using NUnit.Framework;
using ProjectM.Simulation;
using Unity.Entities;

namespace ProjectM.Tests
{
    /// <summary>
    /// Plain-Entities EditMode tests for the pure <see cref="InventoryMath"/> stacking logic (the per-player
    /// bag math): top-up-then-append with a per-item stack cap, a max slot count returning a remainder, and
    /// back-to-front withdraw clamped to availability. A bare world hosts an entity that owns the
    /// <see cref="InventorySlot"/> buffer (a DynamicBuffer needs an entity); no systems run.
    /// </summary>
    public class InventoryMathTests
    {
        static (World world, DynamicBuffer<InventorySlot> buffer) MakeBuffer()
        {
            var world = new World("InventoryMathTest");
            var em = world.EntityManager;
            var e = em.CreateEntity();
            var buffer = em.AddBuffer<InventorySlot>(e);
            return (world, buffer);
        }

        [Test]
        public void Deposit_TopsUpExistingStack_ThenAppends_NewStack()
        {
            var (world, buf) = MakeBuffer();
            using (world)
            {
                int r1 = InventoryMath.Deposit(buf, itemId: 1, count: 5, stackMax: 10, maxSlots: 4);
                Assert.AreEqual(0, r1, "5 fits in one fresh stack.");
                Assert.AreEqual(1, buf.Length);

                int r2 = InventoryMath.Deposit(buf, itemId: 1, count: 8, stackMax: 10, maxSlots: 4);
                Assert.AreEqual(0, r2, "8 more tops the first stack to 10 then appends 3.");
                Assert.AreEqual(2, buf.Length, "A second stack is appended once the first fills.");
                Assert.AreEqual(13, InventoryMath.CountOf(buf, 1));
                Assert.AreEqual(10, buf[0].Count, "First stack is capped at stackMax.");
                Assert.AreEqual(3, buf[1].Count);
            }
        }

        [Test]
        public void Deposit_FillsMultipleStacks_UpToSlotCap_ReturnsRemainder()
        {
            var (world, buf) = MakeBuffer();
            using (world)
            {
                // 2 slots * stackMax 10 = 20 capacity; depositing 25 leaves a remainder of 5.
                int r = InventoryMath.Deposit(buf, itemId: 2, count: 25, stackMax: 10, maxSlots: 2);
                Assert.AreEqual(5, r, "Past the slot cap, the overflow is returned as a remainder.");
                Assert.AreEqual(2, buf.Length);
                Assert.AreEqual(20, InventoryMath.CountOf(buf, 2));
            }
        }

        [Test]
        public void Withdraw_TakesAcrossStacks_BackToFront_Clamped_ReturnsTaken()
        {
            var (world, buf) = MakeBuffer();
            using (world)
            {
                InventoryMath.Deposit(buf, itemId: 3, count: 25, stackMax: 10, maxSlots: 4); // 10,10,5
                int taken = InventoryMath.Withdraw(buf, itemId: 3, count: 12);
                Assert.AreEqual(12, taken);
                Assert.AreEqual(13, InventoryMath.CountOf(buf, 3));

                int takenAll = InventoryMath.Withdraw(buf, itemId: 3, count: 100);
                Assert.AreEqual(13, takenAll, "Withdraw clamps to what is available.");
                Assert.AreEqual(0, InventoryMath.CountOf(buf, 3));
                Assert.AreEqual(0, buf.Length, "Emptied stacks are dropped.");
            }
        }

        [Test]
        public void Deposit_ZeroItemId_OrNonPositiveCount_AreNoOps()
        {
            var (world, buf) = MakeBuffer();
            using (world)
            {
                Assert.AreEqual(7, InventoryMath.Deposit(buf, itemId: 0, count: 7, stackMax: 10, maxSlots: 4),
                    "Depositing the empty id deposits nothing and returns the full count.");
                Assert.AreEqual(0, InventoryMath.Deposit(buf, itemId: 1, count: 0, stackMax: 10, maxSlots: 4));
                Assert.AreEqual(0, InventoryMath.Deposit(buf, itemId: 1, count: -3, stackMax: 10, maxSlots: 4));
                Assert.AreEqual(0, buf.Length, "No rows were written.");
            }
        }
    }
}