/*

   Copyright 2001,2003  The Apache Software Foundation 

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       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
   limitations under the License.

 */
package org.apache.batik.svggen;

import java.util.Stack;

import org.apache.batik.ext.awt.g2d.GraphicContext;
import org.apache.batik.ext.awt.g2d.TransformStackElement;
import org.apache.batik.ext.awt.g2d.TransformType;

/**
 * Utility class that converts a GraphicContext transform stack
 * into an SVG transform attribute.
 *
 * @author <a href="mailto:vincent.hardy@eng.sun.com">Vincent Hardy</a>
 * @author <a href="mailto:paul_evenblij@compuware.com">Paul Evenblij</a>
 * @version $Id: SVGTransform.java,v 1.9 2004/08/18 07:15:09 vhardy Exp $
 */
public class SVGTransform extends AbstractSVGConverter{
    /**
     * Ratio used to convert radians to degrees
     */
    private static final double radiansToDegrees = 180.0 / Math.PI;

    /**
     * @param generatorContext used by converter to handle precision
     *        or to create elements.
     */
    public SVGTransform(final SVGGeneratorContext generatorContext) {
        super(generatorContext);
    }

    /**
     * Converts part or all of the input GraphicContext into
     * a set of attribute/value pairs and related definitions
     *
     * @param gc GraphicContext to be converted
     * @return descriptor of the attributes required to represent
     *         some or all of the GraphicContext state, along
     *         with the related definitions
     * @see org.apache.batik.svggen.SVGDescriptor
     */
    public SVGDescriptor toSVG(final GraphicContext gc){
        return new SVGTransformDescriptor(this.toSVGTransform(gc));
    }

    /**
     * @param gc GraphicContext whose transform stack should be converted
     *           to SVG.
     * @return the value of an SVG attribute equivalent to the input
     *         GraphicContext's transform stack.
     */
    public final String toSVGTransform(final GraphicContext gc){
        return this.toSVGTransform(gc.getTransformStack());
    }

    /**
     * This method tries to collapse the transform stack into an SVG
     * string as compact as possible while still conveying the semantic
     * of the stack. Successive stack elements of the same kind (e.g., two
     * successive transforms or scales) are collapsed into a single element.
     *
     * @param transformStack sequence of transform that should
     *        be converted to an SVG transform attribute equivalent
     */
    public final String toSVGTransform(final TransformStackElement transformStack[]){
        final StringBuffer transformStackBuffer = new StringBuffer();
        final int nTransforms = transformStack.length;
        //
        // Append transforms in the presentation stack
        //
        final Stack presentation = new Stack() {
            /**
             * Adapted push implementation
             */
            public Object push(Object o) {
                Object element;
                if(((TransformStackElement)o).isIdentity()) {
                    // identity transform: don't push,
                    // and try to return top of stack
                    element = this.pop();
                } else {
                    // non-identity: push,
                    // and return null
                    super.push(o);
                    element = null;
                }
                return element;
            }
            
            /**
             * Adapted pop implementation
             */
            public Object pop() {
                Object element = null;
                if(!super.empty()) {
                    element = super.pop();
                }
                return element;
            }
        };
        boolean canConcatenate = false;
        int i = 0, j = 0, next = 0;
        TransformStackElement element = null;

        // We keep a separate 'presentation' stack, which contains
        // all concatenated elements. The top of this stack is the
        // element we try to concatenate onto. If this element
        // becomes an identity transform, we discard it and look at
        // the element underneath it instead.
        // The presentation stack is guaranteed not to contain
        // identity transforms.

        while(i < nTransforms) {

            // If we do not have an element to concatenate onto,
            // we grab one here.
            next = i;
            if(element == null) {
                element = (TransformStackElement) transformStack[i].clone();
                next++;
            }

            // try to concatenate as much as possible
            canConcatenate = true;
            for(j = next; j < nTransforms; j++) {
                canConcatenate = element.concatenate(transformStack[j]);
                if(!canConcatenate)
                    break;
            }
            // loop variable assertion: 
            // If "i" does not increment during this iteration, it is guaranteed
            // to do so in the next, since "i" can only keep the same value as a
            // result of "element" having a non-null value on starting this
            // iteration, which can only be the case if it was popped from the
            // stack during the previous one. The stack does not contain
            // identities, and since "i" has not grown, "element" has remained
            // unchanged and will be pushed onto the stack again. "element" will
            // then become null, so "i" will eventually increment.
            i = j;
 
            // Get rid of identity transforms within the stack.
            // If an identity is pushed, it is immediately removed, and
            // the current top of stack will be returned to concatenate onto.
            // Otherwise, null will be returned.
            element = (TransformStackElement) presentation.push(element);
        }

        // Push back teh last element popped, if not null
        if (element != null){
            presentation.push(element);
        }
 
        //
        // Transform presentation stack to SVG
        //
        final int nPresentations = presentation.size();
        
        for(i = 0; i < nPresentations; i++) {
            transformStackBuffer.append(this.convertTransform((TransformStackElement) presentation.elementAt(i)));
            transformStackBuffer.append(SPACE);
        }

        final String transformValue = transformStackBuffer.toString().trim();
        return transformValue;
    }

    /**
     * Converts an AffineTransform to an SVG transform string
     */
    final String convertTransform(final TransformStackElement transformElement){
        final StringBuffer transformString = new StringBuffer();
        final double transformParameters[] = transformElement.getTransformParameters();
        switch(transformElement.getType().toInt()){
        case TransformType.TRANSFORM_TRANSLATE:
            if(!transformElement.isIdentity()) {
                transformString.append(TRANSFORM_TRANSLATE);
                transformString.append(OPEN_PARENTHESIS);
                transformString.append(this.doubleString(transformParameters[0]));
                transformString.append(COMMA);
                transformString.append(this.doubleString(transformParameters[1]));
                transformString.append(CLOSE_PARENTHESIS);
            }
            break;
        case TransformType.TRANSFORM_ROTATE:
            if(!transformElement.isIdentity()) {
                transformString.append(TRANSFORM_ROTATE);
                transformString.append(OPEN_PARENTHESIS);
                transformString.append(this.doubleString(radiansToDegrees*transformParameters[0]));
                transformString.append(CLOSE_PARENTHESIS);
            }
            break;
        case TransformType.TRANSFORM_SCALE:
            if(!transformElement.isIdentity()) {
                transformString.append(TRANSFORM_SCALE);
                transformString.append(OPEN_PARENTHESIS);
                transformString.append(this.doubleString(transformParameters[0]));
                transformString.append(COMMA);
                transformString.append(this.doubleString(transformParameters[1]));
                transformString.append(CLOSE_PARENTHESIS);
            }
            break;
        case TransformType.TRANSFORM_SHEAR:
            if(!transformElement.isIdentity()) {
                transformString.append(TRANSFORM_MATRIX);
                transformString.append(OPEN_PARENTHESIS);
                transformString.append(1);
                transformString.append(COMMA);
                transformString.append(this.doubleString(transformParameters[1]));
                transformString.append(COMMA);
                transformString.append(this.doubleString(transformParameters[0]));
                transformString.append(COMMA);
                transformString.append(1);
                transformString.append(COMMA);
                transformString.append(0);
                transformString.append(COMMA);
                transformString.append(0);
                transformString.append(CLOSE_PARENTHESIS);
            }
            break;
        case TransformType.TRANSFORM_GENERAL:
            if(!transformElement.isIdentity()) {
                transformString.append(TRANSFORM_MATRIX);
                transformString.append(OPEN_PARENTHESIS);
                transformString.append(this.doubleString(transformParameters[0]));
                transformString.append(COMMA);
                transformString.append(this.doubleString(transformParameters[1]));
                transformString.append(COMMA);
                transformString.append(this.doubleString(transformParameters[2]));
                transformString.append(COMMA);
                transformString.append(this.doubleString(transformParameters[3]));
                transformString.append(COMMA);
                transformString.append(this.doubleString(transformParameters[4]));
                transformString.append(COMMA);
                transformString.append(this.doubleString(transformParameters[5]));
                transformString.append(CLOSE_PARENTHESIS);
            }
            break;
        default:
            // This should never happen. If it does, there is a
            // serious error.
            throw new Error();
        }

        return transformString.toString();
    }
}
