20 files changed, 882 insertions, 433 deletions

diff --git a/logic/BaseInstaller.cpp b/logic/BaseInstaller.cpp
new file mode 100644
index 00000000..92aa0c92
--- /dev/null
+++ b/logic/BaseInstaller.cpp
@@ -0,0 +1,66 @@
+/* Copyright 2013 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "BaseInstaller.h"
+
+#include <QFile>
+
+#include "OneSixVersion.h"
+#include "OneSixLibrary.h"
+#include "OneSixInstance.h"
+
+#include "cmdutils.h"
+
+BaseInstaller::BaseInstaller()
+{
+
+}
+
+bool BaseInstaller::isApplied(OneSixInstance *on)
+{
+	return QFile::exists(filename(on->instanceRoot()));
+}
+
+bool BaseInstaller::add(OneSixInstance *to)
+{
+	if (!patchesDir(to->instanceRoot()).exists())
+	{
+		QDir(to->instanceRoot()).mkdir("patches");
+	}
+
+	if (isApplied(to))
+	{
+		if (!remove(to))
+		{
+			return false;
+		}
+	}
+
+	return true;
+}
+
+bool BaseInstaller::remove(OneSixInstance *from)
+{
+	return QFile::remove(filename(from->instanceRoot()));
+}
+
+QString BaseInstaller::filename(const QString &root) const
+{
+	return patchesDir(root).absoluteFilePath(id() + ".json");
+}
+QDir BaseInstaller::patchesDir(const QString &root) const
+{
+	return QDir(root + "/patches/");
+}
diff --git a/logic/BaseInstaller.h b/logic/BaseInstaller.h
new file mode 100644
index 00000000..df7eab89
--- /dev/null
+++ b/logic/BaseInstaller.h
@@ -0,0 +1,39 @@
+/* Copyright 2013 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <memory>
+
+class OneSixInstance;
+class QDir;
+class QString;
+
+class BaseInstaller
+{
+public:
+	BaseInstaller();
+
+	virtual bool canApply(OneSixInstance *instance) const { return true; }
+	bool isApplied(OneSixInstance *on);
+
+	virtual bool add(OneSixInstance *to);
+	virtual bool remove(OneSixInstance *from);
+
+protected:
+	virtual QString id() const = 0;
+	QString filename(const QString &root) const;
+	QDir patchesDir(const QString &root) const;
+};
diff --git a/logic/ForgeInstaller.cpp b/logic/ForgeInstaller.cpp
index 8d4c5b41..863c3dfd 100644
--- a/logic/ForgeInstaller.cpp
+++ b/logic/ForgeInstaller.cpp
@@ -22,6 +22,12 @@
 #include <pathutils.h>
 #include <QStringList>
 #include "MultiMC.h"
+#include "OneSixInstance.h"
+
+#include <QJsonDocument>
+#include <QJsonArray>
+#include <QSaveFile>
+#include <QCryptographicHash>
 
 ForgeInstaller::ForgeInstaller(QString filename, QString universal_url)
 {
@@ -103,13 +109,22 @@ ForgeInstaller::ForgeInstaller(QString filename, QString universal_url)
 	realVersionId = m_forge_version->id = installObj.value("minecraft").toString();
 }
 
-bool ForgeInstaller::apply(std::shared_ptr<OneSixVersion> to)
+bool ForgeInstaller::add(OneSixInstance *to)
 {
+	if (!BaseInstaller::add(to))
+	{
+		return false;
+	}
+
+	QJsonObject obj;
+	obj.insert("order", 5);
+
 	if (!m_forge_version)
 		return false;
-	to->externalUpdateStart();
 	int sliding_insert_window = 0;
 	{
+		QJsonArray librariesPlus;
+
 		// for each library in the version we are adding (except for the blacklisted)
 		QSet<QString> blacklist{"lwjgl", "lwjgl_util", "lwjgl-platform"};
 		for (auto lib : m_forge_version->libraries)
@@ -128,28 +143,43 @@ bool ForgeInstaller::apply(std::shared_ptr<OneSixVersion> to)
 			if (blacklist.contains(libName))
 				continue;
 
-			// find an entry that matches this one
+			QJsonObject libObj = lib->toJson();
+
 			bool found = false;
-			for (auto tolib : to->libraries)
+			// find an entry that matches this one
+			for (auto tolib : to->getFullVersion()->libraries)
 			{
 				if (tolib->name() != libName)
 					continue;
 				found = true;
 				// replace lib
-				tolib = lib;
+				libObj.insert("insert", QString("apply"));
 				break;
 			}
 			if (!found)
 			{
 				// add lib
-				to->libraries.insert(sliding_insert_window, lib);
+				QJsonObject insertObj;
+				insertObj.insert("before", to->getFullVersion()->libraries.at(sliding_insert_window)->rawName());
+				libObj.insert("insert", insertObj);
 				sliding_insert_window++;
 			}
+			librariesPlus.append(libObj);
 		}
-		to->mainClass = m_forge_version->mainClass;
-		to->minecraftArguments = m_forge_version->minecraftArguments;
-		to->processArguments = m_forge_version->processArguments;
+		obj.insert("+libraries", librariesPlus);
+		obj.insert("mainClass", m_forge_version->mainClass);
+		obj.insert("minecraftArguments", m_forge_version->minecraftArguments);
+		obj.insert("processArguments", m_forge_version->processArguments);
+	}
+
+	QFile file(filename(to->instanceRoot()));
+	if (!file.open(QFile::WriteOnly))
+	{
+		QLOG_ERROR() << "Error opening" << file.fileName() << "for reading:" << file.errorString();
+		return false;
 	}
-	to->externalUpdateFinish();
-	return to->toOriginalFile();
+	file.write(QJsonDocument(obj).toJson());
+	file.close();
+
+	return true;
 }
diff --git a/logic/ForgeInstaller.h b/logic/ForgeInstaller.h
index 0b9f9c77..eb8ecd79 100644
--- a/logic/ForgeInstaller.h
+++ b/logic/ForgeInstaller.h
@@ -14,17 +14,22 @@
  */
 
 #pragma once
+
+#include "BaseInstaller.h"
+
 #include <QString>
 #include <memory>
 
 class OneSixVersion;
 
-class ForgeInstaller
+class ForgeInstaller : public BaseInstaller
 {
 public:
 	ForgeInstaller(QString filename, QString universal_url);
 
-	bool apply(std::shared_ptr<OneSixVersion> to);
+	bool add(OneSixInstance *to) override;
+
+	QString id() const override { return "net.minecraftforge"; }
 
 private:
 	// the version, read from the installer
diff --git a/logic/InstanceFactory.cpp b/logic/InstanceFactory.cpp
index 1f1a5879..807bccd0 100644
--- a/logic/InstanceFactory.cpp
+++ b/logic/InstanceFactory.cpp
@@ -24,6 +24,7 @@
 #include "OneSixInstance.h"
 #include "OneSixFTBInstance.h"
 #include "NostalgiaInstance.h"
+#include "OneSixInstance.h"
 #include "BaseVersion.h"
 #include "MinecraftVersion.h"
 
@@ -50,13 +51,13 @@ InstanceFactory::InstLoadError InstanceFactory::loadInstance(BaseInstance *&inst
 	QString inst_type = m_settings->get("InstanceType").toString();
 
 	// FIXME: replace with a map lookup, where instance classes register their types
-	if (inst_type == "Legacy")
+	if (inst_type == "OneSix")
 	{
-		inst = new LegacyInstance(instDir, m_settings, this);
+		inst = new OneSixInstance(instDir, m_settings, this);
 	}
-	else if (inst_type == "OneSix")
+	else if (inst_type == "Legacy")
 	{
-		inst = new OneSixInstance(instDir, m_settings, this);
+		inst = new LegacyInstance(instDir, m_settings, this);
 	}
 	else if (inst_type == "Nostalgia")
 	{
@@ -101,6 +102,7 @@ InstanceFactory::InstCreateError InstanceFactory::createInstance(BaseInstance *&
 		switch (mcVer->type)
 		{
 		case MinecraftVersion::Legacy:
+			// TODO new instance type
 			m_settings->set("InstanceType", "Legacy");
 			inst = new LegacyInstance(instDir, m_settings, this);
 			inst->setIntendedVersionId(version->descriptor());
diff --git a/logic/LiteLoaderInstaller.cpp b/logic/LiteLoaderInstaller.cpp
index 07fffff3..1ce9d3f4 100644
--- a/logic/LiteLoaderInstaller.cpp
+++ b/logic/LiteLoaderInstaller.cpp
@@ -15,12 +15,19 @@
 
 #include "LiteLoaderInstaller.h"
 
+#include <QJsonArray>
+#include <QJsonDocument>
+
+#include "logger/QsLog.h"
+
 #include "OneSixVersion.h"
 #include "OneSixLibrary.h"
+#include "OneSixInstance.h"
 
 QMap<QString, QString> LiteLoaderInstaller::m_launcherWrapperVersionMapping;
 
-LiteLoaderInstaller::LiteLoaderInstaller(const QString &mcVersion) : m_mcVersion(mcVersion)
+LiteLoaderInstaller::LiteLoaderInstaller()
+	: BaseInstaller()
 {
 	if (m_launcherWrapperVersionMapping.isEmpty())
 	{
@@ -31,72 +38,55 @@ LiteLoaderInstaller::LiteLoaderInstaller(const QString &mcVersion) : m_mcVersion
 	}
 }
 
-bool LiteLoaderInstaller::canApply() const
+bool LiteLoaderInstaller::canApply(OneSixInstance *instance) const
 {
-	return m_launcherWrapperVersionMapping.contains(m_mcVersion);
+	return m_launcherWrapperVersionMapping.contains(instance->intendedVersionId());
 }
 
-bool LiteLoaderInstaller::apply(std::shared_ptr<OneSixVersion> to)
+bool LiteLoaderInstaller::add(OneSixInstance *to)
 {
-	to->externalUpdateStart();
-
-	applyLaunchwrapper(to);
-	applyLiteLoader(to);
-
-	to->mainClass = "net.minecraft.launchwrapper.Launch";
-	if (!to->minecraftArguments.contains(
-			 " --tweakClass com.mumfrey.liteloader.launch.LiteLoaderTweaker"))
+	if (!BaseInstaller::add(to))
 	{
-		to->minecraftArguments.append(
-			" --tweakClass com.mumfrey.liteloader.launch.LiteLoaderTweaker");
+		return false;
 	}
 
-	to->externalUpdateFinish();
-	return to->toOriginalFile();
-}
+	QJsonObject obj;
 
-void LiteLoaderInstaller::applyLaunchwrapper(std::shared_ptr<OneSixVersion> to)
-{
-	const QString intendedVersion = m_launcherWrapperVersionMapping[m_mcVersion];
+	obj.insert("mainClass", QString("net.minecraft.launchwrapper.Launch"));
+	obj.insert("+minecraftArguments", QString(" --tweakClass com.mumfrey.liteloader.launch.LiteLoaderTweaker"));
+	obj.insert("order", 10);
 
-	QMutableListIterator<std::shared_ptr<OneSixLibrary>> it(to->libraries);
-	while (it.hasNext())
+	QJsonArray libraries;
+
+	// launchwrapper
 	{
-		it.next();
-		if (it.value()->rawName().startsWith("net.minecraft:launchwrapper:"))
-		{
-			if (it.value()->version() >= intendedVersion)
-			{
-				return;
-			}
-			else
-			{
-				it.remove();
-			}
-		}
+		OneSixLibrary launchwrapperLib("net.minecraft:launchwrapper:" + m_launcherWrapperVersionMapping[to->intendedVersionId()]);
+		launchwrapperLib.finalize();
+		QJsonObject lwLibObj = launchwrapperLib.toJson();
+		lwLibObj.insert("insert", QString("prepend"));
+		libraries.append(lwLibObj);
 	}
 
-	std::shared_ptr<OneSixLibrary> lib(new OneSixLibrary(
-		"net.minecraft:launchwrapper:" + m_launcherWrapperVersionMapping[m_mcVersion]));
-	lib->finalize();
-	to->libraries.prepend(lib);
-}
+	// liteloader
+	{
+		OneSixLibrary liteloaderLib("com.mumfrey:liteloader:" + to->intendedVersionId());
+		liteloaderLib.setBaseUrl("http://dl.liteloader.com/versions/");
+		liteloaderLib.finalize();
+		QJsonObject llLibObj = liteloaderLib.toJson();
+		llLibObj.insert("insert", QString("prepend"));
+		libraries.append(llLibObj);
+	}
 
-void LiteLoaderInstaller::applyLiteLoader(std::shared_ptr<OneSixVersion> to)
-{
-	QMutableListIterator<std::shared_ptr<OneSixLibrary>> it(to->libraries);
-	while (it.hasNext())
+	obj.insert("+libraries", libraries);
+
+	QFile file(filename(to->instanceRoot()));
+	if (!file.open(QFile::WriteOnly))
 	{
-		it.next();
-		if (it.value()->rawName().startsWith("com.mumfrey:liteloader:"))
-		{
-			it.remove();
-		}
+		QLOG_ERROR() << "Error opening" << file.fileName() << "for reading:" << file.errorString();
+		return false;
 	}
+	file.write(QJsonDocument(obj).toJson());
+	file.close();
 
-	std::shared_ptr<OneSixLibrary> lib(
-		new OneSixLibrary("com.mumfrey:liteloader:" + m_mcVersion));
-	lib->setBaseUrl("http://dl.liteloader.com/versions/");
-	lib->finalize();
-	to->libraries.prepend(lib);
+	return true;
 }
diff --git a/logic/LiteLoaderInstaller.h b/logic/LiteLoaderInstaller.h
index 44b306d6..5e01b16c 100644
--- a/logic/LiteLoaderInstaller.h
+++ b/logic/LiteLoaderInstaller.h
@@ -14,26 +14,22 @@
  */
 
 #pragma once
+
+#include "BaseInstaller.h"
+
 #include <QString>
 #include <QMap>
-#include <memory>
-
-class OneSixVersion;
 
-class LiteLoaderInstaller
+class LiteLoaderInstaller : public BaseInstaller
 {
 public:
-	LiteLoaderInstaller(const QString &mcVersion);
+	LiteLoaderInstaller();
 
-	bool canApply() const;
-
-	bool apply(std::shared_ptr<OneSixVersion> to);
+	bool canApply(OneSixInstance *instance) const override;
+	bool add(OneSixInstance *to) override;
 
 private:
-	QString m_mcVersion;
-
-	void applyLaunchwrapper(std::shared_ptr<OneSixVersion> to);
-	void applyLiteLoader(std::shared_ptr<OneSixVersion> to);
+	virtual QString id() const override { return "com.mumfrey.liteloader"; }
 
 	static QMap<QString, QString> m_launcherWrapperVersionMapping;
 };
diff --git a/logic/OneSixFTBInstance.cpp b/logic/OneSixFTBInstance.cpp
index e50a5b53..71bc1470 100644
--- a/logic/OneSixFTBInstance.cpp
+++ b/logic/OneSixFTBInstance.cpp
@@ -60,10 +60,8 @@ slots:
 			emitFailed(tr("Couldn't load the version config"));
 			return;
 		}
-		instance->revertCustomVersion();
-		instance->customizeVersion();
 		auto version = instance->getFullVersion();
-		if (!forge.apply(version))
+		if (!forge.add(instance))
 		{
 			emitFailed(tr("Couldn't install Forge"));
 			return;
diff --git a/logic/OneSixInstance.cpp b/logic/OneSixInstance.cpp
index ab87a1db..c43a5187 100644
--- a/logic/OneSixInstance.cpp
+++ b/logic/OneSixInstance.cpp
@@ -13,32 +13,36 @@
  * limitations under the License.
  */
 
-#include "MultiMC.h"
 #include "OneSixInstance.h"
+
+#include <QIcon>
+
 #include "OneSixInstance_p.h"
 #include "OneSixUpdate.h"
-#include "MinecraftProcess.h"
 #include "OneSixVersion.h"
-#include "JavaChecker.h"
-#include "logic/icons/IconList.h"
-
-#include <setting.h>
-#include <pathutils.h>
-#include <cmdutils.h>
-#include <JlCompress.h>
-#include "gui/dialogs/OneSixModEditDialog.h"
+#include "pathutils.h"
 #include "logger/QsLog.h"
-#include "logic/assets/AssetsUtils.h"
-#include <QIcon>
+#include "assets/AssetsUtils.h"
+#include "MultiMC.h"
+#include "icons/IconList.h"
+#include "MinecraftProcess.h"
+#include "gui/dialogs/OneSixModEditDialog.h"
 
-OneSixInstance::OneSixInstance(const QString &rootDir, SettingsObject *setting_obj,
-							   QObject *parent)
-	: BaseInstance(new OneSixInstancePrivate(), rootDir, setting_obj, parent)
+OneSixInstance::OneSixInstance(const QString &rootDir, SettingsObject *settings, QObject *parent)
+	: BaseInstance(new OneSixInstancePrivate(), rootDir, settings, parent)
 {
 	I_D(OneSixInstance);
 	d->m_settings->registerSetting("IntendedVersion", "");
 	d->m_settings->registerSetting("ShouldUpdate", false);
-	reloadFullVersion();
+	d->version.reset(new OneSixVersion(this, this));
+	if (QDir(instanceRoot()).exists("version.json"))
+	{
+		reloadFullVersion();
+	}
+	else
+	{
+		clearFullVersion();
+	}
 }
 
 std::shared_ptr<Task> OneSixInstance::doUpdate(bool only_prepare)
@@ -282,11 +286,8 @@ bool OneSixInstance::setIntendedVersionId(QString version)
 {
 	settings().set("IntendedVersion", version);
 	setShouldUpdate(true);
-	auto pathCustom = PathCombine(instanceRoot(), "custom.json");
-	auto pathOrig = PathCombine(instanceRoot(), "version.json");
-	QFile::remove(pathCustom);
-	QFile::remove(pathOrig);
-	reloadFullVersion();
+	QFile::remove(PathCombine(instanceRoot(), "version.json"));
+	clearFullVersion();
 	return true;
 }
 
@@ -312,9 +313,9 @@ bool OneSixInstance::shouldUpdate() const
 
 bool OneSixInstance::versionIsCustom()
 {
-	QString verpath_custom = PathCombine(instanceRoot(), "custom.json");
-	QFile versionfile(verpath_custom);
-	return versionfile.exists();
+	QDir patches(PathCombine(instanceRoot(), "patches/"));
+	return QFile::exists(PathCombine(instanceRoot(), "custom.json"))
+			|| (patches.exists() && patches.count() >= 0);
 }
 
 QString OneSixInstance::currentVersionId() const
@@ -322,54 +323,20 @@ QString OneSixInstance::currentVersionId() const
 	return intendedVersionId();
 }
 
-bool OneSixInstance::customizeVersion()
+bool OneSixInstance::reloadFullVersion(QWidget *widgetParent)
 {
-	if (!versionIsCustom())
-	{
-		auto pathCustom = PathCombine(instanceRoot(), "custom.json");
-		auto pathOrig = PathCombine(instanceRoot(), "version.json");
-		QFile::copy(pathOrig, pathCustom);
-		return reloadFullVersion();
-	}
-	else
-		return true;
-}
+	I_D(OneSixInstance);
 
-bool OneSixInstance::revertCustomVersion()
-{
-	if (versionIsCustom())
-	{
-		auto path = PathCombine(instanceRoot(), "custom.json");
-		QFile::remove(path);
-		return reloadFullVersion();
-	}
-	else
-		return true;
+	bool ret = d->version->reload(widgetParent);
+	emit versionReloaded();
+	return ret;
 }
 
-bool OneSixInstance::reloadFullVersion()
+void OneSixInstance::clearFullVersion()
 {
 	I_D(OneSixInstance);
-
-	QString verpath = PathCombine(instanceRoot(), "version.json");
-	{
-		QString verpath_custom = PathCombine(instanceRoot(), "custom.json");
-		QFile versionfile(verpath_custom);
-		if (versionfile.exists())
-			verpath = verpath_custom;
-	}
-
-	auto version = OneSixVersion::fromFile(verpath);
-	if (version)
-	{
-		d->version = version;
-		return true;
-	}
-	else
-	{
-		d->version.reset();
-		return false;
-	}
+	d->version->clear();
+	emit versionReloaded();
 }
 
 std::shared_ptr<OneSixVersion> OneSixInstance::getFullVersion()
@@ -397,7 +364,7 @@ bool OneSixInstance::menuActionEnabled(QString action_name) const
 
 QString OneSixInstance::getStatusbarDescription()
 {
-	QString descr = "One Six : " + intendedVersionId();
+	QString descr = "OneSix : " + intendedVersionId();
 	if (versionIsCustom())
 	{
 		descr + " (custom)";
diff --git a/logic/OneSixInstance.h b/logic/OneSixInstance.h
index f869e345..94577828 100644
--- a/logic/OneSixInstance.h
+++ b/logic/OneSixInstance.h
@@ -15,21 +15,17 @@
 
 #pragma once
 
-#include <QStringList>
-#include <QDir>
-
 #include "BaseInstance.h"
 
-class OneSixVersion;
-class Task;
-class ModList;
+#include "OneSixVersion.h"
+#include "ModList.h"
 
 class OneSixInstance : public BaseInstance
 {
 	Q_OBJECT
 public:
 	explicit OneSixInstance(const QString &rootDir, SettingsObject *settings,
-							QObject *parent = 0);
+						  QObject *parent = 0);
 
 	//////  Mod Lists  //////
 	std::shared_ptr<ModList> loaderModList();
@@ -55,14 +51,12 @@ public:
 
 	virtual QDialog *createModEditDialog(QWidget *parent) override;
 
-	/// reload the full version json file. return true on success!
-	bool reloadFullVersion();
+	/// reload the full version json files. return true on success!
+	bool reloadFullVersion(QWidget *widgetParent = 0);
+	/// clears all version information in preparation for an update
+	void clearFullVersion();
 	/// get the current full version info
 	std::shared_ptr<OneSixVersion> getFullVersion();
-	/// revert the current custom version back to base
-	bool revertCustomVersion();
-	/// customize the current base version
-	bool customizeVersion();
 	/// is the current version original, or custom?
 	virtual bool versionIsCustom() override;
 
@@ -72,6 +66,9 @@ public:
 	virtual bool menuActionEnabled(QString action_name) const override;
 	virtual QString getStatusbarDescription() override;
 
+signals:
+	void versionReloaded();
+
 private:
 	QStringList processMinecraftArgs(MojangAccountPtr account);
 	QDir reconstructAssets(std::shared_ptr<OneSixVersion> version);
diff --git a/logic/OneSixInstance_p.h b/logic/OneSixInstance_p.h
index 6b7ea431..a2b70ac9 100644
--- a/logic/OneSixInstance_p.h
+++ b/logic/OneSixInstance_p.h
@@ -15,16 +15,13 @@
 
 #pragma once
 
-#include <memory>
-
-#include "logic/BaseInstance_p.h"
-#include "logic/OneSixVersion.h"
-#include "logic/OneSixLibrary.h"
-#include "logic/ModList.h"
+#include "BaseInstance_p.h"
+#include "OneSixVersion.h"
+#include "ModList.h"
 
 struct OneSixInstancePrivate : public BaseInstancePrivate
 {
 	std::shared_ptr<OneSixVersion> version;
 	std::shared_ptr<ModList> loader_mod_list;
 	std::shared_ptr<ModList> resource_pack_list;
-};
\ No newline at end of file
+};
diff --git a/logic/OneSixLibrary.cpp b/logic/OneSixLibrary.cpp
index 7b80d5e7..4d892d53 100644
--- a/logic/OneSixLibrary.cpp
+++ b/logic/OneSixLibrary.cpp
@@ -76,11 +76,11 @@ void OneSixLibrary::finalize()
 	}
 }
 
-void OneSixLibrary::setName(QString name)
+void OneSixLibrary::setName(const QString &name)
 {
 	m_name = name;
 }
-void OneSixLibrary::setBaseUrl(QString base_url)
+void OneSixLibrary::setBaseUrl(const QString &base_url)
 {
 	m_base_url = base_url;
 }
@@ -88,7 +88,7 @@ void OneSixLibrary::setIsNative()
 {
 	m_is_native = true;
 }
-void OneSixLibrary::addNative(OpSys os, QString suffix)
+void OneSixLibrary::addNative(OpSys os, const QString &suffix)
 {
 	m_is_native = true;
 	m_native_suffixes[os] = suffix;
@@ -97,41 +97,41 @@ void OneSixLibrary::setRules(QList<std::shared_ptr<Rule>> rules)
 {
 	m_rules = rules;
 }
-bool OneSixLibrary::isActive()
+bool OneSixLibrary::isActive() const
 {
 	return m_is_active;
 }
-bool OneSixLibrary::isNative()
+bool OneSixLibrary::isNative() const
 {
 	return m_is_native;
 }
-QString OneSixLibrary::downloadUrl()
+QString OneSixLibrary::downloadUrl() const
 {
 	if (m_absolute_url.size())
 		return m_absolute_url;
 	return m_download_url;
 }
-QString OneSixLibrary::storagePath()
+QString OneSixLibrary::storagePath() const
 {
 	return m_storage_path;
 }
 
-void OneSixLibrary::setAbsoluteUrl(QString absolute_url)
+void OneSixLibrary::setAbsoluteUrl(const QString &absolute_url)
 {
 	m_absolute_url = absolute_url;
 }
 
-QString OneSixLibrary::absoluteUrl()
+QString OneSixLibrary::absoluteUrl() const
 {
 	return m_absolute_url;
 }
 
-void OneSixLibrary::setHint(QString hint)
+void OneSixLibrary::setHint(const QString &hint)
 {
 	m_hint = hint;
 }
 
-QString OneSixLibrary::hint()
+QString OneSixLibrary::hint() const
 {
 	return m_hint;
 }
diff --git a/logic/OneSixLibrary.h b/logic/OneSixLibrary.h
index 227cdbef..52f89969 100644
--- a/logic/OneSixLibrary.h
+++ b/logic/OneSixLibrary.h
@@ -63,7 +63,7 @@ public:
 
 public:
 	/// Constructor
-	OneSixLibrary(QString name)
+	OneSixLibrary(const QString &name)
 	{
 		m_name = name;
 	}
@@ -84,48 +84,48 @@ public:
 	void finalize();
 
 	/// Set the library composite name
-	void setName(QString name);
+	void setName(const QString &name);
 	/// get a decent-looking name
-	QString name()
+	QString name() const
 	{
 		return m_decentname;
 	}
 	/// get a decent-looking version
-	QString version()
+	QString version() const
 	{
 		return m_decentversion;
 	}
 	/// what kind of library is it? (for display)
-	QString type()
+	QString type() const
 	{
 		return m_decenttype;
 	}
 	/// Set the url base for downloads
-	void setBaseUrl(QString base_url);
+	void setBaseUrl(const QString &base_url);
 
 	/// Call this to mark the library as 'native' (it's a zip archive with DLLs)
 	void setIsNative();
 	/// Attach a name suffix to the specified OS native
-	void addNative(OpSys os, QString suffix);
+	void addNative(OpSys os, const QString &suffix);
 	/// Set the load rules
 	void setRules(QList<std::shared_ptr<Rule>> rules);
 
 	/// Returns true if the library should be loaded (or extracted, in case of natives)
-	bool isActive();
+	bool isActive() const;
 	/// Returns true if the library is native
-	bool isNative();
+	bool isNative() const;
 	/// Get the URL to download the library from
-	QString downloadUrl();
+	QString downloadUrl() const;
 	/// Get the relative path where the library should be saved
-	QString storagePath();
+	QString storagePath() const;
 
 	/// set an absolute URL for the library. This is an MMC extension.
-	void setAbsoluteUrl(QString absolute_url);
-	QString absoluteUrl();
+	void setAbsoluteUrl(const QString &absolute_url);
+	QString absoluteUrl() const;
 
 	/// set a hint about how to treat the library. This is an MMC extension.
-	void setHint(QString hint);
-	QString hint();
+	void setHint(const QString &hint);
+	QString hint() const;
 
 	bool extractTo(QString target_dir);
 	bool filesExist();
diff --git a/logic/OneSixRule.cpp b/logic/OneSixRule.cpp
index 392b1dd1..d8d13b50 100644
--- a/logic/OneSixRule.cpp
+++ b/logic/OneSixRule.cpp
@@ -18,7 +18,7 @@
 
 #include "OneSixRule.h"
 
-QList<std::shared_ptr<Rule>> rulesFromJsonV4(QJsonObject &objectWithRules)
+QList<std::shared_ptr<Rule>> rulesFromJsonV4(const QJsonObject &objectWithRules)
 {
 	QList<std::shared_ptr<Rule>> rules;
 	auto rulesVal = objectWithRules.value("rules");
@@ -86,4 +86,4 @@ RuleAction RuleAction_fromString(QString name)
 	if (name == "disallow")
 		return Disallow;
 	return Defer;
-}
\ No newline at end of file
+}
diff --git a/logic/OneSixRule.h b/logic/OneSixRule.h
index 5a13cbd9..426e2886 100644
--- a/logic/OneSixRule.h
+++ b/logic/OneSixRule.h
@@ -27,7 +27,7 @@ enum RuleAction
 };
 
 RuleAction RuleAction_fromString(QString);
-QList<std::shared_ptr<Rule>> rulesFromJsonV4(QJsonObject &objectWithRules);
+QList<std::shared_ptr<Rule>> rulesFromJsonV4(const QJsonObject &objectWithRules);
 
 class Rule
 {
diff --git a/logic/OneSixUpdate.cpp b/logic/OneSixUpdate.cpp
index ae647bfe..f51b6c23 100644
--- a/logic/OneSixUpdate.cpp
+++ b/logic/OneSixUpdate.cpp
@@ -335,13 +335,13 @@ void OneSixUpdate::prepareForLaunch()
 {
 	setStatus(tr("Preparing for launch..."));
 	QLOG_INFO() << m_inst->name() << ": preparing for launch";
-	auto onesix_inst = (OneSixInstance *)m_inst;
+	auto OneSix_inst = (OneSixInstance *)m_inst;
 
 	// delete any leftovers, if they are present.
-	onesix_inst->cleanupAfterRun();
+	OneSix_inst->cleanupAfterRun();
 
-	QString natives_dir_raw = PathCombine(onesix_inst->instanceRoot(), "natives/");
-	auto version = onesix_inst->getFullVersion();
+	QString natives_dir_raw = PathCombine(OneSix_inst->instanceRoot(), "natives/");
+	auto version = OneSix_inst->getFullVersion();
 	if (!version)
 	{
 		emitFailed("The version information for this instance is not complete. Try re-creating "
diff --git a/logic/OneSixVersion.cpp b/logic/OneSixVersion.cpp
index 8ae685f0..3db3bd77 100644
--- a/logic/OneSixVersion.cpp
+++ b/logic/OneSixVersion.cpp
@@ -13,228 +13,60 @@
  * limitations under the License.
  */
 
-#include "logic/OneSixVersion.h"
-#include "logic/OneSixLibrary.h"
-#include "logic/OneSixRule.h"
+#include "OneSixVersion.h"
 
-#include "logger/QsLog.h"
+#include <QDebug>
 
-std::shared_ptr<OneSixVersion> fromJsonV4(QJsonObject root,
-										  std::shared_ptr<OneSixVersion> fullVersion)
-{
-	fullVersion->id = root.value("id").toString();
-
-	fullVersion->mainClass = root.value("mainClass").toString();
-	auto procArgsValue = root.value("processArguments");
-	if (procArgsValue.isString())
-	{
-		fullVersion->processArguments = procArgsValue.toString();
-		QString toCompare = fullVersion->processArguments.toLower();
-		if (toCompare == "legacy")
-		{
-			fullVersion->minecraftArguments = " ${auth_player_name} ${auth_session}";
-		}
-		else if (toCompare == "username_session")
-		{
-			fullVersion->minecraftArguments =
-				"--username ${auth_player_name} --session ${auth_session}";
-		}
-		else if (toCompare == "username_session_version")
-		{
-			fullVersion->minecraftArguments = "--username ${auth_player_name} "
-											  "--session ${auth_session} "
-											  "--version ${profile_name}";
-		}
-	}
-
-	auto minecraftArgsValue = root.value("minecraftArguments");
-	if (minecraftArgsValue.isString())
-	{
-		fullVersion->minecraftArguments = minecraftArgsValue.toString();
-	}
-
-	auto minecraftTypeValue = root.value("type");
-	if (minecraftTypeValue.isString())
-	{
-		fullVersion->type = minecraftTypeValue.toString();
-	}
-
-	fullVersion->releaseTime = root.value("releaseTime").toString();
-	fullVersion->time = root.value("time").toString();
-
-	auto assetsID = root.value("assets");
-	if (assetsID.isString())
-	{
-		fullVersion->assets = assetsID.toString();
-	}
-	else
-	{
-		fullVersion->assets = "legacy";
-	}
-
-	QLOG_DEBUG() << "Assets version:" << fullVersion->assets;
-
-	// Iterate through the list, if it's a list.
-	auto librariesValue = root.value("libraries");
-	if (!librariesValue.isArray())
-		return fullVersion;
-
-	QJsonArray libList = root.value("libraries").toArray();
-	for (auto libVal : libList)
-	{
-		if (!libVal.isObject())
-		{
-			continue;
-		}
-
-		QJsonObject libObj = libVal.toObject();
-
-		// Library name
-		auto nameVal = libObj.value("name");
-		if (!nameVal.isString())
-			continue;
-		std::shared_ptr<OneSixLibrary> library(new OneSixLibrary(nameVal.toString()));
-
-		auto urlVal = libObj.value("url");
-		if (urlVal.isString())
-		{
-			library->setBaseUrl(urlVal.toString());
-		}
-		auto hintVal = libObj.value("MMC-hint");
-		if (hintVal.isString())
-		{
-			library->setHint(hintVal.toString());
-		}
-		auto urlAbsVal = libObj.value("MMC-absoluteUrl");
-		auto urlAbsuVal = libObj.value("MMC-absulute_url"); // compatibility
-		if (urlAbsVal.isString())
-		{
-			library->setAbsoluteUrl(urlAbsVal.toString());
-		}
-		else if (urlAbsuVal.isString())
-		{
-			library->setAbsoluteUrl(urlAbsuVal.toString());
-		}
-		// Extract excludes (if any)
-		auto extractVal = libObj.value("extract");
-		if (extractVal.isObject())
-		{
-			QStringList excludes;
-			auto extractObj = extractVal.toObject();
-			auto excludesVal = extractObj.value("exclude");
-			if (excludesVal.isArray())
-			{
-				auto excludesList = excludesVal.toArray();
-				for (auto excludeVal : excludesList)
-				{
-					if (excludeVal.isString())
-						excludes.append(excludeVal.toString());
-				}
-				library->extract_excludes = excludes;
-			}
-		}
+#include "OneSixVersionBuilder.h"
 
-		auto nativesVal = libObj.value("natives");
-		if (nativesVal.isObject())
-		{
-			library->setIsNative();
-			auto nativesObj = nativesVal.toObject();
-			auto iter = nativesObj.begin();
-			while (iter != nativesObj.end())
-			{
-				auto osType = OpSys_fromString(iter.key());
-				if (osType == Os_Other)
-					continue;
-				if (!iter.value().isString())
-					continue;
-				library->addNative(osType, iter.value().toString());
-				iter++;
-			}
-		}
-		library->setRules(rulesFromJsonV4(libObj));
-		library->finalize();
-		fullVersion->libraries.append(library);
-	}
-	return fullVersion;
+OneSixVersion::OneSixVersion(OneSixInstance *instance, QObject *parent)
+	: QAbstractListModel(parent), m_instance(instance)
+{
+	clear();
 }
 
-std::shared_ptr<OneSixVersion> OneSixVersion::fromJson(QJsonObject root)
+bool OneSixVersion::reload(QWidget *widgetParent)
 {
-	std::shared_ptr<OneSixVersion> readVersion(new OneSixVersion());
-	int launcher_ver = readVersion->minimumLauncherVersion =
-		root.value("minimumLauncherVersion").toDouble();
-
-	// ADD MORE HERE :D
-	if (launcher_ver > 0 && launcher_ver <= 13)
-		return fromJsonV4(root, readVersion);
-	else
-	{
-		return std::shared_ptr<OneSixVersion>();
-	}
+	return OneSixVersionBuilder::build(this, m_instance, widgetParent);
 }
 
-std::shared_ptr<OneSixVersion> OneSixVersion::fromFile(QString filepath)
+void OneSixVersion::clear()
 {
-	QFile file(filepath);
-	if (!file.open(QIODevice::ReadOnly))
-	{
-		return std::shared_ptr<OneSixVersion>();
-	}
-
-	auto data = file.readAll();
-	QJsonParseError jsonError;
-	QJsonDocument jsonDoc = QJsonDocument::fromJson(data, &jsonError);
-
-	if (jsonError.error != QJsonParseError::NoError)
-	{
-		return std::shared_ptr<OneSixVersion>();
-	}
-
-	if (!jsonDoc.isObject())
-	{
-		return std::shared_ptr<OneSixVersion>();
-	}
-	QJsonObject root = jsonDoc.object();
-	auto version = fromJson(root);
-	if (version)
-		version->original_file = filepath;
-	return version;
+	id.clear();
+	time.clear();
+	releaseTime.clear();
+	type.clear();
+	assets.clear();
+	processArguments.clear();
+	minecraftArguments.clear();
+	minimumLauncherVersion = 0xDEADBEAF;
+	mainClass.clear();
+	libraries.clear();
 }
 
-bool OneSixVersion::toOriginalFile()
+void OneSixVersion::dump() const
 {
-	if (original_file.isEmpty())
-		return false;
-	QSaveFile file(original_file);
-	if (!file.open(QIODevice::WriteOnly))
-	{
-		return false;
-	}
-	// serialize base attributes (those we care about anyway)
-	QJsonObject root;
-	root.insert("minecraftArguments", minecraftArguments);
-	root.insert("mainClass", mainClass);
-	root.insert("minimumLauncherVersion", minimumLauncherVersion);
-	root.insert("time", time);
-	root.insert("id", id);
-	root.insert("type", type);
-	// screw processArguments
-	root.insert("releaseTime", releaseTime);
-	QJsonArray libarray;
-	for (const auto &lib : libraries)
+	qDebug().nospace() << "OneSixVersion("
+				  << "\n\tid=" << id
+				  << "\n\ttime=" << time
+				  << "\n\treleaseTime=" << releaseTime
+				  << "\n\ttype=" << type
+				  << "\n\tassets=" << assets
+				  << "\n\tprocessArguments=" << processArguments
+				  << "\n\tminecraftArguments=" << minecraftArguments
+				  << "\n\tminimumLauncherVersion=" << minimumLauncherVersion
+				  << "\n\tmainClass=" << mainClass
+				  << "\n\tlibraries=";
+	for (auto lib : libraries)
 	{
-		libarray.append(lib->toJson());
+		qDebug().nospace() << "\n\t\t" << lib.get();
 	}
-	if (libarray.count())
-		root.insert("libraries", libarray);
-	QJsonDocument doc(root);
-	file.write(doc.toJson());
-	return file.commit();
+	qDebug().nospace() << "\n)";
 }
 
-QList<std::shared_ptr<OneSixLibrary>> OneSixVersion::getActiveNormalLibs()
+QList<std::shared_ptr<OneSixLibrary> > OneSixVersion::getActiveNormalLibs()
 {
-	QList<std::shared_ptr<OneSixLibrary>> output;
+	QList<std::shared_ptr<OneSixLibrary> > output;
 	for (auto lib : libraries)
 	{
 		if (lib->isActive() && !lib->isNative())
@@ -245,9 +77,9 @@ QList<std::shared_ptr<OneSixLibrary>> OneSixVersion::getActiveNormalLibs()
 	return output;
 }
 
-QList<std::shared_ptr<OneSixLibrary>> OneSixVersion::getActiveNativeLibs()
+QList<std::shared_ptr<OneSixLibrary> > OneSixVersion::getActiveNativeLibs()
 {
-	QList<std::shared_ptr<OneSixLibrary>> output;
+	QList<std::shared_ptr<OneSixLibrary> > output;
 	for (auto lib : libraries)
 	{
 		if (lib->isActive() && lib->isNative())
@@ -258,14 +90,14 @@ QList<std::shared_ptr<OneSixLibrary>> OneSixVersion::getActiveNativeLibs()
 	return output;
 }
 
-void OneSixVersion::externalUpdateStart()
-{
-	beginResetModel();
-}
-
-void OneSixVersion::externalUpdateFinish()
+std::shared_ptr<OneSixVersion> OneSixVersion::fromJson(const QJsonObject &obj)
 {
-	endResetModel();
+	std::shared_ptr<OneSixVersion> version(new OneSixVersion(0));
+	if (OneSixVersionBuilder::read(version.get(), obj))
+	{
+		return version;
+	}
+	return 0;
 }
 
 QVariant OneSixVersion::data(const QModelIndex &index, int role) const
@@ -338,3 +170,25 @@ int OneSixVersion::columnCount(const QModelIndex &parent) const
 {
 	return 3;
 }
+
+QDebug operator<<(QDebug &dbg, const OneSixVersion *version)
+{
+	version->dump();
+	return dbg.maybeSpace();
+}
+QDebug operator<<(QDebug &dbg, const OneSixLibrary *library)
+{
+	dbg.nospace() << "OneSixLibrary("
+				  << "\n\t\t\trawName=" << library->rawName()
+				  << "\n\t\t\tname=" << library->name()
+				  << "\n\t\t\tversion=" << library->version()
+				  << "\n\t\t\ttype=" << library->type()
+				  << "\n\t\t\tisActive=" << library->isActive()
+				  << "\n\t\t\tisNative=" << library->isNative()
+				  << "\n\t\t\tdownloadUrl=" << library->downloadUrl()
+				  << "\n\t\t\tstoragePath=" << library->storagePath()
+				  << "\n\t\t\tabsolutePath=" << library->absoluteUrl()
+				  << "\n\t\t\thint=" << library->hint();
+	dbg.nospace() << "\n\t\t)";
+	return dbg.maybeSpace();
+}
diff --git a/logic/OneSixVersion.h b/logic/OneSixVersion.h
index 036f3d53..00afd010 100644
--- a/logic/OneSixVersion.h
+++ b/logic/OneSixVersion.h
@@ -14,15 +14,23 @@
  */
 
 #pragma once
-#include <QtCore>
+
+#include <QAbstractListModel>
+
+#include <QString>
+#include <QList>
 #include <memory>
 
-class OneSixLibrary;
+#include "OneSixLibrary.h"
+
+class OneSixInstance;
 
 class OneSixVersion : public QAbstractListModel
 {
-	// Things required to implement the Qt list model
+	Q_OBJECT
 public:
+	explicit OneSixVersion(OneSixInstance *instance, QObject *parent = 0);
+
 	virtual QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const;
 	virtual int rowCount(const QModelIndex &parent = QModelIndex()) const;
 	virtual QVariant headerData(int section, Qt::Orientation orientation,
@@ -30,24 +38,19 @@ public:
 	virtual int columnCount(const QModelIndex &parent) const;
 	virtual Qt::ItemFlags flags(const QModelIndex &index) const;
 
-	// serialization/deserialization
-public:
-	bool toOriginalFile();
-	static std::shared_ptr<OneSixVersion> fromJson(QJsonObject root);
-	static std::shared_ptr<OneSixVersion> fromFile(QString filepath);
+	bool reload(QWidget *widgetParent);
+	void clear();
+
+	void dump() const;
 
 public:
 	QList<std::shared_ptr<OneSixLibrary>> getActiveNormalLibs();
 	QList<std::shared_ptr<OneSixLibrary>> getActiveNativeLibs();
-	// called when something starts/stops messing with the object
-	// FIXME: these are ugly in every possible way.
-	void externalUpdateStart();
-	void externalUpdateFinish();
+
+	static std::shared_ptr<OneSixVersion> fromJson(const QJsonObject &obj);
 
 	// data members
 public:
-	/// file this was read from. blank, if none
-	QString original_file;
 	/// the ID - determines which jar to use! ACTUALLY IMPORTANT!
 	QString id;
 	/// Last updated time - as a string
@@ -103,4 +106,10 @@ public:
 	}
 	*/
 	// QList<Rule> rules;
+
+private:
+	OneSixInstance *m_instance;
 };
+
+QDebug operator<<(QDebug &dbg, const OneSixVersion *version);
+QDebug operator<<(QDebug &dbg, const OneSixLibrary *library);
diff --git a/logic/OneSixVersionBuilder.cpp b/logic/OneSixVersionBuilder.cpp
new file mode 100644
index 00000000..85f55a52
--- /dev/null
+++ b/logic/OneSixVersionBuilder.cpp
@@ -0,0 +1,446 @@
+/* Copyright 2013 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "OneSixVersionBuilder.h"
+
+#include <QList>
+#include <QJsonObject>
+#include <QJsonArray>
+#include <QJsonDocument>
+#include <QFile>
+#include <QFileInfo>
+#include <QMessageBox>
+#include <QObject>
+#include <QDir>
+#include <QDebug>
+
+#include "OneSixVersion.h"
+#include "OneSixInstance.h"
+#include "OneSixRule.h"
+#include "logger/QsLog.h"
+
+OneSixVersionBuilder::OneSixVersionBuilder()
+{
+
+}
+
+bool OneSixVersionBuilder::build(OneSixVersion *version, OneSixInstance *instance, QWidget *widgetParent)
+{
+	OneSixVersionBuilder builder;
+	builder.m_version = version;
+	builder.m_instance = instance;
+	builder.m_widgetParent = widgetParent;
+	return builder.build();
+}
+
+bool OneSixVersionBuilder::read(OneSixVersion *version, const QJsonObject &obj)
+{
+	OneSixVersionBuilder builder;
+	builder.m_version = version;
+	builder.m_instance = 0;
+	builder.m_widgetParent = 0;
+	return builder.read(obj);
+}
+
+bool OneSixVersionBuilder::build()
+{
+	m_version->clear();
+
+	QDir root(m_instance->instanceRoot());
+	QDir patches(root.absoluteFilePath("patches/"));
+
+	// version.json -> patches/*.json -> custom.json
+
+	// version.json
+	{
+		QLOG_INFO() << "Reading version.json";
+		QJsonObject obj;
+		if (!read(QFileInfo(root.absoluteFilePath("version.json")), &obj))
+		{
+			return false;
+		}
+		if (!apply(obj))
+		{
+			return false;
+		}
+	}
+
+	// patches/
+	{
+		// load all, put into map for ordering, apply in the right order
+
+		QMap<int, QJsonObject> objects;
+		for (auto info : patches.entryInfoList(QStringList() << "*.json", QDir::Files))
+		{
+			QLOG_INFO() << "Reading" << info.fileName();
+			QJsonObject obj;
+			if (!read(info, &obj))
+			{
+				return false;
+			}
+			if (!obj.contains("order") || !obj.value("order").isDouble())
+			{
+				QMessageBox::critical(m_widgetParent, QObject::tr("Error"), QObject::tr("Missing or invalid 'order' in %1").arg(info.absoluteFilePath()));
+				return false;
+			}
+			objects.insert(obj.value("order").toDouble(), obj);
+		}
+		for (auto object : objects.values())
+		{
+			qDebug() << "Applying object with order" << objects.key(object);
+			if (!apply(object))
+			{
+				return false;
+			}
+		}
+	}
+
+	// custom.json
+	{
+		if (QFile::exists(root.absoluteFilePath("custom.json")))
+		{
+			QLOG_INFO() << "Reading custom.json";
+			QJsonObject obj;
+			if (!read(QFileInfo(root.absoluteFilePath("custom.json")), &obj))
+			{
+				return false;
+			}
+			if (!apply(obj))
+			{
+				return false;
+			}
+		}
+	}
+
+	return true;
+}
+
+bool OneSixVersionBuilder::read(const QJsonObject &obj)
+{
+	m_version->clear();
+
+	return apply(obj);
+}
+
+void applyString(const QJsonObject &obj, const QString &key, QString &out, const bool onlyOverride = true)
+{
+	if (obj.contains(key) && obj.value(key).isString())
+	{
+		out = obj.value(key).toString();
+	}
+	else if (!onlyOverride)
+	{
+		if (obj.contains("+" + key) && obj.value("+" + key).isString())
+		{
+			out += obj.value("+" + key).toString();
+		}
+		else if (obj.contains("-" + key) && obj.value("-" + key).isString())
+		{
+			out.remove(obj.value("-" + key).toString());
+		}
+	}
+}
+void applyString(const QJsonObject &obj, const QString &key, std::shared_ptr<OneSixLibrary> lib, void(OneSixLibrary::*func)(const QString &val))
+{
+	if (obj.contains(key) && obj.value(key).isString())
+	{
+		(lib.get()->*func)(obj.value(key).toString());
+	}
+}
+bool OneSixVersionBuilder::apply(const QJsonObject &object)
+{
+	applyString(object, "id", m_version->id);
+	applyString(object, "mainClass", m_version->mainClass);
+	applyString(object, "minecraftArguments", m_version->minecraftArguments, false);
+	applyString(object, "processArguments", m_version->processArguments, false);
+	if (m_version->minecraftArguments.isEmpty())
+	{
+		const QString toCompare = m_version->processArguments.toLower();
+		if (toCompare == "legacy")
+		{
+			m_version->minecraftArguments = " ${auth_player_name} ${auth_session}";
+		}
+		else if (toCompare == "username_session")
+		{
+			m_version->minecraftArguments = "--username ${auth_player_name} --session ${auth_session}";
+		}
+		else if (toCompare == "username_session_version")
+		{
+			m_version->minecraftArguments = "--username ${auth_player_name} --session ${auth_session} --version ${profile_name}";
+		}
+	}
+	applyString(object, "type", m_version->type);
+	applyString(object, "releaseTime", m_version->releaseTime);
+	applyString(object, "time", m_version->time);
+	applyString(object, "assets", m_version->assets);
+	{
+		if (m_version->assets.isEmpty())
+		{
+			m_version->assets = "legacy";
+		}
+	}
+	if (object.contains("minimumLauncherVersion"))
+	{
+		auto minLauncherVersionVal = object.value("minimumLauncherVersion");
+		if (minLauncherVersionVal.isDouble())
+		{
+			m_version->minimumLauncherVersion = minLauncherVersionVal.toDouble();
+		}
+	}
+
+	// libraries
+	if (object.contains("libraries"))
+	{
+		m_version->libraries.clear();
+		auto librariesValue = object.value("libraries");
+		if (!librariesValue.isArray())
+		{
+			QMessageBox::critical(m_widgetParent, QObject::tr("Error"), QObject::tr("One json files contains a libraries field, but it's not an array"));
+			return false;
+		}
+		auto array = librariesValue.toArray();
+		for (auto libVal : array)
+		{
+			if (libVal.isObject())
+			{
+				if (!applyLibrary(libVal.toObject(), Override))
+				{
+					return false;
+				}
+			}
+
+		}
+	}
+
+	// +libraries
+	if (object.contains("+libraries"))
+	{
+		auto librariesValue = object.value("+libraries");
+		if (!librariesValue.isArray())
+		{
+			QMessageBox::critical(m_widgetParent, QObject::tr("Error"), QObject::tr("One json files contains a libraries field, but it's not an array"));
+			return false;
+		}
+		for (auto libVal : librariesValue.toArray())
+		{
+			if (libVal.isObject())
+			{
+				applyLibrary(libVal.toObject(), Add);
+			}
+
+		}
+	}
+
+	// -libraries
+	if (object.contains("-libraries"))
+	{
+		auto librariesValue = object.value("-libraries");
+		if (!librariesValue.isArray())
+		{
+			QMessageBox::critical(m_widgetParent, QObject::tr("Error"), QObject::tr("One json files contains a libraries field, but it's not an array"));
+			return false;
+		}
+		for (auto libVal : librariesValue.toArray())
+		{
+			if (libVal.isObject())
+			{
+				applyLibrary(libVal.toObject(), Remove);
+			}
+
+		}
+	}
+
+	return true;
+}
+
+int findLibrary(QList<std::shared_ptr<OneSixLibrary> > haystack, const QString &needle)
+{
+	for (int i = 0; i < haystack.size(); ++i)
+	{
+		if (QRegExp(needle, Qt::CaseSensitive, QRegExp::WildcardUnix).indexIn(haystack.at(i)->rawName()) != -1)
+		{
+			return i;
+		}
+	}
+	return -1;
+}
+
+bool OneSixVersionBuilder::applyLibrary(const QJsonObject &lib, const OneSixVersionBuilder::Type type)
+{
+	// Library name
+	auto nameVal = lib.value("name");
+	if (!nameVal.isString())
+	{
+		return false;
+	}
+	auto name = nameVal.toString();
+
+	if (type == Remove)
+	{
+		int index = findLibrary(m_version->libraries, name);
+		if (index >= 0)
+		{
+			m_version->libraries.removeAt(index);
+		}
+		return true;
+	}
+
+	if (type == Add && !lib.contains("insert"))
+	{
+		return false;
+	}
+
+	std::shared_ptr<OneSixLibrary> library;
+
+	if (lib.value("insert").toString() != "apply" && type == Add)
+	{
+		QMutableListIterator<std::shared_ptr<OneSixLibrary> > it(m_version->libraries);
+		while (it.hasNext())
+		{
+			if (it.next()->rawName() == name)
+			{
+				it.remove();
+			}
+		}
+	}
+
+	if (lib.value("insert").toString() == "apply" && type == Add)
+	{
+		library = m_version->libraries[findLibrary(m_version->libraries, name)];
+	}
+	else
+	{
+		library.reset(new OneSixLibrary(nameVal.toString()));
+	}
+
+	applyString(lib, "url", library, &OneSixLibrary::setBaseUrl);
+	applyString(lib, "MMC-hint", library, &OneSixLibrary::setHint);
+	applyString(lib, "MMC-absulute_url", library, &OneSixLibrary::setAbsoluteUrl);
+	applyString(lib, "MMC-absoluteUrl", library, &OneSixLibrary::setAbsoluteUrl);
+
+	auto extractVal = lib.value("extract");
+	if (extractVal.isObject())
+	{
+		QStringList excludes;
+		auto extractObj = extractVal.toObject();
+		auto excludesVal = extractObj.value("exclude");
+		if (excludesVal.isArray())
+		{
+			auto excludesList = excludesVal.toArray();
+			for (auto excludeVal : excludesList)
+			{
+				if (excludeVal.isString())
+				{
+					excludes.append(excludeVal.toString());
+				}
+			}
+			library->extract_excludes = excludes;
+		}
+	}
+
+	auto nativesVal = lib.value("natives");
+	if (nativesVal.isObject())
+	{
+		library->setIsNative();
+		auto nativesObj = nativesVal.toObject();
+		for (auto it = nativesObj.begin(); it != nativesObj.end(); ++it)
+		{
+			auto osType = OpSys_fromString(it.key());
+			if (osType == Os_Other)
+			{
+				continue;
+			}
+			if (!it.value().isString())
+			{
+				continue;
+			}
+			library->addNative(osType, it.value().toString());
+		}
+	}
+
+	if (lib.contains("rules"))
+	{
+		library->setRules(rulesFromJsonV4(lib));
+	}
+	library->finalize();
+	if (type == Override)
+	{
+		m_version->libraries.append(library);
+	}
+	else if (lib.value("insert").toString() != "apply")
+	{
+		if (lib.value("insert").toString() == "append")
+		{
+			m_version->libraries.append(library);
+		}
+		else if (lib.value("insert").toString() == "prepend")
+		{
+			m_version->libraries.prepend(library);
+		}
+		else if (lib.value("insert").isObject())
+		{
+			QJsonObject insertObj = lib.value("insert").toObject();
+			if (insertObj.isEmpty())
+			{
+				QMessageBox::critical(m_widgetParent, QObject::tr("Error"), QObject::tr("'insert' object empty"));
+				return false;
+			}
+			const QString key = insertObj.keys().first();
+			const QString value = insertObj.value(key).toString();
+			const int index = findLibrary(m_version->libraries, value);
+			if (index >= 0)
+			{
+				if (key == "before")
+				{
+					m_version->libraries.insert(index, library);
+				}
+				else if (key == "after")
+				{
+					m_version->libraries.insert(index + 1, library);
+				}
+				else
+				{
+					QMessageBox::critical(m_widgetParent, QObject::tr("Error"), QObject::tr("Invalid value for 'insert': %1").arg(lib.value("insert").toString()));
+					return false;
+				}
+			}
+		}
+		else
+		{
+			QMessageBox::critical(m_widgetParent, QObject::tr("Error"), QObject::tr("Invalid value for 'insert': %1").arg(lib.value("insert").toString()));
+			return false;
+		}
+	}
+	return true;
+}
+
+bool OneSixVersionBuilder::read(const QFileInfo &fileInfo, QJsonObject *out)
+{
+	QFile file(fileInfo.absoluteFilePath());
+	if (!file.open(QFile::ReadOnly))
+	{
+		QMessageBox::critical(m_widgetParent, QObject::tr("Error"), QObject::tr("Unable to open %1: %2").arg(file.fileName(), file.errorString()));
+		return false;
+	}
+	QJsonParseError error;
+	QJsonDocument doc = QJsonDocument::fromJson(file.readAll(), &error);
+	if (error.error != QJsonParseError::NoError)
+	{
+		QMessageBox::critical(m_widgetParent, QObject::tr("Error"), QObject::tr("Unable to parse %1: %2 at %3").arg(file.fileName(), error.errorString()).arg(error.offset));
+		return false;
+	}
+	*out = doc.object();
+	return true;
+}
diff --git a/logic/OneSixVersionBuilder.h b/logic/OneSixVersionBuilder.h
new file mode 100644
index 00000000..a3ba331c
--- /dev/null
+++ b/logic/OneSixVersionBuilder.h
@@ -0,0 +1,53 @@
+/* Copyright 2013 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <QString>
+
+class OneSixVersion;
+class OneSixInstance;
+class QWidget;
+class QJsonObject;
+class QFileInfo;
+
+class OneSixVersionBuilder
+{
+	OneSixVersionBuilder();
+public:
+	static bool build(OneSixVersion *version, OneSixInstance *instance, QWidget *widgetParent);
+	static bool read(OneSixVersion *version, const QJsonObject &obj);
+
+private:
+	OneSixVersion *m_version;
+	OneSixInstance *m_instance;
+	QWidget *m_widgetParent;
+
+	enum Type
+	{
+		Override,
+		Add,
+		Remove
+	};
+
+	bool build();
+	bool read(const QJsonObject &obj);
+
+	void clear();
+	bool apply(const QJsonObject &object);
+	bool applyLibrary(const QJsonObject &lib, const Type type);
+
+	bool read(const QFileInfo &fileInfo, QJsonObject *out);
+};