//! Index rebuild and maintenance operations.
//!
//! This module provides:
//! - **HNSW index rebuild**: Reconstruct vector index from embeddings
//! - **Field index rebuild**: Recreate indexed field lookups
//! - **Key index rebuild**: Reconstruct reverse key lookup index
//! - **Progress tracking**: Monitor rebuild progress for large datasets
//!
//! # When to Rebuild Indexes
//!
//! - After schema changes (new indexed fields)
//! - After bulk updates to embeddings
//! - Index corruption detected
//! - Performance degradation on queries
//! - After restoring from backup (indexes not included)
//!
//! # Example
//!
//! ```rust,no_run
//! use percolate_rocks::admin::{IndexManager, IndexRebuildOptions};
//!
//! # async fn example() -> anyhow::Result<()> {
//! let index_mgr = IndexManager::new("/var/lib/rem/db")?;
//!
//! // Rebuild HNSW vector index
//! index_mgr.rebuild_hnsw_index(None).await?;
//!
//! // Rebuild field indexes for specific schema
//! let options = IndexRebuildOptions {
//!     schema_name: Some("articles".to_string()),
//!     batch_size: 1000,
//!     show_progress: true,
//! };
//! index_mgr.rebuild_field_indexes(options).await?;
//! # Ok(())
//! # }
//! ```

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

/// Manages index rebuild operations.
///
/// Provides tools to reconstruct indexes after schema changes or corruption.
pub struct IndexManager {
    /// Path to RocksDB database
    _db_path: PathBuf,

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

impl IndexManager {
    /// Create new index manager.
    ///
    /// # Arguments
    ///
    /// * `db_path` - Path to RocksDB database
    ///
    /// # Returns
    ///
    /// Configured `IndexManager` 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")
    }

    /// Rebuild HNSW vector index.
    ///
    /// Reconstructs the HNSW index from all embeddings in database.
    ///
    /// # Arguments
    ///
    /// * `options` - Rebuild options (batch size, progress tracking)
    ///
    /// # Returns
    ///
    /// Unit on success
    ///
    /// # Errors
    ///
    /// Returns error if:
    /// - No embeddings found in database
    /// - HNSW construction fails
    /// - Disk space insufficient
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::IndexManager;
    /// # let index_mgr = IndexManager::new("/var/lib/rem/db")?;
    /// index_mgr.rebuild_hnsw_index(None).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn rebuild_hnsw_index(&self, _options: Option<IndexRebuildOptions>) -> Result<()> {
        todo!(
            "1. Drop existing HNSW index
            2. Scan embeddings CF
            3. Build new HNSW index in batches (for progress tracking)
            4. Persist index to disk
            5. Verify index with test queries"
        )
    }

    /// Rebuild field indexes for all schemas.
    ///
    /// Reconstructs indexed field lookups from entity data.
    ///
    /// # Arguments
    ///
    /// * `options` - Rebuild options (can specify specific schema)
    ///
    /// # Returns
    ///
    /// Unit on success
    ///
    /// # Errors
    ///
    /// Returns error if schema not found or rebuild fails
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::{IndexManager, IndexRebuildOptions};
    /// # let index_mgr = IndexManager::new("/var/lib/rem/db")?;
    /// // Rebuild only articles schema
    /// let options = IndexRebuildOptions {
    ///     schema_name: Some("articles".to_string()),
    ///     ..Default::default()
    /// };
    /// index_mgr.rebuild_field_indexes(options).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn rebuild_field_indexes(&self, _options: IndexRebuildOptions) -> Result<()> {
        todo!(
            "1. Get schema definitions
            2. For each schema (or specified schema):
               - Clear existing indexes for schema
               - Scan entities
               - For each indexed field, create index entries
            3. Verify indexes with test queries"
        )
    }

    /// Rebuild reverse key index.
    ///
    /// Reconstructs the global key lookup index from entity data.
    ///
    /// # Returns
    ///
    /// Unit on success
    ///
    /// # Errors
    ///
    /// Returns error if rebuild fails
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::IndexManager;
    /// # let index_mgr = IndexManager::new("/var/lib/rem/db")?;
    /// index_mgr.rebuild_key_index().await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn rebuild_key_index(&self) -> Result<()> {
        todo!(
            "1. Clear key_index CF
            2. Scan all entities
            3. For each entity:
               - Extract key field (uri, name, etc.)
               - Create reverse lookup entry in key_index CF
            4. Verify with test lookups"
        )
    }

    /// Rebuild all indexes.
    ///
    /// Convenience method to rebuild HNSW, field indexes, and key index.
    ///
    /// # Arguments
    ///
    /// * `options` - Rebuild options
    ///
    /// # Returns
    ///
    /// Unit on success
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::IndexManager;
    /// # let index_mgr = IndexManager::new("/var/lib/rem/db")?;
    /// index_mgr.rebuild_all_indexes(None).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn rebuild_all_indexes(&self, _options: Option<IndexRebuildOptions>) -> Result<()> {
        todo!(
            "Run in sequence:
            1. rebuild_hnsw_index
            2. rebuild_field_indexes
            3. rebuild_key_index"
        )
    }

    /// Verify index integrity.
    ///
    /// Checks that indexes are consistent with entity data.
    ///
    /// # Returns
    ///
    /// True if all indexes valid, false if corruption detected
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::IndexManager;
    /// # let index_mgr = IndexManager::new("/var/lib/rem/db")?;
    /// if !index_mgr.verify_indexes().await? {
    ///     println!("Index corruption detected!");
    /// }
    /// # Ok(())
    /// # }
    /// ```
    pub async fn verify_indexes(&self) -> Result<bool> {
        todo!(
            "1. Sample entities and check:
               - HNSW index returns entity in nearest neighbor search
               - Field indexes return entity for indexed values
               - Key index returns correct entity for keys
            2. Return false if any mismatch found"
        )
    }
}

/// Options for index rebuild operations.
///
/// Controls batch size, progress tracking, and scope of rebuild.
#[derive(Debug, Clone)]
pub struct IndexRebuildOptions {
    /// Rebuild only this schema (None = all schemas)
    pub schema_name: Option<String>,

    /// Batch size for processing (default: 1000)
    pub batch_size: usize,

    /// Show progress updates (default: false)
    pub show_progress: bool,

    /// Verify after rebuild (default: true)
    pub verify_after: bool,
}

impl Default for IndexRebuildOptions {
    fn default() -> Self {
        Self {
            schema_name: None,
            batch_size: 1000,
            show_progress: false,
            verify_after: true,
        }
    }
}

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

    #[tokio::test]
    async fn test_rebuild_hnsw_index() {
        // TODO: Test HNSW rebuild with temp database
        todo!("Implement after rebuild_hnsw_index() is implemented")
    }

    #[tokio::test]
    async fn test_rebuild_field_indexes() {
        // TODO: Test field index rebuild
        todo!("Implement after rebuild_field_indexes() is implemented")
    }

    #[tokio::test]
    async fn test_verify_indexes() {
        // TODO: Test index verification
        todo!("Implement after verify_indexes() is implemented")
    }
}
