//! Memory Cache
//!
//! Provides caching for frequently accessed memories to improve
//! retrieval performance.

use crate::types::{MemoryEntry, MemoryType};
use std::collections::HashMap;
use std::time::{Duration, Instant};
use tokio::sync::RwLock;

/// Cache entry with metadata
struct CacheEntry {
    /// The memory entry
    entry: MemoryEntry,
    /// Last access time
    last_accessed: Instant,
    /// Access count
    access_count: u32,
}

/// Cache key for efficient lookups
#[derive(Debug, Clone, Hash, Eq, PartialEq)]
struct CacheKey {
    agent_id: String,
    memory_type: MemoryType,
    category: String,
}

impl From<&MemoryEntry> for CacheKey {
    fn from(entry: &MemoryEntry) -> Self {
        // Parse URI to extract components
        let parts: Vec<&str> = entry.uri.trim_start_matches("agent://").split('/').collect();
        Self {
            agent_id: parts.first().unwrap_or(&"").to_string(),
            memory_type: entry.memory_type,
            category: parts.get(2).unwrap_or(&"").to_string(),
        }
    }
}

/// Memory cache configuration
#[derive(Debug, Clone)]
pub struct CacheConfig {
    /// Maximum number of entries
    pub max_entries: usize,
    /// Time-to-live for entries
    pub ttl: Duration,
    /// Enable/disable caching
    pub enabled: bool,
}

impl Default for CacheConfig {
    fn default() -> Self {
        Self {
            max_entries: 1000,
            ttl: Duration::from_secs(3600), // 1 hour
            enabled: true,
        }
    }
}

/// Memory cache for hot memories
pub struct MemoryCache {
    /// Cache storage
    cache: RwLock<HashMap<String, CacheEntry>>,
    /// Configuration
    config: CacheConfig,
    /// Cache statistics
    stats: RwLock<CacheStats>,
}

/// Cache statistics
#[derive(Debug, Clone, Default)]
pub struct CacheStats {
    /// Total cache hits
    pub hits: u64,
    /// Total cache misses
    pub misses: u64,
    /// Total entries evicted
    pub evictions: u64,
}

impl MemoryCache {
    /// Create a new memory cache
    pub fn new(config: CacheConfig) -> Self {
        Self {
            cache: RwLock::new(HashMap::new()),
            config,
            stats: RwLock::new(CacheStats::default()),
        }
    }

    /// Create with default configuration
    pub fn default_config() -> Self {
        Self::new(CacheConfig::default())
    }

    /// Get a memory from cache
    pub async fn get(&self, uri: &str) -> Option<MemoryEntry> {
        if !self.config.enabled {
            return None;
        }

        let mut cache = self.cache.write().await;

        if let Some(cached) = cache.get_mut(uri) {
            // Check TTL
            if cached.last_accessed.elapsed() > self.config.ttl {
                cache.remove(uri);
                return None;
            }

            // Update access metadata
            cached.last_accessed = Instant::now();
            cached.access_count += 1;

            // Update stats
            let mut stats = self.stats.write().await;
            stats.hits += 1;

            return Some(cached.entry.clone());
        }

        // Update stats
        let mut stats = self.stats.write().await;
        stats.misses += 1;

        None
    }

    /// Put a memory into cache
    pub async fn put(&self, entry: MemoryEntry) {
        if !self.config.enabled {
            return;
        }

        let mut cache = self.cache.write().await;

        // Check capacity and evict if necessary
        if cache.len() >= self.config.max_entries {
            self.evict_lru(&mut cache).await;
        }

        cache.insert(
            entry.uri.clone(),
            CacheEntry {
                entry,
                last_accessed: Instant::now(),
                access_count: 0,
            },
        );
    }

    /// Remove a memory from cache
    pub async fn remove(&self, uri: &str) {
        let mut cache = self.cache.write().await;
        cache.remove(uri);
    }

    /// Clear the cache
    pub async fn clear(&self) {
        let mut cache = self.cache.write().await;
        cache.clear();
    }

    /// Evict least recently used entries
    async fn evict_lru(&self, cache: &mut HashMap<String, CacheEntry>) {
        // Find LRU entry
        let lru_key = cache
            .iter()
            .min_by_key(|(_, v)| (v.access_count, v.last_accessed))
            .map(|(k, _)| k.clone());

        if let Some(key) = lru_key {
            cache.remove(&key);

            let mut stats = self.stats.write().await;
            stats.evictions += 1;
        }
    }

    /// Get cache statistics
    pub async fn stats(&self) -> CacheStats {
        self.stats.read().await.clone()
    }

    /// Get cache hit rate
    pub async fn hit_rate(&self) -> f32 {
        let stats = self.stats.read().await;
        let total = stats.hits + stats.misses;
        if total == 0 {
            return 0.0;
        }
        stats.hits as f32 / total as f32
    }

    /// Get cache size
    pub async fn size(&self) -> usize {
        self.cache.read().await.len()
    }

    /// Warm up cache with frequently accessed entries
    pub async fn warmup(&self, entries: Vec<MemoryEntry>) {
        for entry in entries {
            self.put(entry).await;
        }
    }

    /// Get top accessed entries (for preloading)
    pub async fn get_hot_entries(&self, limit: usize) -> Vec<MemoryEntry> {
        let cache = self.cache.read().await;

        let mut entries: Vec<_> = cache
            .values()
            .map(|c| (c.access_count, c.entry.clone()))
            .collect();

        entries.sort_by(|a, b| b.0.cmp(&a.0));
        entries.truncate(limit);

        entries.into_iter().map(|(_, e)| e).collect()
    }
}

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

    #[tokio::test]
    async fn test_cache_put_and_get() {
        let cache = MemoryCache::default_config();
        let entry = MemoryEntry::new(
            "test-agent",
            MemoryType::Preference,
            "style",
            "User prefers concise responses".to_string(),
        );

        cache.put(entry.clone()).await;
        let retrieved = cache.get(&entry.uri).await;

        assert!(retrieved.is_some());
        assert_eq!(retrieved.unwrap().content, "User prefers concise responses");
    }

    #[tokio::test]
    async fn test_cache_miss() {
        let cache = MemoryCache::default_config();
        let retrieved = cache.get("nonexistent").await;

        assert!(retrieved.is_none());

        let stats = cache.stats().await;
        assert_eq!(stats.misses, 1);
    }

    #[tokio::test]
    async fn test_cache_remove() {
        let cache = MemoryCache::default_config();
        let entry = MemoryEntry::new(
            "test-agent",
            MemoryType::Preference,
            "style",
            "test".to_string(),
        );

        cache.put(entry.clone()).await;
        cache.remove(&entry.uri).await;
        let retrieved = cache.get(&entry.uri).await;

        assert!(retrieved.is_none());
    }

    #[tokio::test]
    async fn test_cache_clear() {
        let cache = MemoryCache::default_config();
        let entry = MemoryEntry::new(
            "test-agent",
            MemoryType::Preference,
            "style",
            "test".to_string(),
        );

        cache.put(entry).await;
        cache.clear().await;
        let size = cache.size().await;

        assert_eq!(size, 0);
    }

    #[tokio::test]
    async fn test_cache_stats() {
        let cache = MemoryCache::default_config();
        let entry = MemoryEntry::new(
            "test-agent",
            MemoryType::Preference,
            "style",
            "test".to_string(),
        );

        cache.put(entry.clone()).await;

        // Hit
        cache.get(&entry.uri).await;
        // Miss
        cache.get("nonexistent").await;

        let stats = cache.stats().await;
        assert_eq!(stats.hits, 1);
        assert_eq!(stats.misses, 1);

        let hit_rate = cache.hit_rate().await;
        assert!((hit_rate - 0.5).abs() < 0.001);
    }

    #[tokio::test]
    async fn test_cache_eviction() {
        let config = CacheConfig {
            max_entries: 2,
            ttl: Duration::from_secs(3600),
            enabled: true,
        };
        let cache = MemoryCache::new(config);

        let entry1 = MemoryEntry::new("test", MemoryType::Preference, "1", "1".to_string());
        let entry2 = MemoryEntry::new("test", MemoryType::Preference, "2", "2".to_string());
        let entry3 = MemoryEntry::new("test", MemoryType::Preference, "3", "3".to_string());

        cache.put(entry1.clone()).await;
        cache.put(entry2.clone()).await;

        // Access entry1 to make it hot
        cache.get(&entry1.uri).await;

        // Add entry3, should evict entry2 (LRU)
        cache.put(entry3).await;

        let size = cache.size().await;
        assert_eq!(size, 2);

        let stats = cache.stats().await;
        assert_eq!(stats.evictions, 1);
    }

    #[tokio::test]
    async fn test_get_hot_entries() {
        let cache = MemoryCache::default_config();

        let entry1 = MemoryEntry::new("test", MemoryType::Preference, "1", "1".to_string());
        let entry2 = MemoryEntry::new("test", MemoryType::Preference, "2", "2".to_string());

        cache.put(entry1.clone()).await;
        cache.put(entry2.clone()).await;

        // Access entry1 multiple times
        cache.get(&entry1.uri).await;
        cache.get(&entry1.uri).await;

        let hot = cache.get_hot_entries(10).await;
        assert_eq!(hot.len(), 2);
        // entry1 should be first (more accesses)
        assert_eq!(hot[0].uri, entry1.uri);
    }
}