module Humidifier
  module Reservoir
    # Represents a CloudFormation stack. This contains all of the logic for
    # interfacing with humidifier to deploy stacks, validate them, and display
    # them.
    class Stack
      # Represents an exported resource in a stack for use in cross-stack
      # references.
      Export =
        Struct.new(:name, :attribute) do
          def value
            if attribute.is_a?(String)
              Humidifier.fn.get_att([name, attribute])
            else
              Humidifier.ref(name)
            end
          end
        end

      attr_reader :name, :pattern, :prefix, :exports

      def initialize(name, pattern: nil, prefix: nil)
        @name    = name
        @pattern = pattern
        @prefix  = prefix
        @exports = []
      end

      def create_change_set
        return unless ensure_resources
        valid?

        opts = { capabilities: %w[CAPABILITY_IAM CAPABILITY_NAMED_IAM] }
        humidifier_stack.create_change_set(opts)
      end

      def deploy(wait = false)
        return unless ensure_resources
        valid?

        opts = { capabilities: %w[CAPABILITY_IAM CAPABILITY_NAMED_IAM] }
        wait ? humidifier_stack.deploy_and_wait(opts) : humidifier_stack.deploy(opts)
      end

      def resources
        Reservoir.files_for(name).each_with_object({}) do |filepath, resources|
          resources.merge!(parse(filepath, File.basename(filepath, '.yml')))
        end
      end

      def stack_name
        @stack_name ||= "#{prefix || Reservoir.stack_prefix}#{name}"
      end

      def to_cf
        humidifier_stack.to_cf
      end

      def valid?
        humidifier_stack.valid?
      rescue Aws::CloudFormation::Errors::AccessDenied
        raise Error, <<-MSG
The authenticated AWS profile does not have the requisite permissions to run
this command. Ensure the profile has cloudformation:ValidateTemplate.
MSG
      end

      private

      def ensure_resources
        return true if humidifier_stack.resources.any?
        puts "Refusing to deploy stack #{humidifier_stack.name} with no resources"
        false
      end

      def humidifier_stack
        Humidifier::Stack.new(
          name: stack_name,
          description: "Resources for #{stack_name}",
          resources: resources,
          outputs: outputs
        )
      end

      def outputs
        exports.each_with_object({}) do |export, exported|
          exported[export.name] =
            Humidifier::Output.new(
              value: export.value,
              export_name: export.name
            )
        end
      end

      def parse(filepath, type)
        mapping = Reservoir.mapping_for(type)
        return {} if mapping.nil?

        loaded = YAML.load_file(filepath)
        return {} unless loaded

        loaded.each_with_object({}) do |(name, attributes), resources|
          next if pattern && name !~ pattern

          attribute = attributes.delete('export')
          exports << Export.new(name, attribute) if attribute

          resources[name] = mapping.resource_for(name, attributes)
        end
      end
    end
  end
end