* Download and Preview Files in OSS

  Some systems use cloud storage services to store file data in the system and store the key of the file on OSS in the database. We hope to be able to download and view these files directly in Arql.

** First you need to install and configure =rclone= tool

   macOS example:

   #+BEGIN_EXAMPLE
    brew install rclone
   #+END_EXAMPLE


** Configure rclone
   
   Add the OSS configuration used by the system to the =~/.config/rclone/rclone.conf= file, for example:

   #+BEGIN_EXAMPLE
     [my_system]
     type = s3
     provider = Alibaba
     env_auth = false
     access_key_id = LTAxuiwqsayuuyea
     secret_access_key = sauiqwYUwqhjsdayuwehjkwehjwehj
     endpoint = oss-cn-beijing.aliyuncs.com
     acl = private
     storage_class = STANDARD
   #+END_EXAMPLE


** Add configuration in =~/.arql.d/init.yaml=

    #+BEGIN_SRC yaml
      dev:
        created_at: ["create_time", "gmt_created"]
        updated_at: ["update_time", "gmt_modified"]
        host: db.dev.com
        port: 3306
        username: admin
        password: 123456
        database: dev_db
        rclone_name: "my_system"
        oss_bucket: "my_system_dev_bucket"
      
      prod:
        created_at: ["create_time", "gmt_created"]
        updated_at: ["update_time", "gmt_modified"]
        host: db.prod.com
        port: 3306
        username: admin
        password: 123456
        database: prod_db
        rclone_name: "my_system"
        oss_bucket: "my_system_prod_bucket"
    #+END_SRC


** Create a file =~/.arql.d/oss.rb=

       #+BEGIN_SRC ruby
     class OSS
       def pry_source_location; end
     
       attr_accessor :path, :bucket
     
       def initialize(path, bucket: nil)
         @path = path
         unless bucket
           bucket = env_config(/./)['oss_bucket']
         end
         @bucket = bucket
       end
     
       def rclone_name
         env_config(/./)['rclone_name']
       end
     
       def info
         `rclone lsl #{rclone_name}:#{bucket}/#{path}`
       end
     
       def download(dir = nil, keep_structure = false)
         dir = File.expand_path(dir) if dir
         dir ||= Dir.mktmpdir('arql-attachment-')
         if keep_structure
           dest_dir = dir + '/' + File.dirname(path)
           FileUtils.mkdir_p(dest_dir)
           system <<~EOF
           rclone copy #{rclone_name}:#{bucket}/#{path} #{dest_dir}/
           EOF
           dest_dir + '/' + File.basename(path)
         else
           system <<~EOF
           rclone copy #{rclone_name}:#{bucket}/#{path} #{dir}/
           EOF
           dir + '/' + File.basename(path)
         end
       end
     
       def copy(dest_name, dest_bucket)
         path_prefix = File.dirname(path)
         system "rclone copy -P #{rclone_name}:#{bucket}/#{path} #{dest_name}:#{dest_bucket}/#{path_prefix}/"
       end
     
       def cat
         `rclone cat #{rclone_name}:#{bucket}/#{path}`
       end
     
       def to_rclone_url
         "#{rclone_name}:#{bucket}/#{path}"
       end
     
       def open
         file = download
         system <<~EOF
         open #{file}
         EOF
         file
       end
     
       def preview
         file = download
         system <<~EOF
         qlmanage -p #{file} &> /dev/null
         EOF
         file
       end
     
       def emacs_open
         file = download
         system <<~EOF
         emacsclient -q --eval "(switch-to-buffer-other-window (current-buffer))" &> /dev/null
         emacsclient -n '#{file}'
         EOF
         file
       end
     end
     
     class String
       def oss(bucket: nil)
         OSS.new(self, bucket: bucket)
       end
     end
   #+END_SRC


** Import this file in =~/.arql.d/init.rb=

    #+BEGIN_SRC ruby
      load(File.absolute_path(File.dirname(__FILE__) + "/oss.rb"))
    #+END_SRC

** Usage


    Assuming that the user table has an avatar field that stores the key of the user's avatar on OSS, we can view and download the avatar like this:
  
      #+BEGIN_SRC ruby
        User.first.avatar.oss.preview  # Preview using macOS Quick Look
        User.first.avatar.oss.download  # Download to a temporary directory and return the file path
        User.first.avatar.oss.open  # Download to a temporary directory and open with the system (macOS) default program
        User.first.avatar.oss.cat  # Output file content directly
      #+END_SRC