<?php
// Price a cart against a published Nexus menu, applying the same checks as the gateway.
// Amounts are integer bani (3700 = 37.00 RON). Unavailable or invalid selections throw
// CartError whose message is the conflict code the gateway would return.
// Decode JSON with json_decode($json, true) so the menu and items are arrays.

final class CartError extends RuntimeException {}

/** Returns the order total in bani for $items (the order's items array). */
function price_cart(array $menu, string $fulfillment, array $items, mixed $tip = 0, ?array $checkoutDiscount = null): int
{
    if (!($menu['accepting_orders'] ?? true)) throw new CartError('restaurant_closed');
    if (!is_int($tip) || $tip < 0 || $tip > 100000000) throw new CartError('invalid_request');
    if ($tip && !($menu['tips_enabled'] ?? false)) throw new CartError('tips_unavailable');
    $products = array_column($menu['products'], null, 'id');
    $total = $tip + ($fulfillment === 'delivery' ? ($menu['delivery_fee'] ?? 0) : 0);
    foreach ($items as $line) {
        $total += unit_price($products[$line['product_id']] ?? null, $line['modifiers'] ?? []) * $line['quantity'];
    }
    if ($checkoutDiscount !== null) {
        $amount = $checkoutDiscount['amount'] ?? null;
        $scope = $checkoutDiscount['product_ids'] ?? null;
        $ids = array_column($items, 'product_id');
        if (!is_int($amount) || $amount < 1 || $amount > 100000000 ||
            ($scope !== null && (!$scope || count(array_unique($scope)) !== count($scope) || array_diff($scope, $ids))))
            throw new CartError('invalid_checkout_discount');
        $eligible = 0;
        foreach ($items as $line) {
            if ($scope === null || in_array($line['product_id'], $scope, true))
                $eligible += unit_price($products[$line['product_id']], $line['modifiers'] ?? [], true) * $line['quantity'];
        }
        if ($amount > $eligible) throw new CartError('invalid_checkout_discount');
        $total -= $amount;
    }
    return $total;
}

function choice_key(string $groupId, string $optionId): string
{
    return json_encode([$groupId, $optionId]);
}

function unit_price(?array $product, array $modifiers, bool $baseOnly = false): int
{
    if ($product === null || !($product['available'] ?? true)) throw new CartError('product_unavailable');
    $selected = [];
    foreach ($modifiers as $choice) $selected[choice_key($choice['group_id'], $choice['option_id'])] = true;
    if (count($selected) !== count($modifiers)) throw new CartError('duplicate_modifier');
    $groups = $product['modifier_groups'] ?? [];
    $known = [];
    foreach ($groups as $group) {
        foreach ($group['options'] as $option) $known[choice_key($group['id'], $option['id'])] = true;
    }
    if (array_diff_key($selected, $known)) throw new CartError('unknown_modifier');

    // A product with variants is priced by the one variant matching all "variant" choices.
    $deposit = $product['deposit'] ?? 0;
    $unit = $product['price'] - ($product['discount'] ?? 0);
    if (!empty($product['variants'])) {
        $definingGroups = [];
        foreach ($groups as $group) {
            if (($group['kind'] ?? 'extra') === 'variant') $definingGroups[$group['id']] = true;
        }
        $defining = [];
        foreach ($modifiers as $choice) {
            if (isset($definingGroups[$choice['group_id']])) $defining[choice_key($choice['group_id'], $choice['option_id'])] = true;
        }
        $variant = null;
        foreach ($product['variants'] as $candidate) {
            $selections = [];
            foreach ($candidate['selections'] as $s) $selections[choice_key($s['group_id'], $s['option_id'])] = true;
            if ($selections == $defining) { $variant = $candidate; break; }
        }
        if ($variant === null || !($variant['available'] ?? true)) throw new CartError('variant_unavailable');
        $deposit = $variant['deposit'] ?? 0;
        $unit = $variant['price'] - ($variant['discount'] ?? 0);
    }
    if ($baseOnly) return $unit;
    $unit += $deposit + ($product['packaging'] ?? 0);

    // Every group enforces its bounds; selected options add their price and deposit.
    foreach ($groups as $group) {
        $chosen = array_filter($group['options'], fn ($option) => isset($selected[choice_key($group['id'], $option['id'])]));
        if (count($chosen) < ($group['minimum'] ?? 0) || count($chosen) > ($group['maximum'] ?? 1)) {
            throw new CartError('modifier_selection_invalid');
        }
        foreach ($chosen as $option) {
            if (!($option['available'] ?? true)) throw new CartError('modifier_unavailable');
            $unit += $option['price'] + ($option['deposit'] ?? 0);
        }
    }
    return $unit;
}