# Builds node name from mask. Mask could be passed in server's +cid:node-name-mask+ tag,
# default mask is used otherwise. Mask is a string with possible several variables inserted, e.g.
# +':project/:env/:instanceid/:instancename/:increment-group1:'+
# Variables meanings:
# - +:project+ is replaced with project name (given in constructor)
# - +:env+ is replaced with env name (given in constructor)
# - +:time+ is replaced with current timestamp
# - +:instanceid+ is replaced with provider instance id (fetched from server info)
# - +:instancename+ is replaced with value of Name tag (fetched from server info)
# - +:increment-groupname:+ is replaced with incremented number tied to group name. There could be several groups in one stack.
# P.S. Colons are used instead of dollar signs, because stacks don't support dollar signs in tags (unlike EC2 instances),
# but it's convenient to set mask tag directly to a stack (not in template): you set tag once and it propagates to all instances.

class ChefNodeNameBuilder
  # We need to ensure that node name is uniq by default. We can't use :time to provide uniqueness because
  # several servers are persisting at once on stack creating at it's likely that Time.now.to_i will give similar values
  # to different servers. So (by default) we should use :instanceid.
  DEFAULT_MASK = ':project-:env-:instanceid'

  # @param attrs [Hash] should contain
  #   +:provider_server_info+
  #   +:project_id+
  #   +:env_id+
  def initialize(attrs)
    @server_info = attrs[:provider_server_info]
    @project, @env = attrs[:project_id], attrs[:env_id]
    @mask = @server_info['tags']['cid:node-name-mask'] || DEFAULT_MASK
  end


  # @param incrementers_values [Hash] is a hash in which key is name of a variable and value is last substituted number for that var.
  # This method modifies +incrementers_values+, updating values for substituted variables.
  #
  # Examples (assume mask is set to +':project-master-:increment-group1:'+):
  #   incremeters_values = {}
  #   builder.build_node_name!(incremeters_values) # returns 'mpda-master-01'
  #   puts incremeters_values # {'group1' => 1}
  #   builder.build_node_name!(incremeters_values) # returns 'mpda-master-02'
  #   puts incremeters_values # {'group1' => 2}
  def build_node_name!(incrementers_values)
    result = @mask.dup
    replace_variables!(result)
    replace_incrementers!(result, incrementers_values)
    result
  end

  private

  def replace_variables!(result)
    result.gsub!(':project', @project)
    result.gsub!(':env', @env)
    result.gsub!(':instanceid', @server_info['id'])
    result.gsub!(':instancename', @server_info['tags']['Name'] || '')
    result.gsub!(':time', Time.now.to_i.to_s)
  end

  def replace_incrementers!(result, incrementers_values)
    groupname_regexp = /(?<=:increment-)\w+(?=:)/
    result.gsub!(/:increment-\w+:/) do |incrementer|
      group_name = groupname_regexp.match(incrementer)[0]
      prev_value = incrementers_values[group_name] || 0
      current_value = prev_value + 1
      incrementers_values[group_name] = current_value
      current_value.to_s.rjust(2, '0')
    end
  end
end