Add summary to `dvc status -c [target]`

[AljoSt]

In order to estimate how long a pull is going to take, it would be good if dvc status -c [target] would supply a summary in the form of Total: N files, X GB

[AljoSt]

had a brief look into this, but I'm not quite sure where to start. I guess we would have a method here that adds the filesize for each object, and then summarized and printed here? Not sure though, how to get the file size

[shcheklein]

@AljoSt this a really great feature request. You pointed the right places to do changes. The biggest question is how do we get file sizes. We don't have that functionality right now in the remote class, only exists method or list all that do check if files exists remotely or returns all files. They both do not provide any additional info currently. So, we would probably need to "teach" them to return more info.

I suppose, we can start with one of the remotes to try. What do you think, @efiop ?

@AljoSt what remote storage you are mostly interested in?

[AljoSt]

@shcheklein I'm currently using S3

[shcheklein]

@AljoSt so, in case of S3 (check the s3.py file) we use s3.head_object and list_objects. I think both of them return sizes so we can extend (might be needed to rename exists or make a second function) them to returns file sizes.

Suggested TODO (@efiop please review :) ):

• Check that s3.head_object returns actual object size (even if it's a multi-part upload).
• Check that s3.list_object and s3.list_object_v2 return sizes. Again, need to be sure that it properly returns it in case of multipart.
• Create a function like get_file_size that returns size of the object it if exists.
• Modify
• Use get_file_size in the status check in the remote base
• Modify cache_exists (and helpers it calls) in the remote base to deal with sizes.
• Modify status itself to collect and print sizes.

If I'm not missing anything for this hight level picture we can start with checks and move forward, I'll try to provide more details and help discussing this.