// Unity C# reference source
// Copyright (c) Unity Technologies. For terms of use, see
// https://unity3d.com/legal/licenses/Unity_Reference_Only_License

using System;
using UnityEngine;
using UnityEngine.Experimental.UIElements;
using UnityEngine.Experimental.UIElements.StyleSheets;

namespace UnityEditor.Experimental.UIElements.GraphView
{
    public class GridBackground : VisualElement
    {
        const string k_SpacingProperty = "spacing";
        const string k_ThickLinesProperty = "thick-lines";
        const string k_LineColorProperty = "line-color";
        const string k_ThickLineColorProperty = "thick-line-color";
        const string k_GridBackgroundColorProperty = "grid-background-color";

        StyleValue<float> m_Spacing;
        float spacing
        {
            get
            {
                return m_Spacing.GetSpecifiedValueOrDefault(50.0f);
            }
        }

        StyleValue<int> m_ThickLines;
        int thickLines
        {
            get
            {
                return m_ThickLines.GetSpecifiedValueOrDefault(10);
            }
        }

        StyleValue<Color> m_LineColor;
        Color lineColor
        {
            get
            {
                return m_LineColor.GetSpecifiedValueOrDefault(new Color(0f, 0f, 0f, 0.18f));
            }
        }

        StyleValue<Color> m_ThickLineColor;
        Color thickLineColor
        {
            get
            {
                return m_ThickLineColor.GetSpecifiedValueOrDefault(new Color(0f, 0f, 0f, 0.38f));
            }
        }

        StyleValue<Color> m_GridBackgroundColor;
        Color gridBackgroundColor
        {
            get
            {
                return m_GridBackgroundColor.GetSpecifiedValueOrDefault(new Color(0.17f, 0.17f, 0.17f, 1.0f));
            }
        }

        private VisualElement m_Container;

        public GridBackground()
        {
            pickingMode = PickingMode.Ignore;

            this.StretchToParentSize();
        }

        private Vector3 Clip(Rect clipRect, Vector3 _in)
        {
            if (_in.x < clipRect.xMin)
                _in.x = clipRect.xMin;
            if (_in.x > clipRect.xMax)
                _in.x = clipRect.xMax;

            if (_in.y < clipRect.yMin)
                _in.y = clipRect.yMin;
            if (_in.y > clipRect.yMax)
                _in.y = clipRect.yMax;

            return _in;
        }

        protected override void OnStyleResolved(ICustomStyle elementStyle)
        {
            base.OnStyleResolved(elementStyle);
            elementStyle.ApplyCustomProperty(k_SpacingProperty, ref m_Spacing);
            elementStyle.ApplyCustomProperty(k_ThickLinesProperty, ref m_ThickLines);
            elementStyle.ApplyCustomProperty(k_ThickLineColorProperty, ref m_ThickLineColor);
            elementStyle.ApplyCustomProperty(k_LineColorProperty, ref m_LineColor);
            elementStyle.ApplyCustomProperty(k_GridBackgroundColorProperty, ref m_GridBackgroundColor);
        }

        public override void DoRepaint()
        {
            VisualElement target = parent;

            var graphView = target as GraphView;
            if (graphView == null)
            {
                throw new InvalidOperationException("GridBackground can only be added to a GraphView");
            }
            m_Container = graphView.contentViewContainer;
            Rect clientRect = graphView.layout;

            // Since we're always stretch to parent size, we will use (0,0) as (x,y) coordinates
            clientRect.x = 0;
            clientRect.y = 0;

            var containerScale = new Vector3(m_Container.transform.matrix.GetColumn(0).magnitude,
                    m_Container.transform.matrix.GetColumn(1).magnitude,
                    m_Container.transform.matrix.GetColumn(2).magnitude);
            var containerTranslation = m_Container.transform.matrix.GetColumn(3);
            var containerPosition = m_Container.layout;

            // background
            HandleUtility.ApplyWireMaterial();

            GL.Begin(GL.QUADS);
            GL.Color(gridBackgroundColor);
            GL.Vertex(new Vector3(clientRect.x, clientRect.y));
            GL.Vertex(new Vector3(clientRect.xMax, clientRect.y));
            GL.Vertex(new Vector3(clientRect.xMax, clientRect.yMax));
            GL.Vertex(new Vector3(clientRect.x, clientRect.yMax));
            GL.End();

            // vertical lines
            Vector3 from = new Vector3(clientRect.x, clientRect.y, 0.0f);
            Vector3 to = new Vector3(clientRect.x, clientRect.height, 0.0f);

            var tx = Matrix4x4.TRS(containerTranslation, Quaternion.identity, Vector3.one);

            from = tx.MultiplyPoint(from);
            to = tx.MultiplyPoint(to);

            from.x += (containerPosition.x * containerScale.x);
            from.y += (containerPosition.y * containerScale.y);
            to.x += (containerPosition.x * containerScale.x);
            to.y += (containerPosition.y * containerScale.y);

            Handles.DrawWireDisc(from, new Vector3(0.0f, 0.0f, -1.0f), 6f);

            float thickGridLineX = from.x;
            float thickGridLineY = from.y;

            // Update from/to to start at beginning of clientRect
            from.x = (from.x % (spacing * (containerScale.x)) - (spacing * (containerScale.x)));
            to.x = from.x;

            from.y = clientRect.y;
            to.y = clientRect.y + clientRect.height;

            while (from.x < clientRect.width)
            {
                from.x += spacing * containerScale.x;
                to.x += spacing * containerScale.x;

                GL.Begin(GL.LINES);
                GL.Color(lineColor);
                GL.Vertex(Clip(clientRect, from));
                GL.Vertex(Clip(clientRect, to));
                GL.End();
            }

            float thickLineSpacing = (spacing * thickLines);
            from.x = to.x = (thickGridLineX % (thickLineSpacing * (containerScale.x)) - (thickLineSpacing * (containerScale.x)));

            while (from.x < clientRect.width + thickLineSpacing)
            {
                GL.Begin(GL.LINES);
                GL.Color(thickLineColor);
                GL.Vertex(Clip(clientRect, from));
                GL.Vertex(Clip(clientRect, to));
                GL.End();

                from.x += (spacing * containerScale.x * thickLines);
                to.x += (spacing * containerScale.x * thickLines);
            }

            // horizontal lines
            from = new Vector3(clientRect.x, clientRect.y, 0.0f);
            to = new Vector3(clientRect.x + clientRect.width, clientRect.y, 0.0f);

            from.x += (containerPosition.x * containerScale.x);
            from.y += (containerPosition.y * containerScale.y);
            to.x += (containerPosition.x * containerScale.x);
            to.y += (containerPosition.y * containerScale.y);

            from = tx.MultiplyPoint(from);
            to = tx.MultiplyPoint(to);

            from.y = to.y = (from.y % (spacing * (containerScale.y)) - (spacing * (containerScale.y)));
            from.x = clientRect.x;
            to.x = clientRect.width;

            while (from.y < clientRect.height)
            {
                from.y += spacing * containerScale.y;
                to.y += spacing * containerScale.y;

                GL.Begin(GL.LINES);
                GL.Color(lineColor);
                GL.Vertex(Clip(clientRect, from));
                GL.Vertex(Clip(clientRect, to));
                GL.End();
            }

            thickLineSpacing = spacing * thickLines;
            from.y = to.y = (thickGridLineY % (thickLineSpacing * (containerScale.y)) - (thickLineSpacing * (containerScale.y)));

            while (from.y < clientRect.height + thickLineSpacing)
            {
                GL.Begin(GL.LINES);
                GL.Color(thickLineColor);
                GL.Vertex(Clip(clientRect, from));
                GL.Vertex(Clip(clientRect, to));
                GL.End();

                from.y += spacing * containerScale.y * thickLines;
                to.y += spacing * containerScale.y * thickLines;
            }
        }
    }
}
