Decrease shortage phase

[wvengen]

For dry ordering, Vokomokum needs a decrease shortage phase: at the end of the ordering period, members can only change amounts that don't increase a shortage in wholesale packages. When a member visits the ordering page, he only sees articles with a shortage, to help him fill it.

[nhoening]

This code lets you see the states used by Vokomokum: https://www.assembla.com/spaces/vokomokum/git/source/master/order/cgi-bin/adm_ord_status.cgi#ln40

[wvengen]

If've started to implement this upstream on feature/boxfills. Configuration works (enable the feature in configuration screen, and setting it for the order).

To document, I'll share my considerations on the rules for the boxill (=reduce shortages) phase.

• If the number of articles ordered decreases, the change should be rejected.
• Increase in tolerance is welcome (perhaps with a maximum of unit_quantity or unit_quantity-1).
• A member is is allowed to increase his quantity or tolerance if the number of missing units decreases.
• A member is allowed to decrease his quantity if the number of missing units decreases. (This makes sure the members who want to get it.)
• A member is not allowed to decrease his quantity if it means that someone else will get extra units in his tolerance (the number of missing units remaining equal).
• A member could be allowed to change his tolerance into quantity (so that another member doesn't need to get something in his tolerance).

I think this would be captured by the following in the decrease shortage phase:

art_q = <sum of all member quantities>
art_t = <sum of all member tolerances>
mem_q = <desired quantity for member>
mem_t = <allowed tolerance for member>
unit_quantity = <how many units make a box>

# how many units are still needed to fulfill all member quantities
missing_units = unit_quantity - ((art_q  % unit_quantity) + art_t)
missing_units = 0 IF missing_units < 0 OR missing_units == unit_quantity

# number of boxes to order at supplier
boxes = FLOOR(art_q/unit_quantity)
IF art_q%unit_quantity>0 AND art%unit_quantity + art_t > unit_quantity THEN boxes += 1

delta_art_q = art_q[after_change] - art_q[before_change]
delta_art_t = art_t[after_change] - art_t[before_change]
(etc.)

IF delta_missing_units < 0 AND delta_boxes >= 0 AND delta_art_t >= 0 THEN ALLOW
ELSE IF delta_art_q > 0 AND delta_art_q == -delta_art_t THEN ALLOW
ELSE DENY

(If the terms quantity, tolerance and unit_quantity are new you to, it is explained here in German.)

One open question:

• Should an admin be able to change member amounts that don't follow these rules (until order closes)? edit since an admin can't change the order until it is closed, this isn't applicable. When the order is closed, it is not in the boxfill phase anymore, so an admin can change it.

[wvengen]

(The open question about admins being able to change in any case, matters because this check could very well go into the OrderArticle model, where it refuses to save when the conditions are not met if the order is in the boxfill phase. If an admin should still be able to save it, either the model should somehow know who initiated the change, or the check should move to the controller, so that it is only executed for member ordering. Both cases require some more thinking for a clean solution.)

[wvengen]

• [x] Server-side
• [x] Client-side
• [x] Port to foodcoop-adam fork

[wvengen]

Upstream supports this via https://github.com/foodcoops/foodsoft/pull/387

[wvengen]

Implemented via #170. It would be useful to have this tested by someone else at some point.