Price Range Algorithm

Price Range Requirements/Algorithm:
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The price ranges for an offergroup are determined by:
    if offergroup has offersets with status 'open' or 'expired' and 1 offer with quantity > 0:
        Using only those offersets, find offers that have quantity available:
            if any offers have quantity available:
                Using those offers, calculate price ranges
                replace '$0.00' with 'FREE' in ourprice range
            else:
                Using all offers with quantity > 0 (from the offersets that are 'open' or 'expired')
                    calculate price ranges
                    override ourprice to 'SOLD OUT'
    else if offergroup has offersets with status 'closed' and 1 offer with quantity > 0:
        Using only those offersets:
            calculate price ranges from offers with quantity > 0
            replace '$0.00' with 'FREE' in ourprice range
    else:
        ourprice and fullprice are 'n/a'
        
        
Subroutines:        
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Quantity Available is: 
    offer.quantity minus the sum of claims.quantity WHERE status = 'completed'

Calculate price ranges:
    Give a set of offers:
        For ourprice and fullprice:
            Find the lowest and highest value. 
            If lowest == highest:
                price range is either in currency format (e.g. "$9.00")
            else:
                price range is lowest - highest in currency format (e.g. "$7.00 - $9.00")
        
        
    
Notes:
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The string 'SOLD OUT' is used by the mailer daemon as a flag to skip that offergroup.

The string 'n/a' is used instead of an empty string to prevent constant cache rebuilds. An empty string would mean that the range needs to be calculated.

Offers with quantity == 0 should not be considered for any price range unless they are the child offer (i.e. shared inventory).

Updates:
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on edit to any offerset or offer of offergroup
on claims becoming completed or cancelled for any offer of offergroup