Articles behind paywall / membersonly protection / fade out preview with concurrent visibility for specific user's segments

Hi,

our article center is divided within sections that are representations of different products in our offer.  
Users are able to see sections of products, that they have purchased. If specific user didn't purchase specific product, then he can't see it section with specific articles about this product. Users may have more than one product at the time. 

Till now, all articles are available on for signed-in users, and - further - method of division mentioned above.
Almost every article has table of content in the upper part.

What I want to do is:

(This is before signing)
To make all articles visible without signing but with paywall/membersonly protection/fade out preview like that:

Something like: we have such article but it's only for customers that have purschased an access.
I want to make visible only table of content in each article or first 300 characters of text.
 

(This is after signing)

To maintain the divison of sections for specific products, what means: if user has purchased product then he has access to the section with articles. If no - he hasn't and there is no section, it's empty or with specific text, ie ‘This article is only for customers that have purchased this product.’.

Is this possible somehow?

The main goal of above is to share the upper part of articles with Google - I want to unlock them for searching.
Should I focus on different approach maybe?

Best regards,
Jakub