-----------   --------   ---------   ---------
|           | |        | |         | |         |
| Directory | | System | | Shard 1 | | Shard 2 | etc..
|           | |        | |         | |         |
 -----------   --------   ---------   ---------

class User < ActiveRecord::Base
  # This model is on the directory server.
  #
  acts_as_directory

  has_many :pets
  has_many :cellphones
  has_many :subscriptions
  has_one :accounts_pricing_plan, :through => :subscriptions
end

class Pet < ActiveRecord::Base
  # This model is on shards.
  #
  acts_as_shard

  belongs_to :user
end

class Cellphone < ActiveRecord::Base
  # This model is on shards.
  #
  acts_as_shard

  belongs_to :user
end

class Subscription < ActiveRecord::Base
  # This model is on shards.
  #
  acts_as_shard

  belongs_to :user
  belongs_to :accounts_pricing_plan
end

class AccountPricingPlan < ActiveRecord::Base
  # This model is not user specific, so it's on the system.
  #

  has_many :subscriptions
  has_many :users, :through => :subscriptions
end

development: &defaults
  reconnect: true
  adapter: mysql
  encoding: utf8
  database: coolapp_development
  username: root
  password:
  pool: 15 # Increase this, we will need them. 

development_directory:
  <<: *defaults
  database: coolapp_development_directory
  # The literal db name can be anything

development_hewey:
  <<: *defaults
  database: coolapp_development_hewey

development_dewey:
  <<: *defaults
  database: coolapp_development_dewey

test:
  <<: *defaults
  database: coolapp_test

test_directory:
  <<: *defaults
  database: coolapp_test_directory

test_shard:
  <<: *defaults
  database: coolapp_test_shard

# Usage of ShardTheLove

ShardTheLove.with('hewey') {
  Pet.all # Only pets on hewey
}

ShardTheLove.with('hewey') {
  ShardTheLove.current_shard # is 'hewey'

  ShardTheLove.with('dewey') {
    ShardTheLove.current_shard # is 'dewey'

    Pet.all # Only pets on hewey

    User.all # All users from the directory

    plan = AccountPricingPlan.first # A plan from the system db
    
    plan.subscriptions # Only subscriptions from dewey!
  }
}

# Walking shards is highly discouraged.  It means you make a connection
# to every shard.  At scale (lots of shards) this would not work smoothly.

ShardTheLove.shards # is ['hewey', 'dewey']

ShardTheLove.shards { |shard|
  shard == ShardTheLove.current_shard # is true
  
  Cellphone.all # gets called twice, once on each shard.
}

# Let's presume the model User has a method or column named
# "shard" that tells us what shard user data is on.

@user = User.find( 'text@example.com' )

ShardTheLove.with(@user.shard) {
  # Now we can access that user's data
  @user.pets
  @user.cellphones
}

Spec::Runner.configure do |config|

  # Your RSpec config here...
  #

  # Transaction setup and teardown for ShardTheLove
  #
  config.before(:all) do
    ShardTheLove.with(DEFAULT_SHARD)

    # The following is only needed in Rails- Merb loads all
    # the model files without this.
    # 
    ar_classes = []
    Dir.foreach("#{RAILS_ROOT}/app/models/") do |file|
      next if file =~ /^\./ || !(file =~ /\.rb$/)
      ar_classes << file.sub(".rb", "").camelize.constantize
    end
    ar_classes.each do |ar_class|
      next unless ar_class.ancestors.include?(ActiveRecord::Base)
      ar_class.connection_handler
    end
  end

  config.before(:each) do
    (
      [ ActiveRecord::Base.connection_handler,
        ShardTheLove.directory_handler ] +
      ShardTheLove.shard_handlers.collect {|name, handle| handle }
    ).each do |handler|
      next unless handler
      handler.connection_pools.each do |name, pool|
        pool.connection.begin_db_transaction
        pool.connection.increment_open_transactions
      end
    end
  end

  config.after(:each) do
    (
      [ ActiveRecord::Base.connection_handler,
        ShardTheLove.directory_handler ] +
      ShardTheLove.shard_handlers.collect {|name, handle| handle }
    ).each do |handler|
      next unless handler
      handler.connection_pools.each do |name, pool|
        if pool.connection.open_transactions != 0
          pool.connection.rollback_db_transaction
          pool.connection.decrement_open_transactions
        end
      end
    end
  end

end

it "should shard with a users shard" do
  User.stubs(:find).returns(stub(:shard => 'the right one'))
  ShardTheLove.expects(:with).with('the right one')
  # now do something...
end