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import dataclasses
from datetime import datetime
from decimal import Decimal
from typing import Generator
import matplotlib.pyplot
@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(self, start: datetime, end: datetime) -> Decimal:
"""Integrate the flow between two dates to an amount of money"""
payments: int = 0
if self.since is not None:
if start < self.since:
start = self.since
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
return self.amount * Decimal(payments)
def monthly_candidates(start: datetime) -> Generator[datetime, None, None]:
current = datetime(start.year, start.month, 1)
while True:
yield current
if current.month == 12:
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)
def display(data: tuple[list[datetime], list[Decimal]]) -> None:
matplotlib.pyplot.plot(
list(data[0]), # type: ignore
[float(i) for i in data[1]],
label="Money",
)
matplotlib.pyplot.xlabel("Time")
matplotlib.pyplot.legend()
matplotlib.pyplot.xticks(rotation=45)
matplotlib.pyplot.show()
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