Cockatrice: Spec for card image download priority order

[Daenyth]

Currently we have a loosely-defined image url download priority order with fallback.

The goal of this ticket is to come up with a flexible, understandable design that helps users get the images they want.

At a high level, we currently have:
if card has muid:

• try main url for every enabled set containing that card in priority order
  If card does not have muid:
• use fallback

I propose instead:

• Allow users to make a list of download urls to attempt, with a priority order.

When a card image is requested:

• For each enabled set in order, try all download url templates in order, skipping url templates which ask for information that the card doesn't have
  
  
  
  • eg if the template asks for muid, and card has none, skip that url.
  
  

In pseudocode:

QList<UrlTemplate> urls = get_urls_for_card(cardInfo, enabledSetConfiguration);
for (UrlTemplate url, urls):
    Url url = UrlTemplate.apply(cardInfo)
    response = download(url)
    if response.ok:
        save(response.image)
    else:
        continue

This ticket supersedes #1984 and #2346

[andrewzwicky]

FYI I'm going to take a look at this (so multiple people aren't working on the same thing). The first thing I'd like to do is just take the 2 existing URLs and fall back as expected: On 404 for the first one, (instead of muid of card), going by set in priority order.

The list of multiple URLs by priority could come in a later PR. No idea how long I expect it to take.

[Daenyth]

@andrewzwicky come grab us in gitter if you get stuck! This is exciting :)

[andrewzwicky]

I have something tentatively working, here's a log in action.

Trying to load picture for card: "Angelic Benediction"  from set: "DD3_DVD"
Picture not found, trying to download
Trying to download picture for card: "Angelic Benediction"  from set: "DD3_DVD" from url: "http://magiccards.info/scans/en/dd3_dvd/19.jpg"
following redirect: "Angelic Benediction" Url: "https://magiccards.info/scans/en/dd3_dvd/19.jpg"
Download failed: "Error transferring https://magiccards.info/scans/en/dd3_dvd/19.jpg - server replied: Not Found"
Possible picture at  "https://magiccards.info/scans/en/dd3_dvd/19.jpg"  could not be loaded
Trying to load picture for card: "Angelic Benediction"  from set: "DD3_DVD"
Picture not found, trying to download
Trying to download picture for card: "Angelic Benediction"  from set: "DD3_DVD" from url: "http://gatherer.wizards.com/Handlers/Image.ashx?multiverseid=394008&type=deck"
Possible picture at  "http://gatherer.wizards.com/Handlers/Image.ashx?multiverseid=394008&type=deck"  could not be loaded
Trying to load picture for card: "Angelic Benediction"  from set: "M13"
Picture not found, trying to download
Trying to download picture for card: "Angelic Benediction"  from set: "M13" from url: "http://magiccards.info/scans/en/m13/4.jpg"
following redirect: "Angelic Benediction" Url: "https://magiccards.info/scans/en/m13/4.jpg"
Image successfully downloaded from  "https://magiccards.info/scans/en/m13/4.jpg"

This is using:
http://magiccards.info/scans/en/!setcode_lower!/!setnumber!.jpg as my primary URL and http://gatherer.wizards.com/Handlers/Image.ashx?multiverseid=!cardid!&type=deck as my secondary URL, (with =deck on the end, so it will intentionally fail).

For the set that doesn't match, the download is attempted, but then it moves the secondary URL, then to the next set. Code needs to be cleaned up and tested more thoroughly, but it's looking good so far.

[Daenyth]

@andrewzwicky awesome! Do you want to open a WIP PR for any early feedback?

[andrewzwicky]

@Daenyth Yeah that's a good idea, I'll do that.