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

namespace ProjectM.Tests
{
    /// <summary>
    /// Pure tests for the save FOUNDATION: the JSON schema round-trips (JsonUtility), version handling is safe,
    /// and the born-correct ledger apply (<see cref="SaveApply.WriteLedger"/>) the server spawn system uses to
    /// overwrite a director's StorageEntry buffer from a staged PendingSave.
    /// </summary>
    public class SavePersistenceTests
    {
        [Test]
        public void SaveData_Json_RoundTrip_PreservesFields()
        {
            var data = new SaveData
            {
                GoalCharge = 42,
                GoalTarget = 10,
                Ledger = new[]
                {
                    new LedgerRow { ItemId = 1, Count = 5 },
                    new LedgerRow { ItemId = 2, Count = 9 },
                },
                SavedAtMs = 1234567890123L,
            };

            var json = JsonUtility.ToJson(data);
            var back = JsonUtility.FromJson<SaveData>(json);

            Assert.AreEqual(SaveData.CurrentVersion, back.Version);
            Assert.AreEqual(42, back.GoalCharge);
            Assert.AreEqual(10, back.GoalTarget);
            Assert.AreEqual(2, back.Ledger.Length);
            Assert.AreEqual(1, back.Ledger[0].ItemId);
            Assert.AreEqual(5, back.Ledger[0].Count);
            Assert.AreEqual(2, back.Ledger[1].ItemId);
            Assert.AreEqual(9, back.Ledger[1].Count);
            Assert.AreEqual(1234567890123L, back.SavedAtMs);
        }

        [Test]
        public void SaveData_EmptyJson_DoesNotThrow_And_EmptyLedgerRoundTrips()
        {
            Assert.DoesNotThrow(() => JsonUtility.FromJson<SaveData>("{}"));

            var empty = new SaveData { GoalCharge = 0, GoalTarget = 10 };
            var back = JsonUtility.FromJson<SaveData>(JsonUtility.ToJson(empty));
            Assert.IsNotNull(back.Ledger);
            Assert.AreEqual(0, back.Ledger.Length);
        }

        [Test]
        public void SaveData_OldVersion_IsDetectable()
        {
            // A stale-version blob round-trips with its Version intact, so SaveService.Load rejects it (-> New Game).
            var old = new SaveData { Version = 0, GoalCharge = 7 };
            var back = JsonUtility.FromJson<SaveData>(JsonUtility.ToJson(old));
            Assert.AreEqual(0, back.Version);
            Assert.AreNotEqual(SaveData.CurrentVersion, back.Version);
        }

        [Test]
        public void WriteLedger_Overwrites_Destination_From_Staged_Rows()
        {
            using var world = new World("SaveApplyTest");
            var em = world.EntityManager;
            var e = em.CreateEntity();
            em.AddBuffer<PendingSaveLedgerRow>(e);
            em.AddBuffer<StorageEntry>(e);

            var src = em.GetBuffer<PendingSaveLedgerRow>(e);
            src.Add(new PendingSaveLedgerRow { ItemId = 3, Count = 7 });
            src.Add(new PendingSaveLedgerRow { ItemId = 5, Count = 12 });

            var dest = em.GetBuffer<StorageEntry>(e);
            dest.Add(new StorageEntry { ItemId = 99, Count = 1 }); // pre-existing junk that must be cleared

            SaveApply.WriteLedger(em.GetBuffer<PendingSaveLedgerRow>(e), em.GetBuffer<StorageEntry>(e));

            var result = em.GetBuffer<StorageEntry>(e);
            Assert.AreEqual(2, result.Length);
            Assert.AreEqual(3, result[0].ItemId);
            Assert.AreEqual(7, result[0].Count);
            Assert.AreEqual(5, result[1].ItemId);
            Assert.AreEqual(12, result[1].Count);
        }

        [Test]
        public void WriteLedger_EmptySource_ClearsDestination()
        {
            using var world = new World("SaveApplyEmptyTest");
            var em = world.EntityManager;
            var e = em.CreateEntity();
            em.AddBuffer<PendingSaveLedgerRow>(e);
            em.AddBuffer<StorageEntry>(e);
            var dest = em.GetBuffer<StorageEntry>(e);
            dest.Add(new StorageEntry { ItemId = 1, Count = 1 });

            SaveApply.WriteLedger(em.GetBuffer<PendingSaveLedgerRow>(e), em.GetBuffer<StorageEntry>(e));

            Assert.AreEqual(0, em.GetBuffer<StorageEntry>(e).Length);
        }
    }
}