# ConfigManager (`assignments::one::ConfigManager`)

## Overview

The `ConfigManager` class is used to be able to store configuration values in a `TOML` file making it
possible to change project settings without the need of recompiling the codebase.

The [`toml++`](https://marzer.github.io/tomlplusplus/) library is used to parse TOML configuration
files and provides type-safe access to configuration parameters. It is automatically installed
using the `FetchContent_Declare` macro inside of the `CMakeLists.txt`.

## Implementation Details

### Dependencies
- **toml++**: Modern header-only C++17 TOML parser and serializer
- **rclcpp**: ROS2 C++ client library for logging
- **filesystem**: C++17 filesystem library for file operations
- **DatabaseConfig**: Custom data structure for database configuration

### Key Components

#### Constructor
```cpp
ConfigManager(rclcpp::Logger logger)
```
- Initializes the configuration manager making use of a ROS2 logger
- Calls `find_config_file()` and `load_config()` for automatic setup
- Automatically attempts to locate and load configuration from a list of pre-defined paths.

#### Configuration Loading

**`bool load_config(const std::string& config_file_path)`**
> Returns `true` on successful load, `false` on failure

- Uses `toml::parse_file()`
- Loads TOML configuration from specified file path
- Validates file existence before attempting to parse
- Error handling for:
  - File not found errors
  - TOML parsing errors
  - General I/O exceptions
- Updates internal `loaded_` state flag

**`std::string find_config_file() const`**
> Returns first found configuration file path
> Returns empty string if no configuration file is found

- Automatically searches for configuration files in predefined locations
- Search paths (in order):
```cpp
std::vector<std::string> default_config_paths_ = {
    "config.toml",
    "./src/config.toml",
    "../config.toml",
    "../../config.toml",
    "../../../config.toml",
    "../../../../config.toml",
    "/etc/ros2_grade_calculator/config.toml"
};
```
#### Configuration Access

**`std::optional<DatabaseConfig> get_database_config() const`**
> Returns `std::optional<DatabaseConfig>` for safe null handling
> Returns `std::nullopt` if:
>   - Configuration is not loaded
>   - Database section is missing
>   - Parsing fails due to invalid format

- Calls `parse_database_config()` for actual parsing

**`bool is_loaded() const`**
> Returns `true` if configuration has been successfully loaded and parsed

- Getter for configuration load status
- Used by other components to verify configuration availability

### Configuration Parsing

**`DatabaseConfig parse_database_config(const toml::table& config) const`**
- parser for database configuration section
- Extracts all database-related parameters with defaults

#### Default Values and Fallbacks
- **host**: `"localhost"` - Local database server
- **port**: `5432` - Standard PostgreSQL port
- **dbname**: `"grades"` - Application-specific database
- **user**: `"postgres"` - Default PostgreSQL user
- **password**: `"postgres"` - Default PostgreSQL password
- **timeout**: `30` seconds - connection timeout
- **ssl**: `false` - Disabled by default for development
- **min_connections**: `1` - Minimal connection pool
- **max_connections**: `10` - connection pool limit

### Logging
- Uses ROS2 logger with `[CFG]` prefix for configuration operations
- Includes file paths in log messages

### Usage Examples

#### Automatic Configuration Loading
```cpp
// ConfigManager automatically finds and loads configuration
ConfigManager config_manager(node->get_logger());

if (config_manager.is_loaded()) {
    auto db_config = config_manager.get_database_config();
    if (db_config.has_value()) {
        // Use database configuration
        DatabaseManager db_manager(db_config.value());
    }
}
```

### Configuration File Format

Example complete TOML configuration:

```toml
# Database connection settings
[database]
host = "localhost"
port = 5432
dbname = "grades"
user = "postgres"
password = "postgres"
timeout = 30
ssl = false

[database.pool]
min_connections = 1
max_connections = 10
```