don't reinstall already installed casks

thanks to @ccutrer for the catch; this implementation is based on his PR

refs #233

lib/cask/cli/install.rb

@@ -1,16 +1,14 @@
 class Cask::CLI::Install
-  def self.run(*cask_names)
+  def self.run(*args)
+    cask_names = args.reject { |a| a == '--force' }
+    force = args.include? '--force'
     cask_names.each do |cask_name|
       begin
        cask = Cask.load(cask_name)
        Cask::Installer.install(cask)
        Cask::AppLinker.new(cask).link
        Cask::PkgInstaller.new(cask).install
-      rescue CaskUnavailableError => e
-        onoe e
-      rescue ChecksumMissingError => e
-        onoe e
-      rescue ChecksumMismatchError => e
+      rescue CaskError => e
         onoe e
       end
     end

lib/cask/exceptions.rb

@@ -1,4 +1,6 @@
-class CaskNotInstalledError < RuntimeError
+class CaskError < RuntimeError; end
+
+class CaskNotInstalledError < CaskError
   attr_reader :cask
   def initialize cask
     @cask = cask
@@ -9,7 +11,7 @@ class CaskNotInstalledError < RuntimeError
   end
 end
 
-class CaskUnavailableError < RuntimeError
+class CaskUnavailableError < CaskError
   attr_reader :name
   def initialize name
     @name = name
@@ -20,7 +22,7 @@ class CaskUnavailableError < RuntimeError
   end
 end
 
-class CaskAlreadyCreatedError < RuntimeError
+class CaskAlreadyCreatedError < CaskError
   attr_reader :name
   def initialize name
     @name = name
@@ -30,3 +32,14 @@ class CaskAlreadyCreatedError < RuntimeError
     "Cask for #{name} already exists. Use `brew cask edit #{name}` to see it."
   end
 end
+
+class CaskAlreadyInstalledError < CaskError
+  attr_reader :name
+  def initialize name
+    @name = name
+  end
+
+  def to_s
+    "Cask for #{name} is already installed. Use `--force` to install anyways."
+  end
+end

lib/cask/installer.rb

@@ -2,7 +2,11 @@ require 'digest'
 
 class Cask::Installer
   class << self
-    def install(cask)
+    def install(cask, force=false)
+      if cask.installed? && !force
+        raise CaskAlreadyInstalledError.new(cask)
+      end
+
       require 'formula_support'
       software_spec = SoftwareSpec.new(cask.url.to_s, cask.version)
       downloader = CurlDownloadStrategy.new(cask.title, software_spec)

test/cask/installer_test.rb

@@ -69,6 +69,33 @@ describe Cask::Installer do
       end
       with_macosx_dir.destination_path.join('__MACOSX').wont_be :directory?
     end
+
+    it "prevents already installed casks from being installed" do
+      transmission = Cask.load('local-transmission')
+      transmission.installed?.must_equal false
+
+      shutup do
+        Cask::Installer.install(transmission)
+      end
+      lambda {
+        shutup do
+          Cask::Installer.install(transmission)
+        end
+      }.must_raise(CaskAlreadyInstalledError)
+    end
+
+    it "allows already installed casks to being installed if force is provided" do
+      transmission = Cask.load('local-transmission')
+      transmission.installed?.must_equal false
+
+      shutup do
+        Cask::Installer.install(transmission)
+      end
+      shutup do
+        Cask::Installer.install(transmission, true)
+      end # wont_raise
+    end
+
   end
 
   describe "uninstall" do

test/cli/install_test.rb

@@ -12,6 +12,26 @@ describe Cask::CLI::Install do
     Cask.appdir.join('Caffeine.app').must_be :symlink?
   end
 
+  it "prevents double install" do
+    shutup do
+      Cask::CLI::Install.run('local-transmission')
+    end
+
+    TestHelper.must_output(self, lambda {
+      Cask::CLI::Install.run('local-transmission')
+    }, 'Error: Cask for local-transmission is already installed. Use `--force` to install anyways.')
+  end
+
+  it "allows double install with --force" do
+    shutup do
+      Cask::CLI::Install.run('local-transmission')
+    end
+
+    TestHelper.must_output(self, lambda {
+      Cask::CLI::Install.run('local-transmission', '--force')
+    }, 'Error: Cask for local-transmission is already installed. Use `--force` to install anyways.')
+  end
+
   it "properly handles casks that are not present" do
     TestHelper.must_output(self, lambda {
       Cask::CLI::Install.run('what-the-balls')

test/support/cleanup.rb

@@ -0,0 +1,10 @@
+module Cask::CleanupHooks
+  def after_teardown
+    super
+    Cask.all.select(&:installed?).each { |c| Cask::Installer.uninstall(c) }
+  end
+end
+
+class MiniTest::Spec
+  include Cask::CleanupHooks
+end

test/test_helper.rb

@@ -72,6 +72,7 @@ end
 require 'support/fake_fetcher'
 require 'support/fake_appdir'
 require 'support/fake_system_command'
+require 'support/cleanup'
 
 # pretend like we installed the cask tap
 project_root = Pathname.new(File.expand_path("#{File.dirname(__FILE__)}/../"))