use serde::{Deserialize, Serialize};
use std::path::Path;

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Config {
    pub oidc: OidcConfig,
    pub server: ServerConfig,
    pub database: DatabaseConfig,
    pub session: SessionConfig,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct OidcConfig {
    pub client_id: String,
    pub client_secret: String,
    pub auth_url: String,
    pub token_url: String,
    pub redirect_url: String,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ServerConfig {
    pub host: String,
    pub port: u16,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DatabaseConfig {
    pub url: String,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SessionConfig {
    pub secret: String,
}

impl Config {
    /// Load configuration from a TOML file and environment variables
    /// config-rs merges file config with environment variables automatically
    pub fn load(path: &str) -> Result<Self, Box<dyn std::error::Error>> {
        let mut builder = config::Config::builder();

        // Add default values first
        let defaults = Self::defaults();
        builder = builder.add_source(
            config::Config::try_from(&defaults)
                .map_err(|e| Box::new(e) as Box<dyn std::error::Error>)?,
        );

        // Load from file if it exists
        if Path::new(path).exists() {
            builder = builder.add_source(config::File::with_name(path).required(false));
        }

        // Override with environment variables
        // Environment variables should be prefixed with the app name and use __ for nesting
        // e.g., WEIGHT_TRACKER_OIDC__CLIENT_ID for oidc.client_id
        builder = builder.add_source(
            config::Environment::with_prefix("WEIGHT_TRACKER")
                .try_parsing(true)
                .separator("__"),
        );

        let config = builder.build()?;
        let result: Config = config.try_deserialize()?;
        Ok(result)
    }

    /// Get default configuration values
    fn defaults() -> Self {
        Config {
            oidc: OidcConfig {
                client_id: "your_client_id".to_string(),
                client_secret: "your_client_secret".to_string(),
                auth_url: "https://your-provider.com/auth".to_string(),
                token_url: "https://your-provider.com/token".to_string(),
                redirect_url: "http://localhost:3000/auth/callback".to_string(),
            },
            server: ServerConfig {
                host: "127.0.0.1".to_string(),
                port: 3000,
            },
            database: DatabaseConfig {
                url: "sqlite:weight_tracker.db".to_string(),
            },
            session: SessionConfig {
                secret: "your_secret_key_that_is_long_enough_so_the_library_does_not_complain"
                    .to_string(),
            },
        }
    }
}