public/dart/sledge/lib/src/storage/kv_encoding.dart

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:typed_data';

import '../document/document_id.dart';
import '../schema/schema.dart';
import '../uint8list_ops.dart';

/// The type of the KV stored in Ledger backing the data
/// stored in Sledge.
/// When modifying this enum:
/// * DO append to the end of the enum.
/// * DO NOT delete entries.
/// * DO NOT re-order entries.
enum KeyValueType {
  /// The type used to identify KVs that store Documents data.
  document,

  /// The type used to identify KVs that store the Schemas used in Sledge.
  schema,

  /// The type used to identify KVs that store the IndexDefinitions.
  indexDefinition,

  /// The type used to identify KVs that store the Indexes.
  indexEntry
}

/// The length of the prefix storing the Type of data.
const int typePrefixLength = 1;

/// Returns the prefix for the KV storing in Ledger items of type [type].
Uint8List prefixForType(KeyValueType type) {
  assert(type.index >= 0 && type.index <= 255);
  return Uint8List.fromList([type.index]);
}

/// Returns the document subId stored in `key`.
Uint8List documentSubIdFromKey(Uint8List key) {
  // Keys are serialized as: `{keyValueType}{schemaId}{documentId}{entryKey}`
  assert(uint8ListsAreEqual(
      getSublistView(key, start: 0, end: typePrefixLength),
      prefixForType(KeyValueType.document)));
  final subId = getSublistView(key,
      start: typePrefixLength + Schema.hashLength,
      end: 1 + DocumentId.prefixLength);
  return subId;
}