class OSwitch

# File lib/oswitch.rb, line 42
def initialize(package, command = [])
  @package = package
  @command = command
  @imgname = "oswitch_#{@package}"
  @cntname = "#{@package.gsub(%r{/|:}, '_')}-#{Process.pid}"
  exec
end

# File lib/oswitch.rb, line 29
def packages
  Dir["#{DOTDIR}/*"].map do |rep|
    pkgs = Dir["#{rep}/*"].select {|pkg| File.directory?(pkg)}
    pkgs = [rep] if pkgs.empty?
    pkgs
  end.
  flatten.
  map {|pkg|
    pkg.gsub("#{DOTDIR}/", '')
  }
end

# File lib/oswitch.rb, line 52
  def exec
    ping and build and switch
  rescue ENODKR => e
    puts e
    exit
  rescue => e
    puts <<MSG

Ouch! Looks like you have hit a bug. Please could you post the error report
below to our issue tracker (https://github.com/wurmlab/oswitch/issues):

#{e}\n#{e.backtrace.join("\n")}

MSG
    exit
  end

# File lib/oswitch.rb, line 83
def build
  return true if Image.exists? imgname
  create_context_dir &&
    system("docker build -t #{imgname} #{context_dir}") || !remove_context_dir
end

# File lib/oswitch.rb, line 130
def context_dir
  File.join(DOTDIR, package)
end

# File lib/oswitch.rb, line 100
def create_context_dir
  FileUtils.mkdir_p context_dir
  FileUtils.cp_r(template_files, context_dir)
  write_dockerfile
end

# File lib/oswitch.rb, line 118
def dockerfile_data
  data = ["FROM #{package}"]
  data << 'COPY _switch /'
  data << 'COPY wheel /etc/sudoers.d/'
  data << "RUN /_switch #{userargs} 2>&1"
  data << 'ENV LC_ALL en_US.UTF-8'
  data << "USER #{username}"
  data << "ENTRYPOINT [\"#{shell}\", \"-c\"]"
  data.join("\n")
end

# File lib/oswitch.rb, line 144
  def motd
    str =<<MOTD
################################################################################
You are now running: #{package}, in container: #{cntname}.

Container is distinct from the shell your launched this container from. Changes
you make here will be lost unless it's made to one of the directories below:

 - #{mountpoints.join("\n - ")}

It's possible you may not be able to write to one or more directories above,
but it should be possible to read data from all. Home directory is often the
safest to write to.

Press Ctrl-D or type 'exit' to go back.
################################################################################
MOTD
    str.shellescape
  end

# File lib/oswitch.rb, line 164
def mountargs
  mountpoints.map do |mountpoint|
    "-v '#{mountpoint}':'#{mountpoint}'"
  end.join(' ')
end

# File lib/oswitch.rb, line 90
def ping
  pong = timeout 5, ENODKR do
    system 'docker info > /dev/null 2>&1'
  end
  pong or raise ENODKR
end

# File lib/oswitch.rb, line 107
def remove_context_dir
  FileUtils.rm_r(context_dir)
end

# File lib/oswitch.rb, line 71
def switch
  cmdline = "docker run --name #{cntname} --hostname #{cntname} -it --rm" \
    " -w #{cwd} #{mountargs} #{imgname} "
  if command.empty?
    # Display motd and run interactive shell.
    cmdline << "\"echo #{motd}; #{shell} -i\""
  else
    cmdline << "\"#{command}\""
  end
  Kernel.exec cmdline
end

# File lib/oswitch.rb, line 135
def template_dir
  File.join(PREFIX, 'share', 'oswitch', 'context')
end

# File lib/oswitch.rb, line 140
def template_files
  Dir[File.join(template_dir, '*')]
end

# File lib/oswitch.rb, line 170
def userargs
  [uid, gid, username, home, shell].join(' ')
end

# File lib/oswitch.rb, line 112
def write_dockerfile
  dockerfile = File.join(context_dir, 'Dockerfile')
  File.write(dockerfile, dockerfile_data)
end