# encoding: utf-8
# This file is distributed under New Relic's license terms.
# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.

module DependencyDetection

  module_function

  @items = []

  def defer(&block)
    item = Dependent.new
    item.instance_eval(&block)

    if item.name
      seen_names = @items.map { |i| i.name }.compact
      if seen_names.include?(item.name)
        NewRelic::Agent.logger.warn("Refusing to re-register DependencyDetection block with name '#{item.name}'")
        return @items
      end
    end

    @items << item
  end

  def detect!
    @items.each do |item|
      if item.dependencies_satisfied?
        item.execute
      end
    end
  end

  def dependency_by_name(name)
    @items.find {|i| i.name == name }
  end

  def installed?(name)
    item = dependency_by_name(name)
    item && item.executed
  end

  def items
    @items
  end

  def items=(new_items)
    @items = new_items
  end

  class Dependent
    attr_reader :executed
    attr_accessor :name
    def executed!
      @executed = true
    end

    attr_reader :dependencies

    def initialize
      @dependencies = []
      @executes = []
      @name = nil
    end

    def dependencies_satisfied?
      !executed and check_dependencies
    end

    def execute
      @executes.each do |x|
        begin
          x.call
        rescue => err
          NewRelic::Agent.logger.error( "Error while installing #{self.name} instrumentation:", err )
          break
        end
      end
    ensure
      executed!
    end

    def check_dependencies
      return false unless allowed_by_config? && dependencies

      dependencies.all? do |dep|
        begin
          dep.call
        rescue => err
          NewRelic::Agent.logger.error( "Error while detecting #{self.name}:", err )
          false
        end
      end
    end

    def depends_on &block
      @dependencies << block if block_given?
    end

    def allowed_by_config?
      # If we don't have a name, can't check config so allow it
      return true if self.name.nil?

      key = "disable_#{self.name}".to_sym
      if (::NewRelic::Agent.config[key] == true)
        ::NewRelic::Agent.logger.debug("Not installing #{self.name} instrumentation because of configuration #{key}")
        false
      else
        true
      end
    end

    def named(new_name)
      self.name = new_name
    end

    def executes &block
      @executes << block if block_given?
    end
  end
end