector, association.attribute)
      end
      instance_backing_record_attributes = instance.instance_variable_get(:@backing_record).attributes
      inverse_association = association.klass.reflect_on_association(inverse_of)
      if inverse_association.collection?
        instance_backing_record_attributes[inverse_of] = if id and id != ""
          Collection.new(@model, instance, inverse_association, association.klass, ["find", id], inverse_of) 
        else
          Collection.new(@model, instance, inverse_association, *vector, association.attribute, inverse_of) 
        end unless instance_backing_record_attributes[inverse_of]
        instance_backing_record_attributes[inverse_of].replace [@ar_instance]
      else
        instance_backing_record_attributes[inverse_of] = @ar_instance 
      end if inverse_of and !instance_backing_record_attributes.has_key?(inverse_of)
      instance
    end
        
    def apply_method(method)
      # Fills in the value returned by sending "method" to the corresponding server side db instance
      if id or vector
        sync_attribute(
          method, 
          if association = @model.reflect_on_association(method)
            if association.collection? 
              Collection.new(association.klass, @ar_instance, association, *vector, method)
            else
              find_association(association, (id and id != "" and self.class.fetch_from_db([@model, [:find, id], method, @model.primary_key])))
            end
          elsif aggregation = @model.reflect_on_aggregation(method)
            new_from_vector(aggregation.klass, self, *vector, method)
          elsif id and id != "" 
            value = self.class.fetch_from_db([@model, [:find, id], method]) || self.class.load_from_db(*vector, method)
          else  # its a attribute in an aggregate or we are on the client and don't know the id
            self.class.fetch_from_db([*vector, method]) || self.class.load_from_db(*vector, method)
          end
        )
      elsif association = @model.reflect_on_association(method) and association.collection?
        @attributes[method] = Collection.new(association.klass, @ar_instance, association)
      elsif aggregation = @model.reflect_on_aggregation(method)
        @attributes[method] = aggregation.klass.new
      end
    end
  
    def self.infer_type_from_hash(klass, hash)
      klass = klass.base_class  
      return klass unless hash
      type = hash[klass.inheritance_column]
      begin
        return Object.const_get(type)
      rescue Exception => e
        message = "Could not subclass #{@model_klass.model_name} as #{type}.  Perhaps #{type} class has not been required. Exception: #{e}"
        `console.error(#{message})`
      end if type
      klass
    end
  
  end
end