incr: add StockQueue manager class

models/inventory/stockQueue.ts

@@ -0,0 +1,88 @@
+export class StockQueue {
+  quantity: number;
+  value: number;
+  queue: { rate: number; quantity: number }[];
+  movingAverage: number;
+
+  constructor() {
+    this.value = 0;
+    this.quantity = 0;
+    this.movingAverage = 0;
+    this.queue = [];
+  }
+
+  get fifo() {
+    /**
+     * Stock value maintained is based on the stock queue
+     * ∴ FIFO by default. This returns FIFO valuation rate.
+     */
+    const valuation = this.value / this.quantity;
+    if (Number.isNaN(valuation)) {
+      return 0;
+    }
+
+    return valuation;
+  }
+
+  inward(rate: number, quantity: number): null | number {
+    if (quantity <= 0 || rate < 0) {
+      return null;
+    }
+
+    const inwardValue = rate * quantity;
+    /**
+     * Update Moving Average valuation
+     */
+    this.movingAverage =
+      (this.movingAverage * this.quantity + inwardValue) /
+      (this.quantity + quantity);
+
+    this.quantity += quantity;
+    this.value += inwardValue;
+
+    const last = this.queue.at(-1);
+    if (last?.rate !== rate) {
+      this.queue.push({ rate, quantity });
+    } else {
+      last.quantity += quantity;
+    }
+
+    return rate;
+  }
+
+  outward(quantity: number): null | number {
+    if (this.quantity < quantity || quantity <= 0) {
+      return null;
+    }
+
+    let incomingRate: number = 0;
+    this.quantity -= quantity;
+    let remaining = quantity;
+
+    while (remaining > 0) {
+      const last = this.queue.shift();
+      if (last === undefined) {
+        return null;
+      }
+
+      const storedQuantity = last.quantity;
+      let quantityRemoved = remaining;
+
+      const quantityLeft = storedQuantity - remaining;
+      remaining = remaining - storedQuantity;
+
+      if (remaining > 0) {
+        quantityRemoved = storedQuantity;
+      }
+
+      if (quantityLeft > 0) {
+        this.queue.unshift({ rate: last.rate, quantity: quantityLeft });
+      }
+
+      this.value -= last.rate * quantityRemoved;
+      incomingRate += quantityRemoved * last.rate;
+    }
+
+    return incomingRate / quantity;
+  }
+}

models/inventory/tests/testStockQueue.spec.ts

@@ -0,0 +1,116 @@
+import test from 'tape';
+import { StockQueue } from '../stockQueue';
+
+test('stockQueue:initialization', (t) => {
+  const q = new StockQueue();
+
+  t.equal(q.quantity, 0);
+  t.equal(q.value, 0);
+  t.equal(q.queue.length, 0);
+
+  t.end();
+});
+
+test('stockQueue:operations', (t) => {
+  const q = new StockQueue();
+
+  t.equal(q.inward(100, 4), 100);
+  t.equal(q.fifo, 100);
+  t.equal(q.movingAverage, 100);
+  t.equal(q.queue.length, 1);
+  t.equal(q.quantity, 4);
+  t.equal(q.value, 400);
+
+  t.equal(q.inward(200, 8), 200);
+  t.equal(q.fifo, (400 + 1600) / 12);
+  t.equal(q.movingAverage, (400 + 1600) / 12);
+  t.equal(q.queue.length, 2);
+  t.equal(q.quantity, 4 + 8);
+  t.equal(q.value, 400 + 1600);
+
+  t.equal(q.inward(300, 3), 300);
+  t.equal(q.fifo, (400 + 1600 + 900) / 15);
+  t.equal(q.movingAverage, (400 + 1600 + 900) / 15);
+  t.equal(q.queue.length, 3);
+  t.equal(q.quantity, 4 + 8 + 3);
+  t.equal(q.value, 400 + 1600 + 900);
+
+  t.equal(q.outward(3), 100);
+  t.equal(q.fifo, (100 + 1600 + 900) / 12);
+  t.equal(q.movingAverage, (400 + 1600 + 900) / 15);
+  t.equal(q.queue.length, 3);
+  t.equal(q.quantity, 1 + 8 + 3);
+  t.equal(q.value, 100 + 1600 + 900);
+
+  t.equal(q.outward(5), (100 + 800) / 5);
+  t.equal(q.fifo, (800 + 900) / 7);
+  t.equal(q.movingAverage, (400 + 1600 + 900) / 15);
+  t.equal(q.queue.length, 2);
+  t.equal(q.quantity, 4 + 3);
+  t.equal(q.value, 800 + 900);
+
+  t.equal(q.outward(4), 200);
+  t.equal(q.fifo, 900 / 3);
+  t.equal(q.movingAverage, (400 + 1600 + 900) / 15);
+  t.equal(q.queue.length, 1);
+  t.equal(q.quantity, 3);
+  t.equal(q.value, 900);
+
+  t.equal(q.outward(3), 300);
+  t.equal(q.fifo, 0);
+  t.equal(q.movingAverage, (400 + 1600 + 900) / 15);
+  t.equal(q.queue.length, 0);
+  t.equal(q.quantity, 0);
+  t.equal(q.value, 0);
+
+  t.equal(q.inward(100, 1), 100);
+  t.equal(q.fifo, 100);
+  t.equal(q.movingAverage, 100);
+  t.equal(q.queue.length, 1);
+  t.equal(q.quantity, 1);
+  t.equal(q.value, 100);
+
+  t.equal(q.inward(150, 1), 150);
+  t.equal(q.fifo, (100 + 150) / 2);
+  t.equal(q.movingAverage, (100 + 150) / 2);
+  t.equal(q.queue.length, 2);
+  t.equal(q.quantity, 2);
+  t.equal(q.value, 100 + 150);
+
+  t.equal(q.inward(100, 1), 100);
+  t.equal(q.fifo, (100 + 150 + 100) / 3);
+  t.equal(q.movingAverage, (100 + 150 + 100) / 3);
+  t.equal(q.queue.length, 3);
+  t.equal(q.quantity, 3);
+  t.equal(q.value, 100 + 150 + 100);
+
+  t.equal(q.outward(1), 100);
+  t.equal(q.fifo, (150 + 100) / 2);
+  t.equal(q.movingAverage, (100 + 150 + 100) / 3);
+  t.equal(q.queue.length, 2);
+  t.equal(q.quantity, 2);
+  t.equal(q.value, 150 + 100);
+
+  t.equal(q.outward(2), (150 + 100) / 2);
+  t.equal(q.fifo, 0);
+  t.equal(q.movingAverage, (100 + 150 + 100) / 3);
+  t.equal(q.queue.length, 0);
+  t.equal(q.quantity, 0);
+  t.equal(q.value, 0);
+
+  t.end();
+});
+
+test('stockQueue:invalidOperations', (t) => {
+  const q = new StockQueue();
+
+  t.equal(q.outward(1), null);
+  t.equal(q.outward(0), null);
+  t.equal(q.outward(-5), null);
+
+  t.equal(q.inward(1000, -1), null);
+  t.equal(q.inward(0, 0), null);
+  t.equal(q.inward(-0.1, 5), null);
+
+  t.end();
+});