using NUnit.Framework;
using ProjectM.Server;
using ProjectM.Simulation;
using Unity.Core;
using Unity.Entities;
using Unity.Mathematics;
using Unity.NetCode;

namespace ProjectM.Tests
{
    /// <summary>
    /// Plain-Entities EditMode tests for the server-only <see cref="ConveyorTransportSystem"/> — the transport step
    /// that PULLS resources off an adjacent upstream <see cref="MachineOutput"/> onto an empty belt, advances a held
    /// <see cref="ConveyorItem"/> exactly one cell per tick along its <see cref="Conveyor.Direction"/>, and DEPOSITS
    /// into a downstream machine's <see cref="MachineInput"/> sink. Determinism (Y-junction tie-break, stall-no-loss,
    /// shuffle-invariance) is exhaustively proven world-free in <see cref="ConveyorMathTests"/>; these tests pin the
    /// SYSTEM wiring: snapshot -> ResolveMoves -> apply (ConveyorItem enable/disable bit + sink deposit + machine pull),
    /// plus the per-conveyor period gate (init on first touch, then move on the production cadence).
    /// </summary>
    public class ConveyorTransportSystemTests
    {
        static (World world, SimulationSystemGroup group) MakeWorld(string name, uint serverTick)
        {
            var world = new World(name);
            var group = world.GetOrCreateSystemManaged<SimulationSystemGroup>();
            group.AddSystemToUpdateList(world.GetOrCreateSystem<ConveyorTransportSystem>());
            group.SortSystems();
            world.SetTime(new TimeData(elapsedTime: 0f, deltaTime: 1f / 60f));
            SetServerTick(world, serverTick);
            return (world, group);
        }

        static void SetServerTick(World world, uint tick)
        {
            var em = world.EntityManager;
            using var q = em.CreateEntityQuery(typeof(NetworkTime));
            Entity e = q.IsEmpty ? em.CreateEntity(typeof(NetworkTime)) : q.GetSingletonEntity();
            em.SetComponentData(e, new NetworkTime { ServerTick = new NetworkTick(tick) });
        }

        static Entity MakeConveyor(EntityManager em, int2 cell, byte dir, int periodTicks, byte itemRes, int itemCnt)
        {
            var e = em.CreateEntity();
            em.AddComponentData(e, new RegionTag { Region = RegionId.Base });
            em.AddComponentData(e, new PlacedStructure
            {
                Type = StructureType.Conveyor,
                Cell = cell,
                NextTick = 0u,
                LastProcessedTick = 0u,
            });
            em.AddComponentData(e, new Conveyor { Direction = dir, PeriodTicks = periodTicks });
            em.AddComponentData(e, new ConveyorItem { ResourceId = itemRes, Count = itemCnt });
            em.SetComponentEnabled<ConveyorItem>(e, itemCnt > 0); // baked DISABLED unless carrying an item
            return e;
        }

        static Entity MakeHarvesterOutput(EntityManager em, int2 cell, byte resourceId, int count)
        {
            // A minimal upstream producer: a PlacedStructure at a cell with a populated MachineOutput buffer.
            var e = em.CreateEntity();
            em.AddComponentData(e, new RegionTag { Region = RegionId.Base });
            em.AddComponentData(e, new PlacedStructure { Type = StructureType.Harvester, Cell = cell, NextTick = 0u, LastProcessedTick = 1u });
            var output = em.AddBuffer<MachineOutput>(e);
            if (count > 0)
                output.Add(new MachineOutput { ResourceId = resourceId, Count = count });
            return e;
        }

        static Entity MakeFabricatorInput(EntityManager em, int2 cell)
        {
            // A minimal downstream sink: a PlacedStructure at a cell with an (empty) MachineInput buffer.
            var e = em.CreateEntity();
            em.AddComponentData(e, new RegionTag { Region = RegionId.Base });
            em.AddComponentData(e, new PlacedStructure { Type = StructureType.Fabricator, Cell = cell, NextTick = 0u, LastProcessedTick = 1u });
            em.AddBuffer<MachineInput>(e);
            return e;
        }

        static int OutputOf(EntityManager em, Entity machine, byte resourceId)
        {
            var buf = em.GetBuffer<MachineOutput>(machine);
            int total = 0;
            for (int i = 0; i < buf.Length; i++)
                if (buf[i].ResourceId == resourceId) total += buf[i].Count;
            return total;
        }

        static int InputOf(EntityManager em, Entity machine, byte resourceId)
        {
            var buf = em.GetBuffer<MachineInput>(machine);
            int total = 0;
            for (int i = 0; i < buf.Length; i++)
                if (buf[i].ResourceId == resourceId) total += buf[i].Count;
            return total;
        }

        /// <summary>Ticks the system past its per-conveyor init gate so subsequent updates actually transport.</summary>
        static void InitThenAdvance(World world, SimulationSystemGroup group, uint initTick, uint moveTick)
        {
            SetServerTick(world, initTick);
            group.Update();                 // first touch: init the conveyor period gate (no move)
            SetServerTick(world, moveTick);
            group.Update();                 // a period later: the transport step runs
        }

        [Test]
        public void Conveyor_Pulls_From_Adjacent_Upstream_MachineOutput_When_Empty()
        {
            var (world, group) = MakeWorld("ConveyorPull", serverTick: 100);
            using (world)
            {
                var em = world.EntityManager;
                // Harvester output at (0,0); an EMPTY belt at (1,0) facing +X. The belt should pull one unit from the
                // upstream output (the harvester's cell (0,0) is belt.cell - DirOffset = (1,0)-(1,0) = (0,0)).
                var harvester = MakeHarvesterOutput(em, new int2(0, 0), ResourceId.Ore, count: 4);
                var belt = MakeConveyor(em, new int2(1, 0), dir: 0 /*+X*/, periodTicks: 30, itemRes: 0, itemCnt: 0);

                InitThenAdvance(world, group, initTick: 100, moveTick: 130);

                Assert.IsTrue(em.IsComponentEnabled<ConveyorItem>(belt), "An empty belt adjacent to an upstream output pulls an item (ConveyorItem enabled).");
                var item = em.GetComponentData<ConveyorItem>(belt);
                Assert.AreEqual(ResourceId.Ore, item.ResourceId, "The pulled item carries the upstream resource id.");
                Assert.AreEqual(3, OutputOf(em, harvester, ResourceId.Ore), "Exactly one unit is pulled off the upstream output (4 -> 3).");
            }
        }

        [Test]
        public void Item_Advances_Exactly_One_Cell_Along_Direction()
        {
            var (world, group) = MakeWorld("ConveyorAdvance", serverTick: 100);
            using (world)
            {
                var em = world.EntityManager;
                // Two +X belts (0,0)->(1,0). The source carries an item; the destination belt is empty. After a tick
                // the item should be on the destination belt and the source belt empty.
                var src = MakeConveyor(em, new int2(0, 0), dir: 0, periodTicks: 30, itemRes: ResourceId.Biomass, itemCnt: 1);
                var dst = MakeConveyor(em, new int2(1, 0), dir: 0, periodTicks: 30, itemRes: 0, itemCnt: 0);

                InitThenAdvance(world, group, initTick: 100, moveTick: 130);

                Assert.IsFalse(em.IsComponentEnabled<ConveyorItem>(src), "The item leaves the source belt (now empty).");
                Assert.IsTrue(em.IsComponentEnabled<ConveyorItem>(dst), "The item arrives on the next belt (exactly one cell along +X).");
                Assert.AreEqual(ResourceId.Biomass, em.GetComponentData<ConveyorItem>(dst).ResourceId, "The carried resource id is preserved across the move.");
            }
        }

        [Test]
        public void Item_Deposits_Into_Downstream_Machine_Input_Sink()
        {
            var (world, group) = MakeWorld("ConveyorSink", serverTick: 100);
            using (world)
            {
                var em = world.EntityManager;
                // A +X belt at (0,0) carrying an item; a fabricator input at (1,0) is the sink. The item should be
                // deposited into the machine's MachineInput and removed from the belt.
                var belt = MakeConveyor(em, new int2(0, 0), dir: 0, periodTicks: 30, itemRes: ResourceId.Ore, itemCnt: 1);
                var fab = MakeFabricatorInput(em, new int2(1, 0));

                InitThenAdvance(world, group, initTick: 100, moveTick: 130);

                Assert.AreEqual(1, InputOf(em, fab, ResourceId.Ore), "The item is deposited into the downstream machine's input.");
                Assert.IsFalse(em.IsComponentEnabled<ConveyorItem>(belt), "The belt is empty after handing its item to the sink.");
            }
        }

        [Test]
        public void Does_Not_Transport_While_Cooling_Down()
        {
            var (world, group) = MakeWorld("ConveyorCooling", serverTick: 100);
            using (world)
            {
                var em = world.EntityManager;
                var src = MakeConveyor(em, new int2(0, 0), dir: 0, periodTicks: 30, itemRes: ResourceId.Ore, itemCnt: 1);
                var dst = MakeConveyor(em, new int2(1, 0), dir: 0, periodTicks: 30, itemRes: 0, itemCnt: 0);

                SetServerTick(world, 100);
                group.Update();             // init (NextTick -> 130)
                SetServerTick(world, 115);
                group.Update();             // 115 < 130 -> belt is still cooling, no move

                Assert.IsTrue(em.IsComponentEnabled<ConveyorItem>(src), "The item stays put while the belt is cooling down.");
                Assert.IsFalse(em.IsComponentEnabled<ConveyorItem>(dst), "Nothing arrives before the belt's period elapses.");
            }
        }
    }
}