[#94] Backend

https://project.mdnd-it.cc/work_packages/94

SerpentRace_Backend/node_modules/stream-chain/utils/takeWhile.js

@@ -0,0 +1,47 @@
+'use strict';
+
+const {Transform} = require('stream');
+
+const alwaysTrue = () => true;
+
+class TakeWhile extends Transform {
+  constructor(options) {
+    super(Object.assign({}, options, {writableObjectMode: true, readableObjectMode: true}));
+    this._condition = alwaysTrue;
+    if (options) {
+      'condition' in options && (this._condition = options.condition);
+    }
+  }
+  _transform(chunk, encoding, callback) {
+    const result = this._condition.call(this, chunk);
+    if (result && typeof result.then == 'function') {
+      result.then(
+        flag => {
+          if (flag) {
+            this.push(chunk);
+          } else {
+            this._transform = this._doNothing;
+          }
+          callback(null);
+        },
+        error => callback(error)
+      );
+    } else {
+      if (result) {
+        this.push(chunk);
+      } else {
+        this._transform = this._doNothing;
+      }
+      callback(null);
+    }
+  }
+  _doNothing(chunk, encoding, callback) {
+    callback(null);
+  }
+  static make(condition) {
+    return new TakeWhile(typeof condition == 'object' ? condition : {condition});
+  }
+}
+TakeWhile.make.Constructor = TakeWhile;
+
+module.exports = TakeWhile.make;