[#94] Backend

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

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

@@ -0,0 +1,40 @@
+'use strict';
+
+const {Writable} = require('stream');
+
+const defaultInitial = 0;
+const defaultReducer = (acc, value) => value;
+
+class Reduce extends Writable {
+  constructor(options) {
+    super(Object.assign({}, options, {objectMode: true}));
+    this.accumulator = defaultInitial;
+    this._reducer = defaultReducer;
+    if (options) {
+      'initial' in options && (this.accumulator = options.initial);
+      'reducer' in options && (this._reducer = options.reducer);
+    }
+  }
+  _write(chunk, encoding, callback) {
+    const result = this._reducer.call(this, this.accumulator, chunk);
+    if (result && typeof result.then == 'function') {
+      result.then(
+        value => {
+          this.accumulator = value;
+          callback(null);
+        },
+        error => callback(error)
+      );
+    } else {
+      this.accumulator = result;
+      callback(null);
+    }
+  }
+  static make(reducer, initial) {
+    return new Reduce(typeof reducer == 'object' ? reducer : {reducer, initial});
+  }
+}
+Reduce.reduce = Reduce.make;
+Reduce.make.Constructor = Reduce;
+
+module.exports = Reduce;