Split flow.py to simulate.py and model.py

model.py should be a file containing only dataclasses to model finance.
simulate.py should take care of the simulation of that finance data to
create a financial forecast.

3 files changed, 32 insertions, 26 deletions

diff --git a/finance/model.py b/finance/model.py
new file mode 100644
index 0000000..8bf2e3d
--- /dev/null
+++ b/finance/model.py
@@ -0,0 +1,12 @@
+import dataclasses
+import datetime
+import decimal
+
+
+@dataclasses.dataclass(kw_only=True, frozen=True)
+class Flow:
+    """Time-discrete flow of money paid on the first day of a month"""
+
+    amount: decimal.Decimal
+    since: None | datetime.datetime
+    until: None | datetime.datetime
diff --git a/finance/flow.py b/finance/simulate.py
index c6b28c0..3f8e3ad 100644
--- a/finance/flow.py
+++ b/finance/simulate.py
@@ -1,37 +1,30 @@
-import dataclasses
 from datetime import datetime
 from decimal import Decimal
 from typing import Generator
 
+from finance.model import Flow
 
-@dataclasses.dataclass(kw_only=True, frozen=True)
-class Flow:
-    """Time-discrete flow of money paid on the first day of a month"""
 
-    amount: Decimal
-    since: None | datetime
-    until: None | datetime
+def integrate(flow: Flow, start: datetime, end: datetime) -> Decimal:
+    """Integrate the flow between two dates to an amount of money"""
 
-    def integrate(self, start: datetime, end: datetime) -> Decimal:
-        """Integrate the flow between two dates to an amount of money"""
+    payments: int = 0
 
-        payments: int = 0
+    if flow.since is not None:
+        if start < flow.since:
+            start = flow.since
 
-        if self.since is not None:
-            if start < self.since:
-                start = self.since
+    if flow.until is not None:
+        if end > flow.until:
+            end = flow.until
 
-        if self.until is not None:
-            if end > self.until:
-                end = self.until
-
-        for candidate in monthly_candidates(start):
-            if start <= candidate <= end:
-                payments += 1
-            if candidate > end:
-                break
+    for candidate in monthly_candidates(start):
+        if start <= candidate <= end:
+            payments += 1
+        if candidate > end:
+            break
 
-        return self.amount * Decimal(payments)
+    return flow.amount * Decimal(payments)
 
 
 def monthly_candidates(start: datetime) -> Generator[datetime, None, None]:
@@ -60,7 +53,7 @@ def simulate(
     for date in dates:
         value = Decimal(0.0)
         for flow in flows:
-            value += flow.integrate(start, date)
+            value += integrate(flow, start, date)
         values.append(value)
 
     return [(date, values[index]) for index, date in enumerate(dates)]
diff --git a/finance/test_flow.py b/finance/test_simulate.py
index 91d189b..3b79c99 100644
--- a/finance/test_flow.py
+++ b/finance/test_simulate.py
@@ -1,7 +1,8 @@
 from datetime import datetime
 from decimal import Decimal
 
-from finance.flow import Flow, simulate
+from finance.model import Flow
+from finance.simulate import simulate, integrate
 
 
 def test_flow_integration() -> None:
@@ -25,7 +26,7 @@ def test_flow_integration() -> None:
     )
 
     for test in tests:
-        assert fl.integrate(start=test[0], end=test[1]) == test[2]
+        assert integrate(fl, start=test[0], end=test[1]) == test[2]
 
 
 def test_simulate() -> None: