import {
  Backend,
  DatabaseConnection,
  DatabaseTransaction,
  Schema,
  RecordStoreRequest,
  IndexProperties,
  RecordGetRequest,
  RecordGetResponse,
  ResultLevel,
  StoreLevel,
  RecordStoreResponse,
} from "./backend-interface";
import structuredClone from "./util/structuredClone";
import {
  InvalidStateError,
  InvalidAccessError,
  ConstraintError,
} from "./util/errors";
import BTree, { ISortedMap, ISortedMapF } from "./tree/b+tree";
import BridgeIDBFactory from "./BridgeIDBFactory";
import compareKeys from "./util/cmp";
import extractKey from "./util/extractKey";
import { Key, Value, KeyPath } from "./util/types";
import { StoreKeyResult, makeStoreKeyValue } from "./util/makeStoreKeyValue";
import getIndexKeys from "./util/getIndexKeys";
import openPromise from "./util/openPromise";
import BridgeIDBKeyRange from "./BridgeIDBKeyRange";
import { resetWarningCache } from "prop-types";

enum TransactionLevel {
  Disconnected = 0,
  Connected = 1,
  Read = 2,
  Write = 3,
  VersionChange = 4,
}

interface ObjectStore {
  originalName: string;
  modifiedName: string | undefined;
  originalData: ISortedMapF<Key, ObjectStoreRecord>;
  modifiedData: ISortedMapF<Key, ObjectStoreRecord> | undefined;
  deleted: boolean;
  originalKeyGenerator: number;
  modifiedKeyGenerator: number | undefined;
}

interface Index {
  originalName: string;
  modifiedName: string | undefined;
  originalData: ISortedMapF<Key, IndexRecord>;
  modifiedData: ISortedMapF<Key, IndexRecord> | undefined;
  deleted: boolean;
}

interface Database {
  committedObjectStores: { [name: string]: ObjectStore };
  modifiedObjectStores: { [name: string]: ObjectStore };
  committedIndexes: { [name: string]: Index };
  modifiedIndexes: { [name: string]: Index };
  committedSchema: Schema;
  /**
   * Was the transaction deleted during the running transaction?
   */
  deleted: boolean;

  txLevel: TransactionLevel;

  connectionCookie: string | undefined;
}

interface Connection {
  dbName: string;

  modifiedSchema: Schema | undefined;

  /**
   * Has the underlying database been deleted?
   */
  deleted: boolean;

  /**
   * Map from the effective name of an object store during
   * the transaction to the real name.
   */
  objectStoreMap: { [currentName: string]: ObjectStore };
  indexMap: { [currentName: string]: Index };
}

interface IndexRecord {
  indexKey: Key;
  primaryKeys: Key[];
}

interface ObjectStoreRecord {
  primaryKey: Key;
  value: Value;
}

class AsyncCondition {
  _waitPromise: Promise<void>;
  _resolveWaitPromise: () => void;
  constructor() {
    const op = openPromise<void>();
    this._waitPromise = op.promise;
    this._resolveWaitPromise = op.resolve;
  }

  wait(): Promise<void> {
    return this._waitPromise;
  }

  trigger(): void {
    this._resolveWaitPromise();
    const op = openPromise<void>();
    this._waitPromise = op.promise;
    this._resolveWaitPromise = op.resolve;
  }
}

function nextStoreKey<T>(
  forward: boolean,
  data: ISortedMapF<Key, ObjectStoreRecord>,
  k: Key | undefined,
) {
  if (k === undefined || k === null) {
    return undefined;
  }
  const res = forward ? data.nextHigherPair(k) : data.nextLowerPair(k);
  if (!res) {
    return undefined;
  }
  return res[1].primaryKey;
}

function furthestKey(
  forward: boolean,
  key1: Key | undefined,
  key2: Key | undefined,
) {
  if (key1 === undefined) {
    return key2;
  }
  if (key2 === undefined) {
    return key1;
  }
  const cmpResult = compareKeys(key1, key2);
  if (cmpResult === 0) {
    // Same result
    return key1;
  }
  if (forward && cmpResult === 1) {
    return key1;
  }
  if (forward && cmpResult === -1) {
    return key2;
  }
  if (!forward && cmpResult === 1) {
    return key2;
  }
  if (!forward && cmpResult === -1) {
    return key1;
  }
}

/**
 * Primitive in-memory backend.
 */
export class MemoryBackend implements Backend {
  databases: { [name: string]: Database } = {};

  connectionIdCounter = 1;

  transactionIdCounter = 1;

  /**
   * Connections by connection cookie.
   */
  connections: { [name: string]: Connection } = {};

  /**
   * Connections by transaction (!!) cookie.  In this implementation,
   * at most one transaction can run at the same time per connection.
   */
  connectionsByTransaction: { [tx: string]: Connection } = {};

  /**
   * Condition that is triggered whenever a client disconnects.
   */
  disconnectCond: AsyncCondition = new AsyncCondition();

  /**
   * Conditation that is triggered whenever a transaction finishes.
   */
  transactionDoneCond: AsyncCondition = new AsyncCondition();

  enableTracing: boolean = true;

  async getDatabases(): Promise<{ name: string; version: number }[]> {
    if (this.enableTracing) {
      console.log("TRACING: getDatabase");
    }
    const dbList = [];
    for (const name in this.databases) {
      dbList.push({
        name,
        version: this.databases[name].committedSchema.databaseVersion,
      });
    }
    return dbList;
  }

  async deleteDatabase(tx: DatabaseTransaction, name: string): Promise<void> {
    if (this.enableTracing) {
      console.log("TRACING: deleteDatabase");
    }
    const myConn = this.connectionsByTransaction[tx.transactionCookie];
    if (!myConn) {
      throw Error("no connection associated with transaction");
    }
    const myDb = this.databases[name];
    if (!myDb) {
      throw Error("db not found");
    }
    if (myDb.committedSchema.databaseName !== name) {
      throw Error("name does not match");
    }
    if (myDb.txLevel < TransactionLevel.VersionChange) {
      throw new InvalidStateError();
    }
    if (myDb.connectionCookie !== tx.transactionCookie) {
      throw new InvalidAccessError();
    }
    myDb.deleted = true;
  }

  async connectDatabase(name: string): Promise<DatabaseConnection> {
    if (this.enableTracing) {
      console.log(`TRACING: connectDatabase(${name})`);
    }
    const connectionId = this.connectionIdCounter++;
    const connectionCookie = `connection-${connectionId}`;

    let database = this.databases[name];
    if (!database) {
      const schema: Schema = {
        databaseName: name,
        indexes: {},
        databaseVersion: 0,
        objectStores: {},
      };
      database = {
        committedSchema: schema,
        deleted: false,
        modifiedIndexes: {},
        committedIndexes: {},
        committedObjectStores: {},
        modifiedObjectStores: {},
        txLevel: TransactionLevel.Disconnected,
        connectionCookie: undefined,
      };
      this.databases[name] = database;
    }

    while (database.txLevel !== TransactionLevel.Disconnected) {
      await this.disconnectCond.wait();
    }

    database.txLevel = TransactionLevel.Connected;
    database.connectionCookie = connectionCookie;

    const myConn: Connection = {
      dbName: name,
      deleted: false,
      indexMap: Object.assign({}, database.committedIndexes),
      objectStoreMap: Object.assign({}, database.committedObjectStores),
      modifiedSchema: structuredClone(database.committedSchema),
    };

    this.connections[connectionCookie] = myConn;

    return { connectionCookie };
  }

  async beginTransaction(
    conn: DatabaseConnection,
    objectStores: string[],
    mode: import("./util/types").TransactionMode,
  ): Promise<DatabaseTransaction> {
    if (this.enableTracing) {
      console.log(`TRACING: beginTransaction`);
    }
    const transactionCookie = `tx-${this.transactionIdCounter++}`;
    const myConn = this.connections[conn.connectionCookie];
    if (!myConn) {
      throw Error("connection not found");
    }
    const myDb = this.databases[myConn.dbName];
    if (!myDb) {
      throw Error("db not found");
    }

    while (myDb.txLevel !== TransactionLevel.Connected) {
      if (this.enableTracing) {
        console.log(`TRACING: beginTransaction -- waiting for others to close`);
      }
      await this.transactionDoneCond.wait();
    }

    if (mode === "readonly") {
      myDb.txLevel = TransactionLevel.Read;
    } else if (mode === "readwrite") {
      myDb.txLevel = TransactionLevel.Write;
    } else {
      throw Error("unsupported transaction mode");
    }

    this.connectionsByTransaction[transactionCookie] = myConn;

    return { transactionCookie };
  }

  async enterVersionChange(
    conn: DatabaseConnection,
    newVersion: number,
  ): Promise<DatabaseTransaction> {
    if (this.enableTracing) {
      console.log(`TRACING: enterVersionChange`);
    }
    const transactionCookie = `tx-vc-${this.transactionIdCounter++}`;
    const myConn = this.connections[conn.connectionCookie];
    if (!myConn) {
      throw Error("connection not found");
    }
    const myDb = this.databases[myConn.dbName];
    if (!myDb) {
      throw Error("db not found");
    }

    while (myDb.txLevel !== TransactionLevel.Connected) {
      await this.transactionDoneCond.wait();
    }

    myDb.txLevel = TransactionLevel.VersionChange;

    this.connectionsByTransaction[transactionCookie] = myConn;

    return { transactionCookie };
  }

  async close(conn: DatabaseConnection): Promise<void> {
    if (this.enableTracing) {
      console.log(`TRACING: close`);
    }
    const myConn = this.connections[conn.connectionCookie];
    if (!myConn) {
      throw Error("connection not found - already closed?");
    }
    if (!myConn.deleted) {
      const myDb = this.databases[myConn.dbName];
      if (myDb.txLevel != TransactionLevel.Connected) {
        throw Error("invalid state");
      }
      myDb.txLevel = TransactionLevel.Disconnected;
    }
    delete this.connections[conn.connectionCookie];
    this.disconnectCond.trigger();
  }

  getSchema(dbConn: DatabaseConnection): Schema {
    if (this.enableTracing) {
      console.log(`TRACING: getSchema`);
    }
    const myConn = this.connections[dbConn.connectionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (myConn.modifiedSchema) {
      return myConn.modifiedSchema;
    }
    return db.committedSchema;
  }

  renameIndex(
    btx: DatabaseTransaction,
    oldName: string,
    newName: string,
  ): void {
    if (this.enableTracing) {
      console.log(`TRACING: renameIndex(?, ${oldName}, ${newName})`);
    }
    const myConn = this.connectionsByTransaction[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.VersionChange) {
      throw Error("only allowed in versionchange transaction");
    }
    let schema = myConn.modifiedSchema;
    if (!schema) {
      throw Error();
    }
    if (schema.indexes[newName]) {
      throw new Error("new index name already used");
    }
    if (!schema.indexes[oldName]) {
      throw new Error("new index name already used");
    }
    const index: Index = myConn.indexMap[oldName];
    if (!index) {
      throw Error("old index missing in connection's index map");
    }
    schema.indexes[newName] = schema.indexes[newName];
    delete schema.indexes[oldName];
    for (const storeName in schema.objectStores) {
      const store = schema.objectStores[storeName];
      store.indexes = store.indexes.map(x => {
        if (x == oldName) {
          return newName;
        } else {
          return x;
        }
      });
    }
    myConn.indexMap[newName] = index;
    delete myConn.indexMap[oldName];
    index.modifiedName = newName;
  }

  deleteIndex(btx: DatabaseTransaction, indexName: string): void {
    if (this.enableTracing) {
      console.log(`TRACING: deleteIndex(${indexName})`);
    }
    const myConn = this.connections[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.VersionChange) {
      throw Error("only allowed in versionchange transaction");
    }
    let schema = myConn.modifiedSchema;
    if (!schema) {
      throw Error();
    }
    if (!schema.indexes[indexName]) {
      throw new Error("index does not exist");
    }
    const index: Index = myConn.indexMap[indexName];
    if (!index) {
      throw Error("old index missing in connection's index map");
    }
    index.deleted = true;
    delete schema.indexes[indexName];
    delete myConn.indexMap[indexName];
    for (const storeName in schema.objectStores) {
      const store = schema.objectStores[storeName];
      store.indexes = store.indexes.filter(x => {
        return x !== indexName;
      });
    }
  }

  deleteObjectStore(btx: DatabaseTransaction, name: string): void {
    if (this.enableTracing) {
      console.log(`TRACING: deleteObjectStore(${name})`);
    }
    const myConn = this.connections[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.VersionChange) {
      throw Error("only allowed in versionchange transaction");
    }
    const schema = myConn.modifiedSchema;
    if (!schema) {
      throw Error();
    }
    const objectStoreProperties = schema.objectStores[name];
    if (!objectStoreProperties) {
      throw Error("object store not found");
    }
    const objectStore = myConn.objectStoreMap[name];
    if (!objectStore) {
      throw Error("object store not found in map");
    }
    const indexNames = objectStoreProperties.indexes;
    for (const indexName of indexNames) {
      this.deleteIndex(btx, indexName);
    }

    objectStore.deleted = true;
    delete myConn.objectStoreMap[name];
    delete schema.objectStores[name];
  }

  renameObjectStore(
    btx: DatabaseTransaction,
    oldName: string,
    newName: string,
  ): void {
    if (this.enableTracing) {
      console.log(`TRACING: renameObjectStore(?, ${oldName}, ${newName})`);
    }

    const myConn = this.connections[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.VersionChange) {
      throw Error("only allowed in versionchange transaction");
    }
    const schema = myConn.modifiedSchema;
    if (!schema) {
      throw Error();
    }
    if (!schema.objectStores[oldName]) {
      throw Error("object store not found");
    }
    if (schema.objectStores[newName]) {
      throw Error("new object store already exists");
    }
    const objectStore = myConn.objectStoreMap[oldName];
    if (!objectStore) {
      throw Error("object store not found in map");
    }
    objectStore.modifiedName = newName;
    schema.objectStores[newName] = schema.objectStores[oldName];
    delete schema.objectStores[oldName];
    delete myConn.objectStoreMap[oldName];
    myConn.objectStoreMap[newName] = objectStore;
  }

  createObjectStore(
    btx: DatabaseTransaction,
    name: string,
    keyPath: string | string[] | null,
    autoIncrement: boolean,
  ): void {
    if (this.enableTracing) {
      console.log(
        `TRACING: createObjectStore(${btx.transactionCookie}, ${name})`,
      );
    }
    const myConn = this.connectionsByTransaction[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.VersionChange) {
      throw Error("only allowed in versionchange transaction");
    }
    const newObjectStore: ObjectStore = {
      deleted: false,
      modifiedName: undefined,
      originalName: name,
      modifiedData: undefined,
      originalData: new BTree([], compareKeys),
      modifiedKeyGenerator: undefined,
      originalKeyGenerator: 1,
    };
    const schema = myConn.modifiedSchema;
    if (!schema) {
      throw Error("no schema for versionchange tx");
    }
    schema.objectStores[name] = {
      autoIncrement,
      keyPath,
      indexes: [],
    };
    myConn.objectStoreMap[name] = newObjectStore;
    db.modifiedObjectStores[name] = newObjectStore;
  }

  createIndex(
    btx: DatabaseTransaction,
    indexName: string,
    objectStoreName: string,
    keyPath: import("./util/types").KeyPath,
    multiEntry: boolean,
    unique: boolean,
  ): void {
    if (this.enableTracing) {
      console.log(`TRACING: createIndex(${indexName})`);
    }
    const myConn = this.connectionsByTransaction[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.VersionChange) {
      throw Error("only allowed in versionchange transaction");
    }
    const indexProperties: IndexProperties = {
      keyPath,
      multiEntry,
      unique,
    };
    const newIndex: Index = {
      deleted: false,
      modifiedData: undefined,
      modifiedName: undefined,
      originalData: new BTree([], compareKeys),
      originalName: indexName,
    };
    myConn.indexMap[indexName] = newIndex;
    db.modifiedIndexes[indexName] = newIndex;
    const schema = myConn.modifiedSchema;
    if (!schema) {
      throw Error("no schema in versionchange tx");
    }
    const objectStoreProperties = schema.objectStores[objectStoreName];
    if (!objectStoreProperties) {
      throw Error("object store not found");
    }
    objectStoreProperties.indexes.push(indexName);
    schema.indexes[indexName] = indexProperties;

    const objectStore = myConn.objectStoreMap[objectStoreName];
    if (!objectStore) {
      throw Error("object store does not exist");
    }

    const storeData = objectStore.modifiedData || objectStore.originalData;

    storeData.forEach((v, k) => {
      this.insertIntoIndex(newIndex, k, v.value, indexProperties);
    });
  }

  async deleteRecord(
    btx: DatabaseTransaction,
    objectStoreName: string,
    range: BridgeIDBKeyRange,
  ): Promise<void> {
    if (this.enableTracing) {
      console.log(`TRACING: deleteRecord from store ${objectStoreName}`);
    }
    const myConn = this.connectionsByTransaction[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.Write) {
      throw Error("only allowed in write transaction");
    }
    if (typeof range !== "object") {
      throw Error("deleteRecord got invalid range (must be object)");
    }
    if (!("lowerOpen" in range)) {
      throw Error("deleteRecord got invalid range (sanity check failed, 'lowerOpen' missing)");
    }

    const schema = myConn.modifiedSchema
      ? myConn.modifiedSchema
      : db.committedSchema;
    const objectStore = myConn.objectStoreMap[objectStoreName];

    if (!objectStore.modifiedData) {
      objectStore.modifiedData = objectStore.originalData;
    }

    let modifiedData = objectStore.modifiedData;
    let currKey: Key | undefined;

    if (range.lower === undefined || range.lower === null) {
      currKey = modifiedData.minKey();
    } else {
      currKey = range.lower;
      // We have a range with an lowerOpen lower bound, so don't start
      // deleting the upper bound.  Instead start with the next higher key.
      if (range.lowerOpen && currKey !== undefined) {
       currKey = modifiedData.nextHigherKey(currKey);
      }
    }

    // invariant: (currKey is undefined) or (currKey is a valid key)

    while (true) {
      if (currKey === undefined) {
        // nothing more to delete!
        break;
      }
      if (range.upper !== null && range.upper !== undefined) {
        if (range.upperOpen && compareKeys(currKey, range.upper) === 0) {
          // We have a range that's upperOpen, so stop before we delete the upper bound.
          break;
        }
        if ((!range.upperOpen) && compareKeys(currKey, range.upper) > 0) {
          // The upper range is inclusive, only stop if we're after the upper range.
          break;
        }
      }

      const storeEntry = modifiedData.get(currKey);
      if (!storeEntry) {
        throw Error("assertion failed");
      }

      for (const indexName of schema.objectStores[objectStoreName].indexes) {
        const index = myConn.indexMap[indexName];
        if (!index) {
          throw Error("index referenced by object store does not exist");
        }
        const indexProperties = schema.indexes[indexName];
        this.deleteFromIndex(index, storeEntry.primaryKey, storeEntry.value, indexProperties);
      }

      modifiedData = modifiedData.without(currKey);

      currKey = modifiedData.nextHigherKey(currKey);
    }

    objectStore.modifiedData = modifiedData;
  }

  private deleteFromIndex(
    index: Index,
    primaryKey: Key,
    value: Value,
    indexProperties: IndexProperties,
  ): void {
    if (this.enableTracing) {
      console.log(
        `deleteFromIndex(${index.modifiedName || index.originalName})`,
      );
    }
    if (value === undefined || value === null) {
      throw Error("cannot delete null/undefined value from index");
    }
    let indexData = index.modifiedData || index.originalData;
    const indexKeys = getIndexKeys(
      value,
      indexProperties.keyPath,
      indexProperties.multiEntry,
    );
    for (const indexKey of indexKeys) {
      const existingRecord = indexData.get(indexKey);
      if (!existingRecord) {
        throw Error("db inconsistent: expected index entry missing");
      }
      const newPrimaryKeys = existingRecord.primaryKeys.filter((x) => compareKeys(x, primaryKey) !== 0);
      if (newPrimaryKeys.length === 0) {
        index.originalData = indexData.without(indexKey);
      } else {
        const newIndexRecord = {
          indexKey,
          primaryKeys: newPrimaryKeys,
        }
        index.modifiedData = indexData.with(indexKey, newIndexRecord, true);
      }
    }
  }

  async getRecords(
    btx: DatabaseTransaction,
    req: RecordGetRequest,
  ): Promise<RecordGetResponse> {
    if (this.enableTracing) {
      console.log(`TRACING: getRecords`);
      console.log("query", req);
    }
    const myConn = this.connectionsByTransaction[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.Read) {
      throw Error("only allowed while running a transaction");
    }
    const objectStore = myConn.objectStoreMap[req.objectStoreName];
    if (!objectStore) {
      throw Error("object store not found");
    }

    let range;
    if (req.range == null || req.range === undefined) {
      range = new BridgeIDBKeyRange(undefined, undefined, true, true);
    } else {
      range = req.range;
    }

    if (typeof range !== "object") {
      throw Error(
        "getRecords was given an invalid range (sanity check failed, not an object)",
      );
    }

    if (!("lowerOpen" in range)) {
      throw Error(
        "getRecords was given an invalid range (sanity check failed, lowerOpen missing)",
      );
    }

    let numResults = 0;
    let indexKeys: Key[] = [];
    let primaryKeys: Key[] = [];
    let values: Value[] = [];

    const forward: boolean =
      req.direction === "next" || req.direction === "nextunique";
    const unique: boolean =
      req.direction === "prevunique" || req.direction === "nextunique";

    const storeData = objectStore.modifiedData || objectStore.originalData;

    const haveIndex = req.indexName !== undefined;

    if (haveIndex) {
      const index = myConn.indexMap[req.indexName!];
      const indexData = index.modifiedData || index.originalData;
      let indexPos = req.lastIndexPosition;

      if (indexPos === undefined) {
        // First time we iterate!  So start at the beginning (lower/upper)
        // of our allowed range.
        indexPos = forward ? range.lower : range.upper;
      }

      let primaryPos = req.lastObjectStorePosition;

      // We might have to advance the index key further!
      if (req.advanceIndexKey !== undefined) {
        const compareResult = compareKeys(req.advanceIndexKey, indexPos);
        if ((forward && compareResult > 0) || (!forward && compareResult > 0)) {
          indexPos = req.advanceIndexKey;
        } else if (compareResult == 0 && req.advancePrimaryKey !== undefined) {
          // index keys are the same, so advance the primary key
          if (primaryPos === undefined) {
            primaryPos = req.advancePrimaryKey;
          } else {
            const primCompareResult = compareKeys(
              req.advancePrimaryKey,
              primaryPos,
            );
            if (
              (forward && primCompareResult > 0) ||
              (!forward && primCompareResult < 0)
            ) {
              primaryPos = req.advancePrimaryKey;
            }
          }
        }
      }

      if (indexPos === undefined || indexPos === null) {
        indexPos = forward ? indexData.minKey() : indexData.maxKey();
      }

      let indexEntry: IndexRecord | undefined;
      indexEntry = indexData.get(indexPos);
      if (!indexEntry) {
        const res = indexData.nextHigherPair(indexPos);
        if (res) {
          indexEntry = res[1];
        }
      }

      let primkeySubPos = 0;

      // Sort out the case where the index key is the same, so we have
      // to get the prev/next primary key
      if (
        indexEntry !== undefined &&
        req.lastIndexPosition !== undefined &&
        compareKeys(indexEntry.indexKey, req.lastIndexPosition) === 0
      ) {
        let pos = forward ? 0 : indexEntry.primaryKeys.length - 1;
        this.enableTracing &&
          console.log("number of primary keys", indexEntry.primaryKeys.length);
        this.enableTracing && console.log("start pos is", pos);
        // Advance past the lastObjectStorePosition
        do {
          const cmpResult = compareKeys(
            req.lastObjectStorePosition,
            indexEntry.primaryKeys[pos],
          );
          this.enableTracing && console.log("cmp result is", cmpResult);
          if ((forward && cmpResult < 0) || (!forward && cmpResult > 0)) {
            break;
          }
          pos += forward ? 1 : -1;
          this.enableTracing && console.log("now pos is", pos);
        } while (pos >= 0 && pos < indexEntry.primaryKeys.length);

        // Make sure we're at least at advancedPrimaryPos
        while (
          primaryPos !== undefined &&
          pos >= 0 &&
          pos < indexEntry.primaryKeys.length
        ) {
          const cmpResult = compareKeys(
            primaryPos,
            indexEntry.primaryKeys[pos],
          );
          if ((forward && cmpResult <= 0) || (!forward && cmpResult >= 0)) {
            break;
          }
          pos += forward ? 1 : -1;
        }
        primkeySubPos = pos;
      } else if (indexEntry !== undefined) {
        primkeySubPos = forward ? 0 : indexEntry.primaryKeys.length - 1;
      }

      if (this.enableTracing) {
        console.log("subPos=", primkeySubPos);
        console.log("indexPos=", indexPos);
      }

      while (1) {
        if (req.limit != 0 && numResults == req.limit) {
          break;
        }
        if (indexPos === undefined) {
          break;
        }
        if (!range.includes(indexPos)) {
          break;
        }
        if (indexEntry === undefined) {
          break;
        }
        if (
          primkeySubPos < 0 ||
          primkeySubPos >= indexEntry.primaryKeys.length
        ) {
          const res = forward
            ? indexData.nextHigherPair(indexPos)
            : indexData.nextLowerPair(indexPos);
          if (res) {
            indexPos = res[1].indexKey;
            indexEntry = res[1];
            primkeySubPos = forward ? 0 : indexEntry.primaryKeys.length - 1;
          } else {
            break;
          }
        }

        // Skip repeated index keys if unique results are requested.
        let skip = false;
        if (unique) {
          if (
            indexKeys.length > 0 &&
            compareKeys(
              indexEntry.indexKey,
              indexKeys[indexKeys.length - 1],
            ) === 0
          ) {
            skip = true;
          }
          if (
            req.lastIndexPosition !== undefined &&
            compareKeys(indexPos, req.lastIndexPosition) === 0
          ) {
            skip = true;
          }
        }
        if (!skip) {
          if (this.enableTracing) {
            console.log(`not skipping!, subPos=${primkeySubPos}`);
          }
          indexKeys.push(indexEntry.indexKey);
          primaryKeys.push(indexEntry.primaryKeys[primkeySubPos]);
          numResults++;
        } else {
          if (this.enableTracing) {
            console.log("skipping!");
          }
        }
        primkeySubPos += forward ? 1 : -1;
      }

      // Now we can collect the values based on the primary keys,
      // if requested.
      if (req.resultLevel === ResultLevel.Full) {
        for (let i = 0; i < numResults; i++) {
          const result = storeData.get(primaryKeys[i]);
          if (!result) {
            throw Error("invariant violated");
          }
          values.push(result.value);
        }
      }
    } else {
      // only based on object store, no index involved, phew!
      let storePos = req.lastObjectStorePosition;
      if (storePos === undefined) {
        storePos = forward ? range.lower : range.upper;
      }

      if (req.advanceIndexKey !== undefined) {
        throw Error("unsupported request");
      }

      storePos = furthestKey(forward, req.advancePrimaryKey, storePos);

      if (storePos !== null && storePos !== undefined) {
        // Advance store position if we are either still at the last returned
        // store key, or if we are currently not on a key.
        const storeEntry = storeData.get(storePos);
        if (this.enableTracing) {
          console.log("store entry:", storeEntry);
        }
        if (
          !storeEntry ||
          (req.lastObjectStorePosition !== undefined &&
            compareKeys(req.lastObjectStorePosition, storePos) === 0)
        ) {
          storePos = storeData.nextHigherKey(storePos);
        }
      } else {
        storePos = forward ? storeData.minKey() : storeData.maxKey();
        if (this.enableTracing) {
          console.log("setting starting store pos to", storePos);
        }
      }

      while (1) {
        if (req.limit != 0 && numResults == req.limit) {
          break;
        }
        if (storePos === null || storePos === undefined) {
          break;
        }
        if (!range.includes(storePos)) {
          break;
        }

        const res = storeData.get(storePos);

        if (res === undefined) {
          break;
        }

        if (req.resultLevel >= ResultLevel.OnlyKeys) {
          primaryKeys.push(structuredClone(storePos));
        }

        if (req.resultLevel >= ResultLevel.Full) {
          values.push(res.value);
        }

        numResults++;
        storePos = nextStoreKey(forward, storeData, storePos);
      }
    }
    if (this.enableTracing) {
      console.log(`TRACING: getRecords got ${numResults} results`);
    }
    return {
      count: numResults,
      indexKeys:
        req.resultLevel >= ResultLevel.OnlyKeys && haveIndex
          ? indexKeys
          : undefined,
      primaryKeys:
        req.resultLevel >= ResultLevel.OnlyKeys ? primaryKeys : undefined,
      values: req.resultLevel >= ResultLevel.Full ? values : undefined,
    };
  }

  async storeRecord(
    btx: DatabaseTransaction,
    storeReq: RecordStoreRequest,
  ): Promise<RecordStoreResponse> {
    if (this.enableTracing) {
      console.log(`TRACING: storeRecord`);
    }
    const myConn = this.connectionsByTransaction[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.Write) {
      throw Error("only allowed while running a transaction");
    }
    const schema = myConn.modifiedSchema
      ? myConn.modifiedSchema
      : db.committedSchema;
    const objectStore = myConn.objectStoreMap[storeReq.objectStoreName];

    if (!objectStore.modifiedData) {
      objectStore.modifiedData = objectStore.originalData;
    }
    const modifiedData = objectStore.modifiedData;

    let key;
    let value;

    if (storeReq.storeLevel === StoreLevel.UpdateExisting) {
      if (storeReq.key === null || storeReq.key === undefined) {
        throw Error("invalid update request (key not given)");
      }

      if (!objectStore.modifiedData.has(storeReq.key)) {
        throw Error("invalid update request (record does not exist)");
      }
      key = storeReq.key;
      value = storeReq.value;
    } else {
      const storeKeyResult: StoreKeyResult = makeStoreKeyValue(
        storeReq.value,
        storeReq.key,
        objectStore.modifiedKeyGenerator || objectStore.originalKeyGenerator,
        schema.objectStores[storeReq.objectStoreName].autoIncrement,
        schema.objectStores[storeReq.objectStoreName].keyPath,
      );
      key = storeKeyResult.key;
      value = storeKeyResult.value;
      objectStore.modifiedKeyGenerator = storeKeyResult.updatedKeyGenerator;
      const hasKey = modifiedData.has(key);

      if (hasKey && storeReq.storeLevel !== StoreLevel.AllowOverwrite) {
        throw Error("refusing to overwrite");
      }
    }

    const objectStoreRecord: ObjectStoreRecord = {
      primaryKey: key,
      value: value,
    };

    objectStore.modifiedData = modifiedData.with(key, objectStoreRecord, true);

    for (const indexName of schema.objectStores[storeReq.objectStoreName]
      .indexes) {
      const index = myConn.indexMap[indexName];
      if (!index) {
        throw Error("index referenced by object store does not exist");
      }
      const indexProperties = schema.indexes[indexName];
      this.insertIntoIndex(index, key, value, indexProperties);
    }

    return { key };
  }

  private insertIntoIndex(
    index: Index,
    primaryKey: Key,
    value: Value,
    indexProperties: IndexProperties,
  ): void {
    if (this.enableTracing) {
      console.log(
        `insertIntoIndex(${index.modifiedName || index.originalName})`,
      );
    }
    let indexData = index.modifiedData || index.originalData;
    const indexKeys = getIndexKeys(
      value,
      indexProperties.keyPath,
      indexProperties.multiEntry,
    );
    for (const indexKey of indexKeys) {
      const existingRecord = indexData.get(indexKey);
      if (existingRecord) {
        if (indexProperties.unique) {
          throw new ConstraintError();
        } else {
          const newIndexRecord = {
            indexKey: indexKey,
            primaryKeys: [primaryKey]
              .concat(existingRecord.primaryKeys)
              .sort(compareKeys),
          };
          index.modifiedData = indexData.with(indexKey, newIndexRecord, true);
        }
      } else {
        const newIndexRecord: IndexRecord = {
          indexKey: indexKey,
          primaryKeys: [primaryKey],
        };
        index.modifiedData = indexData.with(indexKey, newIndexRecord, true);
      }
    }
  }

  async rollback(btx: DatabaseTransaction): Promise<void> {
    if (this.enableTracing) {
      console.log(`TRACING: rollback`);
    }
    const myConn = this.connectionsByTransaction[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.Read) {
      throw Error("only allowed while running a transaction");
    }
    db.modifiedIndexes = {};
    db.modifiedObjectStores = {};
    db.txLevel = TransactionLevel.Connected;
    myConn.modifiedSchema = structuredClone(db.committedSchema);
    myConn.indexMap = Object.assign({}, db.committedIndexes);
    myConn.objectStoreMap = Object.assign({}, db.committedObjectStores);
    for (const indexName in db.committedIndexes) {
      const index = db.committedIndexes[indexName];
      index.deleted = false;
      index.modifiedData = undefined;
      index.modifiedName = undefined;
    }
    for (const objectStoreName in db.committedObjectStores) {
      const objectStore = db.committedObjectStores[objectStoreName];
      objectStore.deleted = false;
      objectStore.modifiedData = undefined;
      objectStore.modifiedName = undefined;
      objectStore.modifiedKeyGenerator = undefined;
    }
    delete this.connectionsByTransaction[btx.transactionCookie];
    this.transactionDoneCond.trigger();
  }

  async commit(btx: DatabaseTransaction): Promise<void> {
    if (this.enableTracing) {
      console.log(`TRACING: commit`);
    }
    const myConn = this.connectionsByTransaction[btx.transactionCookie];
    if (!myConn) {
      throw Error("unknown connection");
    }
    const db = this.databases[myConn.dbName];
    if (!db) {
      throw Error("db not found");
    }
    if (db.txLevel < TransactionLevel.Read) {
      throw Error("only allowed while running a transaction");
    }

    db.committedSchema = myConn.modifiedSchema || db.committedSchema;
    db.txLevel = TransactionLevel.Connected;

    db.committedIndexes = {};
    db.committedObjectStores = {};
    db.modifiedIndexes = {};
    db.committedObjectStores = {};

    for (const indexName in myConn.indexMap) {
      const index = myConn.indexMap[indexName];
      index.deleted = false;
      index.originalData = index.modifiedData || index.originalData;
      index.originalName = index.modifiedName || index.originalName;
      db.committedIndexes[indexName] = index;
    }

    for (const objectStoreName in myConn.objectStoreMap) {
      const objectStore = myConn.objectStoreMap[objectStoreName];
      objectStore.deleted = false;
      objectStore.originalData =
        objectStore.modifiedData || objectStore.originalData;
      objectStore.originalName =
        objectStore.modifiedName || objectStore.originalName;
      if (objectStore.modifiedKeyGenerator !== undefined) {
        objectStore.originalKeyGenerator = objectStore.modifiedKeyGenerator;
      }
      db.committedObjectStores[objectStoreName] = objectStore;
    }

    myConn.indexMap = Object.assign({}, db.committedIndexes);
    myConn.objectStoreMap = Object.assign({}, db.committedObjectStores);

    delete this.connectionsByTransaction[btx.transactionCookie];
    this.transactionDoneCond.trigger();
  }
}

export default MemoryBackend;