<?php

namespace Modules\Core\Cart\Services;

use Illuminate\Support\Collection;
use Illuminate\Support\Facades\Event;
use Lunar\Actions\Carts\GetExistingCartLine;
use Lunar\Base\Purchasable;
use Lunar\Facades\CartSession;
use Lunar\Facades\Discounts;
use Lunar\Models\Cart;
use Lunar\Models\CartLine;
use Modules\Core\Cart\Events\CartCleared;
use Modules\Core\Cart\Events\CartCouponApplied;
use Modules\Core\Cart\Events\CartCouponRemoved;
use Modules\Core\Cart\Events\CartLineAdded;
use Modules\Core\Cart\Events\CartLineMovedToCart;
use Modules\Core\Cart\Events\CartLineRemoved;
use Modules\Core\Cart\Events\CartLineSaved;
use Modules\Core\Cart\Events\CartLineUpdated;
use Modules\Core\Cart\Exceptions\InvalidCouponException;

/**
 * Storefront-facing cart operations, mirroring Modules\Core\Catalog\Services\
 * ProductService/CollectionService's shape — one boboko-owned API a storefront
 * calls, so Lunar's own CartSession/Cart stay an implementation detail rather
 * than something a consuming app depends on directly.
 *
 * Every mutating method dispatches a matching domain event
 * (Modules\Core\Cart\Events\*) after the underlying Lunar operation completes —
 * Lunar itself dispatches zero cart events (see docs/lunar.md's Cart gotchas),
 * so without this, nothing in a consuming app has anything to react to when a
 * cart actually changes (reindexing, notifications, analytics, etc.).
 *
 * All mutating methods return the recalculated Cart — matching Lunar's own
 * Cart::add()/updateLine()/etc., which already return $this after
 * refresh()->recalculate() — so a caller gets fresh totals in the same call,
 * no second fetch needed.
 */
class CartService
{
    /**
     * The current session's cart, or null if none exists yet. Does NOT
     * auto-create one — see currentOrCreate() for that.
     */
    public function current(): ?Cart
    {
        return CartSession::current();
    }

    /**
     * The current session's cart, creating one if none exists yet — the right
     * call for "add to cart" style flows where a cart must exist by the time
     * the method returns.
     */
    public function currentOrCreate(): Cart
    {
        return CartSession::manager();
    }

    public function addLine(Purchasable $purchasable, int $quantity = 1, array $meta = []): Cart
    {
        $cart = $this->currentOrCreate()->add($purchasable, $quantity, $meta);

        $line = app(config('lunar.cart.actions.get_existing_cart_line', GetExistingCartLine::class))
            ->execute($cart, $purchasable, $meta);

        if ($line !== null) {
            Event::dispatch(new CartLineAdded($cart, $line));
        }

        return $cart;
    }

    public function updateLine(int $cartLineId, int $quantity, ?array $meta = null): Cart
    {
        $before = CartLine::findOrFail($cartLineId);
        $old = ['quantity' => $before->quantity, 'meta' => $before->meta->toArray()];

        $cart = $this->currentOrCreate()->updateLine($cartLineId, $quantity, $meta);

        $line = $cart->lines->firstWhere('id', $cartLineId);

        if ($line !== null) {
            Event::dispatch(new CartLineUpdated($cart, $line, $old));
        }

        return $cart;
    }

    public function removeLine(int $cartLineId): Cart
    {
        $line = CartLine::findOrFail($cartLineId);
        $snapshot = $this->snapshotLine($line);

        $cart = $this->currentOrCreate()->remove($cartLineId);

        Event::dispatch(new CartLineRemoved($cart, $snapshot));

        return $cart;
    }

    public function clear(): Cart
    {
        $cart = $this->currentOrCreate();
        $snapshots = $cart->lines->map($this->snapshotLine(...))->all();

        $cart = $cart->clear();

        Event::dispatch(new CartCleared($cart, $snapshots));

        return $cart;
    }

    /**
     * Sets the cart's coupon code, which the ApplyDiscounts pipeline step picks
     * up on the next calculate() — there's no dedicated Lunar action for this
     * (unlike add/update/remove, coupon_code is a plain cast attribute), so
     * this is the closest thing to one for a consuming app to call.
     *
     * Validated via Discounts::validateCoupon() (does a matching, currently
     * active, non-exhausted Discount exist?) before it's set — CouponString's
     * cast only normalizes casing, it doesn't validate anything, so setting
     * coupon_code directly would silently accept a bogus code and just not
     * discount anything once calculated.
     *
     * @throws InvalidCouponException if the code doesn't match a valid, active,
     *   non-exhausted Discount
     */
    public function applyCoupon(string $code): Cart
    {
        if (! Discounts::validateCoupon($code)) {
            throw new InvalidCouponException($code);
        }

        $cart = $this->currentOrCreate();
        $cart->coupon_code = $code;
        $cart->save();
        $cart = $cart->recalculate();

        Event::dispatch(new CartCouponApplied($cart, $cart->coupon_code));

        return $cart;
    }

    public function removeCoupon(): Cart
    {
        $cart = $this->currentOrCreate();
        $code = $cart->coupon_code;

        if ($code === null) {
            return $cart;
        }

        $cart->coupon_code = null;
        $cart->save();
        $cart = $cart->recalculate();

        Event::dispatch(new CartCouponRemoved($cart, $code));

        return $cart;
    }

    /**
     * Lines currently counted toward the cart's totals — everything except
     * ones flagged meta.saved_for_later (see savedLines()). This is the set a
     * cart page's main list / checkout would iterate, since a saved line
     * isn't pending purchase.
     *
     * @return Collection<int, CartLine>
     */
    public function activeLines(?Cart $cart = null): Collection
    {
        $cart ??= $this->currentOrCreate();

        return $cart->lines->reject(fn (CartLine $line) => $line->meta['saved_for_later'] ?? false)->values();
    }

    /**
     * Lines a shopper has deliberately parked rather than deleted — excluded
     * from Cart totals (see Modules\Core\Cart\Pipelines\ZeroSavedForLaterPrice)
     * and from activeLines(). A cart page's "Saved for later" section iterates
     * this set.
     *
     * @return Collection<int, CartLine>
     */
    public function savedLines(?Cart $cart = null): Collection
    {
        $cart ??= $this->currentOrCreate();

        return $cart->lines->filter(fn (CartLine $line) => $line->meta['saved_for_later'] ?? false)->values();
    }

    /**
     * Moves a line OUT of the purchasable cart without deleting it — it stays
     * on the cart (still visible, still re-addable) but is excluded from
     * totals via meta.saved_for_later, zeroed by ZeroSavedForLaterPrice before
     * Lunar's own CalculateLines sums the cart (which has no meta-based
     * exclusion of its own).
     */
    public function saveForLater(int $cartLineId): Cart
    {
        $line = CartLine::findOrFail($cartLineId);
        $meta = [...$line->meta->toArray(), 'saved_for_later' => true];

        $cart = $this->currentOrCreate()->updateLine($cartLineId, $line->quantity, $meta);

        $line = $cart->lines->firstWhere('id', $cartLineId);

        if ($line !== null) {
            Event::dispatch(new CartLineSaved($cart, $line));
        }

        return $cart;
    }

    /**
     * The reverse of saveForLater() — moves a line back into the purchasable
     * cart, counted in totals again.
     */
    public function moveToCart(int $cartLineId): Cart
    {
        $line = CartLine::findOrFail($cartLineId);
        $meta = [...$line->meta->toArray(), 'saved_for_later' => false];

        $cart = $this->currentOrCreate()->updateLine($cartLineId, $line->quantity, $meta);

        $line = $cart->lines->firstWhere('id', $cartLineId);

        if ($line !== null) {
            Event::dispatch(new CartLineMovedToCart($cart, $line));
        }

        return $cart;
    }

    /**
     * @return array{id: int, purchasable_type: string, purchasable_id: int, quantity: int, meta: array}
     */
    private function snapshotLine(CartLine $line): array
    {
        return [
            'id' => $line->id,
            'purchasable_type' => $line->purchasable_type,
            'purchasable_id' => $line->purchasable_id,
            'quantity' => $line->quantity,
            'meta' => $line->meta->toArray(),
        ];
    }
}