"""Pricing engine.

Applies active `price_rules` (cost -> markup bands) and computes net profit:

    retail      = cost * (1 + markup_pct/100)   (floored at cost + shipping + fees)
    net profit  = retail - cost - shipping - fees
    margin_pct  = profit / retail * 100

`min_price` (product floor) is respected — retail is never below it.
"""
from decimal import ROUND_HALF_UP, Decimal

from app.models import PriceRule

CENT = Decimal("0.01")


def _q(value) -> Decimal:
    try:
        return Decimal(str(value or 0))
    except Exception:
        return Decimal("0")


def get_active_rules(db):
    return (
        db.query(PriceRule)
        .filter(PriceRule.active.is_(True))
        .order_by(PriceRule.min_cost)
        .all()
    )


def find_rule(db, cost):
    cost = _q(cost)
    for rule in get_active_rules(db):
        if cost >= _q(rule.min_cost) and (rule.max_cost is None or cost < _q(rule.max_cost)):
            return rule
    return None


def calculate_price(db, cost, shipping=0, fees=0, min_price=None):
    """Return dict(retail, profit, margin, margin_pct, markup_pct, rule_id, ...) or None.

    None means no active rule applies — callers must NOT publish such products.
    """
    cost = _q(cost)
    shipping = _q(shipping)
    fees = _q(fees)
    rule = find_rule(db, cost)
    if rule is None:
        return None

    markup_pct = _q(rule.markup_pct)
    retail = (cost * (1 + markup_pct / 100)).quantize(CENT, rounding=ROUND_HALF_UP)

    # floor: cost + shipping + fees, raised by min_margin_pct if configured
    floor = (cost + shipping + fees).quantize(CENT, rounding=ROUND_HALF_UP)
    min_margin_pct = _q(rule.min_margin_pct)
    if min_margin_pct > 0:
        floor = max(floor, (floor + retail * min_margin_pct / 100).quantize(CENT, rounding=ROUND_HALF_UP))
    if retail < floor:
        retail = floor

    # never below the product's minimum price
    if min_price is not None and retail < _q(min_price):
        retail = _q(min_price).quantize(CENT, rounding=ROUND_HALF_UP)

    profit = (retail - cost - shipping - fees).quantize(CENT, rounding=ROUND_HALF_UP)
    margin_pct = (profit / retail * 100).quantize(Decimal("0.01")) if retail > 0 else Decimal("0")

    return {
        "cost": cost,
        "shipping": shipping,
        "fees": fees,
        "retail": retail,
        "profit": profit,
        "margin": profit,
        "margin_pct": float(margin_pct),
        "markup_pct": float(markup_pct),
        "rule_id": rule.id,
    }


def estimate_net_profit(retail, cost, shipping=0, fees=0):
    """Net profit = retail - (cost + shipping + fees)."""
    return (_q(retail) - _q(cost) - _q(shipping) - _q(fees)).quantize(CENT, rounding=ROUND_HALF_UP)