module Postamt

# File lib/postamt.rb, line 25
def self.configurations
  @configurations ||= begin
    input = ActiveRecord::Base.configurations[Rails.env]
    configs = input.select { |k, v| v.is_a? Hash }
    master_config = input.reject { |k, v| v.is_a? Hash }
    configs.each { |k, v| v.reverse_merge!(master_config) }
    configs['master'] = master_config
    configs
  end
end

# File lib/postamt.rb, line 36
def self.connection_stack
  Thread.current[:postamt_connection_stack] ||= []
end

# File lib/postamt.rb, line 46
def self.hook!
  if Rails::VERSION::MAJOR == 4 and Rails::VERSION::MINOR <= 2
    ActiveRecord::Base.default_connection_handler = Postamt::ConnectionHandler.new
  elsif Rails::VERSION::MAJOR == 3 and Rails::VERSION::MINOR == 2
    ActiveRecord::Base.connection_handler = Postamt::ConnectionHandler.new
  end

  ActiveRecord::Base.instance_eval do
    class_attribute :default_connection

    # disable Model.establish_connection
    def establish_connection(*args)
      # This would be the only place Model.connection_handler.establish_connection is called.
      nil
    end

    # a transaction runs on Postamt.transaction_connection or on the :on option
    def transaction(options = {}, &block)
      if connection = (options.delete(:on) || Postamt.transaction_connection)
        Postamt.on(connection) { super }
      else
        super
      end
    end
  end

  ActionController::Base.instance_eval do
    def use_db_connection(connection, args)
      klass_names = args.delete(:for)
      if klass_names == :all
        around_filter(args) do |controller|
          Postamt.on(connection) { yield }
        end
      else
        default_connections = {}
        klass_names.each do |klass_name|
          default_connections[klass_name] = connection
        end

        before_filter(args) do |controller|
          Postamt.overwritten_default_connections.merge!(default_connections)
        end
      end
    end

    after_filter do
      Postamt.overwritten_default_connections.clear
    end
  end

  ActiveRecord::LogSubscriber.prepend Postamt::LogSubscriber
  ActiveRecord::Relation.prepend Postamt::Relation
end

# File lib/postamt.rb, line 16
def self.on(connection)
  self.connection_stack << connection
  begin
    yield
  ensure
    self.connection_stack.pop
  end
end

# File lib/postamt.rb, line 41
def self.overwritten_default_connections
  Thread.current[:postamt_overwritten_default_connections] ||= {}
end

# File lib/postamt.rb, line 57
def establish_connection(*args)
  # This would be the only place Model.connection_handler.establish_connection is called.
  nil
end

# File lib/postamt.rb, line 63
def transaction(options = {}, &block)
  if connection = (options.delete(:on) || Postamt.transaction_connection)
    Postamt.on(connection) { super }
  else
    super
  end
end

# File lib/postamt.rb, line 73
def use_db_connection(connection, args)
  klass_names = args.delete(:for)
  if klass_names == :all
    around_filter(args) do |controller|
      Postamt.on(connection) { yield }
    end
  else
    default_connections = {}
    klass_names.each do |klass_name|
      default_connections[klass_name] = connection
    end

    before_filter(args) do |controller|
      Postamt.overwritten_default_connections.merge!(default_connections)
    end
  end
end