[Analyzer] Refacto our image analyzers to further expand the gem (#254)

[Mth0158]

No description provided.

[Mth0158]

Self note: ensure #199 is fixed with this?

UPDATED from #199:

It should be fixed by #299 (0 byte size test case). I am closing the issue, feel free to reopen it if it's necessary. The update should be available in the coming release (1.3.5)

[Mth0158]

Self note: ensure #242 is handled with this?

[igorkasyanchuk]

question if we need to require it always here
can we just check if defined?(MiniMagick)?

and maybe raise the error even sooner, in the initializer (check when the app boots if possible)?

[Mth0158]

I agree with you, I think we do not need to require it every time. That's, indeed, not necessary, plus not doing it has performance benefits.

I am updating the code with a unless defined?(MiniMagick) (same for Vips), as it was done previouslu by the metadata.rb file (I should have ketp it).

For the second part, we could raise the error at the app boot, but I think this will enforce the user to have both imagemagick and ruby-vips gem in their Gemfile (which we do not want). Plus, if the user does not use validators based on the image analyzers, it's not necessary to have either imagemagick or ruby-vips gem. Therefore I think it's better to leave it this way? What do you think?

[Mth0158]

Using Object.const_defined?(:Vips) is better than unless defined?(Vips) because we might not have loaded the lib yet, therefore it might not be defined yet. Whereas Object.const_defined?(:Vips) is about presence in the code.

[igorkasyanchuk]

I'm fine with bject.const_defined?(:Vips)

I'm also fine if it just raises an exception and we will have something about it in the docs. Not the most user friendly but this should be expected. Bu this option is least preferable.

[Mth0158]

@igorkasyanchuk I finally opted for defined?(xxx). It is the best option you are right. Let me know if the PR is okay with you now :)