using System;

/// <summary>
/// 跳一跳的跟随相机：固定角度俯视，平滑跟随棋子。
/// 视线大体沿 +X 方向，平台蛇形前进时在画面上呈现左前/右前的斜线运动。
/// </summary>
public sealed class JumpCamera : Component
{
	/// <summary> 相机相对注视点的偏移 </summary>
	[Property] public Vector3 Offset { get; set; } = new Vector3( -500f, 0f, 640f );

	/// <summary> 注视点相对棋子的前探量（把棋子压到画面下方） </summary>
	[Property] public Vector3 LookAhead { get; set; } = new Vector3( 300f, 0f, -40f );

	/// <summary> 跟随速度（越大越紧） </summary>
	[Property] public float FollowSpeed { get; set; } = 5f;

	Vector3 _focus;
	bool _hasFocus;

	public void SnapTo( Vector3 pos )
	{
		_focus = pos;
		_hasFocus = true;
	}

	protected override void OnUpdate()
	{
		var game = JumpGame.Current;
		if ( game is null || !_hasFocus ) return;

		// 失败（下落/结束）后停住，不跟着棋子坠出画面，让玩家看清失误位置
		if ( game.IsGameOver || game.IsFalling ) return;

		var t = 1f - MathF.Exp( -FollowSpeed * Time.Delta );
		_focus = Vector3.Lerp( _focus, game.PiecePosition, t );

		GameObject.WorldPosition = _focus + Offset;
		GameObject.WorldRotation = Rotation.LookAt( ( _focus + LookAhead - GameObject.WorldPosition ).Normal );
	}
}