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 *    The ASF licenses this file to You under the Apache License, Version 2.0
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 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
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package org.apache.poi.sl.draw.geom;

import static org.apache.poi.sl.draw.geom.Formula.OOXML_DEGREE;

import java.awt.geom.Arc2D;
import java.awt.geom.Path2D;
import java.awt.geom.Point2D;

import org.apache.poi.sl.draw.binding.CTPath2DArcTo;

ArcTo command within a shape path in DrawingML: <arcTo wR="wr" hR="hr" stAng="stAng" swAng="swAng"/>
 Where wr and wh are the height and width radiuses of the supposed circle being used to draw the arc. This gives the circle a total height of (2 * hR) and a total width of (2 * wR) stAng is the start angle and swAng is the swing angle /**
 * ArcTo command within a shape path in DrawingML:
 * {@code &lt;arcTo wR="wr" hR="hr" stAng="stAng" swAng="swAng"/&gt;}<p>
 *
 * Where {@code wr} and {@code wh} are the height and width radiuses
 * of the supposed circle being used to draw the arc.  This gives the circle
 * a total height of (2 * hR)  and a total width of (2 * wR)
 *
 * stAng is the {@code start} angle and {@code swAng} is the swing angle
 */
public class ArcToCommand implements PathCommand {
    private String hr, wr, stAng, swAng;

    ArcToCommand(CTPath2DArcTo arc){
        hr = arc.getHR();
        wr = arc.getWR();
        stAng = arc.getStAng();
        swAng = arc.getSwAng();
    }

    @Override
    public void execute(Path2D.Double path, Context ctx){
        double rx = ctx.getValue(wr);
        double ry = ctx.getValue(hr);
        double ooStart = ctx.getValue(stAng) / OOXML_DEGREE;
        double ooExtent = ctx.getValue(swAng) / OOXML_DEGREE;

        // skew the angles for AWT output
        double awtStart = convertOoxml2AwtAngle(ooStart, rx, ry);
        double awtSweep = convertOoxml2AwtAngle(ooStart+ooExtent, rx, ry)-awtStart;

        // calculate the inverse angle - taken from the (reversed) preset definition
        double radStart = Math.toRadians(ooStart);
        double invStart = Math.atan2(rx * Math.sin(radStart), ry * Math.cos(radStart));

        Point2D pt = path.getCurrentPoint();
        // calculate top/left corner
        double x0 = pt.getX() - rx * Math.cos(invStart) - rx;
        double y0 = pt.getY() - ry * Math.sin(invStart) - ry;

        Arc2D arc = new Arc2D.Double(x0, y0, 2 * rx, 2 * ry, awtStart, awtSweep, Arc2D.OPEN);
		path.append(arc, true);
    }

    
Arc2D angles are skewed, OOXML aren't ... so we need to unskew them

Furthermore ooxml angle starts at the X-axis and increases clock-wise,
where as Arc2D api states
"45 degrees always falls on the line from the center of the ellipse to
the upper right corner of the framing rectangle"
so we need to reverse it
AWT:                      OOXML:
           |90/-270                     |270/-90 (16200000)
           |                            |
+/-180-----------0           +/-180-----------0
           |               (10800000)   |
           |270/-90                     |90/-270 (5400000)

Params:
ooAngle – the angle in OOXML units
width – the half width of the bounding box
height – the half height of the bounding box
See Also:
unskew angle
Returns:
the angle in degrees/**
     * Arc2D angles are skewed, OOXML aren't ... so we need to unskew them<p>
     *
     * Furthermore ooxml angle starts at the X-axis and increases clock-wise,
     * where as Arc2D api states
     * "45 degrees always falls on the line from the center of the ellipse to
     * the upper right corner of the framing rectangle"
     * so we need to reverse it
     *
     * <pre>
     * AWT:                      OOXML:
     *            |90/-270                     |270/-90 (16200000)
     *            |                            |
     * +/-180-----------0           +/-180-----------0
     *            |               (10800000)   |
     *            |270/-90                     |90/-270 (5400000)
     * </pre>
     *
     * @param ooAngle the angle in OOXML units
     * @param width the half width of the bounding box
     * @param height the half height of the bounding box
     *
     * @return the angle in degrees
     *
     * @see <a href="http://www.onlinemathe.de/forum/Problem-bei-Winkelberechnungen-einer-Ellipse">unskew angle</a>
     **/
    private double convertOoxml2AwtAngle(double ooAngle, double width, double height) {
        double aspect = (height / width);
        // reverse angle for awt
        double awtAngle = -ooAngle;
        // normalize angle, in case it's < -360 or > 360 degrees
        double awtAngle2 = awtAngle%360.;
        double awtAngle3 = awtAngle-awtAngle2;
        // because of tangens nature, the values left [90°-270°] and right [270°-90°] of the axis are mirrored/the same
        // and the result of atan2 need to be justified
        switch ((int)(awtAngle2 / 90)) {
            case -3:
                // -270 to -360
                awtAngle3 -= 360;
                awtAngle2 += 360;
                break;
            case -2:
            case -1:
                // -90 to -270
                awtAngle3 -= 180;
                awtAngle2 += 180;
                break;
            default:
            case 0:
                // -90 to 90
                break;
            case 2:
            case 1:
                // 90 to 270
                awtAngle3 += 180;
                awtAngle2 -= 180;
                break;
            case 3:
                // 270 to 360
                awtAngle3 += 360;
                awtAngle2 -= 360;
                break;
        }

        // skew
        awtAngle = Math.toDegrees(Math.atan2(Math.tan(Math.toRadians(awtAngle2)), aspect)) + awtAngle3;
        return awtAngle;
    }
}