# This module encapsulates nodes handeling
# Nodes can be declared both on a class level and inside a recipe
# When defining a node an 'id' is associated with its hostname
# and the node can later be reffered by this id (for example
# to get its ip)
module Blender::Manifest::Nodes

  def self.included(base)
    base.send :extend, self
  end

  # this holds the map from host ids to hostnames
  @@internal_hostnames = {}
  @@external_hostnames = {}

  # returns hostname by id or local host's name if the id is nil
  def hostname(id = nil, external = false)
    if id
      (external ? @@external_hostnames : @@internal_hostnames)[id]
    else
      external ? Facter.fqdn : Facter.hostname
    end
  end

  # returns id of the node we are running at
  # Note: will ONLY return non-nil value after (or during) node definition
  #   unless node is forced by environment NODE variable or /etc/node file
  def current_node
    node = ENV['NODE'] ||
      (File.exists?("/etc/node") && File.read("/etc/node").strip) ||
      @@internal_hostnames.index(hostname) ||
      @@external_hostnames.index(hostname(nil, true))
    node && node.to_sym
  end

  # @return true if we are running on the node with the given `id`
  def current_node?(id)
    current_node == id.to_sym
  end

  # resolves host name using 'host' executable
  # @return host's IP by its name or nil if not found
  def host_ip(name)
    return nil unless name && !name.empty?
    res = `host #{name}`.split("\n").grep(/has address/).first
    res && res.split.last
  end

  # define node and conditionally execute code block only on the specific node
  # Note: can be called multiple times without internal_name and external_name parameters
  #   in which case will only do the conditional execution
  # @param [Symbol, String] id of the host to define or test for
  # @param [String] internal_name short hostname for the host
  # @param [String] external_name full dns hostname for the host
  # @example
  #    node :app, "host5", "host5.serverfarm2.localdomain" do
  #      ...
  #    end
  #
  #    node :app do
  #      ...
  #    end
  #
  def node(id, internal_name = nil, external_name = internal_name)
    return if false == internal_name # can be used to temporary 'disable' host's definition
    # like:
    # host :app2, false do .. end
    @@internal_hostnames[id] = internal_name if internal_name
    @@external_hostnames[id] = external_name if external_name

    if block_given? && current_node?(id)
      puts "NODE: #{id} / #{current_node}"
      @node = id
      yield
    end
  end

  # find out node addr. try to use external, then internal, then the host id to determine ip
  # @param [Symbol, String] id id of the host to resolve
  def addr(id)
    [hostname(id, true).to_s, hostname(id).to_s, id.to_s].each do |name|
      ip = host_ip(name)
      return ip if ip
    end

    # if all else fails, we should still be able to address the current node
    current_node?(id) ? "127.0.0.1" : nil
  end

  # same as addr but throws exception if IP can't be found
  def addr!(id)
    addr(id) or raise "Can't find address for '#{id}'"
  end

end