siftdb-core 0.2.2

use crate::tombstone::{TombstoneManager, TombstoneStats};
use crate::types::Manifest;
use anyhow::{Context, Result};
use std::collections::HashMap;
use std::fs;
use std::path::{Path, PathBuf};
use std::time::{SystemTime, UNIX_EPOCH};
use serde::{Deserialize, Serialize};

/// Compaction statistics
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct CompactionStats {
    pub started_at: u64,
    pub completed_at: u64,
    pub duration_secs: u64,
    pub tombstones_removed: usize,
    pub segments_compacted: usize,
    pub space_reclaimed_bytes: u64,
    pub before_epoch: u64,
    pub after_epoch: u64,
}

/// Compaction configuration
#[derive(Debug, Clone)]
pub struct CompactionConfig {
    /// Only compact tombstones older than this many epochs
    pub min_tombstone_age_epochs: u64,
    /// Minimum number of tombstones to trigger compaction
    pub min_tombstone_count: usize,
    /// Maximum time to spend on compaction (seconds)
    pub max_duration_secs: u64,
}

impl Default for CompactionConfig {
    fn default() -> Self {
        Self {
            min_tombstone_age_epochs: 5,    // Only compact tombstones 5+ epochs old
            min_tombstone_count: 100,       // Need at least 100 tombstones
            max_duration_secs: 300,         // 5 minutes max
        }
    }
}

/// Collection compactor for cleaning up tombstones and optimizing storage
pub struct CollectionCompactor {
    collection_path: PathBuf,
    config: CompactionConfig,
}

impl CollectionCompactor {
    pub fn new(collection_path: &Path) -> Self {
        Self {
            collection_path: collection_path.to_path_buf(),
            config: CompactionConfig::default(),
        }
    }

    pub fn with_config(mut self, config: CompactionConfig) -> Self {
        self.config = config;
        self
    }

    /// Check if compaction is needed based on current state
    pub fn needs_compaction(&self) -> Result<bool> {
        let tombstone_manager = TombstoneManager::new(&self.collection_path);
        let stats = tombstone_manager.get_stats()?;
        
        // Load current manifest to get current epoch
        let manifest_path = self.collection_path.join("MANIFEST.a");
        let manifest = Manifest::read_from_file(&manifest_path)?;
        
        // Check if we have enough old tombstones to warrant compaction
        let cutoff_epoch = manifest.epoch.saturating_sub(self.config.min_tombstone_age_epochs);
        let old_tombstones = tombstone_manager.get_compaction_candidates(cutoff_epoch)?;
        
        Ok(stats.total_count >= self.config.min_tombstone_count && 
           old_tombstones.len() >= self.config.min_tombstone_count)
    }

    /// Perform collection compaction
    pub fn compact(&self) -> Result<CompactionStats> {
        let started_at = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap()
            .as_secs();

        println!("🧹 Starting collection compaction...");

        // Load current state
        let manifest_path = self.collection_path.join("MANIFEST.a");
        let manifest = Manifest::read_from_file(&manifest_path)?;
        let before_epoch = manifest.epoch;

        let tombstone_manager = TombstoneManager::new(&self.collection_path);
        let before_stats = tombstone_manager.get_stats()?;

        println!("   Current epoch: {}", before_epoch);
        println!("   Tombstones before: {}", before_stats.total_count);

        // Determine compaction cutoff epoch
        let cutoff_epoch = before_epoch.saturating_sub(self.config.min_tombstone_age_epochs);
        
        // Get tombstones to compact
        let candidates = tombstone_manager.get_compaction_candidates(cutoff_epoch)?;
        
        if candidates.is_empty() {
            println!("   No tombstones eligible for compaction");
            let completed_at = SystemTime::now()
                .duration_since(UNIX_EPOCH)
                .unwrap()
                .as_secs();

            return Ok(CompactionStats {
                started_at,
                completed_at,
                duration_secs: completed_at - started_at,
                tombstones_removed: 0,
                segments_compacted: 0,
                space_reclaimed_bytes: 0,
                before_epoch,
                after_epoch: before_epoch,
            });
        }

        println!("   Compacting {} tombstones older than epoch {}", candidates.len(), cutoff_epoch);

        // Group tombstones by segment for efficient processing
        let mut segments_to_compact: HashMap<u32, Vec<_>> = HashMap::new();
        for tombstone in &candidates {
            segments_to_compact
                .entry(tombstone.segment_id)
                .or_insert_with(Vec::new)
                .push(tombstone);
        }

        println!("   Segments affected: {}", segments_to_compact.len());

        // For now, just remove the tombstone records (full segment rewriting would be more complex)
        let tombstones_removed = tombstone_manager.compact_tombstones(cutoff_epoch)?;
        
        // Calculate space reclaimed (estimate based on average tombstone overhead)
        let space_reclaimed_bytes = (tombstones_removed * 256) as u64; // Rough estimate

        // Update manifest with new epoch to mark compaction
        let new_epoch = before_epoch + 1;
        let mut new_manifest = manifest;
        new_manifest.epoch = new_epoch;
        new_manifest.write_to_file(&manifest_path)?;

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

        let stats = CompactionStats {
            started_at,
            completed_at,
            duration_secs: completed_at - started_at,
            tombstones_removed,
            segments_compacted: segments_to_compact.len(),
            space_reclaimed_bytes,
            before_epoch,
            after_epoch: new_epoch,
        };

        println!("✅ Compaction completed:");
        println!("   Duration: {}s", stats.duration_secs);
        println!("   Tombstones removed: {}", stats.tombstones_removed);
        println!("   Segments compacted: {}", stats.segments_compacted);
        println!("   Space reclaimed: ~{} bytes", stats.space_reclaimed_bytes);
        println!("   New epoch: {}", stats.after_epoch);

        // Save compaction stats
        self.save_compaction_stats(&stats)?;

        Ok(stats)
    }

    /// Get compaction history
    pub fn get_compaction_history(&self) -> Result<Vec<CompactionStats>> {
        let stats_dir = self.collection_path.join("gc");
        let mut history = Vec::new();

        if !stats_dir.exists() {
            return Ok(history);
        }

        for entry in fs::read_dir(&stats_dir)? {
            let entry = entry?;
            let path = entry.path();
            
            if let Some(filename) = path.file_name() {
                if let Some(filename_str) = filename.to_str() {
                    if filename_str.starts_with("compaction-") && filename_str.ends_with(".json") {
                        if let Ok(content) = fs::read_to_string(&path) {
                            if let Ok(stats) = serde_json::from_str::<CompactionStats>(&content) {
                                history.push(stats);
                            }
                        }
                    }
                }
            }
        }

        // Sort by completion time
        history.sort_by_key(|s| s.completed_at);
        Ok(history)
    }

    /// Auto-compaction check - returns true if compaction was performed
    pub fn auto_compact_if_needed(&self) -> Result<bool> {
        if self.needs_compaction()? {
            println!("🔄 Auto-compaction triggered");
            self.compact()?;
            Ok(true)
        } else {
            Ok(false)
        }
    }

    fn save_compaction_stats(&self, stats: &CompactionStats) -> Result<()> {
        let stats_dir = self.collection_path.join("gc");
        fs::create_dir_all(&stats_dir)?;
        
        let stats_file = stats_dir.join(format!("compaction-{:010}.json", stats.completed_at));
        let json = serde_json::to_string_pretty(stats)
            .context("Failed to serialize compaction stats")?;
        
        fs::write(&stats_file, json)
            .context("Failed to write compaction stats")?;
        
        Ok(())
    }
}

/// Compaction manager for scheduling and coordinating compaction operations
pub struct CompactionManager {
    collection_path: PathBuf,
}

impl CompactionManager {
    pub fn new(collection_path: &Path) -> Self {
        Self {
            collection_path: collection_path.to_path_buf(),
        }
    }

    /// Run compaction with custom configuration
    pub fn compact_with_config(&self, config: CompactionConfig) -> Result<CompactionStats> {
        let compactor = CollectionCompactor::new(&self.collection_path)
            .with_config(config);
        compactor.compact()
    }

    /// Quick compaction status check
    pub fn status(&self) -> Result<CompactionStatus> {
        let tombstone_manager = TombstoneManager::new(&self.collection_path);
        let tombstone_stats = tombstone_manager.get_stats()?;
        
        let compactor = CollectionCompactor::new(&self.collection_path);
        let needs_compaction = compactor.needs_compaction()?;
        let history = compactor.get_compaction_history()?;
        
        let last_compaction = history.last().map(|s| s.completed_at);
        
        Ok(CompactionStatus {
            needs_compaction,
            total_tombstones: tombstone_stats.total_count,
            oldest_tombstone_epoch: tombstone_stats.oldest_epoch,
            newest_tombstone_epoch: tombstone_stats.newest_epoch,
            last_compaction_at: last_compaction,
            compaction_count: history.len(),
        })
    }
}

#[derive(Debug, Serialize, Deserialize)]
pub struct CompactionStatus {
    pub needs_compaction: bool,
    pub total_tombstones: usize,
    pub oldest_tombstone_epoch: u64,
    pub newest_tombstone_epoch: u64,
    pub last_compaction_at: Option<u64>,
    pub compaction_count: usize,
}