using Microsoft.Xna.Framework;
using System;

namespace Barotrauma
{
    public class GUIDragHandle : GUIComponent
    {
        private readonly RectTransform elementToMove;

        private Point originalOffset;

        private Vector2 dragStart;
        private bool dragStarted;

        public Rectangle DragArea;

        public Func<RectTransform, bool> ValidatePosition;

        public bool Dragging => dragStarted;

        public GUIDragHandle(RectTransform rectT, RectTransform elementToMove, string style = "GUIDragIndicator")
            : base(style, rectT)
        {
            enabled = true;
            this.elementToMove = elementToMove;
            DragArea = new Rectangle(0, 0, GameMain.GraphicsWidth, GameMain.GraphicsHeight);
        }

        protected override void Update(float deltaTime)
        {
            if (!Visible) { return; }
            base.Update(deltaTime);

            if (enabled)
            {
                if (dragStarted)
                {
                    Point moveAmount = (PlayerInput.MousePosition - dragStart).ToPoint() - elementToMove.ScreenSpaceOffset;
                    Rectangle rect = elementToMove.Rect;
                    rect.Location += moveAmount;
                
                    moveAmount.X += Math.Max(DragArea.X - rect.X, 0);
                    moveAmount.X -= Math.Max(rect.Right - DragArea.Right, 0);
                    moveAmount.Y += Math.Max(DragArea.Y - rect.Y, 0);
                    moveAmount.Y -= Math.Max(rect.Bottom - DragArea.Bottom, 0);

                    if (moveAmount != Point.Zero)
                    {
                        elementToMove.ScreenSpaceOffset += moveAmount;
                    }

                    bool isPositionValid = ValidatePosition == null || ValidatePosition.Invoke(elementToMove);

                    if (!PlayerInput.PrimaryMouseButtonHeld())
                    {
                        if (!isPositionValid)
                        {
                            elementToMove.ScreenSpaceOffset = originalOffset;
                            elementToMove.GUIComponent?.Flash();
                            SoundPlayer.PlayUISound(GUISoundType.PickItemFail);
                        }
                        dragStarted = false;
                    }
                }
                else if (Rect.Contains(PlayerInput.MousePosition) && CanBeFocused && Enabled && GUI.IsMouseOn(this) && !(GUI.MouseOn is GUIButton))
                {
                    State = Selected ? ComponentState.HoverSelected : ComponentState.Hover;
                    if (PlayerInput.PrimaryMouseButtonDown())
                    {
                        originalOffset = elementToMove.ScreenSpaceOffset;
                        dragStart = PlayerInput.MousePosition - elementToMove.ScreenSpaceOffset.ToVector2();
                        dragStarted = true;
                    }
                }
                else
                {
                    if (!ExternalHighlight)
                    {
                        State = Selected ? ComponentState.Selected : ComponentState.None;
                    }
                    else
                    {
                        State = ComponentState.Hover;
                    }
                }
            }

            foreach (GUIComponent child in Children)
            {
                //allow buttons to handle their states themselves
                if (child is GUIButton) { continue; }
                child.State = State;
                child.Enabled = enabled;
            }
        }
    }
}