Parsing negative filesizes

[drusepth]

Is there a reason this gem doesn't parse negative filesizes (e.g. -50KB)? Seems like when you're talking about memory capacities, it'd often make sense to talk about the absence of space (one example use-case given below). I'd be happy to include a PR if it was accidentally left out.

My use-case:

• I offer users X MB of storage space, with Y GB of storage space if they upgrade their plan.
• I display how much storage space that user has remaining in their account on a particular page.
• Users obviously cannot upload more files than they have space for, but if they downgrade their plan they move from Y GB storage space to X MB, which can mean they have some negative quantity of space they need to remove before uploading additional files.
• In this case, my code looks like:

if current_user.bandwidth_kb >= 0
  space_remaining = Filesize.from("#{current_user.bandwidth_kb}KB").pretty
else
  space_remaining = "-" + Filesize.from("#{current_user.bandwidth_kb.abs}KB").pretty
end

You have <%= space_remaining %> of bandwidth remaining.

I would assume negative filesizes are a lot harder to convert from one format to another; is that true? I'd of course love to be able to parse negative filesizes and pretty-print them. :+1:

Reproduction steps:

irb(main):018:0* Filesize.from("50KB").pretty
=> "50.00 kB"
irb(main):019:0> Filesize.from("-50KB").pretty
ArgumentError: Unparseable filesize
	from /app/vendor/bundle/ruby/2.2.0/gems/filesize-0.1.1/lib/filesize.rb:135:in `from'
	from (irb):19
	from /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.7.1/lib/rails/commands/console.rb:110:in `start'
	from /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.7.1/lib/rails/commands/console.rb:9:in `start'
	from /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.7.1/lib/rails/commands/commands_tasks.rb:68:in `console'
	from /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.7.1/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
	from /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.7.1/lib/rails/commands.rb:17:in `<top (required)>'
	from bin/rails:8:in `require'
	from bin/rails:8:in `<main>'
irb(main):020:0>

[dominikh]

I don't see any reason not to support negative sizes. Via Filesize.new, one can already provide negative sizes; however they won't pretty print correctly, as the formula used assumes positive sizes.

I'd accept a PR that adds parsing of negative sizes, and correctly handles them in pretty printing.

Unrelated: You probably shouldn't be using #from to create these file size objects. You already have a numeric value, current_user.bandwidth_kb and a known unit, KB. It'd make much more sense to use Filesize.new(current_user.bandwidth_kb * 1000) here and avoid the whole parsing machinery.