using System;
using UnityEngine;

public class Drawing
{
    //****************************************************************************************************
    //  static function DrawLine(rect : Rect) : void
    //  static function DrawLine(rect : Rect, color : Color) : void
    //  static function DrawLine(rect : Rect, width : float) : void
    //  static function DrawLine(rect : Rect, color : Color, width : float) : void
    //  static function DrawLine(Vector2 pointA, Vector2 pointB) : void
    //  static function DrawLine(Vector2 pointA, Vector2 pointB, color : Color) : void
    //  static function DrawLine(Vector2 pointA, Vector2 pointB, width : float) : void
    //  static function DrawLine(Vector2 pointA, Vector2 pointB, color : Color, width : float) : void
    //  
    //  Draws a GUI line on the screen.
    //  
    //  DrawLine makes up for the severe lack of 2D line rendering in the Unity runtime GUI system.
    //  This function works by drawing a 1x1 texture filled with a color, which is then scaled
    //   and rotated by altering the GUI matrix.  The matrix is restored afterwards.
    //****************************************************************************************************

    public static Texture2D lineTex;

    public static void DrawLine(Rect rect) { DrawLine(rect, GUI.contentColor, 1.0f); }
    public static void DrawLine(Rect rect, Color color) { DrawLine(rect, color, 1.0f); }
    public static void DrawLine(Rect rect, float width) { DrawLine(rect, GUI.contentColor, width); }
    public static void DrawLine(Rect rect, Color color, float width) { DrawLine(new Vector2(rect.x, rect.y), new Vector2(rect.x + rect.width, rect.y + rect.height), color, width); }
    public static void DrawLine(Vector2 pointA, Vector2 pointB) { DrawLine(pointA, pointB, GUI.contentColor, 1.0f); }
    public static void DrawLine(Vector2 pointA, Vector2 pointB, Color color) { DrawLine(pointA, pointB, color, 1.0f); }
    public static void DrawLine(Vector2 pointA, Vector2 pointB, float width) { DrawLine(pointA, pointB, GUI.contentColor, width); }
    public static void DrawLine(Vector2 pointA, Vector2 pointB, Color color, float width)
    {
        // Save the current GUI matrix, since we're going to make changes to it.
        Matrix4x4 matrix = GUI.matrix;

        // Generate a single pixel texture if it doesn't exist
        if (!lineTex) { lineTex = new Texture2D(1, 1); }
        
        // Store current GUI color, so we can switch it back later,
        // and set the GUI color to the color parameter
        Color savedColor = GUI.color;
        GUI.color = color;

        // Determine the angle of the line.
        float angle = Vector3.Angle(pointB - pointA, Vector2.right);

        // Vector3.Angle always returns a positive number.
        // If pointB is above pointA, then angle needs to be negative.
        if (pointA.y > pointB.y) { angle = -angle; }

        // Use ScaleAroundPivot to adjust the size of the line.
        // We could do this when we draw the texture, but by scaling it here we can use
        //  non-integer values for the width and length (such as sub 1 pixel widths).
        // Note that the pivot point is at +.5 from pointA.y, this is so that the width of the line
        //  is centered on the origin at pointA.
        GUIUtility.ScaleAroundPivot(new Vector2((pointB - pointA).magnitude, width), new Vector2(pointA.x, pointA.y + 0.5f));

        // Set the rotation for the line.
        //  The angle was calculated with pointA as the origin.
        GUIUtility.RotateAroundPivot(angle, pointA);

        // Finally, draw the actual line.
        // We're really only drawing a 1x1 texture from pointA.
        // The matrix operations done with ScaleAroundPivot and RotateAroundPivot will make this
        //  render with the proper width, length, and angle.
        GUI.DrawTexture(new Rect(pointA.x, pointA.y, 1, 1), lineTex);

        // We're done.  Restore the GUI matrix and GUI color to whatever they were before.
        GUI.matrix = matrix;
        GUI.color = savedColor;
    }

    public static void DrawPoint(Vector2 point, float size) { DrawPoint(point, GUI.contentColor, size); }
    public static void DrawPoint(Vector2 point, Color color, float size)
    {
        var offset = new Vector2(size, 0);
        DrawLine(point - offset, point + offset, color, size * 2);
    }
}