//! Multi-tier cache management system

use crate::{
    error::{OptimizerError, Result},
    optimizer::CacheConfig,
    pattern_db::CompilationPattern,
};
use dashmap::DashMap;
use parking_lot::RwLock;
use serde::{Deserialize, Serialize};
use std::{sync::Arc, time::Instant};

/// Multi-tier cache manager for compilation artifacts
pub struct CacheManager {
    config: CacheConfig,
    hot_cache: Arc<DashMap<String, CacheEntry>>,
    warm_cache: Arc<DashMap<String, CacheEntry>>,
    cold_cache: Arc<DashMap<String, CacheEntry>>,
    stats: Arc<RwLock<CacheStats>>,
}

impl CacheManager {
    /// Create a new cache manager with default configuration
    pub fn new() -> Result<Self> {
        Ok(Self::with_config(CacheConfig::default())?)
    }

    /// Create with custom configuration
    pub fn with_config(config: CacheConfig) -> Result<Self> {
        Ok(Self {
            config,
            hot_cache: Arc::new(DashMap::new()),
            warm_cache: Arc::new(DashMap::new()),
            cold_cache: Arc::new(DashMap::new()),
            stats: Arc::new(RwLock::new(CacheStats::default())),
        })
    }

    /// Pre-seed caches with known patterns
    pub async fn pre_seed_with_patterns(&self, patterns: &[CompilationPattern]) -> Result<()> {
        let mut stats = self.stats.write();
        stats.pre_seed_operations += 1;

        for pattern in patterns {
            // Simulate pre-seeding by adding pattern entries to warm cache
            let entry = CacheEntry {
                data: pattern.fingerprint.clone(),
                created_at: chrono::Utc::now(),
                last_accessed: chrono::Utc::now(),
                access_count: 0,
                size_bytes: pattern.fingerprint.len(),
            };

            self.warm_cache.insert(pattern.pattern_id.clone(), entry);
            stats.entries_pre_seeded += 1;
        }

        Ok(())
    }

    /// Perform intelligent cache warming
    pub async fn intelligent_warm(&self) -> Result<WarmingResult> {
        let start_time = Instant::now();
        let mut stats = self.stats.write();
        stats.warming_operations += 1;

        // Simulate intelligent warming by promoting entries from cold to warm
        let entries_warmed = self.promote_cold_to_warm().await?;

        let warming_time = start_time.elapsed();
        stats.total_warming_time += warming_time;

        Ok(WarmingResult {
            entries_warmed,
            warming_time,
            cache_hit_rate: self.calculate_hit_rate(),
        })
    }

    /// Get an entry from the cache hierarchy
    pub async fn get(&self, key: &str) -> Option<Vec<u8>> {
        let mut stats = self.stats.write();
        stats.total_accesses += 1;

        // Check hot cache first
        if let Some(mut entry) = self.hot_cache.get_mut(key) {
            entry.last_accessed = chrono::Utc::now();
            entry.access_count += 1;
            stats.hot_hits += 1;
            return Some(entry.data.clone());
        }

        // Check warm cache
        if let Some(entry) = self.warm_cache.get(key) {
            let mut entry_clone = entry.clone();
            entry_clone.last_accessed = chrono::Utc::now();
            entry_clone.access_count += 1;

            // Promote to hot cache
            self.hot_cache.insert(key.to_string(), entry_clone.clone());
            stats.warm_hits += 1;
            return Some(entry_clone.data);
        }

        // Check cold cache
        if let Some(entry) = self.cold_cache.get(key) {
            let mut entry_clone = entry.clone();
            entry_clone.last_accessed = chrono::Utc::now();
            entry_clone.access_count += 1;

            // Promote to warm cache
            self.warm_cache.insert(key.to_string(), entry_clone.clone());
            stats.cold_hits += 1;
            return Some(entry_clone.data);
        }

        stats.misses += 1;
        None
    }

    /// Store an entry in the cache
    pub async fn put(&self, key: String, data: Vec<u8>) -> Result<()> {
        let entry = CacheEntry {
            data,
            created_at: chrono::Utc::now(),
            last_accessed: chrono::Utc::now(),
            access_count: 0,
            size_bytes: 0, // Would calculate actual size
        };

        // Store in hot cache for immediate access
        self.hot_cache.insert(key, entry);

        let mut stats = self.stats.write();
        stats.total_insertions += 1;

        Ok(())
    }

    /// Clear all caches
    pub async fn clear_all(&self) -> Result<()> {
        self.hot_cache.clear();
        self.warm_cache.clear();
        self.cold_cache.clear();

        let mut stats = self.stats.write();
        *stats = CacheStats::default();

        Ok(())
    }

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

    async fn promote_cold_to_warm(&self) -> Result<usize> {
        let mut promoted = 0;

        // Simplified promotion logic
        for entry in self.cold_cache.iter() {
            if entry.access_count > 0 {
                let (key, value) = entry.pair();
                self.warm_cache.insert(key.clone(), value.clone());
                promoted += 1;

                if promoted >= 10 {
                    break; // Limit promotions per warming cycle
                }
            }
        }

        Ok(promoted)
    }

    fn calculate_hit_rate(&self) -> f64 {
        let stats = self.stats.read();
        if stats.total_accesses == 0 {
            return 0.0;
        }

        let total_hits = stats.hot_hits + stats.warm_hits + stats.cold_hits;
        (total_hits as f64) / (stats.total_accesses as f64) * 100.0
    }
}

/// Result of cache warming operation
#[derive(Debug, Clone)]
pub struct WarmingResult {
    /// Number of entries warmed
    pub entries_warmed: usize,
    /// Time spent warming
    pub warming_time: std::time::Duration,
    /// Current cache hit rate
    pub cache_hit_rate: f64,
}

/// Cache entry with metadata
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct CacheEntry {
    /// Cached data
    pub data: Vec<u8>,
    /// When entry was created
    pub created_at: chrono::DateTime<chrono::Utc>,
    /// Last access time
    pub last_accessed: chrono::DateTime<chrono::Utc>,
    /// Number of times accessed
    pub access_count: u64,
    /// Size in bytes
    pub size_bytes: usize,
}

/// Cache performance statistics
#[derive(Debug, Clone, Default)]
pub struct CacheStats {
    /// Total cache accesses
    pub total_accesses: u64,
    /// Hot cache hits
    pub hot_hits: u64,
    /// Warm cache hits
    pub warm_hits: u64,
    /// Cold cache hits
    pub cold_hits: u64,
    /// Cache misses
    pub misses: u64,
    /// Total insertions
    pub total_insertions: u64,
    /// Pre-seed operations performed
    pub pre_seed_operations: u64,
    /// Entries pre-seeded
    pub entries_pre_seeded: u64,
    /// Warming operations performed
    pub warming_operations: u64,
    /// Total time spent warming
    pub total_warming_time: std::time::Duration,
}