//! Database-backed configuration loader for adaptive strategy
//!
//! This module provides functionality to load adaptive strategy configurations
//! from PostgreSQL, replacing hardcoded defaults with database-driven config.
//!
//! Features:
//! - Full configuration loading from database
//! - Hot-reload support via PostgreSQL NOTIFY/LISTEN
//! - Fallback to default configuration on database errors
//! - Validation of loaded configurations

#[cfg(feature = "postgres")]
use sqlx::postgres::PgListener;

#[cfg(feature = "postgres")]
use crate::config_types::{AdaptiveStrategyConfig, AdaptiveStrategyConfigRow, ModelConfigRow, FeatureConfigRow};
#[cfg(feature = "postgres")]
use std::time::Duration;

/// Database-backed configuration loader
///
/// Loads adaptive strategy configurations from PostgreSQL and provides
/// hot-reload capabilities through NOTIFY/LISTEN.
#[cfg(feature = "postgres")]
pub struct DatabaseConfigLoader {
    /// Database connection pool
    pool: sqlx::PgPool,
    /// PostgreSQL listener for hot-reload
    listener: Option<PgListener>,
    /// Cache timeout for loaded configurations (reserved for future caching implementation)
    #[allow(dead_code)]
    cache_timeout: Duration,
}

#[cfg(feature = "postgres")]
impl DatabaseConfigLoader {
    /// Create a new database configuration loader
    ///
    /// # Arguments
    /// * `database_url` - PostgreSQL connection URL
    ///
    /// # Example
    /// ```no_run
    /// # use adaptive_strategy::database_loader::DatabaseConfigLoader;
    /// # async fn example() -> Result<(), Box<dyn std::error::Error>> {
    /// let loader = DatabaseConfigLoader::new("postgresql://localhost/foxhunt").await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn new(database_url: &str) -> Result<Self, sqlx::Error> {
        let pool = sqlx::PgPool::connect(database_url).await?;

        Ok(Self {
            pool,
            listener: None,
            cache_timeout: Duration::from_secs(300), // 5 minutes
        })
    }

    /// Create a loader with an existing connection pool
    ///
    /// # Arguments
    /// * `pool` - Existing PostgreSQL connection pool
    pub fn with_pool(pool: sqlx::PgPool) -> Self {
        Self {
            pool,
            listener: None,
            cache_timeout: Duration::from_secs(300),
        }
    }

    /// Load configuration from database by strategy ID
    ///
    /// # Arguments
    /// * `strategy_id` - Strategy identifier (e.g., "default", "prod_v1")
    ///
    /// # Returns
    /// - `Ok(Some(config))` - Configuration loaded successfully
    /// - `Ok(None)` - Strategy not found in database
    /// - `Err(...)` - Database error occurred
    ///
    /// # Example
    /// ```no_run
    /// # use adaptive_strategy::database_loader::DatabaseConfigLoader;
    /// # async fn example(loader: &DatabaseConfigLoader) -> Result<(), Box<dyn std::error::Error>> {
    /// let config = loader.load_config("default").await?
    ///     .expect("Default strategy not found");
    /// config.validate()?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn load_config(
        &self,
        strategy_id: &str,
    ) -> Result<Option<AdaptiveStrategyConfig>, String> {
        // Load main configuration
        let config_row: Option<AdaptiveStrategyConfigRow> = sqlx::query_as(
            r#"
            SELECT
                id, strategy_id, name, description,
                execution_interval_ms, error_backoff_duration_secs,
                max_concurrent_operations, strategy_timeout_secs,
                max_parallel_models, rebalancing_interval_secs,
                min_model_weight, max_model_weight,
                max_position_size, max_leverage, stop_loss_pct,
                position_sizing_method, max_portfolio_var,
                max_drawdown_threshold, kelly_fraction,
                book_depth, vpin_window, trade_classification_threshold,
                trade_size_buckets, microstructure_features,
                regime_detection_method, regime_lookback_window,
                regime_transition_threshold, regime_features,
                execution_algorithm, max_order_size, min_order_size,
                order_timeout_secs, max_slippage_bps,
                smart_routing_enabled, dark_pool_preference,
                active, version, created_at, updated_at,
                created_by, updated_by, metadata
            FROM adaptive_strategy_config
            WHERE strategy_id = $1 AND active = true
            "#,
        )
        .bind(strategy_id)
        .fetch_optional(&self.pool)
        .await
        .map_err(|e| format!("Failed to load config: {}", e))?;

        let Some(config_row) = config_row else {
            return Ok(None);
        };

        let config_id = config_row.id;

        // Load associated models
        let models: Vec<ModelConfigRow> = sqlx::query_as(
            r#"
            SELECT
                id, strategy_config_id, model_id, model_name, model_type,
                parameters, initial_weight, enabled, display_order,
                created_at, updated_at
            FROM adaptive_strategy_models
            WHERE strategy_config_id = $1
            ORDER BY display_order, created_at
            "#,
        )
        .bind(config_id)
        .fetch_all(&self.pool)
        .await
        .map_err(|e| format!("Failed to load models: {}", e))?;

        // Load associated features
        let features: Vec<FeatureConfigRow> = sqlx::query_as(
            r#"
            SELECT
                id, strategy_config_id, feature_name, feature_type,
                parameters, enabled, required,
                created_at, updated_at
            FROM adaptive_strategy_features
            WHERE strategy_config_id = $1
            ORDER BY feature_name
            "#,
        )
        .bind(config_id)
        .fetch_all(&self.pool)
        .await
        .map_err(|e| format!("Failed to load features: {}", e))?;

        // Convert to structured configuration
        let config = config_row.into_config(models, features)?;

        // Validate configuration
        config.validate()?;

        Ok(Some(config))
    }

    // REMOVED: load_config_or_default() does not make sense for postgres-backed configs
    // The config_types::AdaptiveStrategyConfig has no Default impl (by design).
    // Fallback logic should use config::AdaptiveStrategyConfig::default() at the
    // application level after calling load_config().await.
    //
    // For non-postgres builds, see the stub implementation below which provides
    // the fallback directly to config::AdaptiveStrategyConfig::default().

    /// Enable hot-reload support
    ///
    /// Subscribes to PostgreSQL NOTIFY events for configuration changes.
    /// Call `check_for_updates()` periodically to receive notifications.
    pub async fn enable_hot_reload(&mut self) -> Result<(), sqlx::Error> {
        let mut listener = PgListener::connect_with(&self.pool).await?;
        listener.listen("adaptive_strategy_config_change").await?;
        self.listener = Some(listener);
        Ok(())
    }

    /// Check for configuration change notifications
    ///
    /// Returns the strategy_id if a configuration change notification
    /// was received, or None if no notifications are pending.
    ///
    /// # Example
    /// ```no_run
    /// # use adaptive_strategy::database_loader::DatabaseConfigLoader;
    /// # async fn example(loader: &mut DatabaseConfigLoader) -> Result<(), Box<dyn std::error::Error>> {
    /// // In a background task
    /// loop {
    ///     if let Some(strategy_id) = loader.check_for_updates().await? {
    ///         println!("Configuration changed for strategy: {}", strategy_id);
    ///         // Reload configuration
    ///         let new_config = loader.load_config(&strategy_id).await?;
    ///     }
    ///     tokio::time::sleep(std::time::Duration::from_secs(1)).await;
    /// }
    /// # }
    /// ```
    pub async fn check_for_updates(&mut self) -> Result<Option<String>, sqlx::Error> {
        if let Some(listener) = &mut self.listener {
            if let Some(notification) = listener.try_recv().await? {
                // Parse notification payload
                if let Ok(payload) = serde_json::from_str::<serde_json::Value>(notification.payload()) {
                    if let Some(strategy_id) = payload.get("strategy_id").and_then(|v| v.as_str()) {
                        return Ok(Some(strategy_id.to_string()));
                    }
                }
            }
        }
        Ok(None)
    }

    /// Get the underlying connection pool
    pub fn pool(&self) -> &sqlx::PgPool {
        &self.pool
    }
}

// Synchronous fallback loader for when postgres feature is not enabled
#[cfg(not(feature = "postgres"))]
pub struct DatabaseConfigLoader;

#[cfg(not(feature = "postgres"))]
impl DatabaseConfigLoader {
    /// Always returns default configuration when postgres feature is disabled
    pub fn load_config_or_default(&self, _strategy_id: &str) -> crate::config::AdaptiveStrategyConfig {
        crate::config::AdaptiveStrategyConfig::default()
    }
}

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

    #[test]
    fn test_fallback_loader_without_postgres() {
        // When postgres feature is disabled, should compile and return defaults
        #[cfg(not(feature = "postgres"))]
        {
            let loader = DatabaseConfigLoader;
            let config = loader.load_config_or_default("test");
            assert_eq!(config.general.execution_interval, Duration::from_millis(100));
        }
    }
}