class Metis
  module Mixin
    module ParamsValidate

      # Takes a hash of options, along with a map to validate them.  Returns the original
      # options hash, plus any changes that might have been made (through things like setting
      # default values in the validation map)
      #
      # For example:
      #
      #   validate({ :one => "neat" }, { :one => { :kind_of => String }})
      #
      # Would raise an exception if the value of :one above is not a kind_of? string.  Valid
      # map options are:
      #
      # :default:: Sets the default value for this parameter.
      # :callbacks:: Takes a hash of Procs, which should return true if the argument is valid.
      #              The key will be inserted into the error message if the Proc does not return true:
      #                 "Option #{key}'s value #{value} #{message}!"
      # :kind_of:: Ensure that the value is a kind_of?(Whatever).  If passed an array, it will ensure
      #            that the value is one of those types.
      # :respond_to:: Ensure that the value has a given method.  Takes one method name or an array of
      #               method names.
      # :required:: Raise an exception if this parameter is missing. Valid values are true or false,
      #             by default, options are not required.
      # :regex:: Match the value of the paramater against a regular expression.
      # :equal_to:: Match the value of the paramater with ==.  An array means it can be equal to any
      #             of the values.
      def validate(opts, map)
        #--
        # validate works by taking the keys in the validation map, assuming it's a hash, and
        # looking for _pv_:symbol as methods.  Assuming it find them, it calls the right
        # one.
        #++
        raise ArgumentError, "Options must be a hash" unless opts.kind_of?(Hash)
        raise ArgumentError, "Validation Map must be a hash" unless map.kind_of?(Hash)

        map.each do |key, validation|
          unless key.kind_of?(Symbol) || key.kind_of?(String)
            raise ArgumentError, "Validation map keys must be symbols or strings!"
          end
          case validation
          when true
            _pv_required(opts, key)
          when false
            true
          when Hash
            validation.each do |check, carg|
              check_method = "_pv_#{check.to_s}"
              if self.respond_to?(check_method, true)
                self.send(check_method, opts, key, carg)
              else
                raise ArgumentError, "Validation map has unknown check: #{check}"
              end
            end
          end
        end
        opts
      end

      def set_or_return(symbol, arg, validation)
        map = {
          symbol => validation
        }

        if arg == nil && self.params[symbol]
          self.params[symbol]
        else
          opts = validate({ symbol => arg }, { symbol => validation })
          self.params[symbol] = opts[symbol]
        end
      end

      private

        # Return the value of a parameter, or nil if it doesn't exist.
        def _pv_opts_lookup(opts, key)
          if opts.has_key?(key.to_s)
            opts[key.to_s]
          elsif opts.has_key?(key.to_sym)
            opts[key.to_sym]
          else
            nil
          end
        end

        # Raise an exception if the parameter is not found.
        def _pv_required(opts, key, is_required=true)
          if is_required
            if (opts.has_key?(key.to_s) && !opts[key.to_s].nil?) ||
                (opts.has_key?(key.to_sym) && !opts[key.to_sym].nil?)
              true
            else
              raise Exceptions::ValidationFailed, "Required argument #{key} is missing!"
            end
          end
        end

        def _pv_equal_to(opts, key, to_be)
          value = _pv_opts_lookup(opts, key)
          unless value.nil?
            passes = false
            Array(to_be).each do |tb|
              passes = true if value == tb
            end
            unless passes
              raise Exceptions::ValidationFailed, "Option #{key} must be equal to one of: #{to_be.join(", ")}!  You passed #{value.inspect}."
            end
          end
        end

        # Raise an exception if the parameter is not a kind_of?(to_be)
        def _pv_kind_of(opts, key, to_be)
          value = _pv_opts_lookup(opts, key)
          unless value.nil?
            passes = false
            Array(to_be).each do |tb|
              passes = true if value.kind_of?(tb)
            end
            unless passes
              raise Exceptions::ValidationFailed, "Option #{key} must be a kind of #{to_be}!  You passed #{value.inspect}."
            end
          end
        end

        # Raise an exception if the parameter does not respond to a given set of methods.
        def _pv_respond_to(opts, key, method_name_list)
          value = _pv_opts_lookup(opts, key)
          unless value.nil?
            Array(method_name_list).each do |method_name|
              unless value.respond_to?(method_name)
                raise Exceptions::ValidationFailed, "Option #{key} must have a #{method_name} method!"
              end
            end
          end
        end

        # Assert that parameter returns false when passed a predicate method.
        # For example, :cannot_be => :blank will raise a Exceptions::ValidationFailed
        # error value.blank? returns a 'truthy' (not nil or false) value.
        #
        # Note, this will *PASS* if the object doesn't respond to the method.
        # So, to make sure a value is not nil and not blank, you need to do
        # both :cannot_be => :blank *and* :cannot_be => :nil (or :required => true)
        def _pv_cannot_be(opts, key, predicate_method_base_name)
          value = _pv_opts_lookup(opts, key)
          predicate_method = (predicate_method_base_name.to_s + "?").to_sym

          if value.respond_to?(predicate_method)
            if value.send(predicate_method)
              raise Exceptions::ValidationFailed, "Option #{key} cannot be #{predicate_method_base_name}"
            end
          end
        end

        # Assign a default value to a parameter.
        def _pv_default(opts, key, default_value)
          value = _pv_opts_lookup(opts, key)
          if value == nil
            opts[key] = default_value
          end
        end

        # Check a parameter against a regular expression.
        def _pv_regex(opts, key, regex)
          value = _pv_opts_lookup(opts, key)
          if value != nil
            passes = false
            [ regex ].flatten.each do |r|
              if value != nil
                if r.match(value.to_s)
                  passes = true
                end
              end
            end
            unless passes
              raise Exceptions::ValidationFailed, "Option #{key}'s value #{value} does not match regular expression #{regex.inspect}"
            end
          end
        end

        # Check a parameter against a hash of proc's.
        def _pv_callbacks(opts, key, callbacks)
          raise ArgumentError, "Callback list must be a hash!" unless callbacks.kind_of?(Hash)
          value = _pv_opts_lookup(opts, key)
          if value != nil
            callbacks.each do |message, zeproc|
              if zeproc.call(value) != true
                raise Exceptions::ValidationFailed, "Option #{key}'s value #{value} #{message}!"
              end
            end
          end
        end

        # Allow a parameter to default to @name
        def _pv_name_attribute(opts, key, is_name_attribute=true)
          if is_name_attribute
            if opts[key] == nil
              opts[key] = self.instance_variable_get("@name")
            end
          end
        end
    end
  end
end
