Implement `ask' recipe keyword

features/recipes/ask.feature

@@ -0,0 +1,22 @@
+Feature: `ask' recipe keyword
+
+  Scenario: prompts user with a list of choices on standard output
+    Given a recipe with:
+      """
+      task :ask_letter do
+        letter = ask 'Which letter?', %w[A B]
+
+        echo letter
+      end
+      """
+    When I execute the recipe interactively
+    And I type "1"
+    Then the output must contain:
+      """
+      Which letter?
+      0: A
+      1: B
+      Choice:
+      B
+      """
+    And the exit status must be 0

features/steps/recipe_steps.rb

@@ -10,3 +10,7 @@ When(/^I successfully execute the recipe$/) do
   step 'I execute the recipe'
   assert_exit_status(0)
 end
+
+When(/^I execute the recipe interactively$/) do
+  run_interactive('producer recipe.rb')
+end

lib/producer/core.rb

@@ -14,6 +14,7 @@ require 'producer/core/condition'
 require 'producer/core/condition/dsl'
 require 'producer/core/env'
 require 'producer/core/errors'
+require 'producer/core/prompter'
 require 'producer/core/recipe'
 require 'producer/core/recipe/dsl'
 require 'producer/core/remote'

lib/producer/core/prompter.rb

@@ -0,0 +1,21 @@
+module Producer
+  module Core
+    class Prompter
+      attr_reader :input, :output
+
+      def initialize(input, output)
+        @input  = input
+        @output = output
+      end
+
+      def prompt(question, choices)
+        cs = choices.each_with_index.inject('') do |m, (c, i)|
+          m += "#{i}: #{c}\n"
+        end
+        output.puts "#{question}\n#{cs}Choice:"
+        choice = input.gets
+        choices[choice.to_i]
+      end
+    end
+  end
+end

lib/producer/core/task/dsl.rb

@@ -32,6 +32,10 @@ module Producer
           @condition = Condition.evaluate(@env, &block) if block
           @condition
         end
+
+        def ask(question, choices, prompter: Prompter)
+          prompter.new(env.input, env.output).prompt(question, choices)
+        end
       end
     end
   end

spec/producer/core/prompter_spec.rb

@@ -0,0 +1,41 @@
+require 'spec_helper'
+
+module Producer::Core
+  describe Prompter do
+    let(:input)         { StringIO.new }
+    let(:output)        { StringIO.new }
+    let(:env)           { Env.new(input: input, output: output) }
+    subject(:prompter)  { Prompter.new(input, output) }
+
+    describe '#initialize' do
+      it 'assigns the given input' do
+        expect(prompter.input).to be input
+      end
+
+      it 'assigns the given output' do
+        expect(prompter.output).to be output
+      end
+    end
+
+    describe '#prompt' do
+      let(:question)  { 'Which letter?' }
+      let(:choices)   { %w[A B] }
+
+      it 'prompts choices' do
+        prompter.prompt question, choices
+        expect(output.string).to eq <<-eoh.gsub /^\s+\|/, ''
+          |#{question}
+          |0: A
+          |1: B
+          |Choice:
+        eoh
+      end
+
+      it 'returns value for entry chosen by user' do
+        input.puts '1'
+        input.rewind
+        expect(prompter.prompt question, choices).to eq 'B'
+      end
+    end
+  end
+end

spec/producer/core/task/dsl_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 module Producer::Core
   describe Task::DSL do
     let(:block)   { proc {} }
-    let(:env)     { double 'env' }
+    let(:env)     { Env.new }
     subject(:dsl) { Task::DSL.new(env, &block) }
 
     %w[echo sh file_write].each do |action|
@@ -82,5 +82,25 @@ module Producer::Core
         end
       end
     end
+
+    describe '#ask' do
+      let(:question)        { 'Which letter?' }
+      let(:choices)         { %w[A B] }
+      let(:prompter_class)  { double('prompter class').as_null_object }
+      subject(:ask)         { dsl.ask question, choices,
+                              prompter: prompter_class }
+
+      it 'builds a prompter' do
+        expect(prompter_class).to receive(:new).with(env.input, env.output)
+        ask
+      end
+
+      it 'prompts and returns the choice' do
+        prompter = double 'prompter'
+        allow(prompter_class).to receive(:new) { prompter }
+        allow(prompter).to receive(:prompt) { :choice }
+        expect(ask).to eq :choice
+      end
+    end
   end
 end