3 files changed, 69 insertions, 1 deletions
diff --git a/lib/models/__tests__/config.js b/lib/models/__tests__/config.js
index ff04ffd..abad754 100644
--- a/lib/models/__tests__/config.js
+++ b/lib/models/__tests__/config.js
@@ -55,6 +55,36 @@ describe('Config', function() {
             expect(world).toBe(2);
         });
     });
+
+    describe('toReducedVersion', function() {
+        it('must only return diffs for simple values', function() {
+            var _config = Config.createWithValues({
+                gitbook: '3.0.0'
+            });
+
+            var reducedVersion = _config.toReducedVersion();
+
+            expect(reducedVersion.toJS()).toEqual({
+                gitbook: '3.0.0'
+            });
+        });
+
+        it('must only return diffs for deep values', function() {
+            var _config = Config.createWithValues({
+                structure: {
+                    readme: 'intro.md'
+                }
+            });
+
+            var reducedVersion = _config.toReducedVersion();
+
+            expect(reducedVersion.toJS()).toEqual({
+                structure: {
+                    readme: 'intro.md'
+                }
+            });
+        });
+    });
 });
 
 
diff --git a/lib/models/config.js b/lib/models/config.js
index 00d2b47..6de52f9 100644
--- a/lib/models/config.js
+++ b/lib/models/config.js
@@ -4,6 +4,7 @@ var Immutable = require('immutable');
 var File = require('./file');
 var PluginDependency = require('./pluginDependency');
 var configDefault = require('../constants/configDefault');
+var reducedObject = require('../utils/reducedObject');
 
 var Config = Immutable.Record({
     file:       File(),
@@ -19,11 +20,20 @@ Config.prototype.getValues = function() {
 };
 
 /**
+ * Return minimum version of configuration,
+ * Basically it returns the current config minus the default one
+ * @return {Map}
+ */
+Config.prototype.toReducedVersion = function() {
+    return reducedObject(configDefault, this.getValues());
+};
+
+/**
  * Render config as text
  * @return {Promise<String>}
  */
 Config.prototype.toText = function() {
-    return JSON.stringify(this.getValues().toJS(), null, 4);
+    return JSON.stringify(this.toReducedVersion().toJS(), null, 4);
 };
 
 /**
diff --git a/lib/utils/reducedObject.js b/lib/utils/reducedObject.js
new file mode 100644
index 0000000..fa5d32c
--- /dev/null
+++ b/lib/utils/reducedObject.js
@@ -0,0 +1,28 @@
+var Immutable = require('immutable');
+
+/**
+ *  Reduce the difference between a map and its default version
+ *  @param {Map} defaultVersion
+ *  @param {Map} currentVersion
+ */
+function reducedObject(defaultVersion, currentVersion) {
+    return currentVersion.reduce(function(result, value, key) {
+        var defaultValue = defaultVersion.get(key);
+
+        if (Immutable.Map.isMap(value)) {
+            var diffs = reducedObject(defaultValue, value);
+
+            if (diffs.size > 0) {
+                return result.set(key, diffs);
+            }
+        }
+
+        if (Immutable.is(defaultValue, value)) {
+            return result;
+        }
+
+        return result.set(key, value);
+    }, Immutable.Map());
+}
+
+module.exports = reducedObject;