using System;
using System.Numerics;
using AcDream.App.Rendering;
using AcDream.Core.Rendering;
using Xunit;

namespace AcDream.App.Tests.Rendering;

public class RetailChaseCameraTests
{
    // ── Heading source ────────────────────────────────────────────────

    [Fact]
    public void Heading_StationaryWithSlopeAlign_FallsBackToYawVector()
    {
        var avgVel = Vector3.Zero;
        float yaw  = MathF.PI / 4f;  // 45°

        var h = RetailChaseCamera.ComputeHeading(
            avgVel, yaw,
            isOnGround: true, contactPlaneNormal: Vector3.UnitZ,
            alignToSlope: true);

        Assert.Equal(MathF.Cos(yaw), h.X, 5);
        Assert.Equal(MathF.Sin(yaw), h.Y, 5);
        Assert.Equal(0f,             h.Z, 5);
    }

    [Fact]
    public void Heading_MovingOnFlatGround_HeadingIsHorizontalFacing()
    {
        // Player moving forward (yaw=0 = +X), on flat ground. Heading
        // should be the yaw vector — the projection onto (0,0,1)-normal
        // plane is a no-op since the base is already horizontal.
        var avgVel = new Vector3(3f, 0f, 0f);
        var h = RetailChaseCamera.ComputeHeading(
            avgVel, yaw: 0f,
            isOnGround: true, contactPlaneNormal: Vector3.UnitZ,
            alignToSlope: true);
        Assert.Equal(1f, h.X, 5);
        Assert.Equal(0f, h.Y, 5);
        Assert.Equal(0f, h.Z, 5);
    }

    [Fact]
    public void Heading_OnUphillSlope_TiltsWithSlope()
    {
        // Player facing +Y (yaw=π/2), walking up a slope rising in +Y.
        // Slope normal tilts back-up: (0, -0.5, 0.866) (30° rise).
        // Projection of (0,1,0) onto plane perpendicular to (0,-0.5,0.866):
        //   dot = 1*(-0.5) = -0.5
        //   projected = (0,1,0) - (0,-0.5,0.866)*(-0.5) = (0, 0.75, 0.433)
        //   normalized → (0, 0.866, 0.5) — slope-aligned heading with +Z tilt.
        var avgVel = new Vector3(0f, 3f, 1.5f);   // moving up the slope
        var normal = new Vector3(0f, -0.5f, 0.866f);
        var h = RetailChaseCamera.ComputeHeading(
            avgVel, yaw: MathF.PI / 2f,
            isOnGround: true, contactPlaneNormal: normal,
            alignToSlope: true);
        Assert.True(h.Z > 0.4f, $"expected slope-aligned +Z tilt, got Z={h.Z}");
        Assert.Equal(1f, h.Length(), 4);
    }

    [Fact]
    public void Heading_AirborneJumpingStraightUp_StaysHorizontal()
    {
        // Player standing still, then jumps straight up. avgVel.xy is
        // zero, the horizontal-velocity gate fires → returns the base
        // facing direction. The vertical-velocity component is ignored.
        // This is THE bug the contact-plane fix prevents: in the old
        // code, normalize((0,0,5)) → (0,0,1) → camera basis tilted up.
        var avgVel = new Vector3(0f, 0f, 5f);
        var h = RetailChaseCamera.ComputeHeading(
            avgVel, yaw: 0f,
            isOnGround: false, contactPlaneNormal: Vector3.Zero,
            alignToSlope: true);
        Assert.Equal(1f, h.X, 5);
        Assert.Equal(0f, h.Y, 5);
        Assert.Equal(0f, h.Z, 5);
    }

    [Fact]
    public void Heading_AirborneRunningJump_StaysHorizontal()
    {
        // Running jump: horizontal velocity nonzero, vertical also
        // nonzero. Airborne path projects onto world up — strips Z
        // from the (already horizontal) base heading, no-op. Camera
        // basis stays horizontal even though player is rising.
        var avgVel = new Vector3(3f, 0f, 4f);
        var h = RetailChaseCamera.ComputeHeading(
            avgVel, yaw: 0f,
            isOnGround: false, contactPlaneNormal: Vector3.Zero,
            alignToSlope: true);
        Assert.Equal(1f, h.X, 5);
        Assert.Equal(0f, h.Y, 5);
        Assert.Equal(0f, h.Z, 5);
    }

    [Fact]
    public void Heading_SlopeAlignDisabled_IgnoresVelocityAndContactPlane()
    {
        // Pure-vertical velocity + a tilted contact normal — neither
        // should affect the heading when alignToSlope is off.
        var avgVel = new Vector3(0f, 0f, 1f);
        var tiltedNormal = new Vector3(0f, -0.5f, 0.866f);

        var h = RetailChaseCamera.ComputeHeading(
            avgVel, yaw: 0f,
            isOnGround: true, contactPlaneNormal: tiltedNormal,
            alignToSlope: false);

        Assert.Equal(1f, h.X, 5);   // (cos 0, sin 0, 0) = (1, 0, 0)
        Assert.Equal(0f, h.Y, 5);
        Assert.Equal(0f, h.Z, 5);
    }

    // ── Basis from heading ────────────────────────────────────────────

    [Fact]
    public void Basis_HorizontalHeading_IsOrthonormalAndRightHanded()
    {
        var (forward, right, up) = RetailChaseCamera.BuildBasis(new Vector3(1f, 0f, 0f));

        Assert.Equal(1f, forward.Length(), 5);
        Assert.Equal(1f, right.Length(),   5);
        Assert.Equal(1f, up.Length(),      5);

        // Orthogonal
        Assert.Equal(0f, Vector3.Dot(forward, right), 5);
        Assert.Equal(0f, Vector3.Dot(forward, up),    5);
        Assert.Equal(0f, Vector3.Dot(right,   up),    5);

        // forward = (1,0,0), world up = (0,0,1) → right = (0,-1,0), camera-up = (0,0,1)
        Assert.Equal(0f, up.X, 5);
        Assert.Equal(0f, up.Y, 5);
        Assert.True(up.Z > 0f);
    }

    [Fact]
    public void Basis_NearVerticalHeading_UsesXFallbackForRight()
    {
        // forward nearly straight up (rare; airborne edge case). Must not produce
        // a zero-length right vector from cross(forward, worldUp).
        var (_, right, up) = RetailChaseCamera.BuildBasis(new Vector3(0f, 0f, 1f));

        Assert.Equal(1f, right.Length(), 5);
        Assert.Equal(1f, up.Length(),    5);
        Assert.Equal(0f, Vector3.Dot(right, up), 5);
    }

    // ── Velocity ring & averaging ────────────────────────────────────

    [Fact]
    public void VelocityRing_AveragesLastN()
    {
        var ring = new Vector3[5];
        int count = 0;

        ring = RetailChaseCamera.PushVelocity(ring, ref count, new Vector3(1, 0, 0));
        ring = RetailChaseCamera.PushVelocity(ring, ref count, new Vector3(1, 0, 0));
        ring = RetailChaseCamera.PushVelocity(ring, ref count, new Vector3(2, 0, 0));
        ring = RetailChaseCamera.PushVelocity(ring, ref count, new Vector3(2, 0, 0));
        ring = RetailChaseCamera.PushVelocity(ring, ref count, new Vector3(3, 0, 0));

        Assert.Equal(5, count);
        var avg = RetailChaseCamera.AverageVelocity(ring, count);
        Assert.Equal(1.8f, avg.X, 5);
        Assert.Equal(0f,   avg.Y, 5);
        Assert.Equal(0f,   avg.Z, 5);
    }

    [Fact]
    public void VelocityRing_FifoEvictsOldest()
    {
        var ring = new Vector3[5];
        int count = 0;

        // Push 6 entries; oldest (the first 1,0,0) should be evicted.
        for (int i = 0; i < 5; i++)
            ring = RetailChaseCamera.PushVelocity(ring, ref count, new Vector3(1, 0, 0));
        ring = RetailChaseCamera.PushVelocity(ring, ref count, new Vector3(10, 0, 0));

        Assert.Equal(5, count);   // still capped at 5
        // Sum of newest 5 entries: 4*(1,0,0) + (10,0,0) = (14,0,0), avg = 2.8
        var avg = RetailChaseCamera.AverageVelocity(ring, count);
        Assert.Equal(2.8f, avg.X, 5);
    }

    [Fact]
    public void VelocityRing_PartialFillUsesActualCount()
    {
        var ring = new Vector3[5];
        int count = 0;

        ring = RetailChaseCamera.PushVelocity(ring, ref count, new Vector3(2, 0, 0));
        ring = RetailChaseCamera.PushVelocity(ring, ref count, new Vector3(4, 0, 0));

        Assert.Equal(2, count);
        var avg = RetailChaseCamera.AverageVelocity(ring, count);
        Assert.Equal(3f, avg.X, 5);   // (2+4)/2, not (2+4)/5
    }

    // ── Damping alpha ────────────────────────────────────────────────

    [Fact]
    public void DampingAlpha_RetailDefault_ProducesSevenAndAHalfPercent()
    {
        // stiffness=0.45, dt=1/60 → 0.45 * (1/60) * 10 ≈ 0.075
        float alpha = RetailChaseCamera.ComputeDampingAlpha(stiffness: 0.45f, dt: 1f / 60f);
        Assert.Equal(0.075f, alpha, 4);
    }

    [Fact]
    public void DampingAlpha_LargeDtClampsToOne()
    {
        float alpha = RetailChaseCamera.ComputeDampingAlpha(stiffness: 0.45f, dt: 1f);
        Assert.Equal(1f, alpha);
    }

    [Fact]
    public void DampingAlpha_NegativeOrZero_ClampsToZero()
    {
        Assert.Equal(0f, RetailChaseCamera.ComputeDampingAlpha(stiffness: 0.45f, dt: 0f));
        Assert.Equal(0f, RetailChaseCamera.ComputeDampingAlpha(stiffness: 0.0f,  dt: 1f));
    }

    // ── Mouse low-pass ───────────────────────────────────────────────

    [Fact]
    public void MouseFilter_BeyondWindow_OutputsRaw()
    {
        float lastDelta = 5f;
        float lastTime  = 0f;
        float windowSec = 0.25f;

        float result = RetailChaseCamera.FilterMouseAxis(
            raw: 10f, weight: 0.5f, nowSec: 1.0f,
            ref lastDelta, ref lastTime, windowSec);

        // Beyond window, blended == raw, so out = raw * 0.5 + raw * 0.5 = raw.
        Assert.Equal(10f, result, 5);
    }

    [Fact]
    public void MouseFilter_WithinWindow_AveragesWithPrevious()
    {
        float lastDelta = 10f;
        float lastTime  = 0f;
        float windowSec = 0.25f;

        float result = RetailChaseCamera.FilterMouseAxis(
            raw: 20f, weight: 0.5f, nowSec: 0.1f,
            ref lastDelta, ref lastTime, windowSec);

        // Within window: avg = (10 + 20)/2 = 15.
        // Output: 20 * 0.5 + 15 * 0.5 = 17.5
        Assert.Equal(17.5f, result, 5);
    }

    [Fact]
    public void MouseFilter_WeightZero_OutputsRaw()
    {
        float lastDelta = 10f;
        float lastTime  = 0f;
        float windowSec = 0.25f;

        float result = RetailChaseCamera.FilterMouseAxis(
            raw: 20f, weight: 0f, nowSec: 0.1f,
            ref lastDelta, ref lastTime, windowSec);

        Assert.Equal(20f, result, 5);
    }

    [Fact]
    public void MouseFilter_WeightOne_OutputsAveraged()
    {
        float lastDelta = 10f;
        float lastTime  = 0f;
        float windowSec = 0.25f;

        float result = RetailChaseCamera.FilterMouseAxis(
            raw: 20f, weight: 1f, nowSec: 0.1f,
            ref lastDelta, ref lastTime, windowSec);

        // weight=1 → out = avg = 15
        Assert.Equal(15f, result, 5);
    }

    [Fact]
    public void MouseFilter_UpdatesLastDeltaAndTime()
    {
        float lastDelta = 10f;
        float lastTime  = 0f;
        float windowSec = 0.25f;

        float result = RetailChaseCamera.FilterMouseAxis(
            raw: 20f, weight: 0.5f, nowSec: 0.1f,
            ref lastDelta, ref lastTime, windowSec);

        Assert.Equal(result, lastDelta);   // last is updated to output
        Assert.Equal(0.1f,   lastTime, 5); // last time advances
    }

    // ── Auto-fade translucency ───────────────────────────────────────

    [Fact]
    public void Translucency_AtFarThreshold_IsZero()
    {
        Assert.Equal(0f, RetailChaseCamera.ComputeTranslucency(distance: 0.45f), 5);
        Assert.Equal(0f, RetailChaseCamera.ComputeTranslucency(distance: 1.00f), 5);
    }

    [Fact]
    public void Translucency_MidwayBetweenThresholds_IsHalf()
    {
        // Midpoint between 0.20 and 0.45 = 0.325
        // t = 1 - (0.20 - 0.325) / (0.20 - 0.45)
        //   = 1 - (-0.125) / (-0.25)
        //   = 1 - 0.5 = 0.5
        Assert.Equal(0.5f, RetailChaseCamera.ComputeTranslucency(distance: 0.325f), 4);
    }

    [Fact]
    public void Translucency_AtNearThreshold_IsOne()
    {
        Assert.Equal(1f, RetailChaseCamera.ComputeTranslucency(distance: 0.20f),  5);
        Assert.Equal(1f, RetailChaseCamera.ComputeTranslucency(distance: 0.10f),  5);
        Assert.Equal(1f, RetailChaseCamera.ComputeTranslucency(distance: 0.0f),   5);
    }

    // ── Update() integration ─────────────────────────────────────────

    [Fact]
    public void FirstUpdate_SnapsToTarget()
    {
        bool savedAlign = CameraDiagnostics.AlignToSlope;
        try
        {
            var cam = new RetailChaseCamera { Distance = 5f, Pitch = 0f };
            CameraDiagnostics.AlignToSlope = false;   // deterministic: heading = yaw vec

            cam.Update(
                playerPosition:      new Vector3(10f, 20f, 30f),
                playerYaw:           0f,             // forward = +X
                playerVelocity:      Vector3.Zero,
                isOnGround:          true,
                contactPlaneNormal:  Vector3.UnitZ,  // flat
                dt:                  1f / 60f);

            // Expected target eye:
            //   pivot          = (10, 20, 30+1.5=31.5)
            //   forward (yaw=0)= (1, 0, 0)
            //   right          = (0, -1, 0) since (1,0,0) × (0,0,1) = (0, -1, 0)
            //   up             = right × forward = (0,-1,0) × (1,0,0) = (0,0,1)
            //   viewer_offset  = (0, -5, 0)  (Distance=5, Pitch=0 → -Distance*cos = -5, sin = 0)
            //   eye = pivot + right*0 + forward*-5 + up*0
            //       = (10 - 5, 20, 31.5) = (5, 20, 31.5)
            Assert.Equal(5f,    cam.Position.X, 4);
            Assert.Equal(20f,   cam.Position.Y, 4);
            Assert.Equal(31.5f, cam.Position.Z, 4);
        }
        finally
        {
            CameraDiagnostics.AlignToSlope = savedAlign;
        }
    }

    [Fact]
    public void SecondUpdate_LerpsTowardTarget()
    {
        bool  savedAlign       = CameraDiagnostics.AlignToSlope;
        float savedTranslation = CameraDiagnostics.TranslationStiffness;
        float savedRotation    = CameraDiagnostics.RotationStiffness;
        try
        {
            var cam = new RetailChaseCamera { Distance = 5f, Pitch = 0f };
            CameraDiagnostics.AlignToSlope         = false;
            CameraDiagnostics.TranslationStiffness = 0.45f;
            CameraDiagnostics.RotationStiffness    = 0.45f;

            // First update at origin: dampedEye = (-5, 0, 1.5).
            cam.Update(Vector3.Zero, playerYaw: 0f, playerVelocity: Vector3.Zero,
                isOnGround: true, contactPlaneNormal: Vector3.UnitZ, dt: 1f / 60f);
            var firstEye = cam.Position;

            // Teleport the player one frame later. Target eye now at (10-5, 0, 1.5) = (5, 0, 1.5).
            // alpha = 0.45 * (1/60) * 10 = 0.075.
            // New eye = firstEye + 0.075 * (target - firstEye)
            //         = (-5,0,1.5) + 0.075 * ((5,0,1.5) - (-5,0,1.5))
            //         = (-5,0,1.5) + 0.075 * (10,0,0)
            //         = (-4.25, 0, 1.5)
            cam.Update(new Vector3(10f, 0f, 0f), playerYaw: 0f, playerVelocity: Vector3.Zero,
                isOnGround: true, contactPlaneNormal: Vector3.UnitZ, dt: 1f / 60f);

            Assert.Equal(-4.25f, cam.Position.X, 3);
            Assert.Equal(0f,     cam.Position.Y, 4);
            Assert.Equal(1.5f,   cam.Position.Z, 4);
        }
        finally
        {
            CameraDiagnostics.AlignToSlope         = savedAlign;
            CameraDiagnostics.TranslationStiffness = savedTranslation;
            CameraDiagnostics.RotationStiffness    = savedRotation;
        }
    }

    [Fact]
    public void Translucency_PropertyReflectsCurrentDampedDistance()
    {
        bool savedAlign = CameraDiagnostics.AlignToSlope;
        try
        {
            var cam = new RetailChaseCamera { Distance = 5f, Pitch = 0f, PivotHeight = 1.5f };
            CameraDiagnostics.AlignToSlope = false;

            // Far from pivot — translucency should be 0.
            cam.Update(Vector3.Zero, playerYaw: 0f, playerVelocity: Vector3.Zero,
                isOnGround: true, contactPlaneNormal: Vector3.UnitZ, dt: 1f / 60f);
            Assert.Equal(0f, cam.PlayerTranslucency, 5);
        }
        finally
        {
            CameraDiagnostics.AlignToSlope = savedAlign;
        }
    }

    [Fact]
    public void AdjustDistance_ClampsToRange()
    {
        var cam = new RetailChaseCamera { Distance = 5f };
        cam.AdjustDistance(-100f);
        Assert.Equal(RetailChaseCamera.DistanceMin, cam.Distance);

        cam.AdjustDistance(+200f);
        Assert.Equal(RetailChaseCamera.DistanceMax, cam.Distance);
    }

    [Fact]
    public void AdjustPitch_ClampsToRange()
    {
        var cam = new RetailChaseCamera { Pitch = 0f };
        cam.AdjustPitch(-10f);
        Assert.Equal(RetailChaseCamera.PitchMin, cam.Pitch);

        cam.AdjustPitch(+10f);
        Assert.Equal(RetailChaseCamera.PitchMax, cam.Pitch);
    }
}