public/dart/sledge/lib/src/storage/document_storage.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:async';
import 'dart:typed_data';

import 'package:fidl_fuchsia_ledger/fidl.dart' as ledger;

import '../document/change.dart';
import '../document/document.dart';
import '../document/document_id.dart';
import '../document/values/key_value.dart';
import '../ledger_helpers.dart';
import '../uint8list_ops.dart';
import 'kv_encoding.dart' as sledge_storage;

/// Returns the key prefix used to store [document] in Ledger.
Uint8List _documentStorageKeyPrefix(Document document) {
  final documentId = document.documentId;
  final prefix = concatUint8Lists(
      sledge_storage.prefixForType(sledge_storage.KeyValueType.document),
      documentId.prefix);
  assert(prefix.length ==
      sledge_storage.typePrefixLength + DocumentId.prefixLength);
  return prefix;
}

/// Stores [document] into [page].
/// [document] must not be deleted.
void saveDocumentToPage(Document document, ledger.Page page) {
  assert(document.state == DocumentState.available);

  final Uint8List documentPrefix = _documentStorageKeyPrefix(document);
  final Change change = document.getChange();

  // Forward the "deletes".
  for (Uint8List deletedKey in change.deletedKeys) {
    final Uint8List keyWithDocumentPrefix =
        concatUint8Lists(documentPrefix, deletedKey);
    page.delete(
      keyWithDocumentPrefix,
    );
  }

  // Forward the "puts".
  for (KeyValue kv in change.changedEntries) {
    final Uint8List keyWithDocumentPrefix =
        concatUint8Lists(documentPrefix, kv.key);
    page.put(
      keyWithDocumentPrefix,
      kv.value,
    );
  }
}

void _deleteKeyValues(List<KeyValue> keyValues, ledger.Page page) {
  for (KeyValue kv in keyValues) {
    page.delete(
      kv.key,
    );
  }
}

/// Deletes all the key-values storing [document] from [page] at the time
/// [snapshot] was taken.
Future<void> deleteDocumentFromPage(
    Document document, ledger.Page page, ledger.PageSnapshot snapshot) {
  assert(document.state == DocumentState.pendingDeletion);
  final Uint8List documentPrefix = _documentStorageKeyPrefix(document);
  // TODO: Don't read the values from the snapshot as only the keys are needed.
  Future<List<KeyValue>> futureKeyValues =
      getEntriesFromSnapshotWithPrefix(snapshot, documentPrefix);
  Future<void> futureList = futureKeyValues.then((List<KeyValue> keyValues) {
    _deleteKeyValues(keyValues, page);
  });
  return futureList;
}