[Server] Harden private chat history identity matching

Match both participants by account id and name so a federated user's remote id cannot collide with a local account, and stop storing foreign ids in the local chat log. Extract the paging assembly into a pure helper and cover the whole-second boundary rules with gtests.

tests/private_chat_paging_test.cpp

@@ -0,0 +1,115 @@
+#include "private_chat_paging.h"
+
+#include <gtest/gtest.h>
+
+namespace
+{
+ServerInfo_PrivateChatMessage messageAt(quint64 time, const QString &text)
+{
+    ServerInfo_PrivateChatMessage message;
+    message.set_time(time);
+    message.set_sender_name("sender");
+    message.set_message(text.toStdString());
+    return message;
+}
+
+QList<ServerInfo_PrivateChatMessage> newestFirst(std::initializer_list<quint64> times)
+{
+    QList<ServerInfo_PrivateChatMessage> messages;
+    for (const quint64 time : times) {
+        messages.append(messageAt(time, QString::number(time)));
+    }
+    return messages;
+}
+
+QList<quint64> timesOf(const QList<ServerInfo_PrivateChatMessage> &messages)
+{
+    QList<quint64> times;
+    for (const auto &message : messages) {
+        times.append(message.time());
+    }
+    return times;
+}
+} // namespace
+
+TEST(PrivateChatPaging, EmptyInputProducesEmptyPage)
+{
+    const PrivateChatPage page = assemblePrivateChatPage({}, 50);
+
+    EXPECT_TRUE(page.messages.isEmpty());
+    EXPECT_FALSE(page.hasMore);
+    EXPECT_FALSE(page.needsWholeSecond);
+}
+
+TEST(PrivateChatPaging, PageShorterThanLimitIsReturnedOldestFirst)
+{
+    const PrivateChatPage page = assemblePrivateChatPage(newestFirst({300, 200, 100}), 50);
+
+    EXPECT_EQ(timesOf(page.messages), QList<quint64>({100, 200, 300}));
+    EXPECT_FALSE(page.hasMore);
+    EXPECT_FALSE(page.needsWholeSecond);
+}
+
+TEST(PrivateChatPaging, PageExactlyAtLimitIsReturnedWithoutMore)
+{
+    const PrivateChatPage page = assemblePrivateChatPage(newestFirst({300, 200, 100}), 3);
+
+    EXPECT_EQ(timesOf(page.messages), QList<quint64>({100, 200, 300}));
+    EXPECT_FALSE(page.hasMore);
+}
+
+TEST(PrivateChatPaging, DistinctSecondsKeepWholePage)
+{
+    const PrivateChatPage page = assemblePrivateChatPage(newestFirst({300, 200, 100}), 2);
+
+    EXPECT_EQ(timesOf(page.messages), QList<quint64>({200, 300}));
+    EXPECT_TRUE(page.hasMore);
+    EXPECT_FALSE(page.needsWholeSecond);
+}
+
+TEST(PrivateChatPaging, BoundarySecondIsDeferredToNextPage)
+{
+    const PrivateChatPage page = assemblePrivateChatPage(newestFirst({300, 200, 200}), 2);
+
+    EXPECT_EQ(timesOf(page.messages), QList<quint64>({300}));
+    EXPECT_TRUE(page.hasMore);
+    EXPECT_FALSE(page.needsWholeSecond);
+}
+
+TEST(PrivateChatPaging, WholeSecondIsRequestedWhenNothingElseFits)
+{
+    const PrivateChatPage page = assemblePrivateChatPage(newestFirst({200, 200, 200}), 2);
+
+    EXPECT_TRUE(page.messages.isEmpty());
+    EXPECT_TRUE(page.hasMore);
+    EXPECT_TRUE(page.needsWholeSecond);
+    EXPECT_EQ(page.boundarySecond, 200);
+}
+
+TEST(PrivateChatPaging, WholeSecondIsRequestedForSingleMessageLimit)
+{
+    const PrivateChatPage page = assemblePrivateChatPage(newestFirst({200, 200}), 1);
+
+    EXPECT_TRUE(page.messages.isEmpty());
+    EXPECT_TRUE(page.needsWholeSecond);
+    EXPECT_EQ(page.boundarySecond, 200);
+}
+
+TEST(PrivateChatPaging, BoundarySecondAtPageEdgeIsDropped)
+{
+    const PrivateChatPage page = assemblePrivateChatPage(newestFirst({400, 400, 300, 300}), 3);
+
+    EXPECT_EQ(timesOf(page.messages), QList<quint64>({400, 400}));
+    EXPECT_TRUE(page.hasMore);
+    EXPECT_FALSE(page.needsWholeSecond);
+}
+
+TEST(PrivateChatPaging, ReturnedMessagesKeepSenderAndText)
+{
+    const PrivateChatPage page = assemblePrivateChatPage({messageAt(200, "hello"), messageAt(100, "world")}, 50);
+
+    ASSERT_EQ(page.messages.size(), 2);
+    EXPECT_EQ(page.messages.at(0).message(), "world");
+    EXPECT_EQ(page.messages.at(1).message(), "hello");
+    EXPECT_EQ(page.messages.at(0).sender_name(), "sender");
+}