Add basic hours validations

When configuring the gem, we'll now throw errors when the hours
configuration:
  * is not hash-like.
  * does not contain any blocks of hours.

lib/biz.rb

@@ -51,6 +51,7 @@ def schedule
 require 'biz/day_of_week'
 require 'biz/day_time'
 require 'biz/duration'
+require 'biz/error'
 require 'biz/holiday'
 require 'biz/interval'
 require 'biz/periods'
@@ -59,4 +60,5 @@ def schedule
 require 'biz/time_segment'
 require 'biz/week'
 require 'biz/week_time'
+require 'biz/validation'
 require 'biz/version'

lib/biz/configuration.rb

@@ -5,6 +5,8 @@ class Configuration
 
     def initialize
       @raw = Raw.new.tap do |raw| yield raw if block_given? end
+
+      Validation.perform(raw)
     end
 
     def intervals

lib/biz/error.rb

@@ -0,0 +1,7 @@
+module Biz
+  class Error < StandardError
+
+    Configuration = Class.new(self)
+
+  end
+end

lib/biz/validation.rb

@@ -0,0 +1,50 @@
+module Biz
+  class Validation
+
+    def self.perform(raw)
+      new(raw).perform
+    end
+
+    def initialize(raw)
+      @raw = raw
+    end
+
+    def perform
+      RULES.each do |rule| rule.check(raw) end
+
+      self
+    end
+
+    protected
+
+    attr_reader :raw
+
+    class Rule
+
+      def initialize(message, &condition)
+        @message   = message
+        @condition = condition
+      end
+
+      def check(raw)
+        fail Error::Configuration, message unless condition.call(raw)
+      end
+
+      protected
+
+      attr_reader :message,
+                  :condition
+
+    end
+
+    RULES = Set.new([
+      Rule.new('Hours must be hash-like.') { |raw|
+        raw.hours.respond_to?(:to_h)
+      },
+      Rule.new('Hours must be provided.') { |raw|
+        raw.hours.to_h.any?
+      }
+    ])
+
+  end
+end

spec/configuration_spec.rb

@@ -26,6 +26,18 @@
     end
   end
 
+  context 'when initialized with an invalid configuration' do
+    it 'raises a configuration error' do
+      expect {
+        Biz::Configuration.new do |config|
+          config.hours     = {}
+          config.holidays  = holidays
+          config.time_zone = time_zone
+        end
+      }.to raise_error Biz::Error::Configuration
+    end
+  end
+
   describe '#intervals' do
     context 'when left unconfigured' do
       subject(:configuration) {

spec/error_spec.rb

@@ -0,0 +1,11 @@
+RSpec.describe Biz::Error do
+  it 'is a standard error' do
+    expect(described_class.new.is_a?(StandardError)).to eq true
+  end
+
+  describe Biz::Error::Configuration do
+    it "is a 'biz' error" do
+      expect(described_class.new.is_a?(Biz::Error))
+    end
+  end
+end

spec/validation_spec.rb

@@ -0,0 +1,43 @@
+RSpec.describe Biz::Validation do
+  let(:raw) { Struct.new(:hours, :holidays, :time_zone).new }
+
+  subject(:validation) { described_class.new(raw) }
+
+  describe '.perform' do
+    before { raw.hours = {} }
+
+    it 'performs the validation on the provided raw input' do
+      expect { described_class.perform(raw) }.to raise_error(
+        Biz::Error::Configuration
+      )
+    end
+  end
+
+  describe '#perform' do
+    describe 'when the hours are hash-like' do
+      describe 'and the hours are not empty' do
+        before { raw.hours = {mon: {'09:00' => '17:00'}} }
+
+        it 'does not raise an error' do
+          expect { validation.perform }.not_to raise_error
+        end
+      end
+
+      describe 'and the hours are empty' do
+        before { raw.hours = {} }
+
+        it 'raises a configuration error' do
+          expect { validation.perform }.to raise_error Biz::Error::Configuration
+        end
+      end
+    end
+
+    describe 'when the hours are not hash-like' do
+      before { raw.hours = 1 }
+
+      it 'raises a configuration error' do
+        expect { validation.perform }.to raise_error Biz::Error::Configuration
+      end
+    end
+  end
+end