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

namespace ProjectM.Tests
{
    /// <summary>
    /// Plain-Entities tests for <see cref="ProjectileDamageSystem"/> — the server-authoritative
    /// projectile hit resolver. Boots a bare ECS world, registers the system in the
    /// SimulationSystemGroup (the [WorldSystemFilter] is ignored under manual registration), creates
    /// synthetic targets and projectiles, injects a fixed delta-time, ticks once, and asserts the
    /// queued <see cref="DamageEvent"/>s and projectile lifetime. The system plays its ECB back to the
    /// EntityManager immediately, so no separate ECB system is needed.
    /// <para>
    /// The key case is <see cref="FastProjectile_SweptTest_DoesNotTunnel"/>: it pins the swept
    /// (segment-vs-sphere) hit test that replaced a naive point check, which let fast projectiles —
    /// and any projectile while the server tick-batches under load — pass straight through a target in
    /// a single step. This was caught only at runtime (no EditMode coverage existed), hence this test.
    /// </para>
    /// </summary>
    public class ProjectileDamageSystemTests
    {
        static (World world, SimulationSystemGroup group, EntityManager em) MakeWorld()
        {
            var world = new World("ProjectileDamageTestWorld");
            var group = world.GetOrCreateSystemManaged<SimulationSystemGroup>();
            group.AddSystemToUpdateList(world.GetOrCreateSystem<ProjectileDamageSystem>());
            group.SortSystems();
            return (world, group, world.EntityManager);
        }

        static Entity MakeTarget(EntityManager em, float3 pos, float hitRadius, float health, int ownerId = int.MinValue)
        {
            var e = em.CreateEntity();
            em.AddComponentData(e, LocalTransform.FromPosition(pos));
            em.AddComponentData(e, new HitRadius { Value = hitRadius });
            em.AddComponentData(e, new Health { Current = health, Max = health });
            em.AddBuffer<DamageEvent>(e);
            if (ownerId != int.MinValue)
                em.AddComponentData(e, new GhostOwner { NetworkId = ownerId });
            return e;
        }

        // pos is the projectile's POST-move position for the tick (what the system reads); the system
        // reconstructs the travel segment as [pos - dir*speed*dt, pos].
        static Entity MakeProjectile(EntityManager em, float3 pos, float2 dir, float speed, float damage,
            float range, float distanceTravelled, int ownerId)
        {
            var e = em.CreateEntity();
            em.AddComponentData(e, LocalTransform.FromPosition(pos));
            em.AddComponentData(e, new Projectile
            {
                Direction = dir,
                Speed = speed,
                Damage = damage,
                Range = range,
                DistanceTravelled = distanceTravelled,
            });
            em.AddComponentData(e, new GhostOwner { NetworkId = ownerId });
            return e;
        }

        static void Tick(World world, SimulationSystemGroup group, float dt)
        {
            world.SetTime(new TimeData(elapsedTime: dt, deltaTime: dt));
            group.Update();
        }

        [Test]
        public void DirectHit_AppendsDamageEvent_AndDestroysProjectile()
        {
            using var world = MakeWorld().world;
            var group = world.GetExistingSystemManaged<SimulationSystemGroup>();
            var em = world.EntityManager;

            var target = MakeTarget(em, new float3(0f, 0f, 5f), hitRadius: 0.8f, health: 60f);
            var projectile = MakeProjectile(em, new float3(0f, 0f, 5f), new float2(0f, 1f),
                speed: 10f, damage: 20f, range: 20f, distanceTravelled: 5f, ownerId: 1);

            Tick(world, group, 0.1f);

            var dmg = em.GetBuffer<DamageEvent>(target);
            Assert.AreEqual(1, dmg.Length, "Overlapping projectile should append exactly one DamageEvent.");
            Assert.AreEqual(20f, dmg[0].Amount, 1e-3f, "DamageEvent should carry the projectile's damage.");
            Assert.IsFalse(em.Exists(projectile), "A projectile that hits a target must be destroyed.");
        }

        [Test]
        public void FastProjectile_SweptTest_DoesNotTunnel()
        {
            // Target sits at z=5. The projectile's post-move position is z=10 (already past the target),
            // having moved 10 units this tick (speed 100 * dt 0.1). A point check at z=10 would miss
            // (distance 5 >> 1.0); the swept segment [z=0 -> z=10] passes through the target -> hit.
            using var world = MakeWorld().world;
            var group = world.GetExistingSystemManaged<SimulationSystemGroup>();
            var em = world.EntityManager;

            var target = MakeTarget(em, new float3(0f, 0f, 5f), hitRadius: 0.8f, health: 60f);
            var projectile = MakeProjectile(em, new float3(0f, 0f, 10f), new float2(0f, 1f),
                speed: 100f, damage: 20f, range: 50f, distanceTravelled: 10f, ownerId: 1);

            Tick(world, group, 0.1f);

            Assert.AreEqual(1, em.GetBuffer<DamageEvent>(target).Length,
                "A fast projectile whose step overshoots the target must still register a swept hit (no tunnelling).");
            Assert.IsFalse(em.Exists(projectile), "The tunnelling projectile must be consumed on hit.");
        }

        [Test]
        public void OwnerOwnedTarget_IsSkipped_NoSelfHit()
        {
            using var world = MakeWorld().world;
            var group = world.GetExistingSystemManaged<SimulationSystemGroup>();
            var em = world.EntityManager;

            // Target owned by the same NetworkId as the projectile's owner -> must be skipped.
            var ownTarget = MakeTarget(em, new float3(0f, 0f, 5f), hitRadius: 0.8f, health: 60f, ownerId: 7);
            var projectile = MakeProjectile(em, new float3(0f, 0f, 5f), new float2(0f, 1f),
                speed: 10f, damage: 20f, range: 50f, distanceTravelled: 5f, ownerId: 7);

            Tick(world, group, 0.1f);

            Assert.AreEqual(0, em.GetBuffer<DamageEvent>(ownTarget).Length,
                "A projectile must not damage a target owned by its own caster.");
            Assert.IsTrue(em.Exists(projectile), "With no valid target hit and range remaining, the projectile survives.");
        }

        [Test]
        public void SpentProjectile_BeyondRange_IsDestroyed_WithoutDamage()
        {
            using var world = MakeWorld().world;
            var group = world.GetExistingSystemManaged<SimulationSystemGroup>();
            var em = world.EntityManager;

            // Target far off the path; projectile has already travelled past its range.
            var target = MakeTarget(em, new float3(100f, 0f, 100f), hitRadius: 0.8f, health: 60f);
            var projectile = MakeProjectile(em, new float3(0f, 0f, 0f), new float2(0f, 1f),
                speed: 5f, damage: 20f, range: 10f, distanceTravelled: 12f, ownerId: 1);

            Tick(world, group, 0.1f);

            Assert.AreEqual(0, em.GetBuffer<DamageEvent>(target).Length, "No target in the path: no damage.");
            Assert.IsFalse(em.Exists(projectile), "A projectile past its range must be destroyed.");
        }
    }
}