Release v0.2.0 with incident diagnostics and in-app log viewer

src/platform.cpp

@@ -527,16 +527,112 @@ std::wstring lastError(const std::wstring &context)
 {
     return context + L" (Windows error " + std::to_wstring(GetLastError()) + L")";
 }
+std::wstring diagnosticText(const std::wstring &text)
+{
+    // Escape UTF-16 code units so invisible characters and malformed surrogate pairs
+    // can be reproduced without introducing fake log lines. Bound large selections.
+    std::wstring out = L"\"";
+    constexpr wchar_t hex[] = L"0123456789abcdef";
+    const auto count = std::min<size_t>(text.size(), 512);
+    for (size_t i = 0; i < count; ++i)
+    {
+        auto c = static_cast<unsigned short>(text[i]);
+        if (c == L'"' || c == L'\\')
+        {
+            out += L'\\';
+            out += c;
+        }
+        else if (c < 32 || c >= 127)
+        {
+            out += L"\\u";
+            for (int shift = 12; shift >= 0; shift -= 4)
+                out += hex[(c >> shift) & 15];
+        }
+        else
+            out += c;
+    }
+    return out + L"\" units=" + std::to_wstring(text.size()) +
+           L" truncated=" + std::to_wstring(count != text.size());
+}
+namespace
+{
+std::recursive_mutex logGate;
+bool loggingEnabled = false;
+DiagnosticBuffer diagnosticBuffer;
+}
+std::wstring DiagnosticBuffer::record(const std::wstring &message, bool problem, ULONGLONG now)
+{
+    while (!entries.empty() && (entries.size() >= 40 || now - entries.front().first > 30000))
+        entries.pop_front();
+    entries.emplace_back(now, message);
+    if (!problem)
+        return {};
+    std::wstring out = L"Diagnostic incident (preceding context, up to 30 seconds):";
+    for (const auto &[at, entry] : entries)
+        out += L"\n  ageMs=" + std::to_wstring(now - at) + L" " + entry;
+    entries.clear();
+    return out;
+}
+void setLoggingEnabled(bool enabled)
+{
+    std::lock_guard lock(logGate);
+    loggingEnabled = enabled;
+    if (!enabled)
+        diagnosticBuffer.clear();
+}
+std::wstring readDiagnosticLog(bool previous)
+{
+    std::lock_guard lock(logGate);
+    auto path = dataDirectory() / (previous ? L"kswitcher.log.1" : L"kswitcher.log");
+    if (!std::filesystem::exists(path))
+        return previous ? L"No previous log is available yet." : L"No log yet. Entries will appear when a problem is detected.";
+    auto bytes = readFile(path, 2 * 1024 * 1024);
+    auto text = wide(std::string(bytes.begin(), bytes.end()));
+    std::wstring display;
+    for (size_t i = 0; i < text.size(); ++i)
+    {
+        if (text[i] == L'\n' && (i == 0 || text[i - 1] != L'\r'))
+            display += L'\r';
+        display += text[i];
+    }
+    return display.empty() ? L"The log is empty." : display;
+}
+void clearDiagnosticLog(bool previous)
+{
+    // Serialize clearing with writes and rotation. Never delete the other log.
+    std::lock_guard lock(logGate);
+    auto path = dataDirectory() / (previous ? L"kswitcher.log.1" : L"kswitcher.log");
+    std::filesystem::remove(path);
+    if (!previous)
+        diagnosticBuffer.clear();
+}
+void diagnosticEvent(const std::wstring &message, bool problem)
+{
+    std::lock_guard lock(logGate);
+    if (!loggingEnabled)
+        return;
+    auto incident = diagnosticBuffer.record(message, problem, GetTickCount64());
+    if (!incident.empty())
+        log(incident);
+}
 void log(const std::wstring &message)
 {
-    static std::mutex gate;
-    std::lock_guard lock(gate);
+    std::lock_guard lock(logGate);
+    if (!loggingEnabled)
+        return;
     try
     {
         auto path = dataDirectory() / L"kswitcher.log";
         std::error_code ec;
-        if (std::filesystem::file_size(path, ec) > 256 * 1024)
-            std::filesystem::remove(path, ec);
+        auto size = std::filesystem::file_size(path, ec);
+        if (!ec && size > 256 * 1024)
+        {
+            auto previous = path;
+            previous += L".1";
+            std::filesystem::remove(previous, ec);
+            ec.clear();
+            std::filesystem::rename(path, previous, ec);
+        }
         std::ofstream f(path, std::ios::app);
         SYSTEMTIME t;
         GetLocalTime(&t);