"""Tests for fire_math.py — core FIRE calculation logic."""
import pytest
from fire_math import calculate_fire, calculate_years_to_fi, calculate_scenario, projection_timeline


# ---------------------------------------------------------------------------
# calculate_fire — Core Metrics
# ---------------------------------------------------------------------------

def test_basic_case():
    result = calculate_fire(
        monthly_income=4000,
        monthly_expenses=2000,
        total_portfolio=50000,
        birth_year=1998,
    )
    assert result.fi_number == 600000.0
    assert result.savings_rate == 50.0
    assert result.monthly_savings == 2000.0


def test_already_fi():
    # Portfolio exceeds FI number — years_to_fi must be 0.0, NOT None.
    # This tests the line-68 bug fix: `if years_to_fi is not None` instead of `if years_to_fi`.
    result = calculate_fire(
        monthly_income=2000,
        monthly_expenses=2000,
        total_portfolio=700000,
        birth_year=1998,
    )
    assert result.years_to_fi == 0.0, (
        "years_to_fi must be 0.0 when already FI, not None. "
        "Check the line-68 bug fix."
    )
    assert result.fi_date is not None


def test_zero_income():
    result = calculate_fire(
        monthly_income=0,
        monthly_expenses=2000,
        total_portfolio=50000,
        birth_year=1998,
    )
    assert result.savings_rate == 0


def test_never_fi():
    # Zero savings + zero portfolio → compound growth on 0 stays 0 → never reaches target.
    result = calculate_fire(
        monthly_income=2000,
        monthly_expenses=2000,
        total_portfolio=0,
        birth_year=1998,
    )
    assert result.monthly_savings == 0.0
    assert result.years_to_fi is None
    assert result.fi_date is None


# ---------------------------------------------------------------------------
# calculate_years_to_fi — Iteration Logic
# ---------------------------------------------------------------------------

def test_already_at_target():
    result = calculate_years_to_fi(
        current_portfolio=600000,
        annual_savings=24000,
        target=600000,
        annual_return=0.05,
    )
    assert result == 0.0


def test_normal_projection():
    result = calculate_years_to_fi(
        current_portfolio=50000,
        annual_savings=24000,
        target=600000,
        annual_return=0.05,
    )
    assert result is not None
    assert 13 <= result <= 20, f"Expected 13–20 years, got {result}"


def test_no_savings_no_return():
    result = calculate_years_to_fi(
        current_portfolio=50000,
        annual_savings=0,
        target=600000,
        annual_return=0,
    )
    assert result is None


def test_max_years_cap():
    # Savings so tiny the loop hits the 100-year cap.
    result = calculate_years_to_fi(
        current_portfolio=0,
        annual_savings=12,        # €1/month
        target=10_000_000,
        annual_return=0,
    )
    assert result is None


# ---------------------------------------------------------------------------
# projection_timeline — Chart Data
# ---------------------------------------------------------------------------

def test_timeline_length():
    timeline = projection_timeline(
        total_portfolio=50000,
        monthly_savings=2000,
        annual_return=0.05,
        years=30,
    )
    assert len(timeline) == 31  # year 0 through year 30 inclusive


def test_first_entry():
    starting = 75000.0
    timeline = projection_timeline(
        total_portfolio=starting,
        monthly_savings=1500,
        annual_return=0.05,
        years=20,
    )
    assert timeline[0]["portfolio"] == starting


def test_growth():
    timeline = projection_timeline(
        total_portfolio=10000,
        monthly_savings=500,
        annual_return=0.05,
        years=10,
    )
    for i in range(1, len(timeline)):
        assert timeline[i]["portfolio"] > timeline[i - 1]["portfolio"]


# ---------------------------------------------------------------------------
# calculate_scenario — What-If
# ---------------------------------------------------------------------------

def test_extra_savings():
    base = calculate_fire(
        monthly_income=4000,
        monthly_expenses=2000,
        total_portfolio=50000,
        birth_year=1990,
    )
    scenario = calculate_scenario(
        base=base,
        monthly_income=4000,
        monthly_expenses=2000,
        total_portfolio=50000,
        birth_year=1990,
        extra_monthly_savings=500,
    )
    assert scenario.years_to_fi is not None
    assert base.years_to_fi is not None
    assert scenario.years_to_fi < base.years_to_fi


def test_lower_expenses():
    base = calculate_fire(
        monthly_income=4000,
        monthly_expenses=2000,
        total_portfolio=50000,
        birth_year=1990,
    )
    scenario = calculate_scenario(
        base=base,
        monthly_income=4000,
        monthly_expenses=2000,
        total_portfolio=50000,
        birth_year=1990,
        adjusted_expenses=1500,
    )
    assert scenario.fi_number < base.fi_number


# ---------------------------------------------------------------------------
# fi_date — Edge Cases for Month/Year Boundary Arithmetic
# ---------------------------------------------------------------------------

def test_fi_date_zero_years_to_fi():
    """When already FI (years_to_fi=0.0), fi_date must be first of current month."""
    from datetime import date
    result = calculate_fire(
        monthly_income=2000,
        monthly_expenses=2000,
        total_portfolio=700000,
        birth_year=1998,
    )
    assert result.fi_date is not None
    assert result.fi_date.day == 1
    assert result.fi_date.year == date.today().year
    assert result.fi_date.month == date.today().month


def test_fi_date_whole_years():
    """Fractional part = 0.0 — fi_date must land in the current month of a future year."""
    from datetime import date
    # Force years_to_fi to be a whole number by giving a result we can verify.
    # We use calculate_years_to_fi directly to avoid dependency on date.today() internals.
    from fire_math import calculate_years_to_fi
    result = calculate_years_to_fi(
        current_portfolio=0,
        annual_savings=60000,
        target=600000,
        annual_return=0.0,  # No compounding — pure savings: exactly 10 years
    )
    assert result is not None
    # 10 years of €60k/year = €600k exactly — should be ~10 years
    assert 9.9 <= result <= 10.1


def test_fi_date_fractional_month_no_overflow():
    """Adding fractional months must not produce month > 12 for any start month."""
    from datetime import date
    from unittest.mock import patch

    for start_month in range(1, 13):
        fake_today = date(2026, start_month, 15)
        with patch("fire_math.date") as mock_date:
            mock_date.today.return_value = fake_today
            mock_date.side_effect = lambda *args, **kw: date(*args, **kw)
            result = calculate_fire(
                monthly_income=4000,
                monthly_expenses=2000,
                total_portfolio=50000,
                birth_year=1998,
            )
        if result.fi_date is not None:
            assert 1 <= result.fi_date.month <= 12, (
                f"fi_date.month={result.fi_date.month} out of range for start_month={start_month}"
            )
            assert result.fi_date.year >= 2026


def test_fi_date_december_wrap():
    """December + 9 fractional months = September of next year. Must not add extra year."""
    from datetime import date
    from unittest.mock import patch

    # Simulate running in December with 15.75 years to FI
    # Dec (12) + 9 fractional months = 21 → extra_years=1, final_month=9
    # Expected: year=2026+15+1=2042, month=9
    fake_today = date(2026, 12, 1)
    with patch("fire_math.date") as mock_date:
        mock_date.today.return_value = fake_today
        mock_date.side_effect = lambda *args, **kw: date(*args, **kw)
        result = calculate_fire(
            monthly_income=4000,
            monthly_expenses=2000,
            total_portfolio=50000,
            birth_year=1998,
        )

    if result.fi_date is not None:
        # fi_date must be a valid date
        assert 1 <= result.fi_date.month <= 12
        assert result.fi_date.year > 2026