// Infrastructure shared by interleaved-cursors-{small,large}.html

// Number of objects that each iterator goes over.
const itemCount = 10;

// Ratio of small objects to large objects.
const largeObjectRatio = 5;

// Size of large objects. This should exceed the size of a block in the storage
// method underlying the browser's IndexedDB implementation. For example, this
// needs to exceed the LevelDB block size on Chrome, and the SQLite block size
// on Firefox.
const largeObjectSize = 48 * 1024;

function objectKey(cursorIndex, itemIndex) {
  return `${cursorIndex}-key-${itemIndex}`;
}

function objectValue(cursorIndex, itemIndex) {
  if ((cursorIndex * itemCount + itemIndex) % largeObjectRatio === 0) {
    // We use a typed array (as opposed to a string) because IndexedDB
    // implementations may serialize strings using UTF-8 or UTF-16, yielding
    // larger IndexedDB entries than we'd expect. It's very unlikely that an
    // IndexedDB implementation would use anything other than the raw buffer to
    // serialize a typed array.
    const buffer = new Uint8Array(largeObjectSize);

    // Some IndexedDB implementations, like LevelDB, compress their data blocks
    // before storing them to disk. We use a simple 32-bit xorshift PRNG, which
    // should be sufficient to foil any fast generic-purpose compression scheme.

    // 32-bit xorshift - the seed can't be zero
    let state = 1000 + (cursorIndex * itemCount + itemIndex);

    for (let i = 0; i < largeObjectSize; ++i) {
      state ^= state << 13;
      state ^= state >> 17;
      state ^= state << 5;
      buffer[i] = state & 0xff;
    }

    return buffer;
  }
  return [cursorIndex, 'small', itemIndex];
}

// Writes the objects to be read by one cursor. Returns a promise that resolves
// when the write completes.
//
// We want to avoid creating a large transaction, because that is outside the
// test's scope, and it's a bad practice. So we break up the writes across
// multiple transactions. For simplicity, each transaction writes all the
// objects that will be read by a cursor.
function writeCursorObjects(database, cursorIndex) {
  return new Promise((resolve, reject) => {
    const transaction = database.transaction('cache', 'readwrite', {durability: 'relaxed'});
    transaction.onabort = () => { reject(transaction.error); };

    const store = transaction.objectStore('cache');
    for (let i = 0; i < itemCount; ++i) {
      store.put({
          key: objectKey(cursorIndex, i), value: objectValue(cursorIndex, i)});
    }
    transaction.oncomplete = resolve;
  });
}

// Returns a promise that resolves when the store has been populated.
function populateTestStore(testCase, database, cursorCount) {
  let promiseChain = Promise.resolve();

  for (let i = 0; i < cursorCount; ++i)
    promiseChain = promiseChain.then(() => writeCursorObjects(database, i));

  return promiseChain;
}

// Reads cursors in an interleaved fashion, as shown below.
//
// Given N cursors, each of which points to the beginning of a K-item sequence,
// the following accesses will be made.
//
// OC(i)    = open cursor i
// RD(i, j) = read result of cursor i, which should be at item j
// CC(i)    = continue cursor i
// |        = wait for onsuccess on the previous OC or CC
//
// OC(1)            | RD(1, 1) OC(2) | RD(2, 1) OC(3) | ... | RD(n-1, 1) CC(n) |
// RD(n, 1)   CC(1) | RD(1, 2) CC(2) | RD(2, 2) CC(3) | ... | RD(n-1, 2) CC(n) |
// RD(n, 2)   CC(1) | RD(1, 3) CC(2) | RD(2, 3) CC(3) | ... | RD(n-1, 3) CC(n) |
// ...
// RD(n, k-1) CC(1) | RD(1, k) CC(2) | RD(2, k) CC(3) | ... | RD(n-1, k) CC(n) |
// RD(n, k)           done
function interleaveCursors(testCase, store, cursorCount) {
  return new Promise((resolve, reject) => {
    // The cursors used for iteration are stored here so each cursor's onsuccess
    // handler can call continue() on the next cursor.
    const cursors = [];

    // The results of IDBObjectStore.openCursor() calls are stored here so we
    // we can change the requests' onsuccess handler after every
    // IDBCursor.continue() call.
    const requests = [];

    const checkCursorState = (cursorIndex, itemIndex) => {
      const cursor = cursors[cursorIndex];
      assert_equals(cursor.key, objectKey(cursorIndex, itemIndex));
      assert_equals(cursor.value.key, objectKey(cursorIndex, itemIndex));
      assert_equals(
          cursor.value.value.join('-'),
          objectValue(cursorIndex, itemIndex).join('-'));
    };

    const openCursor = (cursorIndex, callback) => {
      const request = store.openCursor(
          IDBKeyRange.lowerBound(objectKey(cursorIndex, 0)));
      requests[cursorIndex] = request;

      request.onsuccess = testCase.step_func(() => {
        const cursor = request.result;
        cursors[cursorIndex] = cursor;
        checkCursorState(cursorIndex, 0);
        callback();
      });
      request.onerror = event => reject(request.error);
    };

    const readItemFromCursor = (cursorIndex, itemIndex, callback) => {
      const request = requests[cursorIndex];
      request.onsuccess = testCase.step_func(() => {
        const cursor = request.result;
        cursors[cursorIndex] = cursor;
        checkCursorState(cursorIndex, itemIndex);
        callback();
      });

      const cursor = cursors[cursorIndex];
      cursor.continue();
    };

    // We open all the cursors one at a time, then cycle through the cursors and
    // call continue() on each of them. This access pattern causes maximal
    // trashing to an LRU cursor cache. Eviction scheme aside, any cache will
    // have to evict some cursors, and this access pattern verifies that the
    // cache correctly restores the state of evicted cursors.
    const steps = [];
    for (let cursorIndex = 0; cursorIndex < cursorCount; ++cursorIndex)
      steps.push(openCursor.bind(null, cursorIndex));
    for (let itemIndex = 1; itemIndex < itemCount; ++itemIndex) {
      for (let cursorIndex = 0; cursorIndex < cursorCount; ++cursorIndex)
        steps.push(readItemFromCursor.bind(null, cursorIndex, itemIndex));
    }

    const runStep = (stepIndex) => {
      if (stepIndex === steps.length) {
        resolve();
        return;
      }
      steps[stepIndex](() => { runStep(stepIndex + 1); });
    };
    runStep(0);
  });
}

function cursorTest(cursorCount) {
  promise_test(testCase => {
    return createDatabase(testCase, (database, transaction) => {
      const store = database.createObjectStore('cache',
          { keyPath: 'key', autoIncrement: true });
    }).then(database => {
      return populateTestStore(testCase, database, cursorCount).then(
          () => database);
    }).then(database => {
      database.close();
    }).then(() => {
      return openDatabase(testCase);
    }).then(database => {
      const transaction = database.transaction('cache', 'readonly', {durability: 'relaxed'});
      transaction.onabort = () => { reject(transaction.error); };

      const store = transaction.objectStore('cache');
      return interleaveCursors(testCase, store, cursorCount).then(
          () => database);
    }).then(database => {
      database.close();
    });
  }, `${cursorCount} cursors`);
}
