task :heroku_pending_migrations, [:app] => :environment do |t, args|

  # returns an array of the schema_migrations run on heroku app +app_name+
  def get_remote_migrations(app_name)
    connection_string = `heroku pg:credentials DATABASE_URL --app #{app_name} | head -2 | tail -1`.strip
    `psql #{connection_string} -Atc "SELECT * FROM schema_migrations;"`.split
  end

  app_name = args[:app]
  remote_migrations = get_remote_migrations(app_name)
  local_migrations = ActiveRecord::Migrator.new(:up, ActiveRecord::Migrator.migrations_paths).migrations
  pending_migrations = local_migrations.reject { |m| remote_migrations.include?(m.version.to_s) }
  if pending_migrations.present?
    puts 'Pending migrations:'
    puts pending_migrations.map &:version
    exit false
  else
    puts 'No pending migrations'
    exit true
  end
end