Catalog availability count doesn't account for items in the cart

[squidgetx]

Currently the availability count in the catalog doesn't change when the user adds items to the cart. It should change (just as a display function, not actually changing how many are available) so the user can't add 50x of an item to the cart

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added 2014/08/26

• tie count in catalog views to cart
• validate cart item counts on each request and update if necessary
• ensure that if there is a change when requesting the /reservations/new page we redirect to the catalog

[orenyk]

We can pull from the cart items hash to offset the availability number. This doesn't address the multiple users trying to reserve the same item issue (see discussion in #323), but I don't see how we could do that without hitting the server during cart updates, something we've worked very hard to avoid. A display update would be useful though, good idea!

[mnquintana]

We sort of left in a hurry so we didn't update this, but Sylvan and I were talking about this implementation (which I think is the best way to go):

I think updating the availability count via adding an item to the cart (ie. if 2 equipment items are available for an equipment model and you add 1 to the cart, the catalog should immediately update to display 1 left) should be done completely client-side. This would side-step the guaranteed slowness of trying to contact the server after each time "Add to Cart" is clicked. I think the important thing about this feature is the immediate feedback the user would get when clicking Add to Cart, and not necessarily that the availability count be absolutely, up-to-the-second accurate. If a user's cart count of an equipment model ever exceeds what's available (ie. someone checks out the last equipment item for a model), then the next user action that results in either a catalog refresh or a new page request should update the cart accordingly and flash a message saying, more or less "x is no longer available, so it was removed from your cart."

[orenyk]

I definitely agree that this should be client-side for speed reasons, that's basically what I was getting at. Just to make sure I understand correctly, is the second half of that implementation a full validation of the cart during each page request? That's not something that had occurred to me but I think it's a great idea. One thing we might want to do is if we're requesting the "review reservation" page and an item's availability has been reduced, is to redirect to the catalog so it's clear that something critical has happened (otherwise people might gloss over the flash).

[orenyk]

This is pretty useful functionality and should be implemented prior to export. Adding to v4.2 for now.