Toolkit - Dynamic Linking

This post if part of a series about the File System Toolkit - a custom content delivery API for SDL Tridion.

In this post I describe the dynamic link resolving logic as part of the Link Factory.

There are three types of links: Component, Page and Binary links. Each of these links can be resolved using the Link Factory.

Component Link

Resolving a Component link implies finding the URL of the Page the target Component appears on. Using the current Toolkit models, it is quite straight forward to retrieve the URL, because the link information is contained within the Component model.

However, there might be several potential links available when performing Component link resolving. Namely, there can be several cases possible:

• there is no linking information available in the Component model -- this means the link cannot be resolved (i.e. there is no Page published that contains the given Component);
• there is exactly one Page available that contains the Component -- this means we retrieve the Page URL and return it as the link;
• there are several potential Pages available that contain the Component -- in this case we need to pick one page only according to the following algorithm: 
• take the Page that contains the Component with the highest link priority. If there are more than one pages possible, then go to next step;
• take the Page relatively closest to the Page where the link is displayed on. The relative distance is the number of folders one page is away from the other. If there are more than one pages possible, then go to next step;
• take the page that was published the latest;

You might notice that in order for the algorithm to work, we must provide the current Page -- this is the page where the link is displayed on. Without this page, we cannot identify accurately the relatively closest potential page.

public Link getComponentLink(TcmUri pageUri, TcmUri componentUri) {
    LinkImpl result = new LinkImpl();
    ComponentMeta componentMeta = modelFactory.getModel(componentUri);
    List<LinkInfo> linkInfos = componentMeta.getLinkInfos();
    if (linkInfos == null || linkInfos.size() == 0) {
        return result;
    }

    String[] urlParts;
    PageMeta pageMeta = modelFactory.getModel(pageUri);
    if (pageMeta == null) {
        urlParts = new String[0];
    } else {
        urlParts = pageMeta.getUrl().split("/");
    }

    int pageId = pageUri.getItemId();
    int maxPriority = 1;
    int minDistance = Integer.MAX_VALUE;
    List<LinkInfo> filteredInfos = new ArrayList<>();

    for (LinkInfo linkInfo : linkInfos) {
        if (linkInfo.getPage() != pageId) {
            int distance = getDistance(urlParts, linkInfo.getUrl());
            int priority = linkInfo.getPriority();
            if (priority > maxPriority) {
                maxPriority = priority;
                minDistance = distance;
                filteredInfos.clear();
            } else if (distance < minDistance) {
                minDistance = distance;
                filteredInfos.clear();
            }
            if (priority == maxPriority && distance == minDistance) {
                filteredInfos.add(linkInfo);
            }
        }
    }

    LinkInfo linkInfo = getLastPublished(filteredInfos);
    if (linkInfo != null) {
        result.setResolved(true);
        result.setUrl(linkInfo.getUrl());
        result.setTargetUri(new TcmUri(componentUri.getPublicationId(),
                linkInfo.getPage(), ItemTypes.PAGE));
    }

    return result;
}

Below are the two helper methods getDistance between two paths and getLastPublished date out of a collection of Pages.

private int getDistance(String[] parts, String url) {
    int result = 0;

    String[] parts2 = url.split("/");
    int n = Math.min(parts.length, parts2.length) - 1;
    int i = 0;
    boolean loop = true;

    for (; i < n && loop; i++) {
        if (!parts[i].equals(parts2[i])) {
            loop = false;
            i--;
        }
    }

    result += parts.length - i - 1;
    result += parts2.length - i - 1;

    return result;
}

private LinkInfo getLastPublished(List<LinkInfo> linkInfos) {
    switch (linkInfos.size()) {
        case 0:
            return null;

        case 1:
            return linkInfos.get(0);

        default:
            long maxPublished = 0;
            LinkInfo result = linkInfos.get(0);

            for (LinkInfo linkInfo : linkInfos) {
                TcmUri metaUri = new TcmUri(linkInfo.getPublication(), linkInfo.getPage(), ItemTypes.PAGE);
                PageMeta pageMeta = modelFactory.getModel(metaUri);
                if (pageMeta != null) {
                    long lastPublished = pageMeta.getLastPublished().getTime();
                    if (lastPublished > maxPublished) {
                        maxPublished = lastPublished;
                        result = linkInfo;
                    }
                }
            }

            return result;
    }
}

Page Links

Resolving a page link implies retrieving the Page model by TcmUri and returning its URL.

public Link getPageLink(TcmUri pageUri) {
    LinkImpl result = new LinkImpl();
    PageMeta pageMeta = modelFactory.getModel(pageUri);
    if (pageMeta == null) {
        return result;
    }

    result.setResolved(true);
    result.setUrl(pageMeta.getUrl());
    result.setTargetUri(pageMeta.getTcmUri());

    return result;
}

Binary Links

Resolving a binary link implies retrieving the Multimedia Component model and retrieving its link information URL. Binaries can be published using different variants, so we can either identify a link by its variant or, in the absence of a variant, simply serve the first link available.

public Link getBinaryLink(TcmUri binaryUri, String variant) {
    LinkImpl result = new LinkImpl();
    ComponentMeta binaryMeta = modelFactory.getModel(binaryUri);
    if (binaryMeta == null) {
        return result;
    }

    if (!binaryMeta.isMultimedia()) {
        return result;
    }

    List<LinkInfo> linkInfos = binaryMeta.getLinkInfos();
    if (linkInfos == null || linkInfos.size() == 0) {
        return result;
    }

    variant = variant == null ? "" : variant;

    for (LinkInfo linkInfo : linkInfos) {
        String linkVariant = linkInfo.getVariant();
        linkVariant = linkVariant == null ? "" : linkVariant;
        if (variant.equals(linkVariant)) {
            result.setResolved(true);
            result.setUrl(linkInfo.getUrl());
            result.setTargetUri(binaryUri);
            break;
        }
    }

    return result;
}