Add brew cask --prefix [cask] command

lib/hbc/cli.rb

@@ -16,6 +16,7 @@ class Hbc::CLI; end
 require 'hbc/cli/info'
 require 'hbc/cli/install'
 require 'hbc/cli/list'
+require 'hbc/cli/prefix'
 require 'hbc/cli/search'
 require 'hbc/cli/uninstall'
 require 'hbc/cli/update'

lib/hbc/cli/prefix.rb

@@ -0,0 +1,29 @@
+class Hbc::CLI::Prefix < Hbc::CLI::Base
+  def self.run(*args)
+    cask_tokens = cask_tokens_from(args)
+    if cask_tokens.empty?
+      puts install_prefix
+    else
+      cask_tokens.each { |cask_token| puts cask_prefix(cask_token) }
+    end
+  end
+
+  def self.install_prefix
+    @install_prefix ||= Pathname.new(HOMEBREW_PREFIX).join('opt', 'brew-cask')
+  end
+
+  def self.cask_prefix(cask_token)
+    cask = Hbc.load(cask_token)
+    raise Hbc::CaskNotInstalledError.new(cask) unless cask.installed?
+    cask.staged_path
+  end
+
+  def self.command_name
+    @command_name ||= '--prefix'
+  end
+
+  def self.help
+    "with no args, displays Homebrew-cask's install path; given installed #{
+    }Casks, lists the locations in the Caskroom where the Casks are installed"
+  end
+end

test/cask/cli/prefix_test.rb

@@ -0,0 +1,61 @@
+require 'test_helper'
+
+describe Hbc::CLI::Prefix do
+  describe 'given no args' do
+    before do
+      @expected_output = "#{HOMEBREW_PREFIX}/opt/brew-cask\n"
+    end
+
+    it 'displays the install location for Homebrew-cask' do
+      lambda {
+        Hbc::CLI::Prefix.run
+      }.must_output(@expected_output)
+    end
+  end
+
+  describe 'given one or more Casks' do
+    before do
+      @caffeine = Hbc.load('local-caffeine')
+      @transmission = Hbc.load('local-transmission')
+
+      shutup do
+        Hbc::Installer.new(@caffeine).install
+        Hbc::Installer.new(@transmission).install
+      end
+    end
+
+    after do
+      shutup do
+        Hbc::CLI::Uninstall.run('local-caffeine', 'local-transmission')
+      end
+    end
+
+    it 'displays the install location for an installed Cask' do
+      lambda {
+        Hbc::CLI::Prefix.run('local-caffeine')
+      }.must_output("#{@caffeine.staged_path}\n")
+
+      lambda {
+        Hbc::CLI::Prefix.run('local-transmission')
+      }.must_output("#{@transmission.staged_path}\n")
+    end
+
+    it 'displays the install locations for multiple installed Casks' do
+      lambda {
+        Hbc::CLI::Prefix.run('local-caffeine', 'local-transmission')
+      }.must_output("#{@caffeine.staged_path}\n#{@transmission.staged_path}\n")
+    end
+
+    it 'shows an error when a bad Cask is provided' do
+      lambda {
+        Hbc::CLI::Prefix.run('notacask')
+      }.must_raise Hbc::CaskUnavailableError
+    end
+
+    it "shows an error when a Cask is provided that's not installed" do
+      lambda {
+        Hbc::CLI::Prefix.run('anvil')
+      }.must_raise Hbc::CaskNotInstalledError
+    end
+  end
+end