require 'representable/deprecations'
require 'representable/definition'

# Representable can be used in two ways.
#
# == On class level
#
# To try out Representable you might include the format module into the represented class directly and then
# define the properties.
#
#   class Hero < ActiveRecord::Base
#     include Representable::JSON
#     property :name
#
# This will give you to_/from_json for each instance. However, this approach limits your class to one representation.
#
# == On module level
#
# Modules give you much more flexibility since you can mix them into objects at runtime, following the DCI
# pattern.
#
#   module HeroRepresenter
#     include Representable::JSON
#     property :name
#   end
#
#   hero.extend(HeroRepresenter).to_json
module Representable
  attr_writer :representable_attrs
  
  def self.included(base)
    base.class_eval do
      extend ClassInclusions, ModuleExtensions
      extend ClassMethods
      extend ClassMethods::Declarations
      
      include Deprecations
    end
  end
  
  # Reads values from +doc+ and sets properties accordingly.
  def update_properties_from(doc, options, format)
    representable_bindings_for(format).each do |bin|
      next if skip_property?(bin, options)
      
      uncompile_fragment(bin, doc)
    end
    self
  end
  
private
  # Compiles the document going through all properties.
  def create_representation_with(doc, options, format)
    representable_bindings_for(format).each do |bin|
      next if skip_property?(bin, options)
      
      compile_fragment(bin, doc)
    end
    doc
  end
  
  # Checks and returns if the property should be included.
  def skip_property?(binding, options)
    return true if skip_excluded_property?(binding, options)  # no need for further evaluation when :exclude'ed
    
    skip_conditional_property?(binding)
  end
  
  def skip_excluded_property?(binding, options)
    return unless props = options[:exclude] || options[:include]
    res   = props.include?(binding.definition.name.to_sym)
    options[:include] ? !res : res
  end
  
  def skip_conditional_property?(binding)
    return unless condition = binding.definition.options[:if]
    not instance_exec(&condition)
  end
  
  # Retrieve value and write fragment to the doc.
  def compile_fragment(bin, doc)
    value = send(bin.definition.getter)
    value = bin.definition.default_for(value)
    
    write_fragment_for(bin, value, doc)
  end
  
  # Parse value from doc and update the model property.
  def uncompile_fragment(bin, doc)
    value = read_fragment_for(bin, doc)
    
    if value == Binding::FragmentNotFound
      return unless bin.definition.has_default?
      value = bin.definition.default
    end
    
    send(bin.definition.setter, value)
  end
  
  def write_fragment_for(bin, value, doc) # DISCUSS: move to Binding?
    return if bin.definition.skipable_nil_value?(value)
    bin.write(doc, value)
  end
  
  def read_fragment_for(bin, doc) # DISCUSS: move to Binding?
    bin.read(doc)
  end
  
  def representable_attrs
    @representable_attrs ||= self.class.representable_attrs # DISCUSS: copy, or better not?
  end
  
  def representable_bindings_for(format)
    representable_attrs.map {|attr| send("#{format}_binding_for_definition", attr) }  # DISCUSS: call that on attr directly?
  end
  
  # Returns the wrapper for the representation. Mostly used in XML.
  def representation_wrap
    representable_attrs.wrap_for(self.class.name)
  end
  
  
  module ClassInclusions
    def included(base)
      super
      base.representable_attrs.push(*representable_attrs.clone) # "inherit".
    end
  end
  
  module ModuleExtensions
    # Copies the representable_attrs to the extended object.
    def extended(object)
      super
      object.representable_attrs=(representable_attrs)
    end
  end
  
  
  module ClassMethods
    # Create and yield object and options. Called in .from_json and friends. 
    def create_represented(document, *args)
      new.tap do |represented|
        yield represented, *args if block_given?
      end
    end
    
    
    module Declarations
      def representable_attrs
        @representable_attrs ||= Config.new
      end
      
      def representation_wrap=(name)
        representable_attrs.wrap = name
      end
      
      # Declares a represented document node, which is usually a XML tag or a JSON key.
      #
      # Examples:
      #
      #   property :name
      #   property :name, :from => :title
      #   property :name, :class => Name
      #   property :name, :default => "Mike"
      #   property :name, :render_nil => true
      def property(name, options={})
        representable_attrs << definition_class.new(name, options)
      end
      
      # Declares a represented document node collection.
      #
      # Examples:
      #
      #   collection :products
      #   collection :products, :from => :item
      #   collection :products, :class => Product
      def collection(name, options={})
        options[:collection] = true
        property(name, options)
      end
      
      def hash(name=nil, options={})
        return super() unless name  # allow Object.hash.
        
        options[:hash] = true
        property(name, options)
      end
      
    private
      def definition_class
        Definition
      end
    end
  end
  
  
  class Config < Array
    attr_accessor :wrap
    
    # Computes the wrap string or returns false.
    def wrap_for(name)
      return unless wrap
      return infer_name_for(name) if wrap === true
      wrap
    end
    
    def clone
      self.class.new(collect { |d| d.clone })
    end
    
  private
    def infer_name_for(name)
      name.to_s.split('::').last.
       gsub(/([A-Z]+)([A-Z][a-z])/,'\1_\2').
       gsub(/([a-z\d])([A-Z])/,'\1_\2').
       downcase
    end
  end
end