Add python demurrage calculator

python/erc20_demurrage_token/demurrage.py

@@ -0,0 +1,38 @@
+#
+import logging
+import datetime
+import math
+
+logging.basicConfig(level=logging.DEBUG)
+logg = logging.getLogger()
+
+
+class DemurrageCalculator:
+
+    def __init__(self, interest_f_minute):
+
+        self.r_min = interest_f_minute
+        self.r_hour = 1 - ((1 -self.r_min) ** 60)
+        self.r_day = 1 - ((1 -self.r_hour) ** 24)
+        #self.r_week = interest_f_day ** 7
+        logg.info('demurrage calculator set with min {:.32f} hour {:.32f} day {:.32f}'.format(self.r_min, self.r_hour, self.r_day))
+
+
+    def amount_since(self, amount, timestamp):
+        delta = datetime.datetime.utcnow() - datetime.datetime.fromtimestamp(timestamp)
+        adjusted_amount = amount * ((1 - self.r_day) ** (delta.days))
+        logg.debug('adjusted for {} days {} -> {}'.format(delta.days, amount, adjusted_amount))
+
+        remainder = delta.seconds
+        remainder_hours = math.floor(remainder / (60 * 60))
+        adjusted_delta = adjusted_amount * ((1 - self.r_hour) ** remainder_hours)
+        adjusted_amount -= (adjusted_amount - adjusted_delta)
+        logg.debug('adjusted for {} hours {} -> {} delta {}'.format(remainder_hours, amount, adjusted_amount, adjusted_delta))
+
+        remainder -= (remainder_hours * (60 * 60))
+        remainder_minutes = math.floor(remainder / 60)
+        adjusted_delta = adjusted_amount * ((1 - self.r_min) ** remainder_minutes)
+        adjusted_amount -= (adjusted_amount - adjusted_delta)
+        logg.debug('adjusted for {} hours {} -> {} delta {}'.format(remainder_minutes, amount, adjusted_amount, adjusted_delta))
+
+        return adjusted_amount