def from(str)
  case str.split("/")
  in [name] then "github.com/#{name}/#{name}"
  in [owner, name] then "github.com/#{owner}/#{name}"
  in [host, owner, name] then "#{host}/#{owner}/#{name}"
  end
end

puts from("name")
# => github.com/name/name
puts from("owner/name")
# => github.com/owner/name
puts from("github.com/owner/name")
# => github.com/owner/name