using BansheeEngine;

namespace BansheeEditor
{
    /// <summary>
    /// Handles camera movement in the scene view.
    /// </summary>
    [RunInEditor]
    internal sealed class SceneCamera : Component
    {
        public const string MoveForwardBinding = "SceneForward";
	    public const string MoveLeftBinding = "SceneLeft";
	    public const string MoveRightBinding = "SceneRight";
	    public const string MoveBackBinding = "SceneBackward";
	    public const string FastMoveBinding = "SceneFastMove";
	    public const string RotateBinding = "SceneRotate";
	    public const string HorizontalAxisBinding = "SceneHorizontal";
	    public const string VerticalAxisBinding = "SceneVertical";

	    private const float StartSpeed = 4.0f;
	    private const float TopSpeed = 12.0f;
	    private const float Acceleration = 1.0f;
	    private const float FastModeMultiplier = 2.0f;
	    private const float RotationalSpeed = 360.0f; // Degrees/second
        private readonly Degree FieldOfView = 90.0f;

        private VirtualButton moveForwardBtn;
        private VirtualButton moveLeftBtn;
        private VirtualButton moveRightBtn;
        private VirtualButton moveBackwardBtn;
        private VirtualButton fastMoveBtn;
        private VirtualButton activeBtn;
        private VirtualAxis horizontalAxis;
        private VirtualAxis verticalAxis;

        private float currentSpeed;
        private Degree yaw;
        private Degree pitch;
        private bool lastButtonState;
        private Camera camera;
        private bool inputEnabled = true;

        // Animating camera transitions
        private CameraAnimation animation = new CameraAnimation();
        private float frustumWidth = 50.0f;
        private float lerp;
        private bool isAnimating;

        private void OnReset()
        {
            camera = SceneObject.GetComponent<Camera>();

            moveForwardBtn = new VirtualButton(MoveForwardBinding);
            moveLeftBtn = new VirtualButton(MoveLeftBinding);
            moveRightBtn = new VirtualButton(MoveRightBinding);
            moveBackwardBtn = new VirtualButton(MoveBackBinding);
            fastMoveBtn = new VirtualButton(FastMoveBinding);
            activeBtn = new VirtualButton(RotateBinding);
            horizontalAxis = new VirtualAxis(HorizontalAxisBinding);
            verticalAxis = new VirtualAxis(VerticalAxisBinding);
        }

        private void OnUpdate()
        {
		    bool goingForward = VirtualInput.IsButtonHeld(moveForwardBtn);
		    bool goingBack = VirtualInput.IsButtonHeld(moveBackwardBtn);
		    bool goingLeft = VirtualInput.IsButtonHeld(moveLeftBtn);
		    bool goingRight = VirtualInput.IsButtonHeld(moveRightBtn);
		    bool fastMove = VirtualInput.IsButtonHeld(fastMoveBtn);
		    bool camActive = VirtualInput.IsButtonHeld(activeBtn);

            if (camActive != lastButtonState)
            {
                if (camActive)
                    Cursor.Hide();
                else
                    Cursor.Show();

                lastButtonState = camActive;
            }

		    float frameDelta = Time.FrameDelta;
		    if (camActive)
		    {
		        float horzValue = VirtualInput.GetAxisValue(horizontalAxis);
                float vertValue = VirtualInput.GetAxisValue(verticalAxis);

                yaw += new Degree(horzValue * RotationalSpeed * frameDelta);
                pitch += new Degree(vertValue * RotationalSpeed * frameDelta);

                yaw = MathEx.WrapAngle(yaw);
                pitch = MathEx.WrapAngle(pitch);

		        Quaternion yRot = Quaternion.FromAxisAngle(Vector3.YAxis, yaw);
                Quaternion xRot = Quaternion.FromAxisAngle(Vector3.XAxis, pitch);

                Quaternion camRot = yRot * xRot;
                camRot.Normalize();

                SceneObject.Rotation = camRot;

                Vector3 direction = Vector3.Zero;
                if (goingForward) direction += SceneObject.Forward;
                if (goingBack) direction -= SceneObject.Forward;
                if (goingRight) direction += SceneObject.Right;
                if (goingLeft) direction -= SceneObject.Right;

                if (direction.SqrdLength != 0)
                {
                    direction.Normalize();

                    float multiplier = 1.0f;
                    if (fastMove)
                        multiplier = FastModeMultiplier;

                    currentSpeed = MathEx.Clamp(currentSpeed + Acceleration * frameDelta, StartSpeed, TopSpeed);
                    currentSpeed *= multiplier;
                }
                else
                {
                    currentSpeed = 0.0f;
                }

                const float tooSmall = 0.0001f;
                if (currentSpeed > tooSmall)
                {
                    Vector3 velocity = direction * currentSpeed;
                    SceneObject.Move(velocity * frameDelta);
                }
		    }

            UpdateAnim();
        }

        /// <summary>
        /// Enables or disables camera controls.
        /// </summary>
        /// <param name="enable">True to enable controls, false to disable.</param>
        public void EnableInput(bool enable)
        {
            if (inputEnabled == enable)
                return;

            inputEnabled = enable;

            if (!inputEnabled)
            {
                if (VirtualInput.IsButtonHeld(activeBtn))
                    Cursor.Show();
            }
        }

        /// <summary>
        /// Focuses the camera on the currently selected object(s).
        /// </summary>
        public void FrameSelected()
        {
            SceneObject[] selectedObjects = Selection.SceneObjects;
            if (selectedObjects.Length > 0)
            {
                AABox box = EditorUtility.CalculateBounds(Selection.SceneObjects);
                FrameBounds(box);
            }
        }

        /// <summary>
        /// Moves and orients a camera so that the provided bounds end covering the camera's viewport.
        /// </summary>
        /// <param name="bounds">Bounds to frame in camera's view.</param>
        /// <param name="padding">Amount of padding to leave on the borders of the viewport, in percent [0, 1].</param>
        private void FrameBounds(AABox bounds, float padding = 0.0f)
        {
            // TODO - Use AABox bounds directly instead of a sphere to be more accurate
            float worldWidth = bounds.Size.Length;
            float worldHeight = worldWidth;

            if (worldWidth == 0.0f)
                worldWidth = 1.0f;

            if (worldHeight == 0.0f)
                worldHeight = 1.0f;

            float boundsAspect = worldWidth / worldHeight;
            float paddingScale = MathEx.Clamp01(padding) + 1.0f;
            float frustumWidth;

            // If camera has wider aspect than bounds then height will be the limiting dimension
            if (camera.AspectRatio > boundsAspect)
                frustumWidth = worldHeight * camera.AspectRatio * paddingScale;
            else // Otherwise width
                frustumWidth = worldWidth * paddingScale;

            float distance = CalcDistanceForFrustumWidth(frustumWidth);

            Vector3 forward = bounds.Center - SceneObject.Position;
            forward.Normalize();

            CameraState state = new CameraState();
            state.Position = bounds.Center - forward * distance;
            state.Rotation = Quaternion.LookRotation(forward, Vector3.YAxis);
            state.Ortographic = camera.ProjectionType == ProjectionType.Orthographic;
            state.FrustumWidth = frustumWidth;

            SetState(state);
        }

        /// <summary>
        /// Changes the state of the camera, either instantly or animated over several frames. The state includes
        /// camera position, rotation, type and possibly other parameters.
        /// </summary>
        /// <param name="state">New state of the camera.</param>
        /// <param name="animated">Should the state be linearly interpolated over a course of several frames.</param>
        private void SetState(CameraState state, bool animated = true)
        {
            CameraState startState = new CameraState();

            startState.Position = SceneObject.Position;
            startState.Rotation = SceneObject.Rotation;
            startState.Ortographic = camera.ProjectionType == ProjectionType.Orthographic;
            startState.FrustumWidth = frustumWidth;

            animation.Start(startState, state);
            if (!animated)
            {
                ApplyState(1.0f);

                isAnimating = false;
            }
            else
            {
                isAnimating = true;
                lerp = 0.0f;
            }
        }

        /// <summary>
        /// Applies the animation target state depending on the interpolation parameter. <see cref="SetState"/>.
        /// </summary>
        /// <param name="t">Interpolation parameter ranging [0, 1] that interpolated between the start state and the
        ///                 target state.</param>
        private void ApplyState(float t)
        {
            animation.Update(t);

            SceneObject.Position = animation.State.Position;
            SceneObject.Rotation = animation.State.Rotation;
            frustumWidth = animation.State.FrustumWidth;

            Vector3 eulerAngles = SceneObject.Rotation.ToEuler();
            pitch = eulerAngles.x;
            yaw = eulerAngles.y;

            Degree FOV = (1.0f - animation.State.OrtographicPct)*FieldOfView;
            if (FOV < 5.0f)
            {
                camera.ProjectionType = ProjectionType.Orthographic;
                camera.OrthoHeight = frustumWidth * 0.5f / camera.AspectRatio;
            }
            else
            {
                camera.ProjectionType = ProjectionType.Perspective;
                camera.FieldOfView = FOV;
            }

            // Note: Consider having a global setting for near/far planes as changing it here might confuse the user
            float distance = CalcDistanceForFrustumWidth(frustumWidth);
            if (distance < 1)
            {
                camera.NearClipPlane = 0.005f;
                camera.FarClipPlane = 1000f;
            }
            if (distance < 100)
            {
                camera.NearClipPlane = 0.05f;
                camera.FarClipPlane = 2500f;
            }
            else if (distance < 1000)
            {
                camera.NearClipPlane = 0.5f;
                camera.FarClipPlane = 10000f;
            }
            else
            {
                camera.NearClipPlane = 5.0f;
                camera.FarClipPlane = 1000000f;
            }
        }

        /// <summary>
        /// Calculates distance at which the camera's frustum width is equal to the provided width.
        /// </summary>
        /// <param name="frustumWidth">Frustum width to find the distance for, in world units.</param>
        /// <returns>Distance at which the camera's frustum is the specified width, in world units.</returns>
        private float CalcDistanceForFrustumWidth(float frustumWidth)
        {
            if (camera.ProjectionType == ProjectionType.Perspective)
                return (frustumWidth*0.5f)/MathEx.Tan(camera.FieldOfView*0.5f);
            else
                return frustumWidth * 2.0f;
        }

        /// <summary>
        /// Updates camera state transition animation. Should be called every frame.
        /// </summary>
        private void UpdateAnim()
        {
            if (!isAnimating)
                return;

            const float ANIM_TIME = 0.5f; // 0.5f seconds
            lerp += Time.FrameDelta * (1.0f / ANIM_TIME);

            if (lerp >= 1.0f)
            {
                lerp = 1.0f;
                isAnimating = false;
            }

            ApplyState(lerp);
        }

        /// <summary>
        /// Contains data for a possible camera state. Camera states can be interpolated between each other as needed.
        /// </summary>
        private struct CameraState
        {
            private float _ortographic;

            public Vector3 Position { get; set; }
            public Quaternion Rotation { get; set; }
            public float FrustumWidth { get; set; }

            public bool Ortographic
            {
                get { return _ortographic > 0.5; }
                set { _ortographic = value ? 1.0f : 0.0f; }
            }

            public float OrtographicPct
            {
                get { return _ortographic; }
                set { _ortographic = value; }
            }
        }

        /// <summary>
        /// Helper class that performs linear interpolation between two camera states.
        /// </summary>
        private struct CameraAnimation
        {
            private CameraState start;
            private CameraState target;
            private CameraState interpolated;

            /// <summary>
            /// Returns currently interpolated animation state.
            /// </summary>
            public CameraState State
            {
                get { return interpolated; }
            }

            /// <summary>
            /// Initializes the animation with initial and target states.
            /// </summary>
            /// <param name="start">Initial state to animate from.</param>
            /// <param name="target">Target state to animate towards.</param>
            public void Start(CameraState start, CameraState target)
            {
                this.start = start;
                this.target = target;
            }

            /// <summary>
            /// Updates the animation by interpolating between the start and target states.
            /// </summary>
            /// <param name="t">Interpolation parameter in range [0, 1] that determines how much to interpolate between
            ///                 start and target states.</param>
            public void Update(float t)
            {
                interpolated.Position = start.Position * (1.0f - t) + target.Position * t;
                interpolated.Rotation = Quaternion.Slerp(start.Rotation, target.Rotation, t);
                interpolated.OrtographicPct = start.OrtographicPct * (1.0f - t) + target.OrtographicPct * t;

                interpolated.FrustumWidth = start.FrustumWidth * (1.0f - t) + target.FrustumWidth * t;
            }
        };
    }
}