//! Full backup and restore operations with S3 storage.
//!
//! This module provides:
//! - **Full backups**: Consistent RocksDB checkpoint snapshots
//! - **S3 upload**: Compressed, chunked uploads to S3
//! - **S3 download**: Parallel download and extraction
//! - **Metadata tracking**: Backup size, timestamp, entity counts
//! - **Integrity verification**: SHA256 checksums for corruption detection
//!
//! # Backup Strategy
//!
//! Full backups use RocksDB checkpoints which are:
//! - **Consistent**: Snapshot at a single point in time
//! - **Fast**: Hardlinks SST files (no copy), copies WAL/MANIFEST
//! - **Space-efficient**: Shared storage with main database
//!
//! Compression with zstd provides ~3-4x reduction in size.
//!
//! # S3 Layout
//!
//! ```text
//! s3://${P8_S3_BUCKET}/backups/full/{tenant_id}/{timestamp}/
//!   metadata.json         - Backup metadata (size, counts, checksum)
//!   rocksdb.tar.zst       - Compressed database files
//!   schemas.json          - Schema definitions at backup time
//! ```
//!
//! # Example
//!
//! ```rust,no_run
//! use percolate_rocks::admin::BackupManager;
//!
//! # async fn example() -> anyhow::Result<()> {
//! let backup_mgr = BackupManager::new("my-rem-backups")?;
//!
//! // Create and upload full backup
//! let backup_ref = backup_mgr.create_full_backup(
//!     "tenant-abc123",
//!     "/var/lib/rem/db",
//!     Some("before-migration".to_string())
//! ).await?;
//!
//! println!("Backup created: {}", backup_ref.s3_path());
//! println!("Size: {} MB", backup_ref.metadata.size_bytes / 1_000_000);
//!
//! // List backups for tenant
//! let backups = backup_mgr.list_backups("tenant-abc123").await?;
//! for backup in backups {
//!     println!("{}: {} entities", backup.name, backup.metadata.entity_count);
//! }
//!
//! // Restore from S3
//! backup_mgr.restore_full_backup(
//!     &backup_ref,
//!     "/tmp/restored-db"
//! ).await?;
//! # Ok(())
//! # }
//! ```

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

/// Backup manager for creating and restoring full database backups.
///
/// Uses S3 for storage with the following conventions:
/// - Bucket: `P8_S3_BUCKET` environment variable
/// - Path: `backups/full/{tenant_id}/{timestamp}/`
/// - Compression: zstd level 3 (configurable via `P8_BACKUP_COMPRESSION`)
/// - Multipart uploads: 100MB chunks (configurable via `P8_BACKUP_CHUNK_SIZE_MB`)
pub struct BackupManager {
    /// S3 bucket name
    bucket: String,

    /// S3 client (not yet implemented - will use aws-sdk-s3)
    _s3_client: (),

    /// Local temporary directory for staging
    temp_dir: PathBuf,

    /// Compression level (1-22, default: 3)
    compression_level: i32,

    /// Multipart upload chunk size in bytes
    chunk_size_bytes: usize,
}

impl BackupManager {
    /// Create new backup manager.
    ///
    /// # Arguments
    ///
    /// * `bucket` - S3 bucket name (typically from `P8_S3_BUCKET`)
    ///
    /// # Returns
    ///
    /// Configured `BackupManager` instance
    ///
    /// # Errors
    ///
    /// Returns error if:
    /// - AWS credentials not configured
    /// - S3 bucket not accessible
    /// - Temporary directory cannot be created
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// use percolate_rocks::admin::BackupManager;
    ///
    /// # fn example() -> anyhow::Result<()> {
    /// let bucket = std::env::var("P8_S3_BUCKET")?;
    /// let backup_mgr = BackupManager::new(&bucket)?;
    /// # Ok(())
    /// # }
    /// ```
    pub fn new(_bucket: &str) -> Result<Self> {
        todo!("Initialize S3 client, validate credentials, create temp dir")
    }

    /// Create full backup and upload to S3.
    ///
    /// # Process
    ///
    /// 1. Create RocksDB checkpoint (consistent snapshot)
    /// 2. Compress to .tar.zst (parallel compression)
    /// 3. Calculate SHA256 checksum
    /// 4. Upload to S3 in chunks (multipart upload)
    /// 5. Store metadata (size, counts, timestamp)
    /// 6. Clean up local checkpoint
    ///
    /// # Arguments
    ///
    /// * `tenant_id` - Tenant identifier for isolation
    /// * `db_path` - Path to RocksDB database
    /// * `name` - Optional backup name (defaults to timestamp)
    ///
    /// # Returns
    ///
    /// `BackupRef` with S3 location and metadata
    ///
    /// # Errors
    ///
    /// Returns error if:
    /// - Database path invalid or inaccessible
    /// - RocksDB checkpoint creation fails
    /// - S3 upload fails
    /// - Disk space insufficient for temporary files
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::BackupManager;
    /// # let backup_mgr = BackupManager::new("bucket")?;
    /// let backup_ref = backup_mgr.create_full_backup(
    ///     "tenant-123",
    ///     "/var/lib/rem/db",
    ///     Some("daily-backup".to_string())
    /// ).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn create_full_backup(
        &self,
        _tenant_id: &str,
        _db_path: &Path,
        _name: Option<String>,
    ) -> Result<BackupRef> {
        todo!(
            "1. Create RocksDB checkpoint using Database::create_checkpoint()
            2. Tar and compress with zstd (use tokio::task::spawn_blocking)
            3. Calculate SHA256 checksum
            4. Upload to S3 with multipart upload
            5. Store metadata JSON to S3
            6. Return BackupRef with S3 location"
        )
    }

    /// List all backups for a tenant.
    ///
    /// # Arguments
    ///
    /// * `tenant_id` - Tenant identifier
    ///
    /// # Returns
    ///
    /// Vector of `BackupRef` sorted by timestamp (newest first)
    ///
    /// # Errors
    ///
    /// Returns error if S3 list operation fails
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::BackupManager;
    /// # let backup_mgr = BackupManager::new("bucket")?;
    /// let backups = backup_mgr.list_backups("tenant-123").await?;
    /// for backup in backups {
    ///     println!("{}: {} MB", backup.name, backup.metadata.size_bytes / 1_000_000);
    /// }
    /// # Ok(())
    /// # }
    /// ```
    pub async fn list_backups(&self, tenant_id: &str) -> Result<Vec<BackupRef>> {
        let _ = tenant_id;
        todo!(
            "1. List S3 objects under backups/full/{{tenant_id}}/
            2. Parse metadata.json for each backup
            3. Return sorted by timestamp descending"
        )
    }

    /// Download and restore backup from S3.
    ///
    /// # Process
    ///
    /// 1. Download compressed backup from S3
    /// 2. Verify SHA256 checksum
    /// 3. Decompress and extract to target path
    /// 4. Run RocksDB repair if needed
    /// 5. Verify database opens successfully
    ///
    /// # Arguments
    ///
    /// * `backup_ref` - Reference to backup in S3
    /// * `target_path` - Local path to restore database
    ///
    /// # Errors
    ///
    /// Returns error if:
    /// - S3 download fails
    /// - Checksum verification fails (corruption detected)
    /// - Target path not empty or not writable
    /// - Database cannot be opened after restore
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::BackupManager;
    /// # let backup_mgr = BackupManager::new("bucket")?;
    /// # let backup_ref = todo!();
    /// backup_mgr.restore_full_backup(
    ///     &backup_ref,
    ///     "/tmp/restored-db"
    /// ).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn restore_full_backup(
        &self,
        _backup_ref: &BackupRef,
        _target_path: &Path,
    ) -> Result<()> {
        todo!(
            "1. Download from S3 to temp directory
            2. Verify checksum matches metadata
            3. Decompress with zstd (parallel)
            4. Extract tar to target_path
            5. Run RocksDB repair if needed
            6. Verify database opens
            7. Clean up temp files"
        )
    }

    /// Delete backup from S3.
    ///
    /// # Arguments
    ///
    /// * `backup_ref` - Reference to backup to delete
    ///
    /// # Errors
    ///
    /// Returns error if S3 delete operation fails
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # async fn example() -> anyhow::Result<()> {
    /// # use percolate_rocks::admin::BackupManager;
    /// # let backup_mgr = BackupManager::new("bucket")?;
    /// # let backup_ref = todo!();
    /// backup_mgr.delete_backup(&backup_ref).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn delete_backup(&self, _backup_ref: &BackupRef) -> Result<()> {
        todo!(
            "1. Delete all objects under backup S3 prefix
            2. Verify deletion succeeded"
        )
    }
}

/// Reference to a backup stored in S3.
///
/// Contains all information needed to locate and restore a backup.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct BackupRef {
    /// Backup name (user-provided or auto-generated)
    pub name: String,

    /// Tenant ID this backup belongs to
    pub tenant_id: String,

    /// S3 bucket name
    pub bucket: String,

    /// S3 key prefix (backups/full/{tenant_id}/{timestamp}/)
    pub s3_prefix: String,

    /// Backup metadata
    pub metadata: BackupMetadata,
}

impl BackupRef {
    /// Get full S3 path for this backup.
    ///
    /// # Returns
    ///
    /// S3 URI: `s3://{bucket}/{s3_prefix}/`
    ///
    /// # Example
    ///
    /// ```rust,no_run
    /// # use percolate_rocks::admin::BackupRef;
    /// # let backup_ref: BackupRef = todo!();
    /// let s3_path = backup_ref.s3_path();
    /// // Returns: "s3://my-bucket/backups/full/tenant-123/2025-10-25T02-00-00Z/"
    /// ```
    pub fn s3_path(&self) -> String {
        format!("s3://{}/{}/", self.bucket, self.s3_prefix)
    }
}

/// Metadata about a backup.
///
/// Stored in S3 as `metadata.json` alongside the backup data.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct BackupMetadata {
    /// Timestamp when backup was created
    pub timestamp: DateTime<Utc>,

    /// Total size of backup in bytes (compressed)
    pub size_bytes: u64,

    /// Number of entities in backup
    pub entity_count: u64,

    /// Number of schemas in backup
    pub schema_count: u64,

    /// SHA256 checksum of compressed backup file
    pub checksum_sha256: String,

    /// RocksDB version used
    pub rocksdb_version: String,

    /// Database schema version
    pub schema_version: String,
}

/// Options for restore operations.
///
/// Controls behavior when restoring from backup.
#[derive(Debug, Clone)]
pub struct RestoreOptions {
    /// Verify checksums before restore (default: true)
    pub verify_checksum: bool,

    /// Run RocksDB repair after restore (default: false)
    pub run_repair: bool,

    /// Overwrite target path if exists (default: false)
    pub overwrite: bool,
}

impl Default for RestoreOptions {
    fn default() -> Self {
        Self {
            verify_checksum: true,
            run_repair: false,
            overwrite: false,
        }
    }
}

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

    #[test]
    fn test_backup_ref_s3_path() {
        // TODO: Test S3 path construction
        todo!("Implement after BackupRef::s3_path() is implemented")
    }

    #[tokio::test]
    async fn test_create_full_backup() {
        // TODO: Test backup creation with temp database
        todo!("Implement after create_full_backup() is implemented")
    }

    #[tokio::test]
    async fn test_restore_full_backup() {
        // TODO: Test restore with checksum verification
        todo!("Implement after restore_full_backup() is implemented")
    }
}
