Feature/BE-38: Bidding System

[BElifb]

• Created Bid model and updated ArtItem and User models accordingly.

• Created 2 endpoints with 5 APIs in total.
  

• Added new_bid_flag to user, that will be set to true when one of user's art items gets bid on, and it will be set to false when user visits their own profile (after being sent as true).

• Possible sale status for art item are;

  •     NOTFORSALE = 'NS', _('Not For Sale')
    

  •  FORSALE = 'FS', _('For Sale')
    

  •  SOLD = 'SO', _('Sold')
    

• Possible responses for a bid are;

  •     REJECTED = 'RE', _('Rejected')
    

  •  ACCEPTED = 'AC', _('Accepted')
    

  •  NORESPONSE = 'NR', _('No Response')
    

• Created detailed swagger documentation for APIs. :8000/api/v1/swagger/schema/

• Tested through Postman, Admin site and swagger.

[BElifb]

• Created a model called NewBids, that stores new bids that each user has received.
• Created a signal so that a single instance of NewBids model is created whenever a user account is created via /auth/register/ API.
• Everytime an art item of a user receives a bid. That art item is added to NewBids of the user.
• When a user visits their own profile, all of the art items in NewBids are returned and NewBids is set to null for that user.
• I updated the /users/profile/me/ api so that it returns the art items that have received new bids. Swagger documentation is also updated. Here's a preview:
  
• I was thinking for the frontend, when a user visits their profile we could check for newbids, and if there exist any we could add a pop-up of all art items that have received offers with links.
• Also updated profile serializer so that it returns the necessary information for all of the art items.

[KarahanS]

• I got the following warning when I run the code:

  WARNINGS:
  api.NewBids.new_bids: (fields.W340) null has no effect on ManyToManyField

  Removed null = True from new_bids, it's resolved.

• When we click on the artitems/bids/{id} endpoint on Swagger, artitems/{artitemid}/bids/ is also opened as you stated earlier. I found out the problem: They had the same operation IDs (generated by Swagger automatically): artitemds_bids_update. I fixed that part by manually setting the operation_id to artitems_bids_response for artitems/bids/{id} endpoint. (URL is still the same)

Btw, 403 error message for artitems/{artitemid}/bids/ made me feel sad :(

[KarahanS]

I realize you required authentication even for GET requests - which means, guest users won't be able to see the bids on the art items. Did you do it that way intentionally? @BElifb

[KarahanS]

• As ArtItemSerializer now returns sale_status, minimum_price, bought_by fields, updated documentation of art item related APIs in Swagger.
• bought_by field was only returning the id of the user for ArtItemSerializer. When an art item is displayed, frontend may want to display the username of the buyer - to avoid a redundant call to profile API, I updated that field to return some information about the buyer as follows (using CommentUserSerializer):

"bought_by": {
        "id": 2,
        "username": "use1r2222d22222222222",
        "profile_path": "avatar/default.png"
    }

Tested the APIs with Postman, everything seems ok. Thanks for the efforts. Approved. (We may update GET requests not to require authentication for them, it's up to you)

[BElifb]

I realize you required authentication even for GET requests - which means, guest users won't be able to see the bids on the art items. Did you do it that way intentionally? @BElifb

Yes, after our discussions about bidding system in the meetings, we landed on max bid not being visible to users. So only the owner of the art item will be able to see all the bids on item. Other than that owner and the buyer can reach a specific bid via id.

[BElifb]

Btw, 403 error message for artitems/{artitemid}/bids/ made me feel sad :(

Sorry 😈

@KarahanS Thank you for the review and updates. I am merging the PR.