Clang: Add sources manager

Indexing source files multiple times is unneeded overhead in many cases.
The source manager is a support class to handle that cases.

Change-Id: Id737eaa9a691c54563279562833493a221eb3431
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/tools/clangrefactoringbackend/source/sourcesmanager.h

@@ -0,0 +1,106 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include <filepathid.h>
+
+#include <ctime>
+
+namespace ClangBackEnd {
+
+class SourcesManager
+{
+    struct FilePathIdTime
+    {
+        FilePathIdTime(FilePathId filePathId, std::time_t modifiedTime)
+            : filePathId(filePathId),
+              modifiedTime(modifiedTime)
+        {}
+        FilePathId filePathId;
+        std::time_t modifiedTime = 0;
+    };
+
+public:
+    bool alreadyParsed(FilePathId filePathId, std::time_t modifiedTime)
+    {
+        auto found = std::lower_bound(m_modifiedTimeStamps.cbegin(),
+                                      m_modifiedTimeStamps.cend(),
+                                      filePathId,
+                                      [] (FilePathIdTime entry, FilePathId filePathId) {
+                return entry.filePathId < filePathId;
+        });
+
+        bool upToDate = found != m_modifiedTimeStamps.end() && found->filePathId == filePathId
+                && modifiedTime <= found->modifiedTime;
+
+        if (!upToDate)
+           addOrUpdateNewEntry(filePathId, modifiedTime);
+
+        return upToDate ;
+    }
+
+    void updateModifiedTimeStamps()
+    {
+        std::vector<FilePathIdTime> mergedModifiedTimeStamps;
+        mergedModifiedTimeStamps.reserve(m_newModifiedTimeStamps.size() + m_modifiedTimeStamps.size());
+
+        auto compare = [](FilePathIdTime first, FilePathIdTime second) {
+            return first.filePathId < second.filePathId;
+        };
+
+        std::set_union(m_newModifiedTimeStamps.begin(),
+                       m_newModifiedTimeStamps.end(),
+                       m_modifiedTimeStamps.begin(),
+                       m_modifiedTimeStamps.end(),
+                       std::back_inserter(mergedModifiedTimeStamps),
+                       compare);
+
+        m_modifiedTimeStamps = std::move(mergedModifiedTimeStamps);
+        m_newModifiedTimeStamps.clear();
+    }
+
+private:
+    void addOrUpdateNewEntry(FilePathId filePathId, std::time_t modifiedTime)
+    {
+        auto found = std::lower_bound(m_newModifiedTimeStamps.begin(),
+                                      m_newModifiedTimeStamps.end(),
+                                      filePathId,
+                                      [] (FilePathIdTime entry, FilePathId filePathId) {
+                return entry.filePathId < filePathId;
+        });
+
+        if (found != m_newModifiedTimeStamps.end() && found->filePathId == filePathId)
+            found->modifiedTime = modifiedTime;
+        else
+            m_newModifiedTimeStamps.emplace(found, filePathId, modifiedTime);
+    }
+
+private:
+    std::vector<FilePathIdTime> m_modifiedTimeStamps;
+    std::vector<FilePathIdTime> m_newModifiedTimeStamps;
+};
+
+}