//! Vacuum operations for reclaiming space from soft-deleted entities.
//!
//! This module provides:
//! - **Vacuum deleted entities**: Remove entities with `deleted_at` set
//! - **Vacuum old versions**: Remove superseded entity versions (if versioning enabled)
//! - **Vacuum orphaned data**: Clean up embeddings/indexes for deleted entities
//! - **Statistics**: Space reclaimed, entities removed
//!
//! # Soft Delete Model
//!
//! REM database uses soft deletes by default:
//! - Delete operations set `deleted_at` timestamp
//! - Entity remains in database (hidden from queries)
//! - Vacuum permanently removes soft-deleted entities
//!
//! # When to Vacuum
//!
//! - After large batch deletes
//! - Scheduled maintenance (e.g., monthly)
//! - Before backups (reduce backup size)
//! - When disk space is low
//!
//! # Example
//!
//! ```rust,no_run
//! use percolate_rocks::admin::VacuumManager;
//! use chrono::{Utc, Duration};
//!
//! # async fn example() -> anyhow::Result<()> {
//! let vacuum_mgr = VacuumManager::new("/var/lib/rem/db")?;
//!
//! // Remove entities deleted >30 days ago
//! let cutoff = Utc::now() - Duration::days(30);
//! let stats = vacuum_mgr.vacuum_deleted_entities(Some(cutoff)).await?;
//! println!("Removed {} entities, reclaimed {} MB",
//!     stats.entities_removed,
//!     stats.space_reclaimed_mb()
//! );
//! # Ok(())
//! # }
//! ```

use anyhow::Result;
use chrono::{DateTime, Utc};
use std::path::{Path, PathBuf};

/// Manages vacuum operations for reclaiming space.
///
/// Safely removes soft-deleted data while maintaining referential integrity.
pub struct VacuumManager {
    /// Path to RocksDB database
    _db_path: PathBuf,

    /// RocksDB instance (not yet implemented)
    _db: (),
}

impl VacuumManager {
    /// Create new vacuum manager.
    ///
    /// # Arguments
    ///
    /// * `db_path` - Path to RocksDB database
    ///
    /// # Returns
    ///
    /// Configured `VacuumManager` instance
    ///
    /// # Errors
    ///
    /// Returns error if database path invalid or cannot be opened
    pub fn new(_db_path: &Path) -> Result<Self> {
        todo!("Open RocksDB in read-write mode")
    }

    /// Vacuum soft-deleted entities.
    ///
    /// Permanently removes entities where `deleted_at` is set and before cutoff.
    ///
    /// # Arguments
    ///
    /// * `deleted_before` - Only vacuum entities deleted before this time.
    ///                      None means vacuum all deleted entities.
    ///
    /// # Returns
    ///
    /// `VacuumStats` with count of removed entities and space reclaimed
    ///
    /// # Errors
    ///
    /// Returns error if vacuum operation fails
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::VacuumManager;
    /// # use chrono::{Utc, Duration};
    /// # let vacuum_mgr = VacuumManager::new("/var/lib/rem/db")?;
    /// // Remove entities deleted >7 days ago
    /// let cutoff = Utc::now() - Duration::days(7);
    /// let stats = vacuum_mgr.vacuum_deleted_entities(Some(cutoff)).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn vacuum_deleted_entities(
        &self,
        _deleted_before: Option<DateTime<Utc>>,
    ) -> Result<VacuumStats> {
        todo!(
            "1. Scan entities CF for deleted_at != null
            2. Filter by deleted_before cutoff if provided
            3. For each entity:
               - Delete from entities CF
               - Delete embeddings (if exists)
               - Delete edges (forward and reverse)
               - Delete from indexes
            4. Return VacuumStats with counts and size"
        )
    }

    /// Vacuum orphaned embeddings.
    ///
    /// Removes embedding vectors that no longer have corresponding entities.
    ///
    /// # Returns
    ///
    /// `VacuumStats` with count of orphaned embeddings removed
    ///
    /// # Errors
    ///
    /// Returns error if vacuum operation fails
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::VacuumManager;
    /// # let vacuum_mgr = VacuumManager::new("/var/lib/rem/db")?;
    /// let stats = vacuum_mgr.vacuum_orphaned_embeddings().await?;
    /// println!("Removed {} orphaned embeddings", stats.embeddings_removed);
    /// # Ok(())
    /// # }
    /// ```
    pub async fn vacuum_orphaned_embeddings(&self) -> Result<VacuumStats> {
        todo!(
            "1. Scan embeddings CF
            2. For each embedding:
               - Check if entity exists in entities CF
               - If not, delete embedding
            3. Return VacuumStats"
        )
    }

    /// Vacuum orphaned edges.
    ///
    /// Removes edges where source or destination entity no longer exists.
    ///
    /// # Returns
    ///
    /// `VacuumStats` with count of orphaned edges removed
    ///
    /// # Errors
    ///
    /// Returns error if vacuum operation fails
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::VacuumManager;
    /// # let vacuum_mgr = VacuumManager::new("/var/lib/rem/db")?;
    /// let stats = vacuum_mgr.vacuum_orphaned_edges().await?;
    /// println!("Removed {} orphaned edges", stats.edges_removed);
    /// # Ok(())
    /// # }
    /// ```
    pub async fn vacuum_orphaned_edges(&self) -> Result<VacuumStats> {
        todo!(
            "1. Scan edges CF and edges_reverse CF
            2. For each edge:
               - Check if src and dst entities exist
               - If either missing, delete edge (from both CFs)
            3. Return VacuumStats"
        )
    }

    /// Dry run vacuum operation.
    ///
    /// Estimates what would be removed without actually deleting.
    ///
    /// # Arguments
    ///
    /// * `deleted_before` - Cutoff time for deleted entities
    ///
    /// # Returns
    ///
    /// `VacuumStats` with estimated counts (no actual deletion)
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::VacuumManager;
    /// # use chrono::{Utc, Duration};
    /// # let vacuum_mgr = VacuumManager::new("/var/lib/rem/db")?;
    /// let cutoff = Utc::now() - Duration::days(30);
    /// let stats = vacuum_mgr.dry_run(Some(cutoff)).await?;
    /// println!("Would remove {} entities ({} MB)",
    ///     stats.entities_removed,
    ///     stats.space_reclaimed_mb()
    /// );
    /// # Ok(())
    /// # }
    /// ```
    pub async fn dry_run(&self, _deleted_before: Option<DateTime<Utc>>) -> Result<VacuumStats> {
        todo!(
            "Run vacuum_deleted_entities logic but only count, don't delete.
            Return estimated stats."
        )
    }
}

/// Statistics from vacuum operation.
///
/// Tracks entities removed, space reclaimed, and related data cleaned.
#[derive(Debug, Clone)]
pub struct VacuumStats {
    /// Number of entities removed
    pub entities_removed: u64,

    /// Number of embeddings removed
    pub embeddings_removed: u64,

    /// Number of edges removed
    pub edges_removed: u64,

    /// Number of index entries removed
    pub index_entries_removed: u64,

    /// Space reclaimed (bytes)
    pub space_reclaimed_bytes: u64,

    /// Time taken (milliseconds)
    pub duration_ms: u64,
}

impl VacuumStats {
    /// Calculate space reclaimed in megabytes.
    ///
    /// # Returns
    ///
    /// Space reclaimed in MB
    pub fn space_reclaimed_mb(&self) -> f64 {
        self.space_reclaimed_bytes as f64 / 1_000_000.0
    }

    /// Total items removed.
    ///
    /// # Returns
    ///
    /// Sum of all removed items (entities + embeddings + edges + indexes)
    pub fn total_items_removed(&self) -> u64 {
        self.entities_removed
            + self.embeddings_removed
            + self.edges_removed
            + self.index_entries_removed
    }
}

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

    #[test]
    fn test_vacuum_stats() {
        let stats = VacuumStats {
            entities_removed: 1000,
            embeddings_removed: 800,
            edges_removed: 2000,
            index_entries_removed: 500,
            space_reclaimed_bytes: 50_000_000,
            duration_ms: 3000,
        };

        assert_eq!(stats.space_reclaimed_mb(), 50.0);
        assert_eq!(stats.total_items_removed(), 4300);
    }

    #[tokio::test]
    async fn test_vacuum_deleted_entities() {
        // TODO: Test vacuum with temp database containing soft-deleted entities
        todo!("Implement after vacuum_deleted_entities() is implemented")
    }
}
