use super::types::{Event, EventType};
use crate::middleware::metrics::{
    AUTH_LOGIN_ATTEMPTS_TOTAL, COMMITMENTS_CREATED_TOTAL, COMMITMENTS_VERIFIED_TOTAL,
    ORDERS_CREATED_TOTAL, TOKENS_CREATED_TOTAL, TRADES_EXECUTED_TOTAL, USERS_REGISTERED_TOTAL,
};
use anyhow::Result;
use async_trait::async_trait;
use sqlx::PgPool;
use std::sync::Arc;

/// Event handler trait
#[async_trait]
pub trait EventHandler: Send + Sync {
    /// Handle an event
    async fn handle(&self, event: Event) -> Result<()>;

    /// Get handler name
    fn name(&self) -> &str;
}

/// Audit log event handler
pub struct AuditLogHandler {
    pool: Option<Arc<PgPool>>,
}

impl AuditLogHandler {
    /// Create a new audit log handler
    pub fn new(pool: Option<Arc<PgPool>>) -> Self {
        Self { pool }
    }
}

#[async_trait]
impl EventHandler for AuditLogHandler {
    async fn handle(&self, event: Event) -> Result<()> {
        // Log to tracing first
        tracing::info!(
            "AUDIT: Event {} of type {:?} at {}",
            event.id(),
            std::mem::discriminant(&event.event_type),
            event.timestamp()
        );

        // Persist to database if pool is available
        if let Some(pool) = &self.pool {
            let event_type_str = format!("{:?}", std::mem::discriminant(&event.event_type));
            let event_data =
                serde_json::to_value(&event.event_type).unwrap_or(serde_json::Value::Null);

            // Try to insert into audit_events table
            // Note: This table should be created via migrations
            // Using non-macro query to avoid compile-time database requirement
            let result = sqlx::query(
                r#"
                INSERT INTO audit_events (id, timestamp, event_type, event_data, source, correlation_id, user_id)
                VALUES ($1, $2, $3, $4, $5, $6, $7)
                ON CONFLICT (id) DO NOTHING
                "#,
            )
            .bind(event.id())
            .bind(event.timestamp())
            .bind(event_type_str)
            .bind(event_data)
            .bind(&event.metadata.source)
            .bind(&event.metadata.correlation_id)
            .bind(event.metadata.user_id)
            .execute(pool.as_ref())
            .await;

            if let Err(e) = result {
                // Don't fail the event processing if audit logging fails
                tracing::error!("Failed to persist audit event to database: {}", e);
            }
        }

        Ok(())
    }

    fn name(&self) -> &str {
        "AuditLogHandler"
    }
}

/// Metrics event handler
pub struct MetricsHandler;

#[async_trait]
impl EventHandler for MetricsHandler {
    async fn handle(&self, event: Event) -> Result<()> {
        // Update Prometheus metrics based on event type
        match &event.event_type {
            EventType::UserRegistered { .. } => {
                USERS_REGISTERED_TOTAL.inc();
                AUTH_LOGIN_ATTEMPTS_TOTAL
                    .with_label_values(&["register_success"])
                    .inc();
            }
            EventType::TokenCreated { .. } => {
                TOKENS_CREATED_TOTAL.inc();
            }
            EventType::OrderCreated { order_type, .. } => {
                ORDERS_CREATED_TOTAL.with_label_values(&[order_type]).inc();
            }
            EventType::OrderCompleted { .. } => {
                ORDERS_CREATED_TOTAL.with_label_values(&["completed"]).inc();
            }
            EventType::OrderCancelled { .. } => {
                ORDERS_CREATED_TOTAL.with_label_values(&["cancelled"]).inc();
            }
            EventType::TradeExecuted { .. } => {
                TRADES_EXECUTED_TOTAL.inc();
            }
            EventType::CommitmentCreated { .. } => {
                COMMITMENTS_CREATED_TOTAL.inc();
            }
            EventType::CommitmentVerified { approved, .. } => {
                let status = if *approved { "approved" } else { "rejected" };
                COMMITMENTS_VERIFIED_TOTAL
                    .with_label_values(&[status])
                    .inc();
            }
            _ => {
                // Other events don't have specific metrics
                tracing::debug!(
                    "METRICS: Event {} processed (no specific metric)",
                    event.id()
                );
            }
        }

        Ok(())
    }

    fn name(&self) -> &str {
        "MetricsHandler"
    }
}

/// Notification event handler
pub struct NotificationHandler;

#[async_trait]
impl EventHandler for NotificationHandler {
    async fn handle(&self, event: Event) -> Result<()> {
        // Trigger notifications based on event type
        match &event.event_type {
            EventType::UserRegistered { user_id, email } => {
                tracing::info!("Triggering welcome email for user: {}", user_id);
                // In production: send welcome email via EmailNotifier or job queue
                // Example: queue.enqueue(Job::SendEmail { to: email, subject: "Welcome", body: "..." })
                tracing::debug!("Would send welcome email to: {}", email);
            }
            EventType::TokenCreated {
                token_id, symbol, ..
            } => {
                tracing::info!("Triggering token creation notification for: {}", symbol);
                // In production: notify token creator via email/push
                tracing::debug!("Token {} created", token_id);
            }
            EventType::OrderCreated {
                order_id, user_id, ..
            } => {
                tracing::info!(
                    "Triggering order created notification for user: {}",
                    user_id
                );
                // In production: send order confirmation email
                tracing::debug!("Order {} created", order_id);
            }
            EventType::OrderCompleted {
                order_id, user_id, ..
            } => {
                tracing::info!(
                    "Triggering order completion notification for user: {}",
                    user_id
                );
                // In production: send order completion email/push notification
                // Example: notify user that their order is completed and tokens are available
                tracing::debug!("Order {} completed", order_id);
            }
            EventType::TradeExecuted {
                trade_id,
                buyer_id,
                seller_id,
                ..
            } => {
                tracing::info!("Triggering trade execution notifications");
                // In production: notify both buyer and seller
                tracing::debug!(
                    "Trade {} executed - buyer: {}, seller: {:?}",
                    trade_id,
                    buyer_id,
                    seller_id
                );
            }
            EventType::CommitmentCreated {
                commitment_id,
                user_id,
                ..
            } => {
                tracing::info!("Triggering commitment created notification");
                // In production: notify user and admins
                tracing::debug!("Commitment {} created by user {}", commitment_id, user_id);
            }
            EventType::CommitmentVerified {
                commitment_id,
                approved,
                ..
            } => {
                tracing::info!("Triggering commitment verification notification");
                let status = if *approved { "approved" } else { "rejected" };
                // In production: notify commitment creator of verification result
                tracing::debug!("Commitment {} {}", commitment_id, status);
            }
            _ => {
                tracing::debug!(
                    "NOTIFICATION: Event {} - no specific notification configured",
                    event.id()
                );
            }
        }
        Ok(())
    }

    fn name(&self) -> &str {
        "NotificationHandler"
    }
}

/// Webhook event handler
pub struct WebhookHandler;

#[async_trait]
impl EventHandler for WebhookHandler {
    async fn handle(&self, event: Event) -> Result<()> {
        // Send webhooks to subscribed endpoints based on event type
        let event_category = match &event.event_type {
            EventType::UserRegistered { .. } => "user",
            EventType::TokenCreated { .. } => "token",
            EventType::OrderCreated { .. }
            | EventType::OrderCompleted { .. }
            | EventType::OrderCancelled { .. } => "order",
            EventType::TradeExecuted { .. } => "trade",
            EventType::CommitmentCreated { .. } | EventType::CommitmentVerified { .. } => {
                "commitment"
            }
            EventType::KycSubmitted { .. } | EventType::KycVerified { .. } => "kyc",
            _ => "other",
        };

        tracing::debug!(
            "WEBHOOK: Event {} (category: {}) would trigger webhook delivery",
            event.id(),
            event_category
        );

        // In production:
        // 1. Query webhooks table for active webhooks subscribed to this event_category
        // 2. For each webhook:
        //    - Serialize event to JSON
        //    - Generate HMAC signature using webhook secret
        //    - Send POST request to webhook URL with:
        //      - Headers: X-Webhook-Signature, X-Event-Type, X-Event-ID
        //      - Body: JSON serialized event
        // 3. Record delivery attempt in webhook_deliveries table
        // 4. Retry failed deliveries with exponential backoff

        // Example webhook payload structure:
        let _webhook_payload = serde_json::json!({
            "event_id": event.id(),
            "event_type": event_category,
            "timestamp": event.timestamp(),
            "data": &event.event_type,
            "metadata": {
                "source": &event.metadata.source,
                "correlation_id": &event.metadata.correlation_id,
                "user_id": event.metadata.user_id,
            }
        });

        // Log webhook delivery simulation
        tracing::info!(
            "Would deliver webhook for event {} to subscribed endpoints",
            event.id()
        );

        Ok(())
    }

    fn name(&self) -> &str {
        "WebhookHandler"
    }
}

/// Analytics event handler
pub struct AnalyticsHandler;

#[async_trait]
impl EventHandler for AnalyticsHandler {
    async fn handle(&self, event: Event) -> Result<()> {
        // Track analytics events for business intelligence
        match &event.event_type {
            EventType::UserRegistered { user_id, .. } => {
                tracing::debug!("ANALYTICS: Tracking user registration - user: {}", user_id);
                // In production: track in analytics system (Mixpanel, Amplitude, custom DB)
                // - User acquisition metrics
                // - Registration funnel tracking
                // - Cohort analysis data
            }
            EventType::TokenCreated {
                token_id,
                symbol,
                issuer_id,
                ..
            } => {
                tracing::debug!(
                    "ANALYTICS: Tracking token creation - {} by {}",
                    symbol,
                    issuer_id
                );
                // In production: track token creation metrics
                // - Tokens created per day/week/month
                // - Most active token creators
                // - Token category distribution
                let _analytics_event = serde_json::json!({
                    "action": "token_created",
                    "token_id": token_id,
                    "symbol": symbol,
                    "issuer_id": issuer_id,
                    "timestamp": event.timestamp(),
                });
            }
            EventType::OrderCreated {
                order_id,
                order_type,
                ..
            } => {
                tracing::debug!(
                    "ANALYTICS: Tracking order creation - {} order {}",
                    order_type,
                    order_id
                );
                // In production: track order metrics
                // - Buy vs sell order ratio
                // - Average order size
                // - Order frequency per user
            }
            EventType::TradeExecuted {
                trade_id,
                token_id,
                amount,
                price_btc,
                ..
            } => {
                tracing::debug!(
                    "ANALYTICS: Tracking trade execution - {} tokens at {} BTC",
                    amount,
                    price_btc
                );
                // In production: track trading metrics
                // - Trading volume (daily/weekly/monthly)
                // - Price trends and volatility
                // - Most traded tokens
                // - User trading patterns
                let _analytics_event = serde_json::json!({
                    "action": "trade_executed",
                    "trade_id": trade_id,
                    "token_id": token_id,
                    "amount": amount,
                    "price_btc": price_btc,
                    "timestamp": event.timestamp(),
                });
            }
            EventType::CommitmentCreated {
                commitment_id,
                user_id,
                ..
            } => {
                tracing::debug!(
                    "ANALYTICS: Tracking commitment creation - {} by {}",
                    commitment_id,
                    user_id
                );
                // In production: track commitment metrics
                // - Commitments created per token
                // - Commitment completion rates
                // - User engagement with commitments
            }
            EventType::CommitmentVerified {
                commitment_id,
                approved,
                ..
            } => {
                tracing::debug!(
                    "ANALYTICS: Tracking commitment verification - {} (approved: {})",
                    commitment_id,
                    approved
                );
                // In production: track verification metrics
                // - Approval/rejection rates
                // - Average verification time
                // - Quality score distributions
            }
            EventType::KycSubmitted { user_id, level, .. } => {
                tracing::debug!(
                    "ANALYTICS: Tracking KYC submission - user {} level {:?}",
                    user_id,
                    level
                );
                // In production: track KYC metrics
                // - KYC submission rates
                // - Verification times
                // - Level distribution
            }
            _ => {
                tracing::debug!("ANALYTICS: Event {} tracked (generic)", event.id());
            }
        }

        Ok(())
    }

    fn name(&self) -> &str {
        "AnalyticsHandler"
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::events::types::EventType;
    use uuid::Uuid;

    #[tokio::test]
    async fn test_audit_log_handler() {
        let handler = AuditLogHandler::new(None);
        assert_eq!(handler.name(), "AuditLogHandler");

        let event = Event::new(EventType::UserRegistered {
            user_id: Uuid::new_v4(),
            email: "test@example.com".to_string(),
        });

        handler.handle(event).await.unwrap();
    }

    #[tokio::test]
    async fn test_metrics_handler() {
        let handler = MetricsHandler;
        assert_eq!(handler.name(), "MetricsHandler");

        let event = Event::new(EventType::TradeExecuted {
            trade_id: Uuid::new_v4(),
            token_id: Uuid::new_v4(),
            buyer_id: Uuid::new_v4(),
            seller_id: Some(Uuid::new_v4()),
            amount: "100".to_string(),
            price_btc: "0.001".to_string(),
        });

        handler.handle(event).await.unwrap();
    }

    #[tokio::test]
    async fn test_notification_handler() {
        let handler = NotificationHandler;
        assert_eq!(handler.name(), "NotificationHandler");

        let event = Event::new(EventType::OrderCompleted {
            order_id: Uuid::new_v4(),
            user_id: Uuid::new_v4(),
            token_id: Uuid::new_v4(),
        });

        handler.handle(event).await.unwrap();
    }
}
