"""Unit tests for the actualbudget client + trailing-spending helper.

We mock the upstream HTTP API with respx so the tests don't need a
live cluster connection. The interesting axes are:

- _trailing_months walks back the right complete-month window
- fetch_month flips sign and skips income groups
- fetch_trailing_spending applies exclusions correctly
"""
from __future__ import annotations

from datetime import date
from decimal import Decimal

import httpx
import pytest
import respx

from fire_planner.actualbudget import (
    ActualBudgetClient,
    _trailing_months,
    fetch_trailing_spending,
)

API_URL = "http://budget-http-api.test"
SYNC_ID = "sync-1"


def _client() -> ActualBudgetClient:
    return ActualBudgetClient(api_url=API_URL, api_key="key", sync_id=SYNC_ID)


def test_trailing_months_skips_current_and_walks_back() -> None:
    # 2025-04 mid-month → trailing 3 months = 2025-01, 2025-02, 2025-03
    result = _trailing_months(date(2025, 4, 15), 3)
    assert result == ["2025-01", "2025-02", "2025-03"]


def test_trailing_months_crosses_year_boundary() -> None:
    result = _trailing_months(date(2025, 2, 1), 4)
    assert result == ["2024-10", "2024-11", "2024-12", "2025-01"]


def test_trailing_months_zero_returns_empty() -> None:
    assert _trailing_months(date(2025, 5, 1), 0) == []


@pytest.mark.asyncio
async def test_fetch_month_flips_sign_and_drops_income(respx_mock: respx.MockRouter) -> None:
    respx_mock.get(f"{API_URL}/v1/budgets/{SYNC_ID}/months/2025-03").mock(
        return_value=httpx.Response(200, json={
            "data": {
                "categoryGroups": [
                    {
                        "name": "Usual Expenses",
                        "is_income": False,
                        "categories": [
                            {"spent": -1500},  # £15.00 spent
                            {"spent": -2000},  # £20.00 spent
                        ],
                    },
                    {
                        "name": "Salary",
                        "is_income": True,
                        "categories": [{"spent": 0}],
                    },
                    {
                        "name": "Empty Group",
                        "is_income": False,
                        "categories": [],
                    },
                ],
            }
        }))
    cli = _client()
    async with httpx.AsyncClient() as h:
        result = await cli.fetch_month(h, "2025-03")
    # Income skipped; outflows positive
    assert result.by_group == {"Usual Expenses": 3500, "Empty Group": 0}
    assert result.total_pence == 3500


@pytest.mark.asyncio
async def test_fetch_trailing_spending_excludes_groups(respx_mock: respx.MockRouter) -> None:
    # Two months, both with Usual + Investments; we exclude Investments.
    respx_mock.get(f"{API_URL}/v1/budgets/{SYNC_ID}/months").mock(
        return_value=httpx.Response(200, json={
            "data": ["2025-01", "2025-02"]
        }))
    for m, usual, invest in [("2025-01", -1000, -50000), ("2025-02", -2000, -10000)]:
        respx_mock.get(f"{API_URL}/v1/budgets/{SYNC_ID}/months/{m}").mock(
            return_value=httpx.Response(200, json={
                "data": {
                    "categoryGroups": [
                        {"name": "Usual Expenses", "is_income": False,
                         "categories": [{"spent": usual}]},
                        {"name": "Investments and Savings", "is_income": False,
                         "categories": [{"spent": invest}]},
                    ],
                }
            }))

    spends, nominal_gbp, real_gbp = await fetch_trailing_spending(
        months=2,
        exclude_groups=frozenset(["Investments and Savings"]),
        annual_inflation_pct=0.0,  # no adjustment for the simple assertion
        client_factory=_client(),
        today=date(2025, 3, 15),
    )
    assert [ms.month for ms in spends] == ["2025-01", "2025-02"]
    # Usual: 1000 + 2000 = 3000 pence = £30
    assert nominal_gbp == Decimal("30.00")
    assert real_gbp == Decimal("30.00")  # 0% inflation → same number


@pytest.mark.asyncio
async def test_fetch_trailing_spending_inflation_adjusts(respx_mock: respx.MockRouter) -> None:
    """At 12% annual inflation, a £10 expense from 12 months ago is
    worth £11.20 in today's £. Sanity-check the compounding via the
    oldest month of a 12-month window (today=2025-04 → 2024-04 is 12mo
    old)."""
    # Only one month available in the window.
    respx_mock.get(f"{API_URL}/v1/budgets/{SYNC_ID}/months").mock(
        return_value=httpx.Response(200, json={"data": ["2024-04"]}))
    respx_mock.get(f"{API_URL}/v1/budgets/{SYNC_ID}/months/2024-04").mock(
        return_value=httpx.Response(200, json={
            "data": {"categoryGroups": [
                {"name": "Usual Expenses", "is_income": False,
                 "categories": [{"spent": -1000}]},  # £10
            ]}
        }))
    _, nominal_gbp, real_gbp = await fetch_trailing_spending(
        months=12,
        exclude_groups=frozenset(),
        annual_inflation_pct=0.12,
        client_factory=_client(),
        today=date(2025, 4, 15),
    )
    assert nominal_gbp == Decimal("10.00")
    assert real_gbp == Decimal("11.20")


@pytest.mark.asyncio
async def test_fetch_trailing_spending_drops_unavailable_months(
    respx_mock: respx.MockRouter,
) -> None:
    """If the API surfaces fewer months than asked, missing months are
    skipped instead of erroring."""
    respx_mock.get(f"{API_URL}/v1/budgets/{SYNC_ID}/months").mock(
        return_value=httpx.Response(200, json={"data": ["2025-02"]}))
    respx_mock.get(f"{API_URL}/v1/budgets/{SYNC_ID}/months/2025-02").mock(
        return_value=httpx.Response(200, json={
            "data": {"categoryGroups": [
                {"name": "Usual Expenses", "is_income": False,
                 "categories": [{"spent": -5000}]},
            ]}
        }))
    spends, nominal_gbp, _real_gbp = await fetch_trailing_spending(
        months=3,
        exclude_groups=frozenset(),
        annual_inflation_pct=0.0,
        client_factory=_client(),
        today=date(2025, 3, 15),
    )
    assert [ms.month for ms in spends] == ["2025-02"]
    assert nominal_gbp == Decimal("50.00")