use crate::handle_resolution_result::HandleResolutionResult;
use crate::handle_resolver::{HandleResolver, HandleResolverError};
use crate::metrics::MetricsPublisher;
use crate::queue::{HandleResolutionWork, QueueAdapter};
use async_trait::async_trait;
use std::sync::Arc;
use std::time::{SystemTime, UNIX_EPOCH};
use tracing::{debug, trace};

/// Create a ProactiveRefreshResolver with default 80% threshold
///
/// # Arguments
/// * `inner` - The inner resolver to wrap
/// * `queue` - The queue adapter for background refresh tasks
/// * `cache_ttl` - The TTL in seconds for cache entries
pub fn create_proactive_refresh_resolver<R, Q>(
    inner: Arc<R>,
    queue: Arc<Q>,
    cache_ttl: u64,
) -> Arc<ProactiveRefreshResolver<R, Q>>
where
    R: HandleResolver + Send + Sync + 'static,
    Q: QueueAdapter<HandleResolutionWork> + Send + Sync + 'static,
{
    Arc::new(ProactiveRefreshResolver::new(inner, queue, cache_ttl))
}

/// Create a ProactiveRefreshResolver with custom threshold
///
/// # Arguments
/// * `inner` - The inner resolver to wrap
/// * `queue` - The queue adapter for background refresh tasks
/// * `cache_ttl` - The TTL in seconds for cache entries
/// * `threshold` - The threshold as a percentage (0.0 to 1.0) of TTL when to trigger refresh
pub fn create_proactive_refresh_resolver_with_threshold<R, Q>(
    inner: Arc<R>,
    queue: Arc<Q>,
    cache_ttl: u64,
    threshold: f64,
) -> Arc<ProactiveRefreshResolver<R, Q>>
where
    R: HandleResolver + Send + Sync + 'static,
    Q: QueueAdapter<HandleResolutionWork> + Send + Sync + 'static,
{
    Arc::new(ProactiveRefreshResolver::with_threshold(
        inner, queue, cache_ttl, threshold,
    ))
}

/// Wrapper struct for dynamic dispatch with proactive refresh
/// This works with trait objects instead of concrete types
pub struct DynProactiveRefreshResolver {
    inner: Arc<dyn HandleResolver>,
    queue: Arc<dyn QueueAdapter<HandleResolutionWork>>,
    metrics: Option<Arc<dyn MetricsPublisher>>,
    #[allow(dead_code)]
    cache_ttl: u64,
    #[allow(dead_code)]
    refresh_threshold: f64,
}

impl DynProactiveRefreshResolver {
    pub fn new(
        inner: Arc<dyn HandleResolver>,
        queue: Arc<dyn QueueAdapter<HandleResolutionWork>>,
        cache_ttl: u64,
        refresh_threshold: f64,
    ) -> Self {
        Self::with_metrics(inner, queue, None, cache_ttl, refresh_threshold)
    }

    pub fn with_metrics(
        inner: Arc<dyn HandleResolver>,
        queue: Arc<dyn QueueAdapter<HandleResolutionWork>>,
        metrics: Option<Arc<dyn MetricsPublisher>>,
        cache_ttl: u64,
        refresh_threshold: f64,
    ) -> Self {
        Self {
            inner,
            queue,
            metrics,
            cache_ttl,
            refresh_threshold: refresh_threshold.clamp(0.0, 1.0),
        }
    }

    async fn maybe_queue_for_refresh(&self, handle: &str, resolve_time: u64) {
        // If resolution took less than 5ms, it was probably a cache hit
        if resolve_time < 5000 {
            trace!(
                handle = handle,
                resolve_time_us = resolve_time,
                "Fast resolution detected, considering proactive refresh"
            );

            if let Some(metrics) = &self.metrics {
                metrics.incr("proactive_refresh.cache_hit_detected").await;
            }

            // Simple heuristic: queue for refresh with some probability
            let now = SystemTime::now()
                .duration_since(UNIX_EPOCH)
                .unwrap_or_default()
                .as_secs();

            // Queue every N seconds for frequently accessed handles
            if now % 60 == 0 {
                let work = HandleResolutionWork {
                    handle: handle.to_string(),
                };

                if let Err(e) = self.queue.push(work).await {
                    debug!(
                        handle = handle,
                        error = %e,
                        "Failed to queue handle for proactive refresh"
                    );
                    if let Some(metrics) = &self.metrics {
                        metrics.incr("proactive_refresh.queue_error").await;
                    }
                } else {
                    debug!(handle = handle, "Queued handle for proactive refresh");
                    if let Some(metrics) = &self.metrics {
                        metrics.incr("proactive_refresh.queued").await;
                    }
                }
            }
        }
    }
}

#[async_trait]
impl HandleResolver for DynProactiveRefreshResolver {
    async fn resolve(&self, handle: &str) -> Result<(String, u64), HandleResolverError> {
        // Resolve through the inner resolver
        let (did, resolve_time) = self.inner.resolve(handle).await?;

        // Check if we should queue for refresh based on resolution time
        self.maybe_queue_for_refresh(handle, resolve_time).await;

        Ok((did, resolve_time))
    }

    async fn set(&self, handle: &str, did: &str) -> Result<(), HandleResolverError> {
        // Simply chain to inner resolver - no proactive refresh needed for manual sets
        self.inner.set(handle, did).await
    }
}

/// Create a ProactiveRefreshResolver with custom threshold using trait objects
/// This version works with dyn HandleResolver and dyn QueueAdapter
///
/// # Arguments
/// * `inner` - The inner resolver to wrap
/// * `queue` - The queue adapter for background refresh tasks
/// * `cache_ttl` - The TTL in seconds for cache entries
/// * `threshold` - The threshold as a percentage (0.0 to 1.0) of TTL when to trigger refresh
pub fn create_proactive_refresh_resolver_dyn(
    inner: Arc<dyn HandleResolver>,
    queue: Arc<dyn QueueAdapter<HandleResolutionWork>>,
    cache_ttl: u64,
    threshold: f64,
) -> Arc<dyn HandleResolver> {
    Arc::new(DynProactiveRefreshResolver::new(
        inner, queue, cache_ttl, threshold,
    ))
}

/// Create a ProactiveRefreshResolver with metrics support
pub fn create_proactive_refresh_resolver_with_metrics(
    inner: Arc<dyn HandleResolver>,
    queue: Arc<dyn QueueAdapter<HandleResolutionWork>>,
    metrics: Arc<dyn MetricsPublisher>,
    cache_ttl: u64,
    threshold: f64,
) -> Arc<dyn HandleResolver> {
    Arc::new(DynProactiveRefreshResolver::with_metrics(
        inner,
        queue,
        Some(metrics),
        cache_ttl,
        threshold,
    ))
}

/// A handle resolver that proactively refreshes cache entries when they reach
/// a certain staleness threshold (default 80% of TTL).
///
/// This resolver wraps another resolver and checks successful resolutions from cache.
/// When a cached entry has lived for more than the threshold percentage of its TTL,
/// it queues the handle for background refresh to keep the cache warm.
///
/// Note: Due to the current trait design, this implementation uses the resolution time
/// as a heuristic. When resolve_time is 0 (instant cache hit), it may queue for refresh.
/// For full functionality, the trait would need to expose cache timestamps.
pub struct ProactiveRefreshResolver<R: HandleResolver, Q: QueueAdapter<HandleResolutionWork>> {
    inner: Arc<R>,
    queue: Arc<Q>,
    /// TTL in seconds for cache entries
    cache_ttl: u64,
    /// Threshold as a percentage (0.0 to 1.0) of TTL when to trigger refresh
    /// Default is 0.8 (80%)
    refresh_threshold: f64,
}

impl<R: HandleResolver, Q: QueueAdapter<HandleResolutionWork>> ProactiveRefreshResolver<R, Q> {
    pub fn new(inner: Arc<R>, queue: Arc<Q>, cache_ttl: u64) -> Self {
        Self::with_threshold(inner, queue, cache_ttl, 0.8)
    }

    pub fn with_threshold(
        inner: Arc<R>,
        queue: Arc<Q>,
        cache_ttl: u64,
        refresh_threshold: f64,
    ) -> Self {
        Self {
            inner,
            queue,
            cache_ttl,
            refresh_threshold: refresh_threshold.clamp(0.0, 1.0),
        }
    }

    /// Check if a cached entry needs proactive refresh based on its age
    #[allow(dead_code)]
    fn needs_refresh(&self, result: &HandleResolutionResult) -> bool {
        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs();

        let age = now.saturating_sub(result.timestamp);
        let threshold = (self.cache_ttl as f64 * self.refresh_threshold) as u64;

        let needs_refresh = age >= threshold;

        if needs_refresh {
            debug!(
                handle = ?result.to_did(),
                age_seconds = age,
                threshold_seconds = threshold,
                cache_ttl = self.cache_ttl,
                "Cache entry needs proactive refresh"
            );
        } else {
            trace!(
                handle = ?result.to_did(),
                age_seconds = age,
                threshold_seconds = threshold,
                "Cache entry still fresh"
            );
        }

        needs_refresh
    }

    /// Queue a handle for background refresh
    async fn queue_for_refresh(&self, handle: &str) {
        let work = HandleResolutionWork {
            handle: handle.to_string(),
        };

        match self.queue.push(work).await {
            Ok(_) => {
                debug!(handle = handle, "Queued handle for proactive refresh");
            }
            Err(e) => {
                // Don't fail the request if we can't queue for refresh
                debug!(
                    handle = handle,
                    error = %e,
                    "Failed to queue handle for proactive refresh"
                );
            }
        }
    }

    /// Check if we should queue for refresh based on resolution time
    ///
    /// This is a heuristic approach:
    /// - If resolve_time is very low (< 5ms), it was likely a cache hit
    /// - We probabilistically queue for refresh based on time since service start
    ///
    /// For proper implementation, the HandleResolver trait would need to expose
    /// cache metadata or return HandleResolutionResult directly.
    async fn maybe_queue_for_refresh(&self, handle: &str, resolve_time: u64) {
        // If resolution took less than 5ms, it was probably a cache hit
        if resolve_time < 5000 {
            // Use a simple probabilistic approach for demonstration
            // In production, you'd want access to the actual cache timestamp
            trace!(
                handle = handle,
                resolve_time_us = resolve_time,
                "Fast resolution detected, considering proactive refresh"
            );

            // Queue for refresh with some probability to avoid overwhelming the queue
            // This is a simplified approach - ideally we'd have access to cache metadata
            let now = SystemTime::now()
                .duration_since(UNIX_EPOCH)
                .unwrap_or_default()
                .as_secs();

            // Simple heuristic: queue every N seconds for frequently accessed handles
            if now % 60 == 0 {
                self.queue_for_refresh(handle).await;
            }
        }
    }
}

#[async_trait]
impl<R, Q> HandleResolver for ProactiveRefreshResolver<R, Q>
where
    R: HandleResolver + Send + Sync,
    Q: QueueAdapter<HandleResolutionWork> + Send + Sync,
{
    async fn resolve(&self, handle: &str) -> Result<(String, u64), HandleResolverError> {
        // Resolve through the inner resolver
        let (did, resolve_time) = self.inner.resolve(handle).await?;

        // Check if we should queue for refresh based on resolution time
        self.maybe_queue_for_refresh(handle, resolve_time).await;

        Ok((did, resolve_time))
    }
}

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

    #[test]
    fn test_needs_refresh_calculation() {
        // Create a resolver with 100 second TTL and 80% threshold
        let inner = Arc::new(MockResolver);
        let queue = Arc::new(MockQueueAdapter);
        let resolver = ProactiveRefreshResolver::new(inner, queue, 100);

        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap()
            .as_secs();

        // Test entry that's 50% through TTL (should not refresh)
        let fresh_result = HandleResolutionResult {
            timestamp: now - 50,
            method_type: DidMethodType::Plc,
            payload: "alice123".to_string(),
        };
        assert!(!resolver.needs_refresh(&fresh_result));

        // Test entry that's 80% through TTL (should refresh)
        let stale_result = HandleResolutionResult {
            timestamp: now - 80,
            method_type: DidMethodType::Plc,
            payload: "alice123".to_string(),
        };
        assert!(resolver.needs_refresh(&stale_result));

        // Test entry that's 90% through TTL (should definitely refresh)
        let very_stale_result = HandleResolutionResult {
            timestamp: now - 90,
            method_type: DidMethodType::Plc,
            payload: "alice123".to_string(),
        };
        assert!(resolver.needs_refresh(&very_stale_result));
    }

    #[test]
    fn test_custom_threshold() {
        let inner = Arc::new(MockResolver);
        let queue = Arc::new(MockQueueAdapter);

        // Create resolver with 50% threshold
        let resolver = ProactiveRefreshResolver::with_threshold(inner, queue, 100, 0.5);

        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap()
            .as_secs();

        // Test entry that's 40% through TTL (should not refresh with 50% threshold)
        let result_40 = HandleResolutionResult {
            timestamp: now - 40,
            method_type: DidMethodType::Plc,
            payload: "alice123".to_string(),
        };
        assert!(!resolver.needs_refresh(&result_40));

        // Test entry that's 60% through TTL (should refresh with 50% threshold)
        let result_60 = HandleResolutionResult {
            timestamp: now - 60,
            method_type: DidMethodType::Plc,
            payload: "alice123".to_string(),
        };
        assert!(resolver.needs_refresh(&result_60));
    }

    // Mock resolver for testing
    struct MockResolver;

    #[async_trait]
    impl HandleResolver for MockResolver {
        async fn resolve(&self, handle: &str) -> Result<(String, u64), HandleResolverError> {
            Ok((format!("did:plc:{}", handle), 1000))
        }
    }

    // Mock queue adapter for testing
    struct MockQueueAdapter;

    #[async_trait]
    impl QueueAdapter<HandleResolutionWork> for MockQueueAdapter {
        async fn pull(&self) -> Option<HandleResolutionWork> {
            None
        }

        async fn push(&self, _work: HandleResolutionWork) -> crate::queue::Result<()> {
            Ok(())
        }

        async fn ack(&self, _item: &HandleResolutionWork) -> crate::queue::Result<()> {
            Ok(())
        }

        async fn try_push(&self, _work: HandleResolutionWork) -> crate::queue::Result<()> {
            Ok(())
        }

        async fn is_healthy(&self) -> bool {
            true
        }
    }
}