"""Golden-value tests for the margin engine.

These assert the exact worked example from the Pricing Analyst playbook (SOP A):
break-even $16.76, MAP $19.00, contribution margin ~28% on the microfiber sheet set.
If these ever drift, the pricing gate's math has changed — fail loudly.
"""
from __future__ import annotations

import pytest

from config.settings import PricingRules
from pricing_agent.tools.margin_engine import (
    compute_fee_stack,
    suggest_price_for_floor,
    worst_case_stack,
)

RULES = PricingRules(
    margin_floor=0.25,
    margin_target=0.30,
    returns_reserve_pct=0.02,
    storage_alloc=0.25,
    worst_case_referral_pct=0.15,
    charm_ending=0.99,
)

# Playbook worked example inputs.
SHEET_SET = dict(selling_price=24.99, landed_cost=8.00, fba_fee=5.50)


def test_break_even_matches_playbook():
    stack = worst_case_stack(rules=RULES, **SHEET_SET)
    assert round(stack.break_even_price, 2) == 16.76


def test_map_matches_playbook():
    stack = worst_case_stack(rules=RULES, **SHEET_SET)
    assert round(stack.map_floor, 2) == 19.00


def test_contribution_margin_is_about_28pct():
    stack = worst_case_stack(rules=RULES, **SHEET_SET)
    assert stack.contribution_margin_pct == pytest.approx(0.28, abs=0.005)


def test_fee_components_sum_to_total_cost():
    stack = worst_case_stack(rules=RULES, **SHEET_SET)
    recomputed = (
        stack.landed_cost
        + stack.fba_fee
        + stack.referral_amt
        + stack.returns_reserve
        + stack.storage_alloc
    )
    assert stack.total_cost == pytest.approx(recomputed, abs=1e-6)
    assert stack.profit == pytest.approx(stack.selling_price - stack.total_cost, abs=1e-6)


def test_price_below_break_even_is_loss_making():
    # At $16.00 (< $16.76 break-even) contribution must be negative.
    stack = worst_case_stack(selling_price=16.00, landed_cost=8.00, fba_fee=5.50, rules=RULES)
    assert stack.profit < 0
    assert stack.contribution_margin_pct < 0


def test_modeled_referral_beats_worst_case():
    # Modeled 12% referral should yield higher margin than worst-case 15%.
    worst = worst_case_stack(rules=RULES, **SHEET_SET)
    modeled = compute_fee_stack(
        referral_pct=0.12, rules=RULES, referral_basis="modeled", **SHEET_SET
    )
    assert modeled.contribution_margin_pct > worst.contribution_margin_pct


def test_suggest_price_for_floor_clears_floor():
    price = suggest_price_for_floor(landed_cost=8.00, fba_fee=5.50, rules=RULES)
    stack = worst_case_stack(selling_price=price, landed_cost=8.00, fba_fee=5.50, rules=RULES)
    assert stack.contribution_margin_pct >= RULES.margin_floor
    # charm pricing => ends in .99
    assert round(price - int(price), 2) == 0.99


def test_invalid_inputs_raise():
    with pytest.raises(ValueError):
        compute_fee_stack(
            selling_price=0, landed_cost=8, fba_fee=5.5, referral_pct=0.15, rules=RULES
        )
    with pytest.raises(ValueError):
        compute_fee_stack(
            selling_price=24.99, landed_cost=8, fba_fee=5.5, referral_pct=1.5, rules=RULES
        )