from .elements import DrawingElement, DrawingParentElement


class DrawingDef(DrawingParentElement):
    ''' Parent class of SVG nodes that must be direct children of <defs> '''
    @property
    def id(self):
        return self.args.get('id', None)
    @id.setter
    def id(self, newId):
        self.args['id'] = newId
    def getSvgDefs(self):
        return (self,)
    def writeSvgDefs(self, idGen, isDuplicate, outputFile):
        DrawingElement.writeSvgDefs(idGen, isDuplicate, outputFile)

class DrawingDefSub(DrawingParentElement):
    ''' Parent class of SVG nodes that are meant to be descendants of a Def '''
    pass

class RadialGradient(DrawingDef):
    ''' A radial gradient to use as a fill or other color

        Has <stop> nodes as children. '''
    TAG_NAME = 'radialGradient'
    def __init__(self, cx, cy, r, gradientUnits='userSpaceOnUse', fy=None, **kwargs):
        yShift = 0
        if gradientUnits != 'userSpaceOnUse':
            yShift = 1
        try: cy = yShift - cy
        except TypeError: pass
        try: fy = yShift - fy
        except TypeError: pass
        super().__init__(cx=cx, cy=cy, r=r, gradientUnits=gradientUnits,
                         fy=fy, **kwargs)
    def addStop(self, offset, color, opacity=None, **kwargs):
        stop = GradientStop(offset=offset, stop_color=color,
                            stop_opacity=opacity, **kwargs)
        self.append(stop)

class GradientStop(DrawingDefSub):
    ''' A control point for a radial or linear gradient '''
    TAG_NAME = 'stop'
    hasContent = False