Simplify .next and .prev for articles

lib/backbone/summary.js

@@ -22,6 +22,8 @@ function TOCArticle(def, parent) {
     // As string indicating the overall position
     // ex: '1.0.0'
     this.level;
+    this._next;
+    this._prev;
 
     // When README has been automatically added
     this.isAutoIntro = def.isAutoIntro;
@@ -103,91 +105,14 @@ TOCArticle.prototype.hasParent = function() {
     return !(this.parent instanceof TOCPart);
 };
 
-// Return true if has a part as parent
-TOCArticle.prototype.hasParentPart = function() {
-    return (this.parent instanceof TOCPart);
-};
-
-// Return first article
-TOCArticle.prototype.first = function() {
-    return _.first(this.articles);
-};
-
-// Return last article
-TOCArticle.prototype.last = function() {
-    var last = _.last(this.articles);
-    if (!last) return null;
-
-    return last.last() || last;
-};
-
-// Return a sibling (next or prev) in the parent
-// Without taking in consideration children/parent
-TOCArticle.prototype.sibling = function(direction) {
-    var parentsArticles = this.parent.articles;
-    var pos = _.findIndex(parentsArticles, this);
-
-    if (parentsArticles[pos + direction]) {
-        return parentsArticles[pos + direction];
-    }
-
-    return null;
-};
-
-// Return a sibling (next or prev)
-// It takes parents.children in consideration
-TOCArticle.prototype._sibling = function(direction) {
-    // Next should go to the first children
-    if (direction > 0 && this.hasChildren()) {
-        return _.first(this.articles);
-    }
-
-    var part;
-    var parentsArticles = this.parent.articles;
-    var pos = _.findIndex(parentsArticles, this);
-
-    // First child and has parent
-    if (pos == 0 && direction < 0) {
-        if (this.hasParent()) {
-            return this.parent;
-        } else if (this.hasParentPart()) {
-            part = this.parent.sibling(-1);
-            return part? part.last() : null;
-        }
-    }
-
-    // Last child and has parent
-    if(pos == (parentsArticles.length - 1) && direction > 0) {
-        if (this.hasParent()) {
-            return this.parent.sibling(1);
-        } else if (this.hasParentPart()) {
-            part = this.parent.sibling(1);
-            return part? part.first() : null;
-        }
-    }
-
-    if (parentsArticles[pos + direction]) {
-        var article = parentsArticles[pos + direction];
-
-        // If goign back, take last children from "brother"
-        if (direction < 0 && article.hasChildren()) {
-            article = _.last(article.articles);
-        }
-
-        return article;
-    }
-
-    return null;
-};
-
 // Return next article in the TOC
 TOCArticle.prototype.next = function() {
-    return this._sibling(1);
+    return this._next;
 };
 
 // Return previous article in the TOC
 TOCArticle.prototype.prev = function() {
-    return this._sibling(-1);
+    return this._prev;
 };
 
 // Map over all articles
@@ -375,10 +300,19 @@ Summary.prototype.count = function() {
 // Update the count and indexing of "level"
 Summary.prototype.update = function() {
     var that = this;
+    var prev = undefined;
 
     that._length = 0;
     that.walk(function(article, level) {
+        // Index level
         article.level = level;
+
+        // Chain articles
+        article._prev = prev;
+        if (prev) prev._next = article;
+
+        prev = article;
+
         that._length += 1;
     });
 };

test/summary.js

@@ -126,7 +126,10 @@ describe('Summary / Table of contents', function() {
                     '* [Hello 6](hello6.md)\n\n\n' +
                     '### Part 2\n\n' +
                     '* [Hello 7](hello7.md)\n' +
-                    '* [Hello 8](hello8.md)\n\n'
+                    '    * [Hello 8](hello8.md)\n\n' +
+                    '### Part 3\n\n' +
+                    '* [Hello 9](hello9.md)\n' +
+                    '* [Hello 10](hello10.md)\n\n'
             })
             .then(function(_book) {
                 book = _book;
@@ -210,19 +213,6 @@ describe('Summary / Table of contents', function() {
             next.path.should.equal('hello6.md');
         });
 
-        it('should return next/prev for a joint <- parts', function() {
-            var article = book.summary.getArticle('hello7.md');
-
-            var prev = article.prev();
-            var next = article.next();
-
-            should(prev).be.ok();
-            should(next).be.ok();
-
-            prev.path.should.equal('hello6.md');
-            next.path.should.equal('hello8.md');
-        });
-
         it('should return next/prev for a joint -> parts', function() {
             var article = book.summary.getArticle('hello6.md');
 
@@ -236,16 +226,42 @@ describe('Summary / Table of contents', function() {
             next.path.should.equal('hello7.md');
         });
 
-        it('should return only prev for last', function() {
+        it('should return next/prev for a joint <- parts', function() {
+            var article = book.summary.getArticle('hello7.md');
+
+            var prev = article.prev();
+            var next = article.next();
+
+            should(prev).be.ok();
+            should(next).be.ok();
+
+            prev.path.should.equal('hello6.md');
+            next.path.should.equal('hello8.md');
+        });
+
+        it('should return next and prev', function() {
             var article = book.summary.getArticle('hello8.md');
 
             var prev = article.prev();
             var next = article.next();
 
+            should(prev).be.ok();
+            should(next).be.ok();
+
+            prev.path.should.equal('hello7.md');
+            next.path.should.equal('hello9.md');
+        });
+
+        it('should return only prev for last', function() {
+            var article = book.summary.getArticle('hello10.md');
+
+            var prev = article.prev();
+            var next = article.next();
+
             should(prev).be.ok();
             should(next).be.not.ok();
 
-            prev.path.should.equal('hello7.md');
+            prev.path.should.equal('hello9.md');
         });
     });
 });