using Sandbox;
using System;
using System.Linq;

/// <summary>
/// Where the camera sits behind the main menu, the course settings and the lobby. Place one in a
/// scene (the menu_camera prefab) and the fly-over's menu orbit is replaced by this view: the
/// object's position and rotation with a gentle sway and a slight push-in. A child object named
/// End makes it drift back and forth between the two points as well. Without one in the scene
/// the old orbit round the start hole is used. Editor gizmo: the camera's frustum, and the path
/// to End when there is one.
/// </summary>
[Title( "Golf Menu Camera" ), Icon( "videocam" ), Category( "Golf" )]
public sealed class GolfMenuCamera : Component
{
	/// <summary>The menu camera in the loaded scene, or null.</summary>
	public static GolfMenuCamera Current { get; private set; }

	/// <summary>How far the sway moves the camera sideways and up, in units. 0 holds it still.</summary>
	[Property, Title( "Drift Amount" ), Range( 0f, 200f )]
	public float DriftAmount { get; set; } = 24f;

	/// <summary>Seconds for one full sway back and forth.</summary>
	[Property, Title( "Drift Period" ), Range( 2f, 60f )]
	public float DriftPeriod { get; set; } = 14f;

	/// <summary>How far the camera eases forward and back along its view, in units.</summary>
	[Property, Title( "Push In" ), Range( 0f, 400f )]
	public float PushIn { get; set; } = 40f;

	/// <summary>Degrees of slow look-around that go with the sway. 0 keeps the rotation fixed.</summary>
	[Property, Title( "Sway Degrees" ), Range( 0f, 10f )]
	public float SwayDegrees { get; set; } = 1.5f;

	/// <summary>Seconds for one trip from here to End and back, when a child named End exists.</summary>
	[Property, Title( "Loop Seconds" ), Range( 4f, 120f )]
	public float LoopSeconds { get; set; } = 30f;

	/// <summary>Vertical field of view of the menu view.</summary>
	[Property, Title( "Field Of View" ), Range( 30f, 110f )]
	public float FieldOfView { get; set; } = 70f;

	protected override void OnEnabled()
	{
		Current = this;
	}

	protected override void OnDisabled()
	{
		if ( Current == this ) Current = null;
	}

	/// <summary>The End child, if the camera loops between two points.</summary>
	GameObject End => GameObject.Children.FirstOrDefault( c => c.IsValid() && string.Equals( c.Name, "End", StringComparison.OrdinalIgnoreCase ) );

	/// <summary>The camera's position and rotation at a moment in time, drift and all.</summary>
	public Transform ViewAt( float time )
	{
		var start = WorldTransform;
		var position = start.Position;
		var rotation = start.Rotation;

		// Back and forth between here and End, easing at both ends.
		var end = End;
		if ( end.IsValid() && LoopSeconds > 0f )
		{
			var phase = (time % LoopSeconds) / LoopSeconds;          // 0..1 over one round trip
			var t = phase < 0.5f ? phase * 2f : 2f - phase * 2f;      // 0 -> 1 -> 0
			t = t * t * (3f - 2f * t);                                // smoothstep
			position = Vector3.Lerp( start.Position, end.WorldPosition, t );
			rotation = Rotation.Slerp( start.Rotation, end.WorldRotation, t );
		}

		// The sway: a slow figure of eight sideways and up, with a push-in on a longer beat.
		var period = MathF.Max( 2f, DriftPeriod );
		var w = MathF.Tau * time / period;
		var sideways = MathF.Sin( w ) * DriftAmount;
		var upward = MathF.Sin( w * 0.5f + 1.3f ) * DriftAmount * 0.5f;
		var forward = (0.5f + 0.5f * MathF.Sin( w * 0.25f )) * PushIn;

		var swayed = rotation * Rotation.From( MathF.Sin( w * 0.5f ) * SwayDegrees * 0.5f, MathF.Sin( w ) * SwayDegrees, 0f );
		position += rotation.Right * sideways + rotation.Up * upward + rotation.Forward * forward;

		return new Transform( position, swayed );
	}

	protected override void DrawGizmos()
	{
		var selected = Gizmo.IsSelected || Gizmo.IsHovered;
		var colour = new Color( 0.37f, 0.83f, 0.42f );
		Gizmo.Draw.LineThickness = selected ? 2f : 1f;
		Gizmo.Draw.Color = colour.WithAlpha( selected ? 0.95f : 0.55f );

		// The frustum in local space: the near and far rectangles of the field of view, joined up.
		var aspect = 16f / 9f;
		var near = 20f;
		var far = selected ? 600f : 300f;
		var tan = MathF.Tan( MathX.DegreeToRadian( FieldOfView ) * 0.5f );
		Vector3[] Corners( float d )
		{
			var h = tan * d;
			var w = h * aspect;
			return new[]
			{
				new Vector3( d, -w, -h ), new Vector3( d, w, -h ),
				new Vector3( d, w, h ), new Vector3( d, -w, h ),
			};
		}
		var n = Corners( near );
		var f = Corners( far );
		for ( var i = 0; i < 4; i++ )
		{
			Gizmo.Draw.Line( n[i], n[(i + 1) % 4] );
			Gizmo.Draw.Line( f[i], f[(i + 1) % 4] );
			Gizmo.Draw.Line( Vector3.Zero, f[i] );
		}

		// A small body so it can be found and clicked.
		Gizmo.Draw.LineBBox( new BBox( new Vector3( -14f, -8f, -8f ), new Vector3( 4f, 8f, 8f ) ) );

		// The loop path to End, in world space.
		var end = End;
		if ( end.IsValid() )
		{
			var local = WorldTransform.PointToLocal( end.WorldPosition );
			Gizmo.Draw.Color = colour.WithAlpha( 0.8f );
			Gizmo.Draw.Arrow( Vector3.Zero, local, 12f, 4f );
		}
	}
}