//! High-performance caching layer using moka.
//!
//! This module provides a comprehensive caching solution with:
//! - LRU eviction with configurable size limits
//! - TTL-based expiration
//! - Smart cache invalidation
//! - Metrics tracking (hit rate, size, evictions)
//! - Specialized caches for different data types

use std::{
  hash::Hash,
  sync::{
    Arc,
    atomic::{AtomicU64, Ordering},
  },
  time::Duration,
};

use moka::future::Cache as MokaCache;

use crate::model::MediaId;

/// Cache statistics for monitoring and debugging.
#[derive(Debug, Clone, Default)]
pub struct CacheStats {
  pub hits:      u64,
  pub misses:    u64,
  pub evictions: u64,
  pub size:      u64,
}

impl CacheStats {
  #[must_use]
  pub fn hit_rate(&self) -> f64 {
    let total = self.hits + self.misses;
    // Compute ratio using integer arithmetic: hits * 10000 / total gives basis
    // points (0..=10000), then scale back to [0.0, 1.0]. Returns 0.0 if total
    // is zero.
    let basis_points = self
      .hits
      .saturating_mul(10_000)
      .checked_div(total)
      .unwrap_or(0);
    f64::from(u32::try_from(basis_points).unwrap_or(u32::MAX)) / 10_000.0
  }
}

/// Atomic counters for cache metrics.
struct CacheMetrics {
  hits:   AtomicU64,
  misses: AtomicU64,
}

impl Default for CacheMetrics {
  fn default() -> Self {
    Self {
      hits:   AtomicU64::new(0),
      misses: AtomicU64::new(0),
    }
  }
}

impl CacheMetrics {
  fn record_hit(&self) {
    self.hits.fetch_add(1, Ordering::Relaxed);
  }

  fn record_miss(&self) {
    self.misses.fetch_add(1, Ordering::Relaxed);
  }

  fn stats(&self) -> (u64, u64) {
    (
      self.hits.load(Ordering::Relaxed),
      self.misses.load(Ordering::Relaxed),
    )
  }
}

/// A high-performance cache with LRU eviction and TTL support.
pub struct Cache<K, V>
where
  K: Hash + Eq + Send + Sync + 'static,
  V: Clone + Send + Sync + 'static,
{
  inner:   MokaCache<K, V>,
  metrics: Arc<CacheMetrics>,
}

impl<K, V> Cache<K, V>
where
  K: Hash + Eq + Send + Sync + 'static,
  V: Clone + Send + Sync + 'static,
{
  /// Create a new cache with the specified TTL and maximum capacity.
  #[must_use]
  pub fn new(ttl: Duration, max_capacity: u64) -> Self {
    let inner = MokaCache::builder()
      .time_to_live(ttl)
      .max_capacity(max_capacity)
      .build();

    Self {
      inner,
      metrics: Arc::new(CacheMetrics::default()),
    }
  }

  /// Create a new cache with TTL, max capacity, and time-to-idle.
  #[must_use]
  pub fn new_with_idle(
    ttl: Duration,
    tti: Duration,
    max_capacity: u64,
  ) -> Self {
    let inner = MokaCache::builder()
      .time_to_live(ttl)
      .time_to_idle(tti)
      .max_capacity(max_capacity)
      .build();

    Self {
      inner,
      metrics: Arc::new(CacheMetrics::default()),
    }
  }

  /// Get a value from the cache.
  pub async fn get(&self, key: &K) -> Option<V> {
    self.inner.get(key).await.map_or_else(
      || {
        self.metrics.record_miss();
        None
      },
      |value| {
        self.metrics.record_hit();
        Some(value)
      },
    )
  }

  /// Insert a value into the cache.
  pub async fn insert(&self, key: K, value: V) {
    self.inner.insert(key, value).await;
  }

  /// Remove a specific key from the cache.
  pub async fn invalidate(&self, key: &K) {
    self.inner.invalidate(key).await;
  }

  /// Clear all entries from the cache.
  pub async fn invalidate_all(&self) {
    self.inner.invalidate_all();
    // Run pending tasks to ensure immediate invalidation
    self.inner.run_pending_tasks().await;
  }

  /// Get the current number of entries in the cache.
  #[must_use]
  pub fn entry_count(&self) -> u64 {
    self.inner.entry_count()
  }

  /// Get cache statistics.
  #[must_use]
  pub fn stats(&self) -> CacheStats {
    let (hits, misses) = self.metrics.stats();
    CacheStats {
      hits,
      misses,
      evictions: 0, // Moka doesn't expose this directly
      size: self.entry_count(),
    }
  }
}

/// Specialized cache for search query results.
pub struct QueryCache {
  /// Cache keyed by (`query_hash`, offset, limit)
  inner: Cache<String, String>,
}

impl QueryCache {
  #[must_use]
  pub fn new(ttl: Duration, max_capacity: u64) -> Self {
    Self {
      inner: Cache::new(ttl, max_capacity),
    }
  }

  /// Generate a cache key from query parameters.
  fn make_key(
    query: &str,
    offset: u64,
    limit: u64,
    sort: Option<&str>,
  ) -> String {
    use std::hash::{DefaultHasher, Hasher};
    let mut hasher = DefaultHasher::new();
    hasher.write(query.as_bytes());
    hasher.write(&offset.to_le_bytes());
    hasher.write(&limit.to_le_bytes());
    if let Some(s) = sort {
      hasher.write(s.as_bytes());
    }
    format!("q:{:016x}", hasher.finish())
  }

  pub async fn get(
    &self,
    query: &str,
    offset: u64,
    limit: u64,
    sort: Option<&str>,
  ) -> Option<String> {
    let key = Self::make_key(query, offset, limit, sort);
    self.inner.get(&key).await
  }

  pub async fn insert(
    &self,
    query: &str,
    offset: u64,
    limit: u64,
    sort: Option<&str>,
    result: String,
  ) {
    let key = Self::make_key(query, offset, limit, sort);
    self.inner.insert(key, result).await;
  }

  pub async fn invalidate_all(&self) {
    self.inner.invalidate_all().await;
  }

  #[must_use]
  pub fn stats(&self) -> CacheStats {
    self.inner.stats()
  }
}

/// Specialized cache for metadata extraction results.
pub struct MetadataCache {
  /// Cache keyed by content hash
  inner: Cache<String, String>,
}

impl MetadataCache {
  #[must_use]
  pub fn new(ttl: Duration, max_capacity: u64) -> Self {
    Self {
      inner: Cache::new(ttl, max_capacity),
    }
  }

  pub async fn get(&self, content_hash: &str) -> Option<String> {
    self.inner.get(&content_hash.to_string()).await
  }

  pub async fn insert(&self, content_hash: &str, metadata_json: String) {
    self
      .inner
      .insert(content_hash.to_string(), metadata_json)
      .await;
  }

  pub async fn invalidate(&self, content_hash: &str) {
    self.inner.invalidate(&content_hash.to_string()).await;
  }

  #[must_use]
  pub fn stats(&self) -> CacheStats {
    self.inner.stats()
  }
}

/// Specialized cache for media item data.
pub struct MediaCache {
  inner: Cache<String, String>,
}

impl MediaCache {
  #[must_use]
  pub fn new(ttl: Duration, max_capacity: u64) -> Self {
    Self {
      inner: Cache::new(ttl, max_capacity),
    }
  }

  pub async fn get(&self, media_id: MediaId) -> Option<String> {
    self.inner.get(&media_id.to_string()).await
  }

  pub async fn insert(&self, media_id: MediaId, item_json: String) {
    self.inner.insert(media_id.to_string(), item_json).await;
  }

  pub async fn invalidate(&self, media_id: MediaId) {
    self.inner.invalidate(&media_id.to_string()).await;
  }

  pub async fn invalidate_all(&self) {
    self.inner.invalidate_all().await;
  }

  #[must_use]
  pub fn stats(&self) -> CacheStats {
    self.inner.stats()
  }
}

/// Configuration for the cache layer.
#[derive(Debug, Clone)]
pub struct CacheConfig {
  /// TTL for response cache in seconds
  pub response_ttl_secs:    u64,
  /// Maximum number of cached responses
  pub response_max_entries: u64,
  /// TTL for query cache in seconds
  pub query_ttl_secs:       u64,
  /// Maximum number of cached query results
  pub query_max_entries:    u64,
  /// TTL for metadata cache in seconds
  pub metadata_ttl_secs:    u64,
  /// Maximum number of cached metadata entries
  pub metadata_max_entries: u64,
  /// TTL for media cache in seconds
  pub media_ttl_secs:       u64,
  /// Maximum number of cached media items
  pub media_max_entries:    u64,
}

impl Default for CacheConfig {
  fn default() -> Self {
    Self {
      response_ttl_secs:    60,
      response_max_entries: 1000,
      query_ttl_secs:       300,
      query_max_entries:    500,
      metadata_ttl_secs:    3600,
      metadata_max_entries: 10000,
      media_ttl_secs:       300,
      media_max_entries:    5000,
    }
  }
}

/// Application-level cache layer wrapping multiple specialized caches.
pub struct CacheLayer {
  /// Cache for serialized API responses
  pub responses: Cache<String, String>,
  /// Cache for search query results
  pub queries:   QueryCache,
  /// Cache for metadata extraction results
  pub metadata:  MetadataCache,
  /// Cache for individual media items
  pub media:     MediaCache,
  /// Configuration
  config:        CacheConfig,
}

impl CacheLayer {
  /// Create a new cache layer with the specified TTL (using defaults for other
  /// settings).
  #[must_use]
  pub fn new(ttl_secs: u64) -> Self {
    let config = CacheConfig {
      response_ttl_secs: ttl_secs,
      ..Default::default()
    };
    Self::with_config(config)
  }

  /// Create a new cache layer with full configuration.
  #[must_use]
  pub fn with_config(config: CacheConfig) -> Self {
    Self {
      responses: Cache::new(
        Duration::from_secs(config.response_ttl_secs),
        config.response_max_entries,
      ),
      queries: QueryCache::new(
        Duration::from_secs(config.query_ttl_secs),
        config.query_max_entries,
      ),
      metadata: MetadataCache::new(
        Duration::from_secs(config.metadata_ttl_secs),
        config.metadata_max_entries,
      ),
      media: MediaCache::new(
        Duration::from_secs(config.media_ttl_secs),
        config.media_max_entries,
      ),
      config,
    }
  }

  /// Invalidate all caches related to a media item update.
  pub async fn invalidate_for_media_update(&self, media_id: MediaId) {
    self.media.invalidate(media_id).await;
    // Query cache should be invalidated as search results may change
    self.queries.invalidate_all().await;
  }

  /// Invalidate all caches related to a media item deletion.
  pub async fn invalidate_for_media_delete(&self, media_id: MediaId) {
    self.media.invalidate(media_id).await;
    self.queries.invalidate_all().await;
  }

  /// Invalidate all caches (useful after bulk imports or major changes).
  pub async fn invalidate_all(&self) {
    self.responses.invalidate_all().await;
    self.queries.invalidate_all().await;
    self.media.invalidate_all().await;
    // Keep metadata cache as it's keyed by content hash which doesn't change
  }

  /// Get aggregated statistics for all caches.
  #[must_use]
  pub fn stats(&self) -> CacheLayerStats {
    CacheLayerStats {
      responses: self.responses.stats(),
      queries:   self.queries.stats(),
      metadata:  self.metadata.stats(),
      media:     self.media.stats(),
    }
  }

  /// Get the current configuration.
  #[must_use]
  pub const fn config(&self) -> &CacheConfig {
    &self.config
  }
}

/// Aggregated statistics for the entire cache layer.
#[derive(Debug, Clone)]
pub struct CacheLayerStats {
  pub responses: CacheStats,
  pub queries:   CacheStats,
  pub metadata:  CacheStats,
  pub media:     CacheStats,
}

impl CacheLayerStats {
  /// Get the overall hit rate across all caches.
  #[must_use]
  pub fn overall_hit_rate(&self) -> f64 {
    let total_hits = self.responses.hits
      + self.queries.hits
      + self.metadata.hits
      + self.media.hits;
    let total_requests = total_hits
      + self.responses.misses
      + self.queries.misses
      + self.metadata.misses
      + self.media.misses;

    let basis_points = total_hits
      .saturating_mul(10_000)
      .checked_div(total_requests)
      .unwrap_or(0);
    f64::from(u32::try_from(basis_points).unwrap_or(u32::MAX)) / 10_000.0
  }

  /// Get the total number of entries across all caches.
  #[must_use]
  pub const fn total_entries(&self) -> u64 {
    self.responses.size
      + self.queries.size
      + self.metadata.size
      + self.media.size
  }
}

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

  #[tokio::test]
  async fn test_cache_basic_operations() {
    let cache: Cache<String, String> = Cache::new(Duration::from_mins(1), 100);

    // Insert and get
    cache.insert("key1".to_string(), "value1".to_string()).await;
    assert_eq!(
      cache.get(&"key1".to_string()).await,
      Some("value1".to_string())
    );

    // Miss
    assert_eq!(cache.get(&"key2".to_string()).await, None);

    // Invalidate
    cache.invalidate(&"key1".to_string()).await;
    assert_eq!(cache.get(&"key1".to_string()).await, None);
  }

  #[tokio::test]
  async fn test_cache_stats() {
    let cache: Cache<String, String> = Cache::new(Duration::from_mins(1), 100);

    cache.insert("key1".to_string(), "value1".to_string()).await;
    let _ = cache.get(&"key1".to_string()).await; // hit
    let _ = cache.get(&"key2".to_string()).await; // miss

    let stats = cache.stats();
    assert_eq!(stats.hits, 1);
    assert_eq!(stats.misses, 1);
    assert!((stats.hit_rate() - 0.5).abs() < 0.01);
  }

  #[tokio::test]
  async fn test_query_cache() {
    let cache = QueryCache::new(Duration::from_mins(1), 100);

    cache
      .insert("test query", 0, 10, Some("name"), "results".to_string())
      .await;
    assert_eq!(
      cache.get("test query", 0, 10, Some("name")).await,
      Some("results".to_string())
    );

    // Different parameters should miss
    assert_eq!(cache.get("test query", 10, 10, Some("name")).await, None);
  }

  #[tokio::test]
  async fn test_cache_layer() {
    let layer = CacheLayer::new(60);

    let media_id = MediaId::new();
    layer.media.insert(media_id, "{}".to_string()).await;
    assert!(layer.media.get(media_id).await.is_some());

    layer.invalidate_for_media_delete(media_id).await;
    assert!(layer.media.get(media_id).await.is_none());
  }
}