From a134878e6773b8dc31cdc101f2cd83a16581257a Mon Sep 17 00:00:00 2001
From: Emily Boudreaux <emily@boudreauxmail.com>
Date: Wed, 19 Feb 2025 16:11:55 -0500
Subject: [PATCH] feat(config): config class added

At many points in the code we may want configurable options, the Config class usses a yaml file to make this easy. It also allows for namespace references "opac:lowtemp:file" etc...
---
 src/config/meson.build        | 26 ++++++++++
 src/config/private/config.cpp | 31 ++++++++++++
 src/config/public/config.h    | 91 +++++++++++++++++++++++++++++++++++
 src/meson.build               |  3 +-
 4 files changed, 150 insertions(+), 1 deletion(-)
 create mode 100644 src/config/meson.build
 create mode 100644 src/config/private/config.cpp
 create mode 100644 src/config/public/config.h

diff --git a/src/config/meson.build b/src/config/meson.build
new file mode 100644
index 0000000..289b086
--- /dev/null
+++ b/src/config/meson.build
@@ -0,0 +1,26 @@
+# Define the library
+config_sources = files(
+  'private/config.cpp',
+)
+
+config_headers = files(
+    'public/config.h'
+)
+
+# Define the libconfig library so it can be linked against by other parts of the build system
+libconfig = static_library('config',
+    config_sources, 
+    include_directories: include_directories('public'),
+    cpp_args: ['-fvisibility=default'],
+    dependencies: [yaml_cpp_dep],
+    install : true)
+
+config_dep = declare_dependency(
+    include_directories: include_directories('public'),
+    link_with: libconfig,
+    sources: config_sources,
+    dependencies: [yaml_cpp_dep],
+)
+
+# Make headers accessible
+install_headers(config_headers, subdir : '4DSSE/config')
\ No newline at end of file
diff --git a/src/config/private/config.cpp b/src/config/private/config.cpp
new file mode 100644
index 0000000..45fcf27
--- /dev/null
+++ b/src/config/private/config.cpp
@@ -0,0 +1,31 @@
+#include <string>
+#include <iostream>
+#include <fstream>
+#include <sstream>
+#include <vector>
+#include <map>
+
+#include "yaml-cpp/yaml.h"
+
+#include "config.h"
+
+Config::Config() {}
+
+Config::~Config() {}
+
+Config& Config::getInstance() {
+    static Config instance;
+    return instance;
+}
+
+bool Config::loadConfig(const std::string& configFile) {
+    configFilePath = configFile;
+    try {
+        yamlRoot = YAML::LoadFile(configFile);
+    } catch (YAML::BadFile& e) {
+        std::cerr << "Error: " << e.what() << std::endl;
+        return false;
+    }
+    return true;
+}
+
diff --git a/src/config/public/config.h b/src/config/public/config.h
new file mode 100644
index 0000000..c79e841
--- /dev/null
+++ b/src/config/public/config.h
@@ -0,0 +1,91 @@
+#ifndef CONFIG_H
+#define CONFIG_H
+
+#include <string>
+#include <iostream>
+#include <fstream>
+#include <sstream>
+#include <vector>
+#include <map>
+
+#include "yaml-cpp/yaml.h"
+
+/**
+ * @class Config
+ * @brief Singleton class to manage configuration settings loaded from a YAML file.
+ */
+class Config {
+ private:
+    /**
+     * @brief Private constructor to prevent instantiation.
+     */
+    Config();
+
+    /**
+     * @brief Destructor.
+     */
+    ~Config();
+
+    YAML::Node yamlRoot; ///< Root node of the YAML configuration.
+    std::string configFilePath; ///< Path to the configuration file.
+
+ public:
+    /**
+     * @brief Get the singleton instance of the Config class.
+     * @return Reference to the Config instance.
+     */
+    static Config& getInstance();
+
+    Config (const Config&) = delete;
+    Config& operator= (const Config&) = delete;
+    Config (Config&&) = delete;
+    Config& operator= (Config&&) = delete;
+
+    /**
+     * @brief Load configuration from a YAML file.
+     * @param configFilePath Path to the YAML configuration file.
+     * @return True if the configuration was loaded successfully, false otherwise.
+     */
+    bool loadConfig(const std::string& configFilePath);
+
+    /**
+     * @brief Get the input table from the configuration.
+     * @return Input table as a string.
+     */
+    std::string getInputTable() const;
+
+    /**
+     * @brief Get a configuration value by key.
+     * @tparam T Type of the value to retrieve.
+     * @param key Key of the configuration value.
+     * @param defaultValue Default value to return if the key does not exist.
+     * @return Configuration value of type T.
+     * 
+     * @example
+     * @code
+     * Config& config = Config::getInstance();
+     * config.loadConfig("example.yaml");
+     * int maxIter = config.get<int>("opac:lowTemp:numeric:maxIter", 10);
+     */
+   template <typename T>
+   T get(const std::string &key, T defaultValue) {
+      YAML::Node node = YAML::Clone(yamlRoot);
+      std::istringstream keyStream(key);
+      std::string subKey;
+      while (std::getline(keyStream, subKey, ':')) {
+         if (!node[subKey]) {
+               return defaultValue;
+         }
+         node = node[subKey]; // go deeper
+      }
+
+      try {
+         return node.as<T>();
+      } catch (const YAML::Exception& e) {
+         return defaultValue; // return default value if the key does not exist
+      }
+   }
+
+};
+
+#endif
\ No newline at end of file
diff --git a/src/meson.build b/src/meson.build
index 9ae232d..bcad636 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -5,4 +5,5 @@ subdir('resources')
 subdir('dobj')
 subdir('const')
 subdir('opatIO')
-subdir('meshIO')
\ No newline at end of file
+subdir('meshIO')
+subdir('config')
\ No newline at end of file