1 files changed, 80 insertions, 0 deletions
diff --git a/lib/utils/navigation.js b/lib/utils/navigation.js
new file mode 100644
index 0000000..21666ad
--- /dev/null
+++ b/lib/utils/navigation.js
@@ -0,0 +1,80 @@
+var _ = require('lodash');
+
+// Cleans up an article/chapter object
+// remove 'articles' attributes
+function clean(obj) {
+    return obj && _.omit(obj, ['articles']);
+}
+
+function flattenChapters(chapters) {
+    return _.reduce(chapters, function(accu, chapter) {
+        return accu.concat([clean(chapter)].concat(flattenChapters(chapter.articles)));
+    }, []);
+}
+
+// Returns from a summary a map of
+/*
+    {
+        "file/path.md": {
+            prev: ...,
+            next: ...,
+        },
+        ...
+    }
+*/
+function navigation(summary, files) {
+    // Support single files as well as list
+    files = _.isArray(files) ? files : (_.isString(files) ? [files] : null);
+
+    // List of all navNodes
+    // Flatten chapters, then add in default README node if needed etc ...
+    var navNodes = flattenChapters(summary.chapters);
+
+    // Mapping of prev/next for a give path
+    var mapping = _.chain(navNodes)
+    .map(function(current, i) {
+        var prev = null, next = null;
+
+        // Skip if no path
+        if(!current.path) return null;
+
+        // Find prev
+        prev = _.chain(navNodes)
+            .slice(0, i)
+            .reverse()
+            .find(function(node) {
+                return node.exists && !node.external;
+            })
+            .value();
+
+        // Find next
+        next = _.chain(navNodes)
+            .slice(i+1)
+            .find(function(node) {
+                return node.exists && !node.external;
+            })
+            .value();
+
+
+        return [current.path, {
+            title: current.title,
+            prev: prev,
+            next: next,
+            level: current.level,
+        }];
+    })
+    .compact()
+    .object()
+    .value();
+
+    // Filter for only files we want
+    if(files) {
+        return _.pick(mapping, files);
+    }
+
+    return mapping;
+}
+
+
+// Exports
+module.exports = navigation;