"""Cycle counting, capacity fade and end-of-life arithmetic."""

from __future__ import annotations

import pytest

from battery_dispatch.battery import BatteryState, implied_life_years


def test_a_fresh_battery_is_at_nominal_capacity(spec):
    state = BatteryState(spec=spec)
    assert state.capacity_mwh == pytest.approx(4.0)
    assert state.capacity_retained == pytest.approx(1.0)
    assert state.equivalent_full_cycles == 0.0


def test_one_full_discharge_counts_as_one_cycle(spec):
    state = BatteryState(spec=spec)
    state.apply_cycles(spec.capacity_mwh)
    assert state.equivalent_full_cycles == pytest.approx(1.0)


def test_partial_discharges_accumulate_into_whole_cycles(spec):
    """Attachment 1's definition: 75% then 25% is one cycle, not two."""
    state = BatteryState(spec=spec)
    state.apply_cycles(0.75 * spec.capacity_mwh)
    state.apply_cycles(0.25 * spec.capacity_mwh)
    assert state.equivalent_full_cycles == pytest.approx(1.0)


def test_capacity_fades_by_one_thousandth_of_a_percent_per_cycle(spec):
    state = BatteryState(spec=spec)
    state.apply_cycles(100 * spec.capacity_mwh)  # 100 cycles

    # 0.001 %/cycle over 100 cycles is a 0.1 % loss.
    assert state.capacity_retained == pytest.approx(0.999)
    assert state.capacity_mwh == pytest.approx(4.0 * 0.999)


def test_the_full_cycle_budget_fades_capacity_by_five_percent(spec):
    state = BatteryState(spec=spec)
    state.apply_cycles(spec.lifetime_cycles * spec.capacity_mwh)

    assert state.equivalent_full_cycles == pytest.approx(5000.0)
    assert state.capacity_retained == pytest.approx(0.95)


def test_commit_accounts_for_discharge_losses(spec):
    """Grid-side export of 0.95 MWh draws 1.0 MWh from storage."""
    state = BatteryState(spec=spec)
    state.commit(soc_mwh=3.0, charged_grid_mwh=0.0, discharged_grid_mwh=0.95)

    assert state.total_discharged_grid_mwh == pytest.approx(0.95)
    assert state.total_discharged_storage_mwh == pytest.approx(1.0)
    assert state.equivalent_full_cycles == pytest.approx(0.25)
    assert state.soc_mwh == pytest.approx(3.0)


def test_commit_is_cumulative(spec):
    state = BatteryState(spec=spec)
    for _ in range(3):
        state.commit(soc_mwh=1.0, charged_grid_mwh=2.0, discharged_grid_mwh=0.95)

    assert state.total_charged_grid_mwh == pytest.approx(6.0)
    assert state.total_discharged_storage_mwh == pytest.approx(3.0)


def test_negative_throughput_is_rejected(spec):
    state = BatteryState(spec=spec)
    with pytest.raises(ValueError):
        state.apply_cycles(-1.0)


def test_calendar_life_binds_when_cycling_is_light(spec):
    # 300 cycles a year exhausts 5,000 cycles only after 16 years.
    assert implied_life_years(spec, 300.0) == pytest.approx(10.0)


def test_cycle_life_binds_when_cycling_is_heavy(spec):
    # 1,000 cycles a year exhausts the budget in 5 years, inside the 10-year life.
    assert implied_life_years(spec, 1000.0) == pytest.approx(5.0)


def test_an_idle_battery_lives_out_its_calendar_life(spec):
    assert implied_life_years(spec, 0.0) == pytest.approx(10.0)