# encoding: utf-8
require "moped/node"

module Moped

  # The cluster represents a cluster of MongoDB server nodes, either a single
  # node, a replica set, or a mongos server.
  #
  # @since 1.0.0
  class Cluster

    # The default interval that a node would be flagged as "down".
    #
    # @since 2.0.0
    DOWN_INTERVAL = 30

    # The default interval that a node should be refreshed in.
    #
    # @since 2.0.0
    REFRESH_INTERVAL = 300

    # The default time to wait to retry an operation.
    #
    # @since 2.0.0
    RETRY_INTERVAL = 0.25

    # @!attribute options
    #   @return [ Hash ] The refresh options.
    # @!attribute peers
    #   @return [ Array<Node> ] The node peers.
    # @!attribute seeds
    #   @return [ Array<Node> ] The seed nodes.
    attr_reader :options, :peers, :seeds

    # Add a credential to the cluster
    #
    # @example Get the applied credentials.
    #   node.credentials
    #
    # @return [ Boolean ] true
    #
    # @since 2.0.0
    def add_credential(db, username, password)
      @credentials ||= {}
      @credentials[db] = [ username, password ]
      apply_credentials
    end

    # Remove a credential from the cluster
    #
    # @example Get the applied credentials.
    #   node.delete_credential(database_name)
    #
    # @return [ Boolean ] true
    #
    # @since 2.0.0
    def delete_credential(db)
      return true unless @credentials
      @credentials.delete(db)
      apply_credentials
    end

    # Disconnects all nodes in the cluster. This should only be used in cases
    # where you know you're not going to use the cluster on the thread anymore
    # and need to force the connections to close.
    #
    # @return [ true ] True if the disconnect succeeded.
    #
    # @since 1.2.0
    def disconnect
      nodes.each { |node| node.disconnect } and true
    end

    # Get the interval at which a node should be flagged as down before
    # retrying.
    #
    # @example Get the down interval, in seconds.
    #   cluster.down_interval
    #
    # @return [ Integer ] The down interval.
    #
    # @since 1.2.7
    def down_interval
      @down_interval ||= options[:down_interval] || DOWN_INTERVAL
    end

    # Initialize the new cluster.
    #
    # @example Initialize the cluster.
    #   Cluster.new([ "localhost:27017" ], down_interval: 20)
    #
    # @param [ Hash ] options The cluster options.
    #
    # @option options :down_interval number of seconds to wait before attempting
    #   to reconnect to a down node. (30)
    # @option options :refresh_interval number of seconds to cache information
    #   about a node. (300)
    # @option options [ Integer ] :timeout The time in seconds to wait for an
    #   operation to timeout. (5)
    #
    # @since 1.0.0
    def initialize(hosts, options)
      @seeds = hosts.map{ |host| Node.new(host, options) }
      @peers = []
      @options = options
    end

    # Provide a pretty string for cluster inspection.
    #
    # @example Inspect the cluster.
    #   cluster.inspect
    #
    # @return [ String ] A nicely formatted string.
    #
    # @since 1.0.0
    def inspect
      "#<#{self.class.name}:#{object_id} @seeds=#{seeds.inspect}>"
    end

    # Get the number of times an operation should be retried before raising an
    # error.
    #
    # @example Get the maximum retries.
    #   cluster.max_retries
    #
    # @return [ Integer ] The max retries.
    #
    # @since 1.2.7
    def max_retries
      @max_retries ||= options[:max_retries] || seeds.size
    end

    # Returns the list of available nodes, refreshing 1) any nodes which were
    # down and ready to be checked again and 2) any nodes whose information is
    # out of date. Arbiter nodes are not returned.
    #
    # @example Get the available nodes.
    #   cluster.nodes
    #
    # @return [ Array<Node> ] the list of available nodes.
    #
    # @since 1.0.0
    def nodes
      # Find the nodes that were down but are ready to be refreshed, or those
      # with stale connection information.
      needs_refresh, available = seeds.partition do |node|
        refreshable?(node)
      end

      # Refresh those nodes.
      available.concat(refresh(needs_refresh))

      # Now return all the nodes that are available and participating in the
      # replica set.
      available.reject{ |node| node.down? }
    end

    # Refreshes information for each of the nodes provided. The node list
    # defaults to the list of all known nodes.
    #
    # If a node is successfully refreshed, any newly discovered peers will also
    # be refreshed.
    #
    # @example Refresh the nodes.
    #   cluster.refresh
    #
    # @param [ Array<Node> ] nodes_to_refresh The nodes to refresh.
    #
    # @return [ Array<Node> ] the available nodes
    #
    # @since 1.0.0
    def refresh(nodes_to_refresh = seeds)
      refreshed_nodes = []
      seen = {}
      # Set up a recursive lambda function for refreshing a node and it's peers.
      refresh_node = ->(node) do
        unless seen[node]
          seen[node] = true
          # Add the node to the global list of known nodes.
          seeds.push(node) unless seeds.include?(node)
          begin
            node.refresh
            # This node is good, so add it to the list of nodes to return.
            refreshed_nodes.push(node) unless refreshed_nodes.include?(node)
            # Now refresh any newly discovered peer nodes - this will also
            # remove nodes that are not included in the peer list.
            refresh_peers(node, &refresh_node)
          rescue Errors::ConnectionFailure
            # We couldn't connect to the node.
          end
        end
      end

      nodes_to_refresh.each(&refresh_node)
      refreshed_nodes
    end

    # Get the interval in which the node list should be refreshed.
    #
    # @example Get the refresh interval, in seconds.
    #   cluster.refresh_interval
    #
    # @return [ Integer ] The refresh interval.
    #
    # @since 1.2.7
    def refresh_interval
      @refresh_interval ||= options[:refresh_interval] || REFRESH_INTERVAL
    end

    # Get the operation retry interval - the time to wait before retrying a
    # single operation.
    #
    # @example Get the retry interval, in seconds.
    #   cluster.retry_interval
    #
    # @return [ Integer ] The retry interval.
    #
    # @since 1.2.7
    def retry_interval
      @retry_interval ||= options[:retry_interval] || RETRY_INTERVAL
    end

    # Yields the replica set's primary node to the provided block. This method
    # will retry the block in case of connection errors or replica set
    # reconfiguration.
    #
    # @example Yield the primary to the block.
    #   cluster.with_primary do |node|
    #     # ...
    #   end
    #
    # @param [ Integer ] retries The number of times to retry.
    #
    # @raises [ ConnectionFailure ] When no primary node can be found
    #
    # @return [ Object ] The result of the yield.
    #
    # @since 1.0.0
    def with_primary(&block)
      if node = nodes.find(&:primary?)
        begin
          node.ensure_primary do
            return yield(node)
          end
        rescue Errors::ConnectionFailure, Errors::ReplicaSetReconfigured
        end
      end
      raise Errors::ConnectionFailure, "Could not connect to a primary node for replica set #{inspect}"
    end

    # Yields a secondary node if available, otherwise the primary node. This
    # method will retry the block in case of connection errors.
    #
    # @example Yield the secondary to the block.
    #   cluster.with_secondary do |node|
    #     # ...
    #   end
    #
    # @param [ Integer ] retries The number of times to retry.
    #
    # @raises [ ConnectionFailure ] When no primary node can be found
    #
    # @return [ Object ] The result of the yield.
    #
    # @since 1.0.0
    def with_secondary(&block)
      available_nodes = nodes.select(&:secondary?).shuffle!
      while node = available_nodes.shift
        begin
          return yield(node)
        rescue Errors::ConnectionFailure => e
          next
        end
      end
      raise Errors::ConnectionFailure, "Could not connect to a secondary node for replica set #{inspect}"
    end

    private

    # Apply the credentials on all nodes
    #
    # @api private
    #
    # @example Apply the credentials.
    #   cluster.apply_credentials
    #
    # @return [ Boolean ] True
    #
    # @since 2.0.0
    def apply_credentials
      seeds.each do |node|
        node.credentials = @credentials || {}
      end
      true
    end

    # Get the boundary where a node that is down would need to be refreshed.
    #
    # @api private
    #
    # @example Get the down boundary.
    #   cluster.down_boundary
    #
    # @return [ Time ] The down boundary.
    #
    # @since 2.0.0
    def down_boundary
      Time.new - down_interval
    end

    # Get the standard refresh boundary to discover new nodes.
    #
    # @api private
    #
    # @example Get the refresh boundary.
    #   cluster.refresh_boundary
    #
    # @return [ Time ] The refresh boundary.
    #
    # @since 2.0.0
    def refresh_boundary
      Time.new - refresh_interval
    end

    # Is the provided node refreshable? This is in the case where the refresh
    # boundary has passed, or the node has been down longer than the down
    # boundary.
    #
    # @api private
    #
    # @example Is the node refreshable?
    #   cluster.refreshable?(node)
    #
    # @param [ Node ] node The Node to check.
    #
    # @since 2.0.0
    def refreshable?(node)
      return false if node.arbiter?
      node.down? ? node.down_at < down_boundary : node.needs_refresh?(refresh_boundary)
    end

    # Creating a cloned cluster requires cloning all the seed nodes.
    #
    # @api prviate
    #
    # @example Clone the cluster.
    #   cluster.clone
    #
    # @return [ Cluster ] The cloned cluster.
    #
    # @since 1.0.0
    def initialize_copy(_)
      @seeds = seeds.map(&:dup)
    end

    # Refresh the peers based on the node's peers.
    #
    # @api private
    #
    # @example Refresh the peers.
    #   cluster.refresh_peers(node)
    #
    # @param [ Node ] node The node to refresh the peers for.
    #
    # @since 1.0.0
    def refresh_peers(node, &block)
      node.peers.each do |node|
        block.call(node) unless seeds.include?(node)
        peers.push(node) unless peers.include?(node)
      end
    end
  end
end