Implement fake data provider

1 files changed, 36 insertions, 0 deletions

diff --git a/projects/3-realtime-stocks/src/stock-data.js b/projects/3-realtime-stocks/src/stock-data.js
index e69de29..c70e2b4 100644
--- a/projects/3-realtime-stocks/src/stock-data.js
+++ b/projects/3-realtime-stocks/src/stock-data.js
@@ -0,0 +1,36 @@
+export const generateValue = () => {
+  const plusOrMinus = Math.round(Math.random()) ? 1 : -1
+  return 1 + plusOrMinus * Math.random() * 0.5
+}
+export const generateStartingPoints = (n, pollPeriod) => {
+  return new Array(n).fill(1).map((k, i) => {
+    return {
+      value: generateValue(),
+      datetime: Date.now() - (n - i) * 1000
+    }
+  })
+}
+const N_STARTING_POINTS = 50
+
+export class StockDataProvider {
+  constructor() {}
+  subscribeToStockData(pollFrequency, callback) {
+    // generate 100 random points
+    // 15 minutes apart
+    let points = generateStartingPoints(N_STARTING_POINTS)
+    const pushCallback = () => {
+      points.push({ value: generateValue(), datetime: Date.now() })
+      points.shift()
+      callback(points)
+    }
+    pushCallback()
+    const interval = setInterval(pushCallback, pollFrequency)
+    // give the caller a way to cancel
+    // the subscription
+    return {
+      unsubscribe() {
+        clearInterval(interval)
+      }
+    }
+  }
+}