Implement finance.flow.simulate()

2 files changed, 48 insertions, 2 deletions

diff --git a/finance/flow.py b/finance/flow.py
index 9ea72c8..836c137 100644
--- a/finance/flow.py
+++ b/finance/flow.py
@@ -42,3 +42,25 @@ def monthly_candidates(start: datetime) -> Generator[datetime, None, None]:
             current = datetime(current.year + 1, 1, 1)
         else:
             current = datetime(current.year, current.month + 1, 1)
+
+
+def simulate(
+    start: datetime, end: datetime, flows: tuple[Flow]
+) -> tuple[list[datetime], list[Decimal]]:
+    dates: list[datetime] = []
+    values: list[Decimal] = []
+
+    for candidate in monthly_candidates(start):
+        if start <= candidate <= end:
+            dates.append(candidate)
+
+        if candidate > end:
+            break
+
+    for date in dates:
+        value = Decimal(0.0)
+        for flow in flows:
+            value += flow.integrate(start, date)
+        values.append(value)
+
+    return (dates, values)
diff --git a/finance/test_flow.py b/finance/test_flow.py
index 497c8d7..db1b695 100644
--- a/finance/test_flow.py
+++ b/finance/test_flow.py
@@ -1,11 +1,11 @@
 from datetime import datetime
 from decimal import Decimal
 
-from finance import flow
+from finance.flow import Flow, simulate
 
 
 def test_flow_integration() -> None:
-    fl = flow.Flow(
+    fl = Flow(
         amount=Decimal(3000.0),
         since=datetime(2023, 1, 1),
         until=datetime(2026, 1, 5),
@@ -26,3 +26,27 @@ def test_flow_integration() -> None:
 
     for test in tests:
         assert fl.integrate(start=test[0], end=test[1]) == test[2]
+
+
+def test_simulate() -> None:
+    flows = (Flow(amount=Decimal(100.0), since=None, until=None),)
+
+    dates, values = simulate(
+        start=datetime(2024, 1, 1),
+        end=datetime(2024, 4, 1),
+        flows=flows,
+    )
+
+    assert dates == [
+        datetime(2024, 1, 1),
+        datetime(2024, 2, 1),
+        datetime(2024, 3, 1),
+        datetime(2024, 4, 1),
+    ]
+
+    assert values == [
+        Decimal(100.0),
+        Decimal(200.0),
+        Decimal(300.0),
+        Decimal(400.0),
+    ]