require 'json'
require 'yaml'
require_relative 'blobject/version'

# Wraps a hash to provide arbitrarily nested object-style attribute access
class Blobject

  # filter :to_ary else Blobject#to_ary returns a
  # blobject which is not cool, especially if you are puts.
  ProhibitedNames = [:to_ary]

  # pass an optional hash of values to preload
  # you can also pass a block, the new Blobject will be yield
  def initialize hash = {}

    @hash = Hash.new

    hash.each do |key, value|
      key = key.to_sym unless key.is_a? Symbol
      @hash[key] = value
    end

    @hash.each do |name, node|
      @hash[name] = self.class.send(:__blobjectify__, node)
    end

    yield self if block_given?
  end

  # indicates whether the blobject contains any data
  def empty?
    @hash.empty?
  end

  # delegates to the internal Hash
  def inspect

    @hash.inspect
  end

  # access the internal hash. be careful, this is _not_ a copy
  def hash
    @hash
  end

  # creates a recursive copy of the internal hash
  def to_hash

    h = hash.dup
    @hash.each do |name, node|
      h[name] = node.to_hash if node.respond_to? :to_hash
    end
    h
  end

  # method_missing is only called the first time an attribute is used. successive calls use
  # memoized getters, setters and checkers
  def method_missing method, *params, &block

    __tag_and_raise__ NoMethodError.new(method) if ProhibitedNames.include?(method)

    case
    # assignment in conditionals is usually a bad smell, here it helps minimize regex matching
    when (name = method[/^\w+$/, 0]) && params.length == 0
      # the call is an attribute reader

      return self.class.new.freeze if frozen? and not @hash.has_key?(method)
      self.class.send :__define_attribute__, name

      return send(method) if @hash.has_key? method

      # close the scope for storing call chain
      parent          = self
      nested_blobject = self.class.new

      store_in_parent = lambda do
        parent.send "#{name}=", nested_blobject
        nested_blobject.send :remove_instance_variable, :@store_in_parent
      end

      nested_blobject.instance_variable_set :@store_in_parent, store_in_parent

      return nested_blobject

    when (name = method[/^(\w+)=$/, 1]) && params.length == 1
      # the call is an attribute writer

      self.class.send :__define_attribute__, name
      return send method, params.first

    when (name = method[/^(\w+)\?$/, 1]) && params.length == 0
      # the call is an attribute checker

      self.class.send :__define_attribute__, name
      return send method
    end

    super
  end

  def respond_to? method
    super || self.__respond_to__?(method)
  end

  def respond_to_missing?(method, *)
    super || self.__respond_to__?(method)
  end

  # compares Blobjects to Blobjects or Hashes for equality
  def == other
    return @hash == other.hash if other.class <= Blobject
    return @hash == other      if other.class <= Hash
    super
  end

  # hash-like access to the Blobject's attributes
  def [] name

    send name
  end

  # hash-like attribute setter
  def []= name, value

    send "#{name.to_s}=", value
  end

  # freeze a Blobject to prevent it being modified
  def freeze
    self.class.send(:__freeze_r__, @hash) unless frozen?
    super
  end

  # for rails: `render json: blobject`
  def as_json *args
    return hash.as_json(*args) if hash.respond_to? :as_json
    to_hash
  end

  # serialize the Blobject as a json string
  def to_json *args
    as_json.to_json *args
  end

  # serialize the Blobject as a yaml string
  def to_yaml

    as_yaml.to_yaml
  end

  # get a Blobject from a json string, if the yaml string describes an array, an array will be returned
  def self.from_json json

    __blobjectify__(JSON.parse(json))
  end

  # get a Blobject from a yaml string, if the yaml string describes an array, an array will be returned
  def self.from_yaml yaml

    __blobjectify__(YAML.load(yaml))
  end

  protected
  # to avoid naming collisions private method names are prefixed and suffix with double unerscores (__)

  # Used to tag and re-raise errors from a Blobject
  # Refer to "Tagging exceptions with modules" on p97 in Exceptional Ruby by Avdi Grimm
  # errors from this library can be handled with rescue Blobject::Error
  module Error; end

  def __tag_and_raise__ e
    raise e
  rescue
    e.extend Blobject::Error
    raise e
  end

  def __respond_to__?(method)
    return false if ProhibitedNames.include?(method)

    method = method.to_s

    [/^(\w+)=$/, /^(\w+)\?$/, /^\w+$/].any? do |r|
      r.match(method)
    end
  end

  class << self

    protected

    def __freeze_r__ object

      if object.respond_to?(:each) && object.each.is_a?(Enumerator)
        values = object.is_a?(Hash) ? object.values : object
        values.each do |v|
          v.freeze
          __freeze_r__(v)
        end
      end

      object.freeze
    end

    def __blobjectify__ object

      array = object if object.is_a? Array
      hash  = object if object.is_a? Hash

      return array.map{|a| __blobjectify__(a)} if array
      return Blobject.new(hash) if hash
      return object
    end

    def __define_attribute__ name

      __tag_and_raise__ NameError.new("invalid attribute name #{name}") unless name =~ /^\w+$/
      name = name.to_sym

      methods = self.instance_methods

      setter_name = (name.to_s + '=').to_sym
      unless methods.include? setter_name
        self.send :define_method, setter_name do |value|
          begin
            value = self.class.send(:__blobjectify__, value)
            @hash[name] = value
          rescue => ex
            __tag_and_raise__(ex)
          end
          @store_in_parent.call unless @store_in_parent.nil?
        end
      end

      unless methods.include? name
        self.send :define_method, name do

          value = @hash[name]

          if value.nil? && !frozen?
            value = self.class.new

            # close the scope for storing call chain
            parent          = self

            store_in_parent = lambda do
              parent.send "#{name}=", value
              value.send :remove_instance_variable, :@store_in_parent
            end

            value.instance_variable_set :@store_in_parent, store_in_parent
          end

          value
        end
      end

      checker_name = (name.to_s + '?').to_sym
      unless methods.include? checker_name
        self.send :define_method, checker_name do
          @hash[name] ? true : false
        end
      end

      name
    end
  end
end