Opts: Make singleton; senseApi: check senseApiLibPath, get senseApiDescFn pointer.

* OptionsParser now has a singleton.
* We now use the cmdline opt -p <senseApiLibPath>, and search for
  the specified library in:
  * senseApiLibPath, then CWD, then the place where our executable
    is running from, and then finally we let the hosting OS do
    its own search.
* We now call dlsym() on dlopen()'d libs to to get the senseApiDescFn
  pointer.

hcore/senseApis/senseApiManager.cpp

@@ -1,19 +1,63 @@
 #include <iostream>
 #include <stdexcept>
 #include <optional>
+#include <filesystem>
 #include <senseApis/senseApiManager.h>
 #include <senseApis/senseApiLib.h>
+#include <opts.h>
+#include <user/senseApiDesc.h>
+
+namespace fs = std::filesystem;
 
 namespace hk {
 namespace sense_api {
 
+static std::optional<std::string> findLibraryPath(
+    const std::string& libraryPath)
+{
+    std::vector<std::string> searchPaths = {
+        OptionParser::getOptions().senseApiLibPath,
+        fs::current_path().string(),
+        fs::path("/proc/self/exe").parent_path().string()
+    };
+
+    for (const auto& path : searchPaths)
+    {
+        fs::path fullPath = fs::path(path) / libraryPath;
+        if (fs::exists(fullPath))
+        {
+            return fullPath.string();
+        }
+    }
+
+    std::cerr << std::string(__func__) + ": library '"
+              + libraryPath + "' isn't in search bespoke search paths: ";
+    for (const auto& path : searchPaths)
+    {
+        std::cerr << path << " ";
+    }
+    std::cerr << std::endl;
+    std::cerr << "Trying to load " + libraryPath + " from system default search "
+        "paths\n";
+
+    return std::nullopt;
+}
+
 SenseApiLib& SenseApiManager::loadSenseApiLib(const std::string& libraryPath)
 {
-    auto lib = std::make_unique<SenseApiLib>(libraryPath);
+    std::optional<std::string> fullPath = findLibraryPath(libraryPath);
+    auto lib = std::make_unique<SenseApiLib>(fullPath.value_or(libraryPath));
 
     // Clear any existing error
     dlerror();
-    lib->handle.reset(dlopen(libraryPath.c_str(), RTLD_LAZY));
+    lib->handle.reset(dlopen(lib->libraryPath.c_str(), RTLD_LAZY));
+    if (!lib->handle && fullPath.has_value())
+    {
+        // Fallback to using the supplied libraryPath
+        dlerror();
+        lib->handle.reset(dlopen(libraryPath.c_str(), RTLD_LAZY));
+    }
+
     if (!lib->handle)
     {
         std::string error = dlerror()
@@ -25,6 +69,18 @@ SenseApiLib& SenseApiManager::loadSenseApiLib(const std::string& libraryPath)
             + error);
     }
 
+    // Initialize getSenseApiDescriptor
+    auto func = reinterpret_cast<SenseApiLib::SenseApiDescGetterFn*>(
+        dlsym(lib->handle.get(), HK_SENSE_API_DESC_GETTER_FN_NAME));
+    if (!func)
+    {
+        throw std::runtime_error(
+            std::string(__func__) + ": dlsym("
+            HK_SENSE_API_DESC_GETTER_FN_NAME ") failed for library '"
+            + lib->libraryPath + "'");
+    }
+    lib->getSenseApiDescriptor = func;
+
     senseApiLibs.push_back(std::move(lib));
     return *senseApiLibs.back();
 }