Reduce amount of required labeled segments for learning #147 (#153)

* rm labeled segments amount check && change query range algorithm

* review fix

* typo fix

* minor fix

server/src/controllers/analytics_controller.ts

@@ -74,15 +74,16 @@ async function runTask(task: AnalyticsTask): Promise<TaskResult> {
  * @param segments labeled segments
  */
 function getQueryRangeForLearningBySegments(segments: Segment.Segment[]) {
-  if(segments.length < 2) {
-    throw new Error('Need at least 2 labeled segments');
+  if(segments.length === 0) {
+    throw new Error('Need at least 1 labeled segment');
   }
 
   let from = _.minBy(segments, s => s.from).from;
   let to = _.maxBy(segments, s => s.to).to;
-  let diff = to - from;
-  from -= Math.round(diff);
-  to = Date.now();
+  let now = Date.now();
+  let leftOffset = now - to;
+  from -= Math.round(leftOffset);
+  to = now;
 
   return { from, to };
 }
@@ -96,8 +97,8 @@ export async function runLearning(id: AnalyticUnit.AnalyticUnitId) {
     }
 
     let segments = await Segment.findMany(id, { labeled: true });
-    if(segments.length < 2) {
-      throw new Error('Need at least 2 labeled segments');
+    if(segments.length === 0) {
+      throw new Error('Need at least 1 labeled segment');
     }
 
     let segmentObjs = segments.map(s => s.toObject());
@@ -140,8 +141,8 @@ export async function runPredict(id: AnalyticUnit.AnalyticUnitId) {
     let pattern = unit.type;
 
     let segments = await Segment.findMany(id, { labeled: true });
-    if(segments.length < 2) {
-      throw new Error('Need at least 2 labeled segments');
+    if(segments.length === 0) {
+      throw new Error('Need at least 1 labeled segment');
     }
 
     let { from, to } = getQueryRangeForLearningBySegments(segments);