halldyll-robots 0.1.0

//! Cache - Robots.txt caching with TTL and optional persistence

use crate::types::{RobotsCacheKey, RobotsPolicy};
use dashmap::DashMap;
use std::path::Path;
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::Arc;
use std::time::Duration;
use tokio::fs;
use tokio::io::{AsyncReadExt, AsyncWriteExt};
use tracing::{debug, info};

/// Maximum cache TTL (24 hours per RFC 9309)
pub const MAX_CACHE_TTL: Duration = Duration::from_secs(24 * 60 * 60);

/// Default cache TTL (1 hour)
pub const DEFAULT_CACHE_TTL: Duration = Duration::from_secs(60 * 60);

/// Cache statistics
#[derive(Debug, Default)]
pub struct CacheStats {
    /// Number of cache hits
    pub hits: AtomicU64,
    /// Number of cache misses
    pub misses: AtomicU64,
    /// Number of cache evictions
    pub evictions: AtomicU64,
    /// Number of cache entries
    pub entries: AtomicU64,
}

impl CacheStats {
    /// Record a cache hit
    pub fn record_hit(&self) {
        self.hits.fetch_add(1, Ordering::Relaxed);
    }

    /// Record a cache miss
    pub fn record_miss(&self) {
        self.misses.fetch_add(1, Ordering::Relaxed);
    }

    /// Record a cache eviction
    pub fn record_eviction(&self) {
        self.evictions.fetch_add(1, Ordering::Relaxed);
    }

    /// Get hit rate
    pub fn hit_rate(&self) -> f64 {
        let hits = self.hits.load(Ordering::Relaxed);
        let misses = self.misses.load(Ordering::Relaxed);
        let total = hits + misses;
        if total == 0 {
            0.0
        } else {
            hits as f64 / total as f64
        }
    }

    /// Get snapshot of stats
    pub fn snapshot(&self) -> CacheStatsSnapshot {
        CacheStatsSnapshot {
            hits: self.hits.load(Ordering::Relaxed),
            misses: self.misses.load(Ordering::Relaxed),
            evictions: self.evictions.load(Ordering::Relaxed),
            entries: self.entries.load(Ordering::Relaxed),
        }
    }
}

/// Snapshot of cache statistics
#[derive(Debug, Clone)]
pub struct CacheStatsSnapshot {
    /// Number of cache hits
    pub hits: u64,
    /// Number of cache misses
    pub misses: u64,
    /// Number of cache evictions
    pub evictions: u64,
    /// Number of cache entries
    pub entries: u64,
}

/// Robots.txt cache
pub struct RobotsCache {
    /// In-memory cache
    cache: Arc<DashMap<RobotsCacheKey, RobotsPolicy>>,
    /// Default TTL for new entries
    default_ttl: Duration,
    /// Optional persistence directory
    persist_dir: Option<String>,
    /// Cache statistics
    stats: Arc<CacheStats>,
}

impl Default for RobotsCache {
    fn default() -> Self {
        Self::new(DEFAULT_CACHE_TTL)
    }
}

impl RobotsCache {
    /// Create a new in-memory cache
    pub fn new(default_ttl: Duration) -> Self {
        // Enforce max TTL
        let default_ttl = default_ttl.min(MAX_CACHE_TTL);
        
        Self {
            cache: Arc::new(DashMap::new()),
            default_ttl,
            persist_dir: None,
            stats: Arc::new(CacheStats::default()),
        }
    }

    /// Create a cache with file persistence
    pub fn with_persistence(default_ttl: Duration, persist_dir: &str) -> Self {
        let default_ttl = default_ttl.min(MAX_CACHE_TTL);
        
        Self {
            cache: Arc::new(DashMap::new()),
            default_ttl,
            persist_dir: Some(persist_dir.to_string()),
            stats: Arc::new(CacheStats::default()),
        }
    }

    /// Get the default TTL
    pub fn default_ttl(&self) -> Duration {
        self.default_ttl
    }

    /// Get cache statistics
    pub fn stats(&self) -> Arc<CacheStats> {
        self.stats.clone()
    }

    /// Get a policy from cache if not expired
    pub fn get(&self, key: &RobotsCacheKey) -> Option<RobotsPolicy> {
        if let Some(entry) = self.cache.get(key) {
            if !entry.is_expired() {
                self.stats.record_hit();
                debug!("Cache hit for {}", key.robots_url());
                return Some(entry.clone());
            }
            // Expired, remove it
            drop(entry);
            self.cache.remove(key);
            self.stats.record_eviction();
        }
        
        self.stats.record_miss();
        debug!("Cache miss for {}", key.robots_url());
        None
    }

    /// Insert a policy into cache
    pub fn insert(&self, key: RobotsCacheKey, policy: RobotsPolicy) {
        let old = self.cache.insert(key.clone(), policy);
        if old.is_none() {
            self.stats.entries.fetch_add(1, Ordering::Relaxed);
        }
        debug!("Cached robots.txt for {}", key.robots_url());
    }

    /// Remove a policy from cache
    pub fn remove(&self, key: &RobotsCacheKey) -> Option<RobotsPolicy> {
        let removed = self.cache.remove(key).map(|(_, v)| v);
        if removed.is_some() {
            self.stats.entries.fetch_sub(1, Ordering::Relaxed);
            self.stats.record_eviction();
        }
        removed
    }

    /// Clear expired entries
    pub fn evict_expired(&self) -> usize {
        let mut evicted = 0;
        self.cache.retain(|_, policy| {
            if policy.is_expired() {
                evicted += 1;
                false
            } else {
                true
            }
        });
        
        if evicted > 0 {
            self.stats.entries.fetch_sub(evicted as u64, Ordering::Relaxed);
            self.stats.evictions.fetch_add(evicted as u64, Ordering::Relaxed);
            info!("Evicted {} expired robots.txt entries", evicted);
        }
        
        evicted
    }

    /// Clear all entries
    pub fn clear(&self) {
        let count = self.cache.len();
        self.cache.clear();
        self.stats.entries.store(0, Ordering::Relaxed);
        info!("Cleared {} robots.txt cache entries", count);
    }

    /// Get number of entries
    pub fn len(&self) -> usize {
        self.cache.len()
    }

    /// Check if cache is empty
    pub fn is_empty(&self) -> bool {
        self.cache.is_empty()
    }

    /// List all cached domains
    pub fn domains(&self) -> Vec<String> {
        self.cache
            .iter()
            .map(|entry| entry.key().authority.clone())
            .collect()
    }

    /// Save cache to disk (if persistence enabled)
    pub async fn save_to_disk(&self) -> std::io::Result<usize> {
        let persist_dir = match &self.persist_dir {
            Some(dir) => dir,
            None => return Ok(0),
        };

        // Create directory if needed
        fs::create_dir_all(persist_dir).await?;

        let mut saved = 0;
        for entry in self.cache.iter() {
            let key = entry.key();
            let policy = entry.value();
            
            // Skip expired entries
            if policy.is_expired() {
                continue;
            }

            let filename = self.cache_filename(key);
            let filepath = Path::new(persist_dir).join(&filename);
            
            // Serialize to JSON
            if let Ok(json) = serde_json::to_string_pretty(&CacheEntry {
                key: key.clone(),
                groups: policy.groups.clone(),
                sitemaps: policy.sitemaps.clone(),
                content_size: policy.content_size,
                ttl_secs: policy.ttl().as_secs(),
            }) {
                if let Ok(mut file) = fs::File::create(&filepath).await {
                    if file.write_all(json.as_bytes()).await.is_ok() {
                        saved += 1;
                    }
                }
            }
        }

        info!("Saved {} robots.txt entries to disk", saved);
        Ok(saved)
    }

    /// Load cache from disk (if persistence enabled)
    pub async fn load_from_disk(&self) -> std::io::Result<usize> {
        let persist_dir = match &self.persist_dir {
            Some(dir) => dir,
            None => return Ok(0),
        };

        let path = Path::new(persist_dir);
        if !path.exists() {
            return Ok(0);
        }

        let mut loaded = 0;
        let mut entries = fs::read_dir(persist_dir).await?;
        
        while let Some(entry) = entries.next_entry().await? {
            let filepath = entry.path();
            if filepath.extension().is_some_and(|ext| ext == "json") {
                if let Ok(mut file) = fs::File::open(&filepath).await {
                    let mut content = String::new();
                    if file.read_to_string(&mut content).await.is_ok() {
                                if let Ok(cache_entry) = serde_json::from_str::<CacheEntry>(&content) {
                            // Reconstruct policy
                            let ttl = Duration::from_secs(cache_entry.ttl_secs);
                            if ttl > Duration::ZERO {
                                let now = std::time::SystemTime::now()
                                    .duration_since(std::time::UNIX_EPOCH)
                                    .unwrap_or_default()
                                    .as_millis() as u64;
                                let policy = RobotsPolicy {
                                    fetched_at_ms: now,
                                    expires_at_ms: now + ttl.as_millis() as u64,
                                    fetch_status: crate::types::FetchStatus::Success,
                                    groups: cache_entry.groups,
                                    sitemaps: cache_entry.sitemaps,
                                    content_size: cache_entry.content_size,
                                    etag: None,
                                    last_modified: None,
                                };
                                self.insert(cache_entry.key, policy);
                                loaded += 1;
                            }
                        }
                    }
                }
            }
        }

        info!("Loaded {} robots.txt entries from disk", loaded);
        Ok(loaded)
    }

    /// Generate a filename for a cache key
    fn cache_filename(&self, key: &RobotsCacheKey) -> String {
        // Use base64 encoding for safe filenames
        let combined = format!("{}_{}", key.scheme, key.authority);
        let encoded = base64_encode(&combined);
        format!("{}.json", encoded)
    }
}

/// Entry for disk persistence
#[derive(serde::Serialize, serde::Deserialize)]
struct CacheEntry {
    key: RobotsCacheKey,
    groups: Vec<crate::types::Group>,
    sitemaps: Vec<String>,
    content_size: usize,
    ttl_secs: u64,
}

/// Simple base64-like encoding for filenames
fn base64_encode(s: &str) -> String {
    // Simple hex encoding for safety
    s.bytes()
        .map(|b| format!("{:02x}", b))
        .collect()
}

/// Parse Cache-Control header for TTL
pub fn parse_cache_control(header: &str) -> Option<Duration> {
    for directive in header.split(',') {
        let directive = directive.trim();
        if let Some(value) = directive.strip_prefix("max-age=") {
            if let Ok(secs) = value.trim().parse::<u64>() {
                return Some(Duration::from_secs(secs).min(MAX_CACHE_TTL));
            }
        }
    }
    None
}

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

    fn create_test_policy() -> RobotsPolicy {
        let parser = RobotsParser::new();
        parser.parse("User-agent: *\nDisallow: /admin", Duration::from_secs(3600))
    }

    #[test]
    fn test_cache_insert_get() {
        let cache = RobotsCache::new(Duration::from_secs(3600));
        let key = RobotsCacheKey {
            scheme: "https".to_string(),
            authority: "example.com".to_string(),
        };
        let policy = create_test_policy();
        
        cache.insert(key.clone(), policy);
        
        assert!(cache.get(&key).is_some());
        assert_eq!(cache.len(), 1);
    }

    #[test]
    fn test_cache_miss() {
        let cache = RobotsCache::new(Duration::from_secs(3600));
        let key = RobotsCacheKey {
            scheme: "https".to_string(),
            authority: "example.com".to_string(),
        };
        
        assert!(cache.get(&key).is_none());
    }

    #[test]
    fn test_cache_stats() {
        let cache = RobotsCache::new(Duration::from_secs(3600));
        let key = RobotsCacheKey {
            scheme: "https".to_string(),
            authority: "example.com".to_string(),
        };
        
        // Miss
        cache.get(&key);
        
        // Insert and hit
        cache.insert(key.clone(), create_test_policy());
        cache.get(&key);
        
        let stats = cache.stats().snapshot();
        assert_eq!(stats.hits, 1);
        assert_eq!(stats.misses, 1);
    }

    #[test]
    fn test_cache_clear() {
        let cache = RobotsCache::new(Duration::from_secs(3600));
        let key = RobotsCacheKey {
            scheme: "https".to_string(),
            authority: "example.com".to_string(),
        };
        
        cache.insert(key, create_test_policy());
        assert_eq!(cache.len(), 1);
        
        cache.clear();
        assert!(cache.is_empty());
    }

    #[test]
    fn test_parse_cache_control() {
        assert_eq!(
            parse_cache_control("max-age=3600"),
            Some(Duration::from_secs(3600))
        );
        assert_eq!(
            parse_cache_control("public, max-age=7200"),
            Some(Duration::from_secs(7200))
        );
        assert_eq!(
            parse_cache_control("no-cache"),
            None
        );
        // Should clamp to max 24h
        assert_eq!(
            parse_cache_control("max-age=999999"),
            Some(MAX_CACHE_TTL)
        );
    }

    #[test]
    fn test_max_ttl_enforcement() {
        // TTL should be clamped to max 24h
        let cache = RobotsCache::new(Duration::from_secs(100000));
        assert_eq!(cache.default_ttl(), MAX_CACHE_TTL);
    }
}