For Libraries:
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Multiple items selected:
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Download and share will be highlighted regardless of library permission level, just in case they happen to have custom permissions that allow these. We cannot check in advance. User will try, and get error if all items don't have appropriate permissions. Added note at top of Share window to that effect, for when multiple items are selected.
Single item selected:
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Checks to see if item has individual authzs that are greater than the library has;
TEST CASE:
have a library that User A has read on, and give User A admin or download on one of the items.
When User A clicks only on that item, download or share should be highlighted.
Albums/Search Results:
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Multiple items selected:
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Download and share will be highlighted in all cases, because permissions are determined by the item and the library they live in, NOT by the album. Since we cannot check in advance, actions are available, and user will have to try and fail if they do not have appropriate permissions. Added note at top of Share window to that effect, for when multiple items are selected.
Single item selected:
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Do an authz check on item which returns either item-specific, or inherited from library permissions - basically, just get a 'yes' or 'no' on if user can do a certain action. If it has admin or download, those icons are enabled, if not they are disabled.
Slideshows:
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I don't think any of this is relevant to slideshows, so did not implement it there.
Share Window:
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If multiple items are selected, share window will open. There is a warning at the top, explaining that the action may be disallowed. Other than that, user must try to share, and backend will report error if it fails.
If single item is selected, we shouldn't be able to get to this window if user does not have admin authz, either on item itself, or inherited from library. So, if you do find yourself there with one item selected, and get an error when you try and set permissions, please file it as a bug for Robin to look into.