import pytest

from engine.forecast import ForecastError, ForecastService


class TestForecastService:
    def test_forecast_returns_results(self, sample_model):
        service = ForecastService(sample_model)
        results = service.forecast_cashflow(months=12)
        assert len(results) > 0
        assert "balance" in results[0]
        assert "month" in results[0]

    def test_forecast_12_months(self, sample_model):
        service = ForecastService(sample_model)
        results = service.forecast_cashflow(months=12)
        months = set(r["month"] for r in results)
        assert max(months) == 12

    def test_invalid_months(self, sample_model):
        service = ForecastService(sample_model)
        with pytest.raises(ForecastError):
            service.forecast_cashflow(months=0)

    def test_summary(self, sample_model):
        service = ForecastService(sample_model)
        s = service.summary(months=6)
        assert "total_balance" in s
        assert "total_income" in s
        assert "total_expenses" in s
        assert s["months"] == 6

    def test_empty_model(self, empty_model):
        service = ForecastService(empty_model)
        results = service.forecast_cashflow(months=3)
        assert results == []