created find_previous_bill and use it to help work out gaps in bills - e.g. like with internet where I added only the new costs

bills.py

@@ -6,6 +6,44 @@ def qtr(d):
     m = int(d[5:7])
     return ( (m-1)//3 + 1 )
    
+def find_previous_bill( bill_type, bill_info, bill_date ):
+#    print( f"{bill_type}: find_previous_bill -> {bill_date}" )
+    wanted_year = int(bill_date[:4])
+    wanted_mm = int(bill_date[5:7])
+    # if we don't have a bill before this date, no way to set price
+    if int(wanted_year) < int(bill_info[bill_type]['first_bill_year']):
+#        print(f"{bill_type}: find_previous_bill - failed.  wanted_year={wanted_year} is older than our first_bill={bill_info[bill_type]['first_bill_year']}" )
+        return None
+
+    # start loop from bill_date, go backwards and find which one it is (same year, should be month-based)
+    # earlier year, then just last one from the year.
+    yr_range=range( wanted_year, bill_info[bill_type]['first_bill_year'], -1 )
+    if wanted_year == int(bill_info[bill_type]['first_bill_year']):
+        # range of this year with -1, does not return anything, so force this year.
+        yr_range=[ wanted_year ]
+    for yr in yr_range:
+        # start with bills in the year wanted (if any)
+        # must include 'estimated' bills to deal with growth of future years
+        if yr in bill_info[bill_type]['year']:
+            # okay, we have the previous billing year, and we wanted one for a year in the future,
+            # just return the last one in this year as its the most recent
+            if wanted_year > yr:
+#                print("should be return last of {yr} - date={bill_info[bill_type]['year'][yr][-1]['bill_date']}" )
+                return bill_info[bill_type]['year'][yr][-1]
+            else:
+                # lets go through the newest to oldest of these bills
+                for bill in bill_info[bill_type]['year'][wanted_year][::-1]:
+                    bill_mm = int(bill['bill_date'][5:7])
+                    # reversing the bills, means we start with the 'most recent' in this year to the oldest
+                    # if the month we want is after the bill, we are done
+                    if wanted_mm > bill_mm:
+                        return bill
+
+#    print(f"{bill_type}: find_previous_bill - failed.  Seems our first bill = {bill_info[bill_type]['first_bill']['bill_date']} is in same year, but after wanted month={wanted_mm}, so no base to rely on" )
+    return None
+
+
+
 # missing annual bill, find date based on MM-DD and add new year - given we start with first_bill anyway, will only be used for future bill predictions
 # future only, so add ann_growth (based on drop-down) for each future year
 # NOTE: only ever called when there is a need to add a new bill
@@ -37,11 +75,6 @@ def add_missing_monthly_bills_in_yr( bill_type, bill_info, yr ):
     mm = bill_info[bill_type]['first_bill']['bill_date'][5:7]
     lb_mm = bill_info[bill_type]['last_bill']['bill_date'][5:7]
 
-    # choose last bill from last amount to grow from as its most relevant
-    if not 'last_bill_amount' in bill_info[bill_type]:
-        bill_info[bill_type]['last_bill_amount']=bill_info[bill_type]['last_bill']['amount']
-    amt = bill_info[bill_type]['last_bill_amount']
-
     #okay add monthly bills for the rest of this year if its the first year
     if bill_info[bill_type]['first_bill_year'] == yr:
         start_m=int(mm)
@@ -61,6 +94,12 @@ def add_missing_monthly_bills_in_yr( bill_type, bill_info, yr ):
                     bill_found=True
                     break
         if not bill_found:
+            pb=find_previous_bill( bill_type, bill_info, new_date )
+            if not pb:
+                print("Failed to find previous_bill, can't calculate missing bill - returning" )
+                return
+
+            amt = pb['amount']
             # if this month is the same as the last bill month and as per above
             # we don't have a bill for this date, then add annual grotwh
             if i == int(lb_mm):
@@ -69,6 +108,15 @@ def add_missing_monthly_bills_in_yr( bill_type, bill_info, yr ):
                 bill_info[bill_type]['last_bill_amount']=amt
             # last param is estimated (and this is an estimate for a future bill / not real)
             new_bill( bill_type, amt, new_date, 1 )
+            if not yr in bill_info[bill_type]['year']:
+                bill_info[bill_type]['year'][yr]=[]
+            bill={}
+            bill['bill_date']=new_date
+            bill['amount']=amt
+            bill['estimated']=1
+            # need this for find_previous_bill to work but only need the above 2 fields?
+            bill_info[bill_type]['year'][yr].append(bill)
+
     return
 
 # given the bill_type has a which_growth contain min/avg/max, return the corresponding growth number