require 'yaml'
require 'capistrano/recipes/deploy/scm'
require 'capistrano/recipes/deploy/strategy'
 
def _cset(name, *args, &block)
  unless exists?(name)
    set(name, *args, &block)
  end
end
 
# =========================================================================
# These variables MUST be set in the client capfiles. If they are not set,
# the deploy will fail with an error.
# =========================================================================
 
_cset(:application) { abort "Please specify the name of your application, set :application, 'foo'" }
_cset(:repository)  { abort "Please specify the repository that houses your application's code, set :repository, 'foo'" }
 
# =========================================================================
# These variables may be set in the client capfile if their default values
# are not sufficient.
# =========================================================================
 
_cset :scm, :subversion
_cset :deploy_via, :checkout
 
_cset(:deploy_to) { "/u/apps/#{application}" }
_cset(:revision)  { source.head }
 
# =========================================================================
# These variables should NOT be changed unless you are very confident in
# what you are doing. Make sure you understand all the implications of your
# changes if you do decide to muck with these!
# =========================================================================
 
_cset(:source)            { Capistrano::Deploy::SCM.new(scm, self) }
_cset(:real_revision)     { source.local.query_revision(revision) { |cmd| with_env("LC_ALL", "C") { run_locally(cmd) } } }
 
_cset(:strategy)          { Capistrano::Deploy::Strategy.new(deploy_via, self) }
 
_cset(:release_name)      { set :deploy_timestamped, true; Time.now.utc.strftime("%Y%m%d%H%M%S") }
 
_cset :version_dir,       "releases"
_cset :shared_dir,        "shared"
_cset :shared_children,   %w(system log pids)
_cset :current_dir,       "current"
 
_cset(:releases_path)     { File.join(deploy_to, version_dir) }
_cset(:shared_path)       { File.join(deploy_to, shared_dir) }
_cset(:current_path)      { File.join(deploy_to, current_dir) }
_cset(:release_path)      { File.join(releases_path, release_name) }
 
_cset(:releases)          { capture("ls -xt #{releases_path}").split.reverse }
_cset(:current_release)   { File.join(releases_path, releases.last) }
_cset(:previous_release)  { releases.length > 1 ? File.join(releases_path, releases[-2]) : nil }
 
_cset(:current_revision)  { capture("cat #{current_path}/REVISION").chomp }
_cset(:latest_revision)   { capture("cat #{current_release}/REVISION").chomp }
_cset(:previous_revision) { capture("cat #{previous_release}/REVISION").chomp }
 
_cset(:run_method)        { fetch(:use_sudo, true) ? :sudo : :run }
 
# some tasks, like symlink, need to always point at the latest release, but
# they can also (occassionally) be called standalone. In the standalone case,
# the timestamped release_path will be inaccurate, since the directory won't
# actually exist. This variable lets tasks like symlink work either in the
# standalone case, or during deployment.
_cset(:latest_release) { exists?(:deploy_timestamped) ? release_path : current_release }
 
# =========================================================================
# These are helper methods that will be available to your recipes.
# =========================================================================
 
# Auxiliary helper method for the `deploy:check' task. Lets you set up your
# own dependencies.
def depend(location, type, *args)
  deps = fetch(:dependencies, {})
  deps[location] ||= {}
  deps[location][type] ||= []
  deps[location][type] << args
  set :dependencies, deps
end
 
# Temporarily sets an environment variable, yields to a block, and restores
# the value when it is done.
def with_env(name, value)
  saved, ENV[name] = ENV[name], value
  yield
ensure
  ENV[name] = saved
end
 
# logs the command then executes it locally.
# returns the command output as a string
def run_locally(cmd)
  logger.trace "executing locally: #{cmd.inspect}" if logger
  `#{cmd}`
end
 
# If a command is given, this will try to execute the given command, as
# described below. Otherwise, it will return a string for use in embedding in
# another command, for executing that command as described below.
#
# If :run_method is :sudo (or :use_sudo is true), this executes the given command
# via +sudo+. Otherwise is uses +run+. If :as is given as a key, it will be
# passed as the user to sudo as, if using sudo. If the :as key is not given,
# it will default to whatever the value of the :admin_runner variable is,
# which (by default) is unset.
#
# THUS, if you want to try to run something via sudo, and what to use the
# root user, you'd just to try_sudo('something'). If you wanted to try_sudo as
# someone else, you'd just do try_sudo('something', :as => "bob"). If you
# always wanted sudo to run as a particular user, you could do 
# set(:admin_runner, "bob").
def try_sudo(*args)
  options = args.last.is_a?(Hash) ? args.pop : {}
  command = args.shift
  raise ArgumentError, "too many arguments" if args.any?
 
  as = options.fetch(:as, fetch(:admin_runner, nil))
  via = fetch(:run_method, :sudo)
  if command
    invoke_command(command, :via => via, :as => as)
  elsif via == :sudo
    sudo(:as => as)
  else
    ""
  end
end
 
# Same as sudo, but tries sudo with :as set to the value of the :runner
# variable (which defaults to "app").
def try_runner(*args)
  options = args.last.is_a?(Hash) ? args.pop : {}
  args << options.merge(:as => fetch(:runner, "app"))
  try_sudo(*args)
end
 
# =========================================================================
# These are the tasks that are available to help with deploying web apps,
# and specifically, Rails applications. You can have cap give you a summary
# of them with `cap -T'.
# =========================================================================
 
namespace :deploy do
  desc <<-DESC
    Deploys your project. This calls both `update' and `restart'. Note that \
    this will generally only work for applications that have already been deployed \
    once. For a "cold" deploy, you'll want to take a look at the `deploy:cold' \
    task, which handles the cold start specifically.
  DESC
  task :default do
    update
    restart
  end
 
  desc <<-DESC
    Prepares one or more servers for deployment. Before you can use any \
    of the Capistrano deployment tasks with your project, you will need to \
    make sure all of your servers have been prepared with `cap deploy:setup'. When \
    you add a new server to your cluster, you can easily run the setup task \
    on just that server by specifying the HOSTS environment variable:
 
      $ cap HOSTS=new.server.com deploy:setup
 
    It is safe to run this task on servers that have already been set up; it \
    will not destroy any deployed revisions or data.
  DESC
  task :setup, :except => { :no_release => true } do
    dirs = [deploy_to, releases_path, shared_path]
    dirs += shared_children.map { |d| File.join(shared_path, d) }
    run "#{try_sudo} mkdir -p #{dirs.join(' ')} && #{try_sudo} chmod g+w #{dirs.join(' ')}"
  end
 
  desc <<-DESC
    Copies your project and updates the symlink. It does this in a \
    transaction, so that if either `update_code' or `symlink' fail, all \
    changes made to the remote servers will be rolled back, leaving your \
    system in the same state it was in before `update' was invoked. Usually, \
    you will want to call `deploy' instead of `update', but `update' can be \
    handy if you want to deploy, but not immediately restart your application.
  DESC
  task :update do
    transaction do
      update_code
      symlink
    end
  end
 
  desc <<-DESC
    Copies your project to the remote servers. This is the first stage \
    of any deployment; moving your updated code and assets to the deployment \
    servers. You will rarely call this task directly, however; instead, you \
    should call the `deploy' task (to do a complete deploy) or the `update' \
    task (if you want to perform the `restart' task separately).
 
    You will need to make sure you set the :scm variable to the source \
    control software you are using (it defaults to :subversion), and the \
    :deploy_via variable to the strategy you want to use to deploy (it \
    defaults to :checkout).
  DESC
  task :update_code, :except => { :no_release => true } do
    on_rollback { run "rm -rf #{release_path}; true" }
    strategy.deploy!
    finalize_update
  end
 
  desc <<-DESC
    [internal] Touches up the released code. This is called by update_code \
    after the basic deploy finishes. It assumes a Rails project was deployed, \
    so if you are deploying something else, you may want to override this \
    task with your own environment's requirements.
 
    This task will make the release group-writable (if the :group_writable \
    variable is set to true, which is the default). It will then set up \
    symlinks to the shared directory for the log, system, and tmp/pids \
    directories, and will lastly touch all assets in public/images, \
    public/stylesheets, and public/javascripts so that the times are \
    consistent (so that asset timestamping works).  This touch process \
    is only carried out if the :normalize_asset_timestamps variable is \
    set to true, which is the default.
  DESC
  task :finalize_update, :except => { :no_release => true } do
    run "chmod -R g+w #{latest_release}" if fetch(:group_writable, true)
 
    # mkdir -p is making sure that the directories are there for some SCM's that don't
    # save empty folders
    run <<-CMD
      rm -rf #{latest_release}/log #{latest_release}/public/system #{latest_release}/tmp/pids &&
      mkdir -p #{latest_release}/public &&
      mkdir -p #{latest_release}/tmp &&
      ln -s #{shared_path}/log #{latest_release}/log &&
      ln -s #{shared_path}/system #{latest_release}/public/system &&
      ln -s #{shared_path}/pids #{latest_release}/tmp/pids
    CMD
 
    if fetch(:normalize_asset_timestamps, true)
      stamp = Time.now.utc.strftime("%Y%m%d%H%M.%S")
      asset_paths = %w(images stylesheets javascripts).map { |p| "#{latest_release}/public/#{p}" }.join(" ")
      run "find #{asset_paths} -exec touch -t #{stamp} {} ';'; true", :env => { "TZ" => "UTC" }
    end
  end
 
  desc <<-DESC
    Updates the symlink to the most recently deployed version. Capistrano works \
    by putting each new release of your application in its own directory. When \
    you deploy a new version, this task's job is to update the `current' symlink \
    to point at the new version. You will rarely need to call this task \
    directly; instead, use the `deploy' task (which performs a complete \
    deploy, including `restart') or the 'update' task (which does everything \
    except `restart').
  DESC
  task :symlink, :except => { :no_release => true } do
    on_rollback do
      if previous_release
        run "rm -f #{current_path}; ln -s #{previous_release} #{current_path}; true"
      else
        logger.important "no previous release to rollback to, rollback of symlink skipped"
      end
    end
 
    run "rm -f #{current_path} && ln -s #{latest_release} #{current_path}"
  end
 
  desc <<-DESC
    Copy files to the currently deployed version. This is useful for updating \
    files piecemeal, such as when you need to quickly deploy only a single \
    file. Some files, such as updated templates, images, or stylesheets, \
    might not require a full deploy, and especially in emergency situations \
    it can be handy to just push the updates to production, quickly.
 
    To use this task, specify the files and directories you want to copy as a \
    comma-delimited list in the FILES environment variable. All directories \
    will be processed recursively, with all files being pushed to the \
    deployment servers.
 
      $ cap deploy:upload FILES=templates,controller.rb
 
    Dir globs are also supported:
 
      $ cap deploy:upload FILES='config/apache/*.conf'
  DESC
  task :upload, :except => { :no_release => true } do
    files = (ENV["FILES"] || "").split(",").map { |f| Dir[f.strip] }.flatten
    abort "Please specify at least one file or directory to update (via the FILES environment variable)" if files.empty?
 
    files.each { |file| top.upload(file, File.join(current_path, file)) }
  end
 
  desc <<-DESC
    Restarts your application. This works by calling the script/process/reaper \
    script under the current path.
    
    By default, this will be invoked via sudo as the `app' user. If \
    you wish to run it as a different user, set the :runner variable to \
    that user. If you are in an environment where you can't use sudo, set \
    the :use_sudo variable to false:
    
      set :use_sudo, false
  DESC
  task :restart, :roles => :app, :except => { :no_release => true } do
    try_runner "#{current_path}/script/process/reaper"
  end
 
  namespace :rollback do
    desc <<-DESC
      [internal] Points the current symlink at the previous revision.
      This is called by the rollback sequence, and should rarely (if
      ever) need to be called directly.
    DESC
    task :revision, :except => { :no_release => true } do
      if previous_release
        run "rm #{current_path}; ln -s #{previous_release} #{current_path}"
      else
        abort "could not rollback the code because there is no prior release"
      end
    end
 
    desc <<-DESC
      [internal] Removes the most recently deployed release.
      This is called by the rollback sequence, and should rarely
      (if ever) need to be called directly.
    DESC
    task :cleanup, :except => { :no_release => true } do
      run "if [ `readlink #{current_path}` != #{current_release} ]; then rm -rf #{current_release}; fi"
    end
 
    desc <<-DESC
      Rolls back to the previously deployed version. The `current' symlink will \
      be updated to point at the previously deployed version, and then the \
      current release will be removed from the servers. You'll generally want \
      to call `rollback' instead, as it performs a `restart' as well.
    DESC
    task :code, :except => { :no_release => true } do
      revision
      cleanup
    end
 
    desc <<-DESC
      Rolls back to a previous version and restarts. This is handy if you ever \
      discover that you've deployed a lemon; `cap rollback' and you're right \
      back where you were, on the previously deployed version.
    DESC
    task :default do
      revision
      restart
      cleanup
    end
  end
 
  desc <<-DESC
    Run the migrate rake task. By default, it runs this in most recently \
    deployed version of the app. However, you can specify a different release \
    via the migrate_target variable, which must be one of :latest (for the \
    default behavior), or :current (for the release indicated by the \
    `current' symlink). Strings will work for those values instead of symbols, \
    too. You can also specify additional environment variables to pass to rake \
    via the migrate_env variable. Finally, you can specify the full path to the \
    rake executable by setting the rake variable. The defaults are:
 
      set :rake,           "rake"
      set :rails_env,      "production"
      set :migrate_env,    ""
      set :migrate_target, :latest
  DESC
  task :migrate, :roles => :db, :only => { :primary => true } do
    rake = fetch(:rake, "rake")
    rails_env = fetch(:rails_env, "production")
    migrate_env = fetch(:migrate_env, "")
    migrate_target = fetch(:migrate_target, :latest)
 
    directory = case migrate_target.to_sym
      when :current then current_path
      when :latest  then current_release
      else raise ArgumentError, "unknown migration target #{migrate_target.inspect}"
      end
 
    run "cd #{directory}; #{rake} RAILS_ENV=#{rails_env} #{migrate_env} db:migrate"
  end
 
  desc <<-DESC
    Deploy and run pending migrations. This will work similarly to the \
    `deploy' task, but will also run any pending migrations (via the \
    `deploy:migrate' task) prior to updating the symlink. Note that the \
    update in this case it is not atomic, and transactions are not used, \
    because migrations are not guaranteed to be reversible.
  DESC
  task :migrations do
    set :migrate_target, :latest
    update_code
    migrate
    symlink
    restart
  end
 
  desc <<-DESC
    Clean up old releases. By default, the last 5 releases are kept on each \
    server (though you can change this with the keep_releases variable). All \
    other deployed revisions are removed from the servers. By default, this \
    will use sudo to clean up the old releases, but if sudo is not available \
    for your environment, set the :use_sudo variable to false instead.
  DESC
  task :cleanup, :except => { :no_release => true } do
    count = fetch(:keep_releases, 5).to_i
    if count >= releases.length
      logger.important "no old releases to clean up"
    else
      logger.info "keeping #{count} of #{releases.length} deployed releases"
 
      directories = (releases - releases.last(count)).map { |release|
        File.join(releases_path, release) }.join(" ")
 
      try_sudo "rm -rf #{directories}"
    end
  end
 
  desc <<-DESC
    Test deployment dependencies. Checks things like directory permissions, \
    necessary utilities, and so forth, reporting on the things that appear to \
    be incorrect or missing. This is good for making sure a deploy has a \
    chance of working before you actually run `cap deploy'.
 
    You can define your own dependencies, as well, using the `depend' method:
 
      depend :remote, :gem, "tzinfo", ">=0.3.3"
      depend :local, :command, "svn"
      depend :remote, :directory, "/u/depot/files"
  DESC
  task :check, :except => { :no_release => true } do
    dependencies = strategy.check!
 
    other = fetch(:dependencies, {})
    other.each do |location, types|
      types.each do |type, calls|
        if type == :gem
          dependencies.send(location).command(fetch(:gem_command, "gem")).or("`gem' command could not be found. Try setting :gem_command")
        end
 
        calls.each do |args|
          dependencies.send(location).send(type, *args)
        end
      end
    end
 
    if dependencies.pass?
      puts "You appear to have all necessary dependencies installed"
    else
      puts "The following dependencies failed. Please check them and try again:"
      dependencies.reject { |d| d.pass? }.each do |d|
        puts "--> #{d.message}"
      end
      abort
    end
  end
 
  desc <<-DESC
    Deploys and starts a `cold' application. This is useful if you have not \
    deployed your application before, or if your application is (for some \
    other reason) not currently running. It will deploy the code, run any \
    pending migrations, and then instead of invoking `deploy:restart', it will \
    invoke `deploy:start' to fire up the application servers.
  DESC
  task :cold do
    update
    migrate
    start
  end
 
  desc <<-DESC
    Start the application servers. This will attempt to invoke a script \
    in your application called `script/spin', which must know how to start \
    your application listeners. For Rails applications, you might just have \
    that script invoke `script/process/spawner' with the appropriate \
    arguments.
 
    By default, the script will be executed via sudo as the `app' user. If \
    you wish to run it as a different user, set the :runner variable to \
    that user. If you are in an environment where you can't use sudo, set \
    the :use_sudo variable to false.
  DESC
  task :start, :roles => :app do
    run "cd #{current_path} && #{try_runner} nohup script/spin"
  end
 
  desc <<-DESC
    Stop the application servers. This will call script/process/reaper for \
    both the spawner process, and all of the application processes it has \
    spawned. As such, it is fairly Rails specific and may need to be \
    overridden for other systems.
 
    By default, the script will be executed via sudo as the `app' user. If \
    you wish to run it as a different user, set the :runner variable to \
    that user. If you are in an environment where you can't use sudo, set \
    the :use_sudo variable to false.
  DESC
  task :stop, :roles => :app do
    run "if [ -f #{current_path}/tmp/pids/dispatch.spawner.pid ]; then #{try_runner} #{current_path}/script/process/reaper -a kill -r dispatch.spawner.pid; fi"
    try_runner "#{current_path}/script/process/reaper -a kill"
  end
 
  namespace :pending do
    desc <<-DESC
      Displays the `diff' since your last deploy. This is useful if you want \
      to examine what changes are about to be deployed. Note that this might \
      not be supported on all SCM's.
    DESC
    task :diff, :except => { :no_release => true } do
      system(source.local.diff(current_revision))
    end
 
    desc <<-DESC
      Displays the commits since your last deploy. This is good for a summary \
      of the changes that have occurred since the last deploy. Note that this \
      might not be supported on all SCM's.
    DESC
    task :default, :except => { :no_release => true } do
      from = source.next_revision(current_revision)
      system(source.local.log(from))
    end
  end
 
  namespace :web do
    desc <<-DESC
      Present a maintenance page to visitors. Disables your application's web \
      interface by writing a "maintenance.html" file to each web server. The \
      servers must be configured to detect the presence of this file, and if \
      it is present, always display it instead of performing the request.
 
      By default, the maintenance page will just say the site is down for \
      "maintenance", and will be back "shortly", but you can customize the \
      page by specifying the REASON and UNTIL environment variables:
 
        $ cap deploy:web:disable \\
              REASON="hardware upgrade" \\
              UNTIL="12pm Central Time"
 
      Further customization will require that you write your own task.
    DESC
    task :disable, :roles => :web, :except => { :no_release => true } do
      require 'erb'
      on_rollback { run "rm #{shared_path}/system/maintenance.html" }
 
      reason = ENV['REASON']
      deadline = ENV['UNTIL']
 
      template = File.read(File.join(File.dirname(__FILE__), "templates", "maintenance.rhtml"))
      result = ERB.new(template).result(binding)
 
      put result, "#{shared_path}/system/maintenance.html", :mode => 0644
    end
 
    desc <<-DESC
      Makes the application web-accessible again. Removes the \
      "maintenance.html" page generated by deploy:web:disable, which (if your \
      web servers are configured correctly) will make your application \
      web-accessible again.
    DESC
    task :enable, :roles => :web, :except => { :no_release => true } do
      run "rm #{shared_path}/system/maintenance.html"
    end
  end
end