// BatchWriteItem and BatchGetItem storage operations
//
// BatchWriteItem: Puts or deletes multiple items across one or more tables.
//   - Up to 25 items per batch (DynamoDB limit)
//   - Each item is an independent PutRequest or DeleteRequest
//   - Partial failures are reported via UnprocessedItems
//
// BatchGetItem: Retrieves multiple items from one or more tables.
//   - Up to 100 items per batch (DynamoDB limit)
//   - Each table request contains a list of Keys
//   - Partial failures reported via UnprocessedKeys
package dynamodb

// ============================================================================
// BatchWriteItem Types
// ============================================================================

Write_Request_Type :: enum {
	Put,
	Delete,
}

Write_Request :: struct {
	type:  Write_Request_Type,
	item:  Item,   // For Put: the full item.  For Delete: the key item.
}

Batch_Write_Table_Request :: struct {
	table_name: string,
	requests:   []Write_Request,
}

Batch_Write_Result :: struct {
	// UnprocessedItems — requests that failed and should be retried.
	// For now we process everything or return an error, so this is
	// typically empty. Populated only on partial failures.
	unprocessed: [dynamic]Batch_Write_Table_Request,
}

batch_write_result_destroy :: proc(result: ^Batch_Write_Result) {
	for &table_req in result.unprocessed {
		for &req in table_req.requests {
			item_destroy(&req.item)
		}
		delete(table_req.requests)
	}
	delete(result.unprocessed)
}

// ============================================================================
// BatchWriteItem — Execute a batch of put/delete operations
//
// DynamoDB semantics:
//   - Operations within a batch are NOT atomic (some may succeed, some fail)
//   - Each operation is validated independently
//   - Failed operations go into UnprocessedItems
//   - Limit: 25 operations total across all tables
// ============================================================================

batch_write_item :: proc(
	engine: ^Storage_Engine,
	table_requests: []Batch_Write_Table_Request,
) -> (Batch_Write_Result, Storage_Error) {
	result := Batch_Write_Result{
		unprocessed = make([dynamic]Batch_Write_Table_Request),
	}

	// Count total operations across all tables
	total_ops := 0
	for table_req in table_requests {
		total_ops += len(table_req.requests)
	}

	// Enforce DynamoDB limit: 25 operations per batch
	if total_ops > 25 {
		return result, .Validation_Error
	}

	for table_req in table_requests {
		failed_requests := make([dynamic]Write_Request)

		for req in table_req.requests {
			var_err: Storage_Error

			switch req.type {
			case .Put:
				var_err = put_item(engine, table_req.table_name, req.item)
			case .Delete:
				var_err = delete_item(engine, table_req.table_name, req.item)
			}

			// Distinguish validation errors from transient failures
			if var_err != .None {
				#partial switch var_err {
				case .Missing_Key_Attribute, .Invalid_Key, .Serialization_Error:
					// Hard validation errors — fail the entire batch
					batch_write_result_destroy(&result)
					delete(failed_requests)
					return result, var_err

				case .Table_Not_Found:
					// Non-existent table is a hard request failure, not a retryable condition.
					// DynamoDB returns ResourceNotFoundException for the whole request.
					batch_write_result_destroy(&result)
					delete(failed_requests)
					return result, .Table_Not_Found

				case .RocksDB_Error, .Item_Not_Found:
					// Genuinely transient/infrastructure errors — add to UnprocessedItems.
					failed_item := item_deep_copy(req.item)
					append(&failed_requests, Write_Request{
						type = req.type,
						item = failed_item,
					})

				case .None, .Validation_Error, .Internal_Error:
					// Should not happen, but handle gracefully
					failed_item := item_deep_copy(req.item)
					append(&failed_requests, Write_Request{
						type = req.type,
						item = failed_item,
					})
				}
			}
		}

		if len(failed_requests) > 0 {
			append(&result.unprocessed, Batch_Write_Table_Request{
				table_name = table_req.table_name,
				requests   = failed_requests[:],
			})
		} else {
			delete(failed_requests)
		}
	}

	return result, .None
}


// ============================================================================
// BatchGetItem Types
// ============================================================================

Batch_Get_Table_Request :: struct {
	table_name: string,
	keys:       []Item,
}

Batch_Get_Table_Result :: struct {
	table_name: string,
	items:      []Item,
}

Batch_Get_Result :: struct {
	responses:       [dynamic]Batch_Get_Table_Result,
	unprocessed_keys: [dynamic]Batch_Get_Table_Request,
}

batch_get_result_destroy :: proc(result: ^Batch_Get_Result) {
	for &table_result in result.responses {
		for &item in table_result.items {
			item_destroy(&item)
		}
		delete(table_result.items)
	}
	delete(result.responses)

	for &table_req in result.unprocessed_keys {
		for &key in table_req.keys {
			item_destroy(&key)
		}
		delete(table_req.keys)
	}
	delete(result.unprocessed_keys)
}

// ============================================================================
// BatchGetItem — Retrieve multiple items from one or more tables
//
// DynamoDB semantics:
//   - Each key is fetched independently
//   - Missing items are silently omitted (no error)
//   - Failed lookups go into UnprocessedKeys
//   - Limit: 100 keys total across all tables
// ============================================================================

batch_get_item :: proc(
	engine: ^Storage_Engine,
	table_requests: []Batch_Get_Table_Request,
) -> (Batch_Get_Result, Storage_Error) {
	result := Batch_Get_Result{
		responses        = make([dynamic]Batch_Get_Table_Result),
		unprocessed_keys = make([dynamic]Batch_Get_Table_Request),
	}

	// Count total keys across all tables
	total_keys := 0
	for table_req in table_requests {
		total_keys += len(table_req.keys)
	}

	// Enforce DynamoDB limit: 100 keys per batch
	if total_keys > 100 {
		return result, .Validation_Error
	}

	for table_req in table_requests {
		found_items := make([dynamic]Item)
		failed_keys := make([dynamic]Item)

		for key in table_req.keys {
			item_result, get_err := get_item(engine, table_req.table_name, key)

			// Distinguish validation errors from transient failures
			if get_err != .None && get_err != .Item_Not_Found {
				#partial switch get_err {
				case .Missing_Key_Attribute, .Invalid_Key, .Serialization_Error:
					// Hard validation error — fail the entire batch
					batch_get_result_destroy(&result)
					delete(found_items)
					delete(failed_keys)
					return result, get_err

				case .RocksDB_Error, .Table_Not_Found:
					// Transient error — add to unprocessed
					append(&failed_keys, item_deep_copy(key))
					continue

				case .None, .Validation_Error, .Internal_Error, .Item_Not_Found:
					// Should not happen here, but handle gracefully
					continue
				}
			}

			if item_val, has_item := item_result.?; has_item {
				append(&found_items, item_val)
			}
			// If item not found, silently omit (DynamoDB behavior)
		}

		if len(found_items) > 0 {
			append(&result.responses, Batch_Get_Table_Result{
				table_name = table_req.table_name,
				items      = found_items[:],
			})
		} else {
			delete(found_items)
		}

		if len(failed_keys) > 0 {
			append(&result.unprocessed_keys, Batch_Get_Table_Request{
				table_name = table_req.table_name,
				keys       = failed_keys[:],
			})
		} else {
			delete(failed_keys)
		}
	}

	return result, .None
}