diff --git a/lecture_5/homework/.rspec b/lecture_5/homework/.rspec
new file mode 100644
index 00000000..c99d2e73
--- /dev/null
+++ b/lecture_5/homework/.rspec
@@ -0,0 +1 @@
+--require spec_helper
diff --git a/lecture_5/homework/Gemfile b/lecture_5/homework/Gemfile
index f10bbf07..07436e96 100644
--- a/lecture_5/homework/Gemfile
+++ b/lecture_5/homework/Gemfile
@@ -35,7 +35,10 @@ gem 'active_model_serializers'
 
 group :development, :test do
   # Call 'byebug' anywhere in the code to stop execution and get a debugger console
+  gem 'awesome_print'
   gem 'byebug', platforms: %i[mri mingw x64_mingw]
+  gem 'database_cleaner'
+  gem 'factory_bot_rails'
 end
 
 group :development do
diff --git a/lecture_5/homework/Gemfile.lock b/lecture_5/homework/Gemfile.lock
index 411593e8..8baee5bf 100644
--- a/lecture_5/homework/Gemfile.lock
+++ b/lecture_5/homework/Gemfile.lock
@@ -49,6 +49,7 @@ GEM
       tzinfo (~> 1.1)
     arel (9.0.0)
     ast (2.4.0)
+    awesome_print (1.8.0)
     bootsnap (1.4.1)
       msgpack (~> 1.0)
     builder (3.2.3)
@@ -57,8 +58,14 @@ GEM
       activesupport
     concurrent-ruby (1.1.5)
     crass (1.0.4)
+    database_cleaner (1.7.0)
     diff-lcs (1.3)
     erubi (1.8.0)
+    factory_bot (5.0.2)
+      activesupport (>= 4.2.0)
+    factory_bot_rails (5.0.2)
+      factory_bot (~> 5.0.2)
+      railties (>= 4.2.0)
     ffi (1.10.0)
     globalid (0.4.2)
       activesupport (>= 4.2.0)
@@ -177,8 +184,11 @@ PLATFORMS
 
 DEPENDENCIES
   active_model_serializers
+  awesome_print
   bootsnap (>= 1.1.0)
   byebug
+  database_cleaner
+  factory_bot_rails
   listen (>= 3.0.5, < 3.2)
   pg
   puma (~> 3.11)
diff --git a/lecture_5/homework/app/controllers/buildings_controller.rb b/lecture_5/homework/app/controllers/buildings_controller.rb
index 9b7e9677..a0a7bd4c 100644
--- a/lecture_5/homework/app/controllers/buildings_controller.rb
+++ b/lecture_5/homework/app/controllers/buildings_controller.rb
@@ -1,7 +1,25 @@
 # frozen_string_literal: true
 
 class BuildingsController < ApplicationController
-  def index; end
+  def index
+    render json: buildings, status: 200
+  end
 
-  def show; end
+  def show
+    render json: building
+  end
+
+  private
+
+  def buildings
+    @buildings ||= fetch_buildings.present? ? fetch_buildings : NoBuildings.new.buildings
+  end
+
+  def fetch_buildings
+    BuildingsQueries.buildings(relation: Building)
+  end
+
+  def building
+    @building ||= BuildingsQueries.building(relation: Building, id: params[:id])
+  end
 end
diff --git a/lecture_5/homework/app/controllers/clans/warriors_controller.rb b/lecture_5/homework/app/controllers/clans/warriors_controller.rb
index 6ccf3ff9..acab2d6a 100644
--- a/lecture_5/homework/app/controllers/clans/warriors_controller.rb
+++ b/lecture_5/homework/app/controllers/clans/warriors_controller.rb
@@ -10,7 +10,7 @@ def index
       warriors = clan.warriors
 
       if params.key?(:alive)
-        if params[:alive].to_i == 0
+        if params[:alive].to_i.zero?
           render json: warriors.dead
         else
           render json: warriors.alive
diff --git a/lecture_5/homework/app/nulls/no_buildings.rb b/lecture_5/homework/app/nulls/no_buildings.rb
new file mode 100644
index 00000000..4930fd08
--- /dev/null
+++ b/lecture_5/homework/app/nulls/no_buildings.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class NoBuildings
+  def buildings
+    { message: 'There are no buildings' }
+  end
+end
diff --git a/lecture_5/homework/app/queries/buildings_queries.rb b/lecture_5/homework/app/queries/buildings_queries.rb
new file mode 100644
index 00000000..0d0e605d
--- /dev/null
+++ b/lecture_5/homework/app/queries/buildings_queries.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+class BuildingsQueries
+  def self.buildings(relation:)
+    relation.includes(:warriors).all
+  end
+
+  def self.building(relation:, id:)
+    relation.find(id)
+  end
+
+  def self.count_warriors_of_specified_type(relation:, building:, type:)
+    relation.find(building.id).warriors.where(type: type).count
+  end
+
+  def self.update_siege_ability(relation:, building:, result:)
+    relation.find(building.id).update(siege_ability: result)
+  end
+end
diff --git a/lecture_5/homework/app/serializers/building_serializer.rb b/lecture_5/homework/app/serializers/building_serializer.rb
index 899c9aa0..92430c53 100644
--- a/lecture_5/homework/app/serializers/building_serializer.rb
+++ b/lecture_5/homework/app/serializers/building_serializer.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class BuildingSerializer < ActiveModel::Serializer
-  attributes :name
+  attributes :name, :siege_ability
 
   has_many :warriors
 end
diff --git a/lecture_5/homework/app/services/reports/siege_report.rb b/lecture_5/homework/app/services/reports/siege_report.rb
index 16a0b3a4..b6d1be4f 100644
--- a/lecture_5/homework/app/services/reports/siege_report.rb
+++ b/lecture_5/homework/app/services/reports/siege_report.rb
@@ -3,10 +3,69 @@
 module Reports
   class SiegeReport
     def initialize(building:)
+      @building = building
     end
 
     def call
-      raise NotImprementedYet
+      no_army? ? no_siege_ability : compute_siege_ability
+    end
+
+    private
+
+    def no_army?
+      @building.warriors.empty?
+    end
+
+    def no_siege_ability
+      save_siege_report_result(0)
+      @building.siege_ability = 0
+    end
+
+    def compute_siege_ability
+      daily_food_demand = compute_daily_food_demand
+      result = siege_ability(daily_food_demand)
+      save_siege_report_result(result)
+    end
+
+    def compute_daily_food_demand
+      stronghold_staff + hussars + samurais
+    end
+
+    def stronghold_staff
+      10
+    end
+
+    def hussars
+      BuildingsQueries.count_warriors_of_specified_type(
+        relation: Building,
+        building: @building,
+        type: 'Warriors::Hussar'
+      ) * 2
+    end
+
+    def samurais
+      BuildingsQueries.count_warriors_of_specified_type(
+        relation: Building,
+        building: @building,
+        type: 'Warriors::Samurai'
+      )
+    end
+
+    def siege_ability(daily_food_demand)
+      granary / daily_food_demand
+    end
+
+    def granary
+      @building.granary
+    end
+
+    def save_siege_report_result(result)
+      BuildingsQueries.update_siege_ability(
+        relation: Building,
+        building: @building,
+        result: result
+      )
+      @building.siege_ability = result
     end
   end
 end
diff --git a/lecture_5/homework/config/initializers/active_model_serializers.rb b/lecture_5/homework/config/initializers/active_model_serializers.rb
index 6f857680..56035bc5 100644
--- a/lecture_5/homework/config/initializers/active_model_serializers.rb
+++ b/lecture_5/homework/config/initializers/active_model_serializers.rb
@@ -1,3 +1,4 @@
 # frozen_string_literal: true
 
 ActiveModelSerializers.config.adapter = :json_api
+ActiveModel::Serializer.config.key_transform = :underscore
diff --git a/lecture_5/homework/db/migrate/20190425195137_add_siege_ability_to_buildings.rb b/lecture_5/homework/db/migrate/20190425195137_add_siege_ability_to_buildings.rb
new file mode 100644
index 00000000..ce361b71
--- /dev/null
+++ b/lecture_5/homework/db/migrate/20190425195137_add_siege_ability_to_buildings.rb
@@ -0,0 +1,5 @@
+class AddSiegeAbilityToBuildings < ActiveRecord::Migration[5.2]
+  def change
+    add_column :buildings, :siege_ability, :integer
+  end
+end
diff --git a/lecture_5/homework/db/migrate/20190428121458_compute_siege_abilities_of_buildings.rb b/lecture_5/homework/db/migrate/20190428121458_compute_siege_abilities_of_buildings.rb
new file mode 100644
index 00000000..d9eb2f4d
--- /dev/null
+++ b/lecture_5/homework/db/migrate/20190428121458_compute_siege_abilities_of_buildings.rb
@@ -0,0 +1,7 @@
+class ComputeSiegeAbilitiesOfBuildings < ActiveRecord::Migration[5.2]
+  def change
+    Building.find_each do |building|
+      Reports::SiegeReport.new(building: building).call
+    end
+  end
+end
diff --git a/lecture_5/homework/db/schema.rb b/lecture_5/homework/db/schema.rb
index 13f968ab..80b5adc2 100644
--- a/lecture_5/homework/db/schema.rb
+++ b/lecture_5/homework/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_04_05_090544) do
+ActiveRecord::Schema.define(version: 2019_04_28_121458) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -20,6 +20,8 @@
     t.string "type", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.integer "granary", default: 0, null: false
+    t.integer "siege_ability"
   end
 
   create_table "clans", force: :cascade do |t|
diff --git a/lecture_5/homework/spec/factories/buildings.rb b/lecture_5/homework/spec/factories/buildings.rb
new file mode 100644
index 00000000..a379ba96
--- /dev/null
+++ b/lecture_5/homework/spec/factories/buildings.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :building, class: Building do
+    sequence(:name) { |i| "Building_#{i}" }
+    sequence(:type) { |i| "Buildings::#{i.even? ? 'Walls' : 'Stronghold'}" }
+    granary { 100 }
+  end
+end
diff --git a/lecture_5/homework/spec/factories/clans.rb b/lecture_5/homework/spec/factories/clans.rb
new file mode 100644
index 00000000..106801f7
--- /dev/null
+++ b/lecture_5/homework/spec/factories/clans.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :clan, class: Clan do
+    sequence(:name) { |i| "Clan number #{i}" }
+  end
+end
diff --git a/lecture_5/homework/spec/factories/warriors.rb b/lecture_5/homework/spec/factories/warriors.rb
new file mode 100644
index 00000000..b1c49f28
--- /dev/null
+++ b/lecture_5/homework/spec/factories/warriors.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :warrior, class: Warrior do
+    association(:clan)
+    association(:building)
+    sequence(:type) { |i| i.even? ? 'Warriors::Hussar' : 'Warriors::Samurai' }
+    sequence(:name) { |i| "Warrior #{i}" }
+    preferred_weapon_kind { 'melee' }
+    armor_quality { 0 }
+    number_of_battles { 0 }
+    join_date { Time.now }
+    death_date { nil }
+
+    trait :hussar do
+      type { 'Warriors::Hussar' }
+    end
+
+    trait :samurai do
+      type { 'Warriors::Samurai' }
+    end
+  end
+end
diff --git a/lecture_5/homework/spec/rails_helper.rb b/lecture_5/homework/spec/rails_helper.rb
new file mode 100644
index 00000000..429ba04c
--- /dev/null
+++ b/lecture_5/homework/spec/rails_helper.rb
@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+# This file is copied to spec/ when you run 'rails generate rspec:install'
+require 'spec_helper'
+ENV['RAILS_ENV'] ||= 'test'
+require File.expand_path('../config/environment', __dir__)
+# Prevent database truncation if the environment is production
+abort('The Rails environment is running in production mode!') if Rails.env.production?
+require 'rspec/rails'
+# Add additional requires below this line. Rails is not loaded until this point!
+
+# Requires supporting ruby files with custom matchers and macros, etc, in
+# spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are
+# run as spec files by default. This means that files in spec/support that end
+# in _spec.rb will both be required and run as specs, causing the specs to be
+# run twice. It is recommended that you do not name files matching this glob to
+# end with _spec.rb. You can configure this pattern with the --pattern
+# option on the command line or in ~/.rspec, .rspec or `.rspec-local`.
+#
+# The following line is provided for convenience purposes. It has the downside
+# of increasing the boot-up time by auto-requiring all files in the support
+# directory. Alternatively, in the individual `*_spec.rb` files, manually
+# require only the support files necessary.
+#
+# Dir[Rails.root.join('spec', 'support', '**', '*.rb')].each { |f| require f }
+
+# Checks for pending migrations and applies them before tests are run.
+# If you are not using ActiveRecord, you can remove these lines.
+begin
+  ActiveRecord::Migration.maintain_test_schema!
+rescue ActiveRecord::PendingMigrationError => e
+  puts e.to_s.strip
+  exit 1
+end
+RSpec.configure do |config|
+  # Remove this line if you're not using ActiveRecord or ActiveRecord fixtures
+  config.fixture_path = "#{::Rails.root}/spec/fixtures"
+
+  config.include FactoryBot::Syntax::Methods
+
+  # If you're not using ActiveRecord, or you'd prefer not to run each of your
+  # examples within a transaction, remove the following line or assign false
+  # instead of true.
+  config.use_transactional_fixtures = true
+
+  # RSpec Rails can automatically mix in different behaviours to your tests
+  # based on their file location, for example enabling you to call `get` and
+  # `post` in specs under `spec/controllers`.
+  #
+  # You can disable this behaviour by removing the line below, and instead
+  # explicitly tag your specs with their type, e.g.:
+  #
+  #     RSpec.describe UsersController, :type => :controller do
+  #       # ...
+  #     end
+  #
+  # The different available types are documented in the features, such as in
+  # https://relishapp.com/rspec/rspec-rails/docs
+  config.infer_spec_type_from_file_location!
+
+  # Filter lines from Rails gems in backtraces.
+  config.filter_rails_from_backtrace!
+  # arbitrary gems may also be filtered via:
+  # config.filter_gems_from_backtrace("gem name")
+
+  config.before(:example) do
+    DatabaseCleaner.clean_with(:truncation)
+  end
+end
diff --git a/lecture_5/homework/spec/requests/buildings_spec.rb b/lecture_5/homework/spec/requests/buildings_spec.rb
new file mode 100644
index 00000000..e78f547f
--- /dev/null
+++ b/lecture_5/homework/spec/requests/buildings_spec.rb
@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'Buildings API', type: :request do
+  describe 'GET /buildings' do
+    subject { get '/buildings' }
+
+    it 'responds with 200' do
+      subject
+      expect(response).to have_http_status(200)
+    end
+
+    context 'when there are no Buildings' do
+      it 'return "There are no buildings" message' do
+        subject
+        response_json = JSON.parse(response.body)
+        expect(response_json['message']).to include('There are no buildings')
+      end
+    end
+
+    context 'with existing Buildings' do
+      before { create_list(:building, 4) }
+
+      it 'responds with 200' do
+        subject
+        expect(response).to have_http_status(200)
+      end
+
+      it 'includes Building data' do
+        subject
+        response_json = JSON.parse(response.body)
+        expect(response_json['data'].size).to eq(4)
+      end
+    end
+  end
+
+  describe 'GET /buildings/:id' do
+    let(:building_id) { 1 }
+    subject { get "/buildings/#{building_id}" }
+
+    context 'when Building is not found' do
+      it 'responds with 404' do
+        subject
+        expect(response).to have_http_status(404)
+      end
+
+      it 'includes the "Couldn\'t find Building with \'id\'=1" message' do
+        subject
+        response_json = JSON.parse(response.body)
+        expect(response_json['error']).to include("Couldn't find Building with 'id'=1")
+      end
+    end
+
+    context 'when Building is found' do
+      before { create(:building, id: building_id, name: 'Building_1') }
+
+      it 'responds with 200' do
+        subject
+        expect(response).to have_http_status(200)
+      end
+
+      it 'returns data of Building with id = 1' do
+        subject
+        response_json = JSON.parse(response.body)
+        expect(response_json['data']).to include(
+          'id' => building_id.to_s,
+          'attributes' => {
+            'name' => 'Building_1',
+            'siege_ability' => nil
+          }
+        )
+      end
+    end
+  end
+end
diff --git a/lecture_5/homework/spec/services/reports/siege_report_spec.rb b/lecture_5/homework/spec/services/reports/siege_report_spec.rb
new file mode 100644
index 00000000..4934e9f4
--- /dev/null
+++ b/lecture_5/homework/spec/services/reports/siege_report_spec.rb
@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Reports::SiegeReport, type: :service do
+  subject(:siege_report) { described_class.new(params).call }
+
+  let(:params)   { { building: building } }
+  let(:building) { create(:building, warriors: army) }
+  let(:army)     { [] }
+
+  describe '#call' do
+    context 'with building without army' do
+      it 'returns report with siege ability equals to 0' do
+        expect(siege_report).to eq(0)
+      end
+    end
+
+    context 'with building which has an army' do
+      context 'when 10 samurais' do
+        let(:army) { create_list(:warrior, 10, :samurai) }
+
+        it 'returns report with siege ability equals to 5' do
+          expect(siege_report).to eq(5)
+        end
+      end
+
+      context 'when 10 hussars' do
+        let(:army) { create_list(:warrior, 10, :hussar) }
+
+        it 'returns report with siege ability equals to 3' do
+          expect(siege_report).to eq(3)
+        end
+      end
+
+      context 'when 5 hussars and 5 samurais' do
+        let(:army) { create_list(:warrior, 10) }
+
+        it 'returns report with siege ability equals to 4' do
+          expect(siege_report).to eq(4)
+        end
+      end
+
+      context 'when the number of warriors exceeds daily granary abilities' do
+        let(:army) { create_list(:warrior, 100) }
+
+        it 'returns report with siege ability equals to 0' do
+          expect(siege_report).to eq(0)
+        end
+      end
+    end
+
+    context 'with building which has an army but the granary is empty' do
+      let(:building) { create(:building, warriors: army, granary: 0) }
+      let(:army) { create_list(:warrior, 10) }
+
+      it 'returns report with siege ability equals to 0' do
+        expect(siege_report).to eq(0)
+      end
+    end
+  end
+end
diff --git a/lecture_5/homework/spec/spec_helper.rb b/lecture_5/homework/spec/spec_helper.rb
new file mode 100644
index 00000000..01f7c974
--- /dev/null
+++ b/lecture_5/homework/spec/spec_helper.rb
@@ -0,0 +1,96 @@
+# frozen_string_literal: true
+
+# This file was generated by the `rails generate rspec:install` command. Conventionally, all
+# specs live under a `spec` directory, which RSpec adds to the `$LOAD_PATH`.
+# The generated `.rspec` file contains `--require spec_helper` which will cause
+# this file to always be loaded, without a need to explicitly require it in any
+# files.
+#
+# Given that it is always loaded, you are encouraged to keep this file as
+# light-weight as possible. Requiring heavyweight dependencies from this file
+# will add to the boot time of your test suite on EVERY test run, even for an
+# individual file that may not need all of that loaded. Instead, consider making
+# a separate helper file that requires the additional dependencies and performs
+# the additional setup, and require it from the spec files that actually need
+# it.
+#
+# See http://rubydoc.info/gems/rspec-core/RSpec/Core/Configuration
+RSpec.configure do |config|
+  # rspec-expectations config goes here. You can use an alternate
+  # assertion/expectation library such as wrong or the stdlib/minitest
+  # assertions if you prefer.
+  config.expect_with :rspec do |expectations|
+    # This option will default to `true` in RSpec 4. It makes the `description`
+    # and `failure_message` of custom matchers include text for helper methods
+    # defined using `chain`, e.g.:
+    #     be_bigger_than(2).and_smaller_than(4).description
+    #     # => "be bigger than 2 and smaller than 4"
+    # ...rather than:
+    #     # => "be bigger than 2"
+    expectations.include_chain_clauses_in_custom_matcher_descriptions = true
+  end
+
+  # rspec-mocks config goes here. You can use an alternate test double
+  # library (such as bogus or mocha) by changing the `mock_with` option here.
+  config.mock_with :rspec do |mocks|
+    # Prevents you from mocking or stubbing a method that does not exist on
+    # a real object. This is generally recommended, and will default to
+    # `true` in RSpec 4.
+    mocks.verify_partial_doubles = true
+  end
+
+  # This option will default to `:apply_to_host_groups` in RSpec 4 (and will
+  # have no way to turn it off -- the option exists only for backwards
+  # compatibility in RSpec 3). It causes shared context metadata to be
+  # inherited by the metadata hash of host groups and examples, rather than
+  # triggering implicit auto-inclusion in groups with matching metadata.
+  config.shared_context_metadata_behavior = :apply_to_host_groups
+
+  # The settings below are suggested to provide a good initial experience
+  # with RSpec, but feel free to customize to your heart's content.
+  #   # This allows you to limit a spec run to individual examples or groups
+  #   # you care about by tagging them with `:focus` metadata. When nothing
+  #   # is tagged with `:focus`, all examples get run. RSpec also provides
+  #   # aliases for `it`, `describe`, and `context` that include `:focus`
+  #   # metadata: `fit`, `fdescribe` and `fcontext`, respectively.
+  #   config.filter_run_when_matching :focus
+  #
+  #   # Allows RSpec to persist some state between runs in order to support
+  #   # the `--only-failures` and `--next-failure` CLI options. We recommend
+  #   # you configure your source control system to ignore this file.
+  #   config.example_status_persistence_file_path = "spec/examples.txt"
+  #
+  #   # Limits the available syntax to the non-monkey patched syntax that is
+  #   # recommended. For more details, see:
+  #   #   - http://rspec.info/blog/2012/06/rspecs-new-expectation-syntax/
+  #   #   - http://www.teaisaweso.me/blog/2013/05/27/rspecs-new-message-expectation-syntax/
+  #   #   - http://rspec.info/blog/2014/05/notable-changes-in-rspec-3/#zero-monkey-patching-mode
+  #   config.disable_monkey_patching!
+  #
+  #   # Many RSpec users commonly either run the entire suite or an individual
+  #   # file, and it's useful to allow more verbose output when running an
+  #   # individual spec file.
+  #   if config.files_to_run.one?
+  #     # Use the documentation formatter for detailed output,
+  #     # unless a formatter has already been configured
+  #     # (e.g. via a command-line flag).
+  #     config.default_formatter = "doc"
+  #   end
+  #
+  #   # Print the 10 slowest examples and example groups at the
+  #   # end of the spec run, to help surface which specs are running
+  #   # particularly slow.
+  #   config.profile_examples = 10
+  #
+  #   # Run specs in random order to surface order dependencies. If you find an
+  #   # order dependency and want to debug it, you can fix the order by providing
+  #   # the seed, which is printed after each run.
+  #   #     --seed 1234
+  #   config.order = :random
+  #
+  #   # Seed global randomization in this process using the `--seed` CLI option.
+  #   # Setting this allows you to use `--seed` to deterministically reproduce
+  #   # test failures related to randomization by passing the same `--seed` value
+  #   # as the one that triggered the failure.
+  #   Kernel.srand config.seed
+end