Gerrit: Display dependent changes as tree.

Add a depth member to GerritChange indicating the tree depth
and populate it by searches over the dependent changes.
Display the root changes sorted by date and add dependent changes
to their deph=1 parent, avoiding deeply nested items.

Change-Id: I66ccf392ce47514841c661820797e81996e9e5cc
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/gerrit/gerritmodel.cpp

@@ -849,11 +849,6 @@ static bool parseOutput(const QSharedPointer<GerritParameters> &parameters,
 }
 #endif // QT_VERSION < 0x050000
 
-bool changeDateLessThan(const GerritChangePtr &c1, const GerritChangePtr &c2)
-{
-    return c1->lastUpdated < c2->lastUpdated;
-}
-
 QList<QStandardItem *> GerritModel::changeToRow(const GerritChangePtr &c) const
 {
     QList<QStandardItem *> row;
@@ -898,12 +893,53 @@ QList<QStandardItem *> GerritModel::changeToRow(const GerritChangePtr &c) const
     return row;
 }
 
+bool gerritChangeLessThan(const GerritChangePtr &c1, const GerritChangePtr &c2)
+{
+    if (c1->depth != c2->depth)
+        return c1->depth < c2->depth;
+    return c1->lastUpdated < c2->lastUpdated;
+}
+
 void GerritModel::queryFinished(const QByteArray &output)
 {
     QList<GerritChangePtr> changes;
     if (!parseOutput(m_parameters, output, changes))
         emit queryError();
-    qStableSort(changes.begin(), changes.end(), changeDateLessThan);
+    // Populate a hash with indices for faster access.
+    QHash<QString, int> idIndexHash;
+    const int count = changes.size();
+    for (int i = 0; i < count; ++i)
+        idIndexHash.insert(changes.at(i)->id, i);
+    // Mark root nodes: Changes that do not have a dependency, depend on a change
+    // not in the list or on a change that is not "NEW".
+    for (int i = 0; i < count; ++i) {
+        if (changes.at(i)->dependsOnId.isEmpty()) {
+            changes.at(i)->depth = 0;
+        } else {
+            const int dependsOnIndex = idIndexHash.value(changes.at(i)->dependsOnId, -1);
+            if (dependsOnIndex < 0 || changes.at(dependsOnIndex)->status != QLatin1String("NEW"))
+                changes.at(i)->depth = 0;
+        }
+    }
+    // Indicate depth of dependent changes by using that of the parent + 1 until no more
+    // changes occur.
+    for (bool changed = true; changed; ) {
+        changed = false;
+        for (int i = 0; i < count; ++i) {
+            if (changes.at(i)->depth < 0) {
+                const int dependsIndex = idIndexHash.value(changes.at(i)->dependsOnId);
+                const int dependsOnDepth = changes.at(dependsIndex)->depth;
+                if (dependsOnDepth >= 0) {
+                    changes.at(i)->depth = dependsOnDepth + 1;
+                    changed = true;
+                }
+            }
+        }
+    }
+    // Sort by depth (root nodes first) and by date.
+    qStableSort(changes.begin(), changes.end(), gerritChangeLessThan);
+    idIndexHash.clear();
+
     foreach (const GerritChangePtr &c, changes) {
         // Avoid duplicate entries for example in the (unlikely)
         // case people do self-reviews.
@@ -912,7 +948,20 @@ void GerritModel::queryFinished(const QByteArray &output)
             // It used for marking the changes pending for review in bold.
             if (m_userName.isEmpty() && !m_query->currentQuery())
                 m_userName = c->owner;
-            appendRow(changeToRow(c));
+            const QList<QStandardItem *> newRow = changeToRow(c);
+            if (c->depth) {
+                QStandardItem *parent = itemForId(c->dependsOnId);
+                // Append changes with depth > 1 to the parent with depth=1 to avoid
+                // too-deeply nested items.
+                for (; changeFromItem(parent)->depth >= 1; parent = parent->parent()) {}
+                parent->appendRow(newRow);
+                QString parentFilterString = parent->data(FilterRole).toString();
+                parentFilterString += QLatin1Char(' ');
+                parentFilterString += newRow.first()->data(FilterRole).toString();
+                parent->setData(QVariant(parentFilterString), FilterRole);
+            } else {
+                appendRow(newRow);
+            }
         }
     }
 }