private getSvgPathForBackwardLink()

in src/sankeyDiagram.ts [2083:2181]
65 lines of code
3 McCabe index (conditional complexity)

    private getSvgPathForBackwardLink(link: SankeyDiagramLink) {
        let pathParams: string = "";
        const distanceBetweenLinks: number = 3;
        const distanceFromNodeToLinks: number = 5;

        let fixedLinkHeight = link.height - distanceBetweenLinks;
        let linkKneeSize: number = link.height;

        let x0: number,
            x1: number,
            xi: (t: number) => number,
            x2: number,
            x3: number,
            y0: number,
            y1: number;

        if (link.destination.x < link.source.x) {
            x0 = link.source.x;
            x1 = link.destination.x + link.destination.width;
        } else {
            x0 = link.source.x + link.source.width;
            x1 = link.destination.x;
        }

        // drawing area as combination of 4 lines in one path element of svg to fill this area with required color

        // upper border of link
        xi = d3.interpolateNumber(x0, x1);
        x2 = xi(this.curvatureOfLinks);
        x3 = xi(1 - this.curvatureOfLinks);
        y0 = link.source.y - (link.height + SankeyDiagram.NodeAndBackwardLinkDistance) + link.dySource + link.height / SankeyDiagram.MiddleFactor - link.height / 2;
        y1 = link.destination.y - (link.height + SankeyDiagram.NodeAndBackwardLinkDistance) + link.dyDestination + link.height / SankeyDiagram.MiddleFactor - link.height / 2;

        pathParams += ` M ${x0} ${y0} C ${x2} ${y0}, ${x3} ${y1}, ${x1} ${y1}`;

        pathParams += `L ${link.destination.x + link.destination.width} ${y1}`;

        pathParams +=
            `C ${link.destination.x + link.destination.width} ${y1}, ` +
            `${link.destination.x + link.destination.width + linkKneeSize} ${y1}, ` +
            `${link.destination.x + link.destination.width + linkKneeSize} ${y1 + linkKneeSize}`;

        // right border of link
        y0 = link.destination.y - (link.height + SankeyDiagram.NodeAndBackwardLinkDistance) + link.dyDestination + link.height / SankeyDiagram.MiddleFactor + link.height / 2;
        y1 = link.destination.y - (link.height + SankeyDiagram.NodeAndBackwardLinkDistance) + link.dyDestination + link.height / SankeyDiagram.MiddleFactor - link.height / 2;

        let limit = y1 + link.destination.width + (fixedLinkHeight) * 2 - link.destination.width;
        if (limit > link.destination.y + fixedLinkHeight - link.destination.width) {
            limit = link.destination.y + fixedLinkHeight - link.destination.width;
        }

        pathParams +=
            `C ${link.destination.x + link.destination.width + linkKneeSize} ${link.destination.y + fixedLinkHeight - linkKneeSize},` +
            ` ${link.destination.x + link.destination.width + linkKneeSize} ${link.destination.y + fixedLinkHeight} ,` +
            ` ${link.destination.x + link.destination.width + distanceFromNodeToLinks} ${link.destination.y + fixedLinkHeight}`;

        pathParams += `L ${link.destination.x + link.destination.width} ${link.destination.y + fixedLinkHeight}`;

        pathParams += `L ${link.destination.x + link.destination.width} ${link.destination.y}`;

        pathParams += `L ${link.destination.x + link.destination.width + distanceFromNodeToLinks} ${link.destination.y}`;

        pathParams += `L ${link.destination.x + link.destination.width + distanceFromNodeToLinks} ${link.destination.y - SankeyDiagram.NodeAndBackwardLinkDistance}`;

        // bottom border of link
        xi = d3.interpolateNumber(x0, x1);
        x2 = xi(this.curvatureOfLinks);
        x3 = xi(1 - this.curvatureOfLinks);
        y0 = link.source.y - (link.height + SankeyDiagram.NodeAndBackwardLinkDistance) + link.dySource + link.height / SankeyDiagram.MiddleFactor + link.height / 2;
        y1 = link.destination.y - (link.height + SankeyDiagram.NodeAndBackwardLinkDistance) + link.dyDestination + link.height / SankeyDiagram.MiddleFactor + link.height / 2;

        pathParams += ` L ${x1 + distanceFromNodeToLinks} ${y1} C ${x2} ${y1}, ${x3} ${y0}, ${x0 - distanceFromNodeToLinks} ${y0}`;

        pathParams += `L ${link.source.x - distanceFromNodeToLinks} ${y0}`;

        pathParams += `L ${link.source.x - distanceFromNodeToLinks} ${y0 + SankeyDiagram.NodeAndBackwardLinkDistance}`;

        pathParams += `L ${link.source.x} ${y0 + SankeyDiagram.NodeAndBackwardLinkDistance}`;

        pathParams += `L ${link.source.x} ${y0 + SankeyDiagram.NodeAndBackwardLinkDistance + fixedLinkHeight}`;

        pathParams += `L ${link.source.x - distanceFromNodeToLinks} ${y0 + SankeyDiagram.NodeAndBackwardLinkDistance + fixedLinkHeight}`;

        pathParams +=
            `C ${link.source.x - distanceFromNodeToLinks} ${y0 + SankeyDiagram.NodeAndBackwardLinkDistance + fixedLinkHeight}, ` +
            `${link.source.x - distanceFromNodeToLinks - linkKneeSize} ${y0 + SankeyDiagram.NodeAndBackwardLinkDistance + link.height}, ` +
            `${link.source.x - distanceFromNodeToLinks - linkKneeSize} ${y0 + SankeyDiagram.NodeAndBackwardLinkDistance + link.height - linkKneeSize}`;

        // left border of link
        y1 = link.source.y - (link.height + SankeyDiagram.NodeAndBackwardLinkDistance) + link.dySource + link.height / SankeyDiagram.MiddleFactor - link.height / 2;

        // tslint:disable-next-line: no-suspicious-comment
        pathParams += `C ${link.source.x - distanceFromNodeToLinks - linkKneeSize} ${y1 + linkKneeSize}, ${link.source.x - distanceFromNodeToLinks - linkKneeSize} ${y1}, ${link.source.x} ${y1}`; // TODO change to C

        // close path to get closed area
        pathParams += ` Z`;

        return pathParams;
    }