Simplify shouldBreak calls for fetching snapshots by timestamp

This change removes or renames `shouldBreak` calls. In `Backend`, for
clarity we instead pre-filter ops, and just pass around the ops we want
to be applied to a snapshot.

In the `MemoryMilestoneDB`, these functions are extracted and renamed to
more descriptive break condition names.

README.md

@@ -485,5 +485,5 @@ The `41xx` and `51xx` codes are reserved for use by ShareDB DB adapters, and the
 * 5018 - Required QueryEmitter listener not assigned
 * 5019 - getMilestoneSnapshot MilestoneDB method unimplemented
 * 5020 - saveMilestoneSnapshot MilestoneDB method unimplemented
-* 5021 - getMilestoneSnapshotBeforeTime MilestoneDB method unimplemented
-* 5022 - getMilestoneSnapshotAfterTime MilestoneDB method unimplemented
+* 5021 - getMilestoneSnapshotAtOrBeforeTime MilestoneDB method unimplemented
+* 5022 - getMilestoneSnapshotAtOrAfterTime MilestoneDB method unimplemented

lib/backend.js

@@ -701,22 +701,14 @@ Backend.prototype._fetchSnapshotByTimestamp = function (collection, id, timestam
       var options = {metadata: true};
       db.getOps(collection, id, from, to, options, function (error, ops) {
         if (error) return callback(error);
-        backend._buildSnapshotFromOps(id, milestoneSnapshot, ops, callback, function shouldBreak(nextOp) {
-          var opTimestamp = nextOp && nextOp.m && nextOp.m.ts;
-          return timestamp !== null && opTimestamp > timestamp;
-        });
+        filterOpsInPlaceBeforeTimestamp(ops, timestamp);
+        backend._buildSnapshotFromOps(id, milestoneSnapshot, ops, callback);
       });
     });
   });
 };
 
-Backend.prototype._buildSnapshotFromOps = function (id, startingSnapshot, ops, callback, shouldBreak) {
-  if (typeof shouldBreak !== 'function') {
-    shouldBreak = function () {
-      return false;
-    };
-  }
-
+Backend.prototype._buildSnapshotFromOps = function (id, startingSnapshot, ops, callback) {
   var type = null;
   var data;
   var fetchedVersion = 0;
@@ -731,10 +723,6 @@ Backend.prototype._buildSnapshotFromOps = function (id, startingSnapshot, ops, c
   for (var index = 0; index < ops.length; index++) {
     var op = ops[index];
 
-    if (shouldBreak(op)) {
-      break;
-    }
-
     fetchedVersion = op.v + 1;
 
     if (op.create) {
@@ -762,3 +750,18 @@ function pluckIds(snapshots) {
   }
   return ids;
 }
+
+function filterOpsInPlaceBeforeTimestamp(ops, timestamp) {
+  if (timestamp === null) {
+    return;
+  }
+
+  for (var i = 0; i < ops.length; i++) {
+    var op = ops[i];
+    var opTimestamp = op.m && op.m.ts;
+    if (opTimestamp > timestamp) {
+      ops.length = i;
+      return;
+    }
+  }
+}

lib/client/connection.js

@@ -642,7 +642,7 @@ Connection.prototype.fetchSnapshot = function(collection, id, version, callback)
 };
 
 /**
- * Fetch a read-only snapshot at a given version
+ * Fetch a read-only snapshot at a given timestamp
  *
  * @param collection - the collection name of the snapshot
  * @param id - the ID of the snapshot

lib/milestone-db/index.js

@@ -41,12 +41,12 @@ MilestoneDB.prototype.saveMilestoneSnapshot = function (collection, snapshot, ca
 };
 
 MilestoneDB.prototype.getMilestoneSnapshotAtOrBeforeTime = function (collection, id, timestamp, callback) {
-  var error = new ShareDBError(5021, 'getMilestoneSnapshotBeforeTime MilestoneDB method unimplemented');
+  var error = new ShareDBError(5021, 'getMilestoneSnapshotAtOrBeforeTime MilestoneDB method unimplemented');
   this._callBackOrEmitError(error, callback);
 };
 
 MilestoneDB.prototype.getMilestoneSnapshotAtOrAfterTime = function (collection, id, timestamp, callback) {
-  var error = new ShareDBError(5022, 'getMilestoneSnapshotAfterTime MilestoneDB method unimplemented');
+  var error = new ShareDBError(5022, 'getMilestoneSnapshotAtOrAfterTime MilestoneDB method unimplemented');
   this._callBackOrEmitError(error, callback);
 };
 

lib/milestone-db/memory.js

@@ -25,15 +25,8 @@ MemoryMilestoneDB.prototype = Object.create(MilestoneDB.prototype);
 MemoryMilestoneDB.prototype.getMilestoneSnapshot = function (collection, id, version, callback) {
   if (!this._isValidVersion(version)) return process.nextTick(callback, new ShareDBError(4001, 'Invalid version'));
 
-  var shouldBreak = function (currentSnapshot, nextSnapshot) {
-    if (version === null) {
-      return false;
-    }
-
-    return nextSnapshot.v > version;
-  };
-
-  this._findMilestoneSnapshot(collection, id, shouldBreak, callback);
+  var predicate = versionLessThanOrEqualTo(version);
+  this._findMilestoneSnapshot(collection, id, predicate, callback);
 };
 
 MemoryMilestoneDB.prototype.saveMilestoneSnapshot = function (collection, snapshot, callback) {
@@ -57,31 +50,15 @@ MemoryMilestoneDB.prototype.saveMilestoneSnapshot = function (collection, snapsh
 MemoryMilestoneDB.prototype.getMilestoneSnapshotAtOrBeforeTime = function (collection, id, timestamp, callback) {
   if (!this._isValidTimestamp(timestamp)) return process.nextTick(callback, new ShareDBError(4001, 'Invalid timestamp'));
 
-  var shouldBreak = function (currentSnapshot, nextSnapshot) {
-    if (timestamp === null) {
-      return !!currentSnapshot;
-    }
-
-    var mtime = nextSnapshot && nextSnapshot.m && nextSnapshot.m.mtime;
-    return mtime > timestamp;
-  };
-
-  this._findMilestoneSnapshot(collection, id, shouldBreak, callback);
+  var filter = timestampLessThanOrEqualTo(timestamp);
+  this._findMilestoneSnapshot(collection, id, filter, callback);
 };
 
 MemoryMilestoneDB.prototype.getMilestoneSnapshotAtOrAfterTime = function (collection, id, timestamp, callback) {
   if (!this._isValidTimestamp(timestamp)) return process.nextTick(callback, new ShareDBError(4001, 'Invalid timestamp'));
 
-  var shouldBreak = function (currentSnapshot) {
-    if (timestamp === null) {
-      return false;
-    }
-
-    var mtime = currentSnapshot && currentSnapshot.m && currentSnapshot.m.mtime;
-    return mtime >= timestamp;
-  }
-
-  this._findMilestoneSnapshot(collection, id, shouldBreak, function (error, snapshot) {
+  var filter = timestampGreaterThanOrEqualTo(timestamp);
+  this._findMilestoneSnapshot(collection, id, filter, function (error, snapshot) {
     if (error) return process.nextTick(callback, error);
 
     var mtime = snapshot && snapshot.m && snapshot.m.mtime;
@@ -93,7 +70,8 @@ MemoryMilestoneDB.prototype.getMilestoneSnapshotAtOrAfterTime = function (collec
   });
 };
 
-MemoryMilestoneDB.prototype._findMilestoneSnapshot = function (collection, id, shouldBreak, callback) {
+// TODO: Rename shouldBreak to something like breakCondition
+MemoryMilestoneDB.prototype._findMilestoneSnapshot = function (collection, id, breakCondition, callback) {
   if (!collection) return process.nextTick(callback, new ShareDBError(4001, 'Missing collection'));
   if (!id) return process.nextTick(callback, new ShareDBError(4001, 'Missing ID'));
 
@@ -102,7 +80,7 @@ MemoryMilestoneDB.prototype._findMilestoneSnapshot = function (collection, id, s
   var milestoneSnapshot;
   for (var i = 0; i < milestoneSnapshots.length; i++) {
     var nextMilestoneSnapshot = milestoneSnapshots[i];
-    if (shouldBreak(milestoneSnapshot, nextMilestoneSnapshot)) {
+    if (breakCondition(milestoneSnapshot, nextMilestoneSnapshot)) {
       break;
     } else {
       milestoneSnapshot = nextMilestoneSnapshot;
@@ -116,3 +94,35 @@ MemoryMilestoneDB.prototype._getMilestoneSnapshotsSync = function (collection, i
   var collectionSnapshots = this._milestoneSnapshots[collection] || (this._milestoneSnapshots[collection] = {});
   return collectionSnapshots[id] || (collectionSnapshots[id] = []);
 };
+
+function versionLessThanOrEqualTo(version) {
+  return function (currentSnapshot, nextSnapshot) {
+    if (version === null) {
+      return false;
+    }
+
+    return nextSnapshot.v > version;
+  };
+}
+
+function timestampGreaterThanOrEqualTo(timestamp) {
+  return function (currentSnapshot) {
+    if (timestamp === null) {
+      return false;
+    }
+
+    var mtime = currentSnapshot && currentSnapshot.m && currentSnapshot.m.mtime;
+    return mtime >= timestamp;
+  };
+}
+
+function timestampLessThanOrEqualTo(timestamp) {
+  return function (currentSnapshot, nextSnapshot) {
+    if (timestamp === null) {
+      return !!currentSnapshot;
+    }
+
+    var mtime = nextSnapshot && nextSnapshot.m && nextSnapshot.m.mtime;
+    return mtime > timestamp;
+  };
+}