//! Application configuration settings.
//!
//! This module provides configuration structures that can be loaded from:
//! - YAML configuration files (base.yaml and environment-specific files)
//! - Environment variables (prefixed with APP__)
//!
//! Settings include application details, Modbus connection parameters, relay configuration,
//! rate limiting, and environment settings.

/// Application configuration settings.
///
/// Loads configuration from YAML files and environment variables.
#[derive(Debug, serde::Deserialize, Clone, Default)]
pub struct Settings {
    /// Application-specific settings (name, version, host, port, etc.)
    pub application: ApplicationSettings,
    /// Debug mode flag
    pub debug: bool,
    /// Frontend URL for CORS configuration
    pub frontend_url: String,
    /// Rate limiting configuration
    #[serde(default)]
    pub rate_limit: RateLimitSettings,
    /// Modbus configuration
    pub modbus: ModbusSettings,
    /// Relay configuration
    pub relay: RelaySettings,
}

impl Settings {
    /// Creates a new `Settings` instance by loading configuration from files and environment variables.
    ///
    /// # Errors
    ///
    /// Returns a `config::ConfigError` if:
    /// - Configuration files cannot be read or parsed
    /// - Required configuration values are missing
    /// - Configuration values cannot be deserialized into the expected types
    ///
    /// # Panics
    ///
    /// Panics if:
    /// - The current directory cannot be determined
    /// - The `APP_ENVIRONMENT` variable contains an invalid value (not "dev", "development", "prod", or "production")
    pub fn new() -> Result<Self, config::ConfigError> {
        // Use CARGO_MANIFEST_DIR to reliably locate settings regardless of where cargo is run from
        let base_path = std::env::var("CARGO_MANIFEST_DIR").map_or_else(
            // Fallback to current_dir for non-cargo builds
            |_| std::env::current_dir().expect("Failed to determine the current directory"),
            std::path::PathBuf::from,
        );
        println!("Reading settings from directory {}", base_path.display());
        let settings_directory = base_path.join("settings");
        let environment: Environment = std::env::var("APP_ENVIRONMENT")
            .unwrap_or_else(|_| "dev".into())
            .try_into()
            .expect("Failed to parse APP_ENVIRONMENT");
        let environment_filename = format!("{environment}.yaml");
        // Lower = takes precedence
        let settings = config::Config::builder()
            .add_source(config::File::from(settings_directory.join("base.yaml")))
            .add_source(config::File::from(
                settings_directory.join(environment_filename),
            ))
            .add_source(
                config::Environment::with_prefix("APP")
                    .prefix_separator("__")
                    .separator("__"),
            )
            .build()?;
        settings.try_deserialize()
    }
}

/// Application-specific configuration settings.
#[derive(Debug, serde::Deserialize, Clone, Default)]
pub struct ApplicationSettings {
    /// Application name
    pub name: String,
    /// Application version
    pub version: String,
    /// Port to bind to
    pub port: u16,
    /// Host address to bind to
    pub host: String,
    /// Base URL of the application
    pub base_url: String,
    /// Protocol (http or https)
    pub protocol: String,
}

/// Application environment.
#[derive(Debug, PartialEq, Eq, Default)]
pub enum Environment {
    /// Development environment
    #[default]
    Development,
    /// Production environment
    Production,
}

impl std::fmt::Display for Environment {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let self_str = match self {
            Self::Development => "development",
            Self::Production => "production",
        };
        write!(f, "{self_str}")
    }
}

impl TryFrom<String> for Environment {
    type Error = String;

    fn try_from(value: String) -> Result<Self, Self::Error> {
        Self::try_from(value.as_str())
    }
}

impl TryFrom<&str> for Environment {
    type Error = String;

    fn try_from(value: &str) -> Result<Self, Self::Error> {
        match value.to_lowercase().as_str() {
            "development" | "dev" => Ok(Self::Development),
            "production" | "prod" => Ok(Self::Production),
            other => Err(format!(
                "{other} is not a supported environment. Use either `development` or `production`"
            )),
        }
    }
}

/// Rate limiting configuration.
#[derive(Debug, serde::Deserialize, Clone)]
pub struct RateLimitSettings {
    /// Whether rate limiting is enabled
    #[serde(default = "default_rate_limit_enabled")]
    pub enabled: bool,
    /// Maximum number of requests allowed in the time window (burst size)
    #[serde(default = "default_burst_size")]
    pub burst_size: u32,
    /// Time window in seconds for rate limiting
    #[serde(default = "default_per_seconds")]
    pub per_seconds: u64,
}

impl Default for RateLimitSettings {
    fn default() -> Self {
        Self {
            enabled: default_rate_limit_enabled(),
            burst_size: default_burst_size(),
            per_seconds: default_per_seconds(),
        }
    }
}

const fn default_rate_limit_enabled() -> bool {
    true
}

const fn default_burst_size() -> u32 {
    100
}

const fn default_per_seconds() -> u64 {
    60
}

/// Modbus TCP connection configuration.
///
/// Configures the connection parameters for communicating with the Modbus relay device
/// using Modbus RTU over TCP protocol.
#[derive(Debug, serde::Deserialize, Clone)]
pub struct ModbusSettings {
    /// IP address or hostname of the Modbus device
    pub host: String,
    /// TCP port for Modbus communication (standard Modbus TCP port is 502)
    pub port: u16,
    /// Modbus slave/device ID (unit identifier)
    pub slave_id: u8,
    /// Operation timeout in seconds
    pub timeout_secs: u8,
}

impl Default for ModbusSettings {
    fn default() -> Self {
        Self {
            host: "192.168.0.200".to_string(),
            port: 502,
            slave_id: 0,
            timeout_secs: 5,
        }
    }
}

/// Relay control configuration.
///
/// Configures parameters for relay management and labeling.
#[derive(Debug, serde::Deserialize, Clone)]
pub struct RelaySettings {
    /// Maximum length for custom relay labels (in characters)
    pub label_max_length: u8,
}

impl Default for RelaySettings {
    fn default() -> Self {
        Self {
            label_max_length: 8,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn environment_display_development() {
        let env = Environment::Development;
        assert_eq!(env.to_string(), "development");
    }

    #[test]
    fn environment_display_production() {
        let env = Environment::Production;
        assert_eq!(env.to_string(), "production");
    }

    #[test]
    fn environment_from_str_development() {
        assert_eq!(
            Environment::try_from("development").unwrap(),
            Environment::Development
        );
        assert_eq!(
            Environment::try_from("dev").unwrap(),
            Environment::Development
        );
        assert_eq!(
            Environment::try_from("Development").unwrap(),
            Environment::Development
        );
        assert_eq!(
            Environment::try_from("DEV").unwrap(),
            Environment::Development
        );
    }

    #[test]
    fn environment_from_str_production() {
        assert_eq!(
            Environment::try_from("production").unwrap(),
            Environment::Production
        );
        assert_eq!(
            Environment::try_from("prod").unwrap(),
            Environment::Production
        );
        assert_eq!(
            Environment::try_from("Production").unwrap(),
            Environment::Production
        );
        assert_eq!(
            Environment::try_from("PROD").unwrap(),
            Environment::Production
        );
    }

    #[test]
    fn environment_from_str_invalid() {
        let result = Environment::try_from("invalid");
        assert!(result.is_err());
        assert!(result.unwrap_err().contains("not a supported environment"));
    }

    #[test]
    fn environment_from_string_development() {
        assert_eq!(
            Environment::try_from("development".to_string()).unwrap(),
            Environment::Development
        );
    }

    #[test]
    fn environment_from_string_production() {
        assert_eq!(
            Environment::try_from("production".to_string()).unwrap(),
            Environment::Production
        );
    }

    #[test]
    fn environment_from_string_invalid() {
        let result = Environment::try_from("invalid".to_string());
        assert!(result.is_err());
    }

    #[test]
    fn environment_default_is_development() {
        let env = Environment::default();
        assert_eq!(env, Environment::Development);
    }

    #[test]
    fn rate_limit_settings_default() {
        let settings = RateLimitSettings::default();
        assert!(settings.enabled);
        assert_eq!(settings.burst_size, 100);
        assert_eq!(settings.per_seconds, 60);
    }

    #[test]
    fn rate_limit_settings_deserialize_full() {
        let json = r#"{"enabled": true, "burst_size": 50, "per_seconds": 30}"#;
        let settings: RateLimitSettings = serde_json::from_str(json).unwrap();
        assert!(settings.enabled);
        assert_eq!(settings.burst_size, 50);
        assert_eq!(settings.per_seconds, 30);
    }

    #[test]
    fn rate_limit_settings_deserialize_partial() {
        let json = r#"{"enabled": false}"#;
        let settings: RateLimitSettings = serde_json::from_str(json).unwrap();
        assert!(!settings.enabled);
        assert_eq!(settings.burst_size, 100); // default
        assert_eq!(settings.per_seconds, 60); // default
    }

    #[test]
    fn rate_limit_settings_deserialize_empty() {
        let json = "{}";
        let settings: RateLimitSettings = serde_json::from_str(json).unwrap();
        assert!(settings.enabled); // default
        assert_eq!(settings.burst_size, 100); // default
        assert_eq!(settings.per_seconds, 60); // default
    }
}