require 'rails/sharding/active_record_extensions'
require 'rails/sharding/config'
require 'rails/sharding/connection_handler'
require 'rails/sharding/errors'
require 'rails/sharding/shard_thread_registry'
require 'rails/sharding/shardable_model'

module Rails::Sharding
  class Core

    # Opens a block where all queries will be directed to the selected shard
    def self.using_shard(shard_group, shard_name)
      raise 'Cannot nest using_shard blocks' if ShardThreadRegistry.connecting_to_shard?

      ShardThreadRegistry.current_shard_group = shard_group
      ShardThreadRegistry.current_shard_name = shard_name
      yield
    ensure
      # Releases connections in case user left some connection in the reserved state
      # (by calling retrieve_connection instead of with_connection). Also, using
      # normal activerecord queries leaves a connection in the reserved state
      ConnectionHandler.connection_pool(*ShardThreadRegistry.current_shard_group_and_name).release_connection
      ShardThreadRegistry.connect_back_to_master!
    end

    def self.configurations(environment=Rails.env)
      @@db_configs ||= YAML.load_file(Config.shards_config_file)
      @@db_configs[environment]
    rescue Errno::ENOENT => e
      raise Errors::ConfigNotFoundError, Config.shards_config_file.to_s + ' file was not found'
    end

    def self.reset_configurations_cache
      @@db_configs = nil
    end

    def self.test_configurations
      self.configurations('test')
    end

    def self.shard_groups
      self.configurations.keys
    end

    def self.shard_names(shard_group)
      self.configurations[shard_group.to_s].keys
    end

    # Method that should be called on a rails initializer
    def self.setup
      if block_given?
        yield Config
      end

      if Config.establish_all_connections_on_setup
        # Establishes connections with all shards specified in config/shards.yml
        ConnectionHandler.establish_all_connections
      end

      if Config.extend_active_record_scope
        # includes the #using_shard method to all AR scopes
        ActiveRecordExtensions.extend_active_record_scope
      end
    end

  end
end