//! Manual RocksDB compaction operations.
//!
//! This module provides:
//! - **Column family compaction**: Reduce SST file count and size
//! - **Range compaction**: Compact specific key ranges
//! - **Full database compaction**: Compact all column families
//! - **Compaction statistics**: Before/after size comparison
//!
//! # When to Use Compaction
//!
//! RocksDB auto-compacts in the background, but manual compaction helps:
//! - After large bulk deletes (reclaim space)
//! - After major schema changes (consolidate files)
//! - Before backup (smaller backup size)
//! - Performance degradation (too many SST files)
//!
//! # Example
//!
//! ```rust,no_run
//! use percolate_rocks::admin::CompactionManager;
//!
//! # async fn example() -> anyhow::Result<()> {
//! let compaction_mgr = CompactionManager::new("/var/lib/rem/db")?;
//!
//! // Compact embeddings column family (typically largest)
//! let stats = compaction_mgr.compact_column_family("embeddings").await?;
//! println!("Reclaimed {} MB", stats.size_reduction_mb());
//!
//! // Full database compaction
//! compaction_mgr.compact_all().await?;
//! # Ok(())
//! # }
//! ```

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

/// Manages manual compaction operations.
///
/// Wraps RocksDB compaction APIs with progress tracking and statistics.
pub struct CompactionManager {
    /// Path to RocksDB database
    _db_path: PathBuf,

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

impl CompactionManager {
    /// Create new compaction manager.
    ///
    /// # Arguments
    ///
    /// * `db_path` - Path to RocksDB database
    ///
    /// # Returns
    ///
    /// Configured `CompactionManager` instance
    ///
    /// # Errors
    ///
    /// Returns error if database path invalid or cannot be opened
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// use percolate_rocks::admin::CompactionManager;
    ///
    /// # fn example() -> anyhow::Result<()> {
    /// let compaction_mgr = CompactionManager::new("/var/lib/rem/db")?;
    /// # Ok(())
    /// # }
    /// ```
    pub fn new(_db_path: &Path) -> Result<Self> {
        todo!("Open RocksDB in read-write mode")
    }

    /// Compact specific column family.
    ///
    /// # Arguments
    ///
    /// * `cf_name` - Column family name (entities, embeddings, edges, etc.)
    ///
    /// # Returns
    ///
    /// `CompactionStats` with before/after size comparison
    ///
    /// # Errors
    ///
    /// Returns error if:
    /// - Column family does not exist
    /// - Compaction fails
    /// - Database is corrupted
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::CompactionManager;
    /// # let mgr = CompactionManager::new("/var/lib/rem/db")?;
    /// let stats = mgr.compact_column_family("embeddings").await?;
    /// println!("Before: {} MB, After: {} MB", stats.size_before_mb, stats.size_after_mb);
    /// # Ok(())
    /// # }
    /// ```
    pub async fn compact_column_family(&self, _cf_name: &str) -> Result<CompactionStats> {
        todo!(
            "1. Get column family handle
            2. Get size before compaction (DB::property_value)
            3. Run compaction: DB::compact_range(cf, None, None)
            4. Get size after compaction
            5. Return CompactionStats"
        )
    }

    /// Compact all column families.
    ///
    /// # Returns
    ///
    /// Vector of `CompactionStats` for each column family
    ///
    /// # Errors
    ///
    /// Returns error if any compaction fails
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::CompactionManager;
    /// # let mgr = CompactionManager::new("/var/lib/rem/db")?;
    /// let all_stats = mgr.compact_all().await?;
    /// for stats in all_stats {
    ///     println!("{}: reclaimed {} MB", stats.cf_name, stats.size_reduction_mb());
    /// }
    /// # Ok(())
    /// # }
    /// ```
    pub async fn compact_all(&self) -> Result<Vec<CompactionStats>> {
        todo!(
            "1. Get all column family names
            2. Compact each CF sequentially (to avoid resource contention)
            3. Collect and return stats for all CFs"
        )
    }

    /// Compact specific key range in column family.
    ///
    /// Useful for targeted compaction after deleting specific entities.
    ///
    /// # Arguments
    ///
    /// * `cf_name` - Column family name
    /// * `start_key` - Start of key range (inclusive), None for beginning
    /// * `end_key` - End of key range (exclusive), None for end
    ///
    /// # Returns
    ///
    /// `CompactionStats` for the range
    ///
    /// # Errors
    ///
    /// Returns error if column family or key range invalid
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::CompactionManager;
    /// # let mgr = CompactionManager::new("/var/lib/rem/db")?;
    /// // Compact all entities for a specific tenant
    /// let stats = mgr.compact_range(
    ///     "entities",
    ///     Some(b"entity:tenant-123:"),
    ///     Some(b"entity:tenant-123:\xff")
    /// ).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn compact_range(
        &self,
        _cf_name: &str,
        _start_key: Option<&[u8]>,
        _end_key: Option<&[u8]>,
    ) -> Result<CompactionStats> {
        todo!(
            "1. Get column family handle
            2. Get size before
            3. Run compaction: DB::compact_range(cf, start_key, end_key)
            4. Get size after
            5. Return stats"
        )
    }
}

/// Statistics from compaction operation.
///
/// Tracks before/after sizes and time taken.
#[derive(Debug, Clone)]
pub struct CompactionStats {
    /// Column family name
    pub cf_name: String,

    /// Size before compaction (bytes)
    pub size_before_bytes: u64,

    /// Size after compaction (bytes)
    pub size_after_bytes: u64,

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

impl CompactionStats {
    /// Calculate size reduction in megabytes.
    ///
    /// # Returns
    ///
    /// Size reduction (positive means space reclaimed)
    pub fn size_reduction_mb(&self) -> f64 {
        (self.size_before_bytes.saturating_sub(self.size_after_bytes)) as f64 / 1_000_000.0
    }

    /// Calculate size reduction percentage.
    ///
    /// # Returns
    ///
    /// Percentage reduction (0-100)
    pub fn size_reduction_percent(&self) -> f64 {
        if self.size_before_bytes == 0 {
            return 0.0;
        }
        let reduction = self.size_before_bytes.saturating_sub(self.size_after_bytes);
        (reduction as f64 / self.size_before_bytes as f64) * 100.0
    }
}

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

    #[test]
    fn test_compaction_stats_reduction() {
        let stats = CompactionStats {
            cf_name: "test".to_string(),
            size_before_bytes: 1_000_000_000,
            size_after_bytes: 600_000_000,
            duration_ms: 5000,
        };

        assert_eq!(stats.size_reduction_mb(), 400.0);
        assert_eq!(stats.size_reduction_percent(), 40.0);
    }

    #[tokio::test]
    async fn test_compact_column_family() {
        // TODO: Test compaction with temp database
        todo!("Implement after compact_column_family() is implemented")
    }
}
