feat(Core/Config): Implement config override with env vars (#16817)

* Core/Config: Implement config override with env vars

Implement overriding of configuration from the .conf file with environment variables.
Environment variables keys are autogenerated based on the keys defined in .conf file.

Usage example:

$ export TC_DATA_DIR=/usr
$ AC_WORLD_SERVER_PORT=8080 ./worldserver

* Add tests for env vars config

src/common/Configuration/Config.cpp

@@ -21,6 +21,7 @@
 #include "StringFormat.h"
 #include "Tokenize.h"
 #include "Util.h"
+#include <cstdlib>
 #include <fstream>
 #include <mutex>
 #include <unordered_map>
@@ -215,6 +216,81 @@ namespace
 
         return false;
     }
+
+    // Converts ini keys to the environment variable key (upper snake case).
+    // Example of conversions:
+    //   SomeConfig => SOME_CONFIG
+    //   myNestedConfig.opt1 => MY_NESTED_CONFIG_OPT_1
+    //   LogDB.Opt.ClearTime => LOG_DB_OPT_CLEAR_TIME
+    std::string IniKeyToEnvVarKey(std::string const& key)
+    {
+        std::string result;
+
+        const char* str = key.c_str();
+        size_t n = key.length();
+
+        char curr;
+        bool isEnd;
+        bool nextIsUpper;
+        bool currIsNumeric;
+        bool nextIsNumeric;
+
+        for (size_t i = 0; i < n; ++i)
+        {
+            curr = str[i];
+            if (curr == ' ' || curr == '.' || curr == '-')
+            {
+                result += '_';
+                continue;
+            }
+
+            isEnd = i == n - 1;
+            if (!isEnd)
+            {
+                nextIsUpper = isupper(str[i + 1]);
+
+                // handle "aB" to "A_B"
+                if (!isupper(curr) && nextIsUpper)
+                {
+                    result += static_cast<char>(std::toupper(curr));
+                    result += '_';
+                    continue;
+                }
+
+                currIsNumeric = isNumeric(curr);
+                nextIsNumeric = isNumeric(str[i + 1]);
+
+                // handle "a1" to "a_1"
+                if (!currIsNumeric && nextIsNumeric)
+                {
+                    result += static_cast<char>(std::toupper(curr));
+                    result += '_';
+                    continue;
+                }
+
+                // handle "1a" to "1_a"
+                if (currIsNumeric && !nextIsNumeric)
+                {
+                    result += static_cast<char>(std::toupper(curr));
+                    result += '_';
+                    continue;
+                }
+            }
+
+            result += static_cast<char>(std::toupper(curr));
+        }
+        return result;
+    }
+
+    Optional<std::string> EnvVarForIniKey(std::string const& key)
+    {
+        std::string envKey = "AC_" + IniKeyToEnvVarKey(key);
+        char* val = std::getenv(envKey.c_str());
+        if (!val)
+            return std::nullopt;
+
+        return std::string(val);
+    }
 }
 
 bool ConfigMgr::LoadInitial(std::string const& file, bool isReload /*= false*/)
@@ -243,25 +319,72 @@ bool ConfigMgr::Reload()
         return false;
     }
 
-    return LoadModulesConfigs(true, false);
+    if (!LoadModulesConfigs(true, false))
+    {
+        return false;
+    }
+
+    OverrideWithEnvVariablesIfAny();
+
+    return true;
+}
+
+std::vector<std::string> ConfigMgr::OverrideWithEnvVariablesIfAny()
+{
+    std::lock_guard<std::mutex> lock(_configLock);
+
+    std::vector<std::string> overriddenKeys;
+
+    for (auto& itr : _configOptions)
+    {
+        if (itr.first.empty())
+            continue;
+
+        Optional<std::string> envVar = EnvVarForIniKey(itr.first);
+        if (!envVar)
+            continue;
+
+        itr.second = *envVar;
+
+        overriddenKeys.push_back(itr.first);
+    }
+
+    return overriddenKeys;
 }
 
 template<class T>
 T ConfigMgr::GetValueDefault(std::string const& name, T const& def, bool showLogs /*= true*/) const
 {
+    std::string strValue;
     auto const& itr = _configOptions.find(name);
     if (itr == _configOptions.end())
     {
-        if (showLogs)
+        Optional<std::string> envVar = EnvVarForIniKey(name);
+        if (!envVar)
         {
-            LOG_ERROR("server.loading", "> Config: Missing property {} in config file {}, add \"{} = {}\" to this file.",
-                name, _filename, name, Acore::ToString(def));
+            if (showLogs)
+            {
+                LOG_ERROR("server.loading", "> Config: Missing property {} in config file {}, add \"{} = {}\" to this file.",
+                    name, _filename, name, Acore::ToString(def));
+            }
+
+            return def;
         }
 
-        return def;
+        if (showLogs)
+        {
+            LOG_WARN("server.loading", "Missing property {} in config file {}, recovered with environment '{}' value.",
+                name.c_str(), _filename.c_str(), envVar->c_str());
+        }
+
+        strValue = *envVar;
+    }
+    else
+    {
+        strValue = itr->second;
     }
 
-    auto value = Acore::StringTo<T>(itr->second);
+    auto value = Acore::StringTo<T>(strValue);
     if (!value)
     {
         if (showLogs)
@@ -282,6 +405,18 @@ std::string ConfigMgr::GetValueDefault<std::string>(std::string const& name, std
     auto const& itr = _configOptions.find(name);
     if (itr == _configOptions.end())
     {
+        Optional<std::string> envVar = EnvVarForIniKey(name);
+        if (envVar)
+        {
+            if (showLogs)
+            {
+                LOG_WARN("server.loading", "Missing property {} in config file {}, recovered with environment '{}' value.",
+                    name.c_str(), _filename.c_str(), envVar->c_str());
+            }
+
+            return *envVar;
+        }
+
         if (showLogs)
         {
             LOG_ERROR("server.loading", "> Config: Missing property {} in config file {}, add \"{} = {}\" to this file.",