1 files changed, 82 insertions, 0 deletions
diff --git a/lib/modifiers/summary/moveArticle.js b/lib/modifiers/summary/moveArticle.js
new file mode 100644
index 0000000..06d82ca
--- /dev/null
+++ b/lib/modifiers/summary/moveArticle.js
@@ -0,0 +1,82 @@
+var is = require('is');
+var removeArticle = require('./removeArticle');
+var insertArticle = require('./insertArticle');
+
+/**
+    Returns a new summary, with the given article removed from its
+    origin level, and placed at the given target level.
+
+    @param {Summary} summary
+    @param {String|SummaryArticle} origin: level to remove
+    @param {String|SummaryArticle} target: the level where the article will be found
+    @return {Summary}
+*/
+function moveArticle(summary, origin, target) {
+    // Coerce to level
+    var originLevel = is.string(origin)? origin : origin.getLevel();
+    var targetLevel = is.string(target)? target : target.getLevel();
+
+    var article = summary.getByLevel(originLevel);
+
+    // Remove
+    var removed = removeArticle(summary, origin);
+
+    // Adjust targetLevel if removing impacted it
+    targetLevel = arrayToLevel(
+        shiftLevel(levelToArray(originLevel),
+                   levelToArray(targetLevel)));
+    // Re-insert
+    return insertArticle(removed, target, article);
+}
+
+/**
+    @param {Array<Number>} removedLevel
+    @param {Array<Number>} level The level to udpate
+    @return {Array<Number>}
+ */
+function shiftLevel(removedLevel, level) {
+    if (level.length === 0) {
+        // `removedLevel` is under level, so no effect
+        return level;
+    } else if (removedLevel.length === 0) {
+        // Either `level` is a child of `removedLevel`... or they are equal
+        // This is undefined behavior.
+        return level;
+    }
+
+    var removedRoot = removedLevel[0];
+    var root = level[0];
+    var removedRest = removedLevel.slice(1);
+    var rest = level.slice(1);
+
+    if (removedRoot < root) {
+        // It will shift levels at this point. The rest is unchanged.
+        return Array.prototype.concat(root - 1, rest);
+    } else if (removedRoot === root) {
+        // Look deeper
+        return Array.prototype.concat(root, shiftLevel(removedRest, rest));
+    } else {
+        // No impact
+        return level;
+    }
+}
+
+/**
+    @param {String}
+    @return {Array<Number>}
+ */
+function levelToArray(l) {
+    return l.split('.').map(function (char) {
+        return parseInt(char, 10);
+    });
+}
+
+/**
+    @param {Array<Number>}
+    @return {String}
+ */
+function arrayToLevel(a) {
+    return a.join('.');
+}
+
+module.exports = moveArticle;