In BillableUsageService we have a metric called "swatch_contract_usage_total" that increments by the total contract amount each time a usage is remitted.  This doesn't give an accurate account of what usage is covered by the contract however since it will increment by the full amount for every remittance that occurs.

Instead it should only increment by the amount of usage that is being covered by the contract during processing of said billable usage. 

This formula can be used to determine what to increment by:

remaining_allowable_contract_usage = max(0, contract_value - (current_total_usage - usage))
swatch_contract_usage_total += min(usage, remaining_allowable_contract_usage)) 

Ex: (Contract value = 10, current_total_usage = 3, usage = 3, swatch_contract_usage_total += 3)

Ex: (Contract value = 10, current_total_usage = 6, usage = 4, swatch_contract_usage_total += 4)

Ex: (Contract value = 10, current_total_usage = 12, usage = 3, swatch_contract_usage_total += 1)

Ex: (Contract value = 10, current_total_usage = 20, usage=5, swatch_contract_usage_total += 0)

Done:

• swatch_contract_usage_total increments by the usage being covered within the given month