using System;
using System.Collections.Generic;
using System.IO;
using CultMath;
using GameCult.Caching;
using Xunit;
using static CultMath.math;
using float2 = CultMath.float2;
using Random = CultMath.Random;

// Floating bodies (aetheria-release cut floating-bodies): the drift loot and mines share, the structured
// dice they roll with, and the zone-scoped ids they carry. The body has no consumer yet; these tests are
// its whole contract.
public sealed class FloatingBodyTests : IDisposable
{
    private readonly string _root = Path.Combine(Path.GetTempPath(), "aetheria-floatingbody-" + Guid.NewGuid().ToString("N"));
    private readonly List<CultCache> _caches = new List<CultCache>();

    public FloatingBodyTests() => Directory.CreateDirectory(_root);

    public void Dispose()
    {
        foreach (var c in _caches) c.Dispose();
        Directory.Delete(_root, true);
    }

    private static GameplaySettings Settings(float drag = .05f, float launchDrag = .2f, float gravity = 1f) => new GameplaySettings
    {
        FloatingBodyDrag = drag, FloatingBodyLaunchDrag = launchDrag, FloatingBodyGravity = gravity
    };

    private Zone NewZone()
    {
        var cache = AetheriaStores.Open(Path.Combine(_root, Guid.NewGuid().ToString("N") + ".cc"), catalogWritable: true);
        _caches.Add(cache);
        var settings = new GameplaySettings
        {
            DefaultEntitySettings = new EntitySettings(),
            Tiers = new[] { new RarityTier { Name = "Common", Quality = .5f, Rarity = 0, Color = new float3(1, 1, 1) } },
            QualityPriceModifier = new ExponentialLerp()
        };
        var items = new ItemManager(cache, new ProvenanceLedger(), settings, _ => { });
        return new Zone(items, new PlanetSettings(), new ZonePack(), new GalaxyZone { Name = "Test Zone", Owner = null }, null);
    }

    private static KinematicBody Run(KinematicBody b, float seconds, float dt, float2 force, GameplaySettings s)
    {
        var steps = (int) Math.Round(seconds / dt);
        for (var i = 0; i < steps; i++) b.Step(dt, force, s);
        return b;
    }

    [Fact]
    public void LaunchVelocityDecaysExponentially()
    {
        var s = Settings();
        // Speed .3: the semi-implicit step's position error is bounded by speed * dt / 2 (about .005 at dt .1), inside the 1e-2 pin.
        var start = new KinematicBody { Velocity = new float2(.18f, .24f) };
        foreach (var dt in new[] { 1f / 120f, .1f })
        {
            var b = Run(start, 3f, dt, float2.zero, s);
            Assert.Equal(.3f * exp(-s.FloatingBodyLaunchDrag * 3f), length(b.Velocity), 4);
        }

        var fine = Run(start, 3f, 1f / 120f, float2.zero, s);
        var coarse = Run(start, 3f, .1f, float2.zero, s);
        Assert.True(length(fine.Position - coarse.Position) < 1e-2f);
        // It really moved, along the launch direction.
        Assert.True(fine.Position.x > 0f && fine.Position.y > fine.Position.x);
    }

    [Fact]
    public void DriftFollowsTheForce()
    {
        var s = Settings();
        var force = new float2(.02f, -.01f);
        var b = Run(new KinematicBody(), 600f, .1f, force, s);
        Assert.Equal(force.x * s.FloatingBodyGravity / s.FloatingBodyDrag, b.Drift.x, 2);
        Assert.Equal(force.y * s.FloatingBodyGravity / s.FloatingBodyDrag, b.Drift.y, 2);
        Assert.Equal(b.Velocity + b.Drift, b.TotalVelocity);

        var noGravity = Run(new KinematicBody(), 10f, .1f, force, Settings(gravity: 0f));
        Assert.Equal(float2.zero, noGravity.Drift);
        Assert.Equal(float2.zero, noGravity.Position);

        var noForce = Run(new KinematicBody { Velocity = new float2(1f, 0f) }, 2f, .1f, float2.zero, s);
        Assert.Equal(float2.zero, noForce.Drift);
        Assert.True(noForce.Position.x > 0f && noForce.Position.y == 0f);
    }

    [Fact]
    public void OneStepMovesByLaunchPlusDrift()
    {
        var s = Settings();
        var b = new KinematicBody { Velocity = new float2(2f, 0f), Drift = new float2(0f, 1f) };
        b.Step(.5f, new float2(.4f, 0f), s);
        var velocity = 2f * exp(-s.FloatingBodyLaunchDrag * .5f);
        var drift = new float2(.4f * .5f, 1f) * exp(-s.FloatingBodyDrag * .5f);
        Assert.Equal(velocity, b.Velocity.x, 4);
        Assert.Equal(drift.x, b.Drift.x, 4);
        Assert.Equal(drift.y, b.Drift.y, 4);
        Assert.Equal((velocity + drift.x) * .5f, b.Position.x, 4);
        Assert.Equal(drift.y * .5f, b.Position.y, 4);
    }

    [Fact]
    public void ShotDiceAreUnchanged()
    {
        // fmix32 as FireControl.MixSeed wrote it, the function this cut moved.
        static uint Reference(uint seed)
        {
            seed ^= seed >> 16; seed *= 0x85ebca6bu; seed ^= seed >> 13; seed *= 0xc2b2ae35u; seed ^= seed >> 16;
            return seed;
        }
        var inputs = new List<uint> { 0u, 0xFFFFFFFFu };
        for (uint i = 1; inputs.Count < 64; i++) inputs.Add(i * 2654435761u);
        foreach (var x in inputs) Assert.Equal(Reference(x), SimulationDice.Mix(x));
        Assert.Equal(0u, SimulationDice.Mix(0u));
        Assert.Equal(0x514E28B7u, SimulationDice.Mix(1u));
    }

    [Fact]
    public void DiceStreamsAreIndependentAndRepeatable()
    {
        var loot = SimulationDice.For(1234u, SimulationDice.LootStream, 5u);
        var mine = SimulationDice.For(1234u, SimulationDice.MineStream, 5u);
        Assert.NotEqual(loot.NextUInt(), mine.NextUInt());

        var a = SimulationDice.For(1234u, SimulationDice.LootStream, 5u);
        var b = SimulationDice.For(1234u, SimulationDice.LootStream, 5u);
        for (var i = 0; i < 8; i++) Assert.Equal(a.NextUInt(), b.NextUInt());

        Assert.NotEqual(SimulationDice.For(1234u, SimulationDice.LootStream, 5u).NextUInt(), SimulationDice.For(1235u, SimulationDice.LootStream, 5u).NextUInt());
        Assert.NotEqual(SimulationDice.For(1234u, SimulationDice.LootStream, 5u).NextUInt(), SimulationDice.For(1234u, SimulationDice.LootStream, 6u).NextUInt());

        // Never seeded 0: the argument set that mixes to zero still rolls.
        var zero = SimulationDice.For(0u, 0u, 0u);
        Assert.Equal(1u, zero.state);
    }

    [Fact]
    public void NeighbouringZonesAndOrdinalsNeverShareADraw()
    {
        // Folding stream and ordinal into the zone seed with one xor would make (zone, n) and (zone ^ 1, n ^ 1)
        // the same seed; the double mix keeps them apart.
        for (uint zone = 0; zone < 64; zone++)
        for (uint n = 0; n < 16; n++)
            Assert.NotEqual(SimulationDice.For(zone, SimulationDice.LootStream, n).NextUInt(),
                SimulationDice.For(zone ^ 1u, SimulationDice.LootStream, n ^ 1u).NextUInt());
    }

    [Fact]
    public void BodyIdsAreUniqueInAZone()
    {
        var zone = NewZone();
        var seen = new HashSet<FloatingBodyId>();
        uint last = 0;
        for (var i = 0; i < 10000; i++)
        {
            var id = zone.NextBodyId();
            Assert.True(id.Value > last);
            last = id.Value;
            Assert.True(seen.Add(id));
        }
        Assert.Equal(1u, NewZone().NextBodyId().Value);
        Assert.Equal("1", new FloatingBodyId(1).ToString());
        Assert.Equal(new FloatingBodyId(7), new FloatingBodyId(7));
        Assert.NotEqual(new FloatingBodyId(7), new FloatingBodyId(8));
    }

    // Ship.Update's own gravity line, through the real ship and a real zone with one well at the origin.
    private Ship ShipAt(float x, out Zone zone)
    {
        var cache = AetheriaStores.Open(Path.Combine(_root, Guid.NewGuid().ToString("N") + ".cc"), Path.Combine(_root, Guid.NewGuid().ToString("N") + ".run.cc"), catalogWritable: true);
        _caches.Add(cache);
        var hullShape = new Shape(5, 5);
        foreach (var cell in hullShape.AllCoordinates) hullShape[cell] = true;
        cache.Upsert(new HullData { Name = "Skiff", HullType = HullType.Ship, Shape = hullShape, Durability = 10, Mass = 1000 });
        cache.FlushAsync().Wait();
        var settings = new GameplaySettings
        {
            DefaultEntitySettings = new EntitySettings(),
            Tiers = new[] { new RarityTier { Name = "Common", Quality = .5f, Rarity = 0, Color = new float3(1, 1, 1) } },
            QualityPriceModifier = new ExponentialLerp()
        };
        var items = new ItemManager(cache, new ProvenanceLedger(), settings, _ => { });
        var planets = new PlanetSettings { HeightExaggeration = 10f }; // the tilt reads force / K, which K = 1 would hide
        var pack = new ZonePack { Radius = 1000 };
        WellFixture.Dig(cache, pack, planets, 300, 100);
        zone = new Zone(items, planets, pack, new GalaxyZone { Name = "Test Zone", Owner = null }, null);
        var design = cache.GetByName<HullData>("Skiff");
        var hull = new EquippableItem
        {
            Data = cache.RefOf<ItemData>(design), Durability = design.Durability,
            Lot = items.Lots.Add(new Lot { Design = cache.RefOf<ItemData>(design), Origin = new Attributed(), Quality = .5f, Roles = new List<RoleFill>() })
        };
        var ship = new Ship(items, zone, hull, new EntitySettings());
        zone.Admit(ship, piloted: false);
        ship.Aim = float3(0, 0, 1);
        ship.Position = float3(x, 0, 0);
        return ship;
    }

    [Fact]
    public void AShipInAWellIsPulledByThePotential()
    {
        foreach (var delta in new[] { 1f / 60f, 1f / 30f })
        {
            var ship = ShipAt(400f, out var zone);
            var at = ship.Position.xz;
            var expected = zone.GetForce(at) * delta;
            Assert.True(expected.x < 0f, "the well must pull a ship at +x toward the centre");

            ship.Update(delta);

            var tolerance = Math.Max(1e-7f, length(expected) * 1e-4f);
            Assert.InRange(ship.Velocity.x, expected.x - tolerance, expected.x + tolerance);
            Assert.InRange(ship.Velocity.y, expected.y - tolerance, expected.y + tolerance);

            // The tilt is the surface of the drawn height (potential / K): its slope is the force over K.
            var slope = zone.GetForce(at) / zone.Settings.HeightExaggeration;
            var normal = normalize(float3(slope.x, 1f, slope.y));
            var q = ship.Rotation;
            var u = float3(q.x, q.y, q.z);
            var v = float3(0, 1, 0);
            var up = v + 2 * (q.w * cross(u, v) + cross(u, cross(u, v)));
            Assert.True(length(up - normal) < 1e-4f, "the ship tilts to the zone's surface normal");
        }
    }

    // Ship.Update's order: position first, then gravity sampled where the ship now is (leapfrog's kick after the drift). A
    // ship already moving falls toward the centre through the field at its new place, not the one it left.
    [Fact]
    public void AMovingShipFeelsTheFieldWhereItHasMoved()
    {
        var ship = ShipAt(400f, out var zone);
        ship.Velocity = float2(-200f, 0f);
        const float delta = .25f;

        ship.Update(delta);

        var moved = float2(400f, 0f) + float2(-200f, 0f) * delta;
        Assert.Equal(moved.x, ship.Position.x, 1e-3f);
        var pulled = (ship.Velocity - float2(-200f, 0f)) / delta;
        var expected = zone.GetForce(moved);
        Assert.True(expected.x < 0f, "the well pulls inward at the ship's new place");
        Assert.InRange(pulled.x, expected.x * (1f + 1e-3f), expected.x * (1f - 1e-3f));
        Assert.InRange(pulled.y, -1e-3f, 1e-3f);
        Assert.NotEqual(zone.GetForce(float2(400f, 0f)).x, expected.x); // the premise: the field differs between the two places
    }
}