class System

  attr_accessor :name
  attr_accessor :attributes # (basebox selection)
  attr_accessor :module_selectors # (filters)
  attr_accessor :module_selections # (after resolution)
  attr_accessor :num_actioned_module_conflicts

  # Initalizes System object
  # @param [Object] name of the system
  # @param [Object] attributes such as base box selection
  # @param [Object] module_selectors these are modules that define filters for selecting the actual modules to use
  def initialize(name, attributes, module_selectors)
    self.name = name
    self.attributes = attributes
    self.module_selectors = module_selectors
    self.module_selections = []
    self.num_actioned_module_conflicts = 0
  end

  # selects from the available modules, based on the selection filters that have been specified
  # @param [Object] available_modules all available modules (vulnerabilities, services, bases)
  # @return [Object] the list of selected modules
  def resolve_module_selection(available_modules)
    retry_count = 0
    begin

      selected_modules = []
      self.num_actioned_module_conflicts = 0

      # for each module specified in the scenario
      module_selectors.each do |module_filter|
        selected_modules += select_modules(module_filter.module_type, module_filter.attributes, available_modules, selected_modules)
      end
      selected_modules

    rescue RuntimeError=>e
      # When the scenario fails to be resolved
      # bruteforce conflict resolution (could be more intelligent)

      Print.err 'Failed to resolve scenario.'
      if self.num_actioned_module_conflicts > 0
        Print.err "During scenario generation #{num_actioned_module_conflicts} module conflict(s) occured..."
      else
        Print.err 'No conflicts, but failed to resolve scenario -- this is a sign there is something wrong in the config (scenario / modules)'
        Print.err 'Please review the scenario -- something is wrong.'
        exit
      end
      if retry_count < RETRIES_LIMIT
        Print.err "Re-attempting to resolve scenario (##{retry_count + 1})..."
        sleep 1
        retry_count += 1
        retry
      else
        Print.err "Tried re-randomising #{RETRIES_LIMIT} times. Still no joy."
        Print.err 'Please review the scenario -- something is wrong.'
        exit
      end
    end
  end

  # returns a list containing a module (plus dependencies recursively) of the module type with the required attributes
  # modules are selected from the list of available modules and will be checked against previously selected modules for conflicts
  # raises an exception when unable to resolve and the retry limit has not been reached
  def select_modules(module_type, required_attributes, available_modules, previously_selected_modules)
    # select based on selected type, access, cve...

    search_list = available_modules.clone
    # shuffle order of available vulnerabilities
    search_list.shuffle!

    # remove any module that is not the type of module we are adding (vulnerabilty/service)
    if module_type != 'any'
      search_list.delete_if{|x|
        x.module_type != module_type
      }
    end

    # filter to those that satisfy the attribute filters
    search_list.delete_if{|module_for_possible_exclusion|
      !module_for_possible_exclusion.matches_attributes_requirement(required_attributes)
    }
    Print.verbose "Filtered to modules matching: #{required_attributes.inspect} ~= (n=#{search_list.size})"

    # remove non-options due to conflicts
    search_list.delete_if{|module_for_possible_exclusion|
      check_conflicts_with_list(module_for_possible_exclusion, previously_selected_modules)
    }

    if search_list.length == 0
      raise 'failed'
      Print.err 'Could not find a matching module. Please check the scenario specification'
    else
      # use from the top of the randomised list
      selected = search_list[0]

      # add any modules that the selected module requires
      dependencies = select_required_modules(selected, available_modules, previously_selected_modules + [selected])
    end

    selected_modules = dependencies + [selected]

    Print.std "Selected module: #{selected.printable_name}"

    selected_modules

  end

  def check_conflicts_with_list(module_for_possible_exclusion, selected_modules)
    found_conflict = false
    selected_modules.each do |prev_selected|
      if module_for_possible_exclusion.conflicts_with(prev_selected) ||
          prev_selected.conflicts_with(module_for_possible_exclusion)
        Print.verbose "Excluding incompatible module: #{module_for_possible_exclusion.module_path} (conflicts with #{prev_selected.module_path})"
        self.num_actioned_module_conflicts += 1
        found_conflict = true
      end
    end
    found_conflict
  end

  # for a single dependency
  # returns a module that satisfies the requirement from a list of modules provided
  # returns nil when the requirement cannot be satisfied
  def resolve_dependency(required, provided_modules)
    provided_modules.each do |possibly_add|
      if possibly_add.matches_attributes_requirement(required)
        return possibly_add
      end
    end
    # couldn't satisfy requirement!
    return nil
  end

  # returns a list of modules that satisfies all dependencies for the given module
  # returns an empty list if there are no requirements
  def select_required_modules(required_by, available_modules, selected_modules)
    modules_to_add = []
    if required_by.requires.size > 0
      Print.verbose "Resolving dependencies for #{required_by.printable_name}"
    end

    required_by.requires.each do |required|
      Print.verbose "Resolving dependency: #{required.inspect}"
      # checking whether dependency is satisfied by previously selected modules
      existing = resolve_dependency(required, selected_modules)
      if existing != nil
        Print.verbose "Dependency satisfied by previously selected module: #{existing.printable_name}"
      else
        Print.verbose 'Adding required modules...'
        modules_to_add += select_modules('any', required, available_modules, modules_to_add + selected_modules)
      end
    end
    modules_to_add
  end

end