messages.rb

class Messages
  include Enumerable
  attr_reader :messages
  delegate :each, to: :messages

  def initialize(messages = {}) # hash of error messages
    @messages = messages
  end

  def full_messages
    @messages.flat_map do |k,v|
      v.map(&:humanize)
    end
  end

  def merge!(other_messages)
    if other_messages.is_a?(self.class)
      other_messages.each do |k,v|
        @messages[k] = [] if @messages[k].blank?
        @messages[k].concat(v)
      end
    elsif other_messages.is_a?(Hash) # hash of error messages
      other_messages.each do |k,v|
        @messages[k] = [] if @messages[k].blank?
        if v.is_a?(Array)
          @messages[k].concat(v.map {|msg| Message.new(:error, k, msg) })
        elsif v.is_a?(String)
          @messages[k].push(Message.new(:error, k, msg))
        end
        @messages[k].uniq! { |msg| "#{msg.level}#{msg.message}" }
      end
    end
  end

  def errors
    by_level(:error)
  end
  def warns
    by_level(:warn)
  end
  def infos
    by_level(:info)
  end
  def successes
    by_level(:success)
  end

  def error(*args, **kw_args)
    add(*args, level: :error, **kw_args)
  end
  def warn(*args, **kw_args)
    add(*args, level: :warn, **kw_args)
  end
  def info(*args, **kw_args)
    add(*args, level: :info, **kw_args)
  end
  def success(*args, **kw_args)
    add(*args, level: :success, **kw_args)
  end

  def add(ns, message, level: :error, full_message: nil, source: nil)
    @messages[ns] ||= []
    @messages[ns].push Message.new(level, ns, message, full_message, source)
  end

  private

  def by_level(level)
    Messages.new Hash[messages.map do |ns,msgs|
      matches = msgs.select {|m| m.level == level }
      next unless matches.present?
      [ns, matches]
    end.compact]
  end
end

Message = Struct.new(:level, :ns, :message, :full_message, :source) do
  def humanize
    full_message.present? ? full_message : "#{ns.to_s.humanize} #{message}"
  end

  def error?
    level == :error
  end
  def warn?
    level == :warn
  end
  def info?
    level == :info
  end
  def success?
    level == :success
  end

  def ==(other)
    if other.is_a? String
      other == message
    else
      other.level == level &&
      other.ns == ns &&
      other.message == message &&
      other.full_message == full_message &&
      other.source == source
    end
  end
end