1 files changed, 24 insertions, 2 deletions
diff --git a/finance/income.py b/finance/income.py
index 12d5d4e..94759ff 100644
--- a/finance/income.py
+++ b/finance/income.py
@@ -1,10 +1,32 @@
 import dataclasses
+from datetime import datetime
 
 
 @dataclasses.dataclass(kw_only=True, frozen=True)
 class Income:
+    """Income models financial income paid on the first day of a month"""
 
     amount: float
 
-    def integrate(self, delta_t: int) -> float:
-        return delta_t * self.amount
+    def integrate(self, start: datetime, end: datetime) -> float:
+        """Integrate the income from a start to an end date"""
+
+        retval = 0.0
+
+        current = datetime(start.year, start.month, 1)
+
+        if start == current:
+            retval += self.amount
+
+        while True:
+            if current.month == 12:
+                current = datetime(current.year + 1, 1, 1)
+            else:
+                current = datetime(current.year, current.month + 1, 1)
+
+            if current <= end:
+                retval += self.amount
+            else:
+                break
+
+        return retval