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// Import necessary libraries and modules
use std::collections::HashMap;
use std::fs::File;
use std::io::{BufRead, BufReader, Error, ErrorKind};
use std::str::FromStr;

// Define a public struct `Config` with fields for configuration options
#[derive(Debug, Default)]
pub struct Config<T> {
    fields: HashMap<String, T>,
}

// Implement methods for the `Config` struct
impl<T> Config<T>
where
    T: std::fmt::Debug + Default + FromStr,
    <T as FromStr>::Err: std::fmt::Debug,
{
    // Define a method to create a `Config` instance from a file
    pub fn from_file(file_path: &str) -> Result<Config<T>, Error> {
        // Attempt to open the specified file
        let file = File::open(file_path)?;

        // Create a default `Config` instance
        let mut config = Config::default();

        // Define characters that indicate comments in the configuration file
        let mut comment_chars = vec!['#', ';'];

        // Iterate over each line in the file
        for line in BufReader::new(file).lines() {
            // Unwrap the line, handling any potential errors
            let line = line?;
            // Trim leading and trailing whitespaces from the line
            let trimmed_line = line.trim();

            // Skip empty lines and lines starting with comment characters
            if !trimmed_line.is_empty()
                && !comment_chars.contains(&trimmed_line.chars().next().unwrap())
            {
                // Split the line into key-value parts based on the '=' character
                let parts: Vec<&str> = trimmed_line.split('=').map(|s| s.trim()).collect();

                // Ensure that there are exactly two parts (key and value)
                if parts.len() != 2 {
                    return Err(Error::new(
                        ErrorKind::InvalidData,
                        "Invalid configuration format",
                    ));
                }

                // Extract key and value
                let key = parts[0].to_string();
                let value_str = parts[1].trim_matches('"'); // Remove surrounding double quotes

                // Use Default::default() for the default value
                let value = if value_str.is_empty() {
                    Default::default()
                } else {
                    value_str
                        .parse()
                        .map_err(|_| Error::new(ErrorKind::InvalidData, "Failed to parse value"))?
                };

                config.fields.insert(key, value);
            }
        }

        // Return the populated `Config` instance
        Ok(config)
    }

    // Define a method to get the value of using the `key`
    pub fn get_value(&self, key: &str) -> Option<&T> {
        self.fields.get(key)
    }
}

// Define tests for the `Config` struct and its methods
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_config_from_file() {
        let config = Config::from_file("example.cfg");
        assert!(config.is_ok(), "Failed to read configuration file: {:?}", config.err());

        let config = config.unwrap();
        assert_eq!(config.get_value("key1"), Some(&"value1".to_string()));
        assert_eq!(config.get_value("key2"), Some(&42.to_string()));
    }
}