Add calendar scheduler to frontend

src/farm_designer/farm_events/calendar/__tests__/scheduler_test.ts

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+import { scheduler } from "../scheduler";
+import * as moment from "moment";
+
+describe("scheduler", () => {
+  it("runs a schedule", () => {
+    // 8am Monday
+    let monday = moment()
+      .add(14, "days")
+      .startOf("isoWeek")
+      .startOf("day")
+      .add(8, "hours");
+    // 3am Tuesday
+    let tuesday = monday.clone().add(19, "hours");
+    // 18pm Thursday
+    let thursday = monday.clone().add(3, "days").add(10, "hours");
+    let interval = moment.duration(4, "hours").asSeconds();
+    let result1 = scheduler({
+      originTime: monday,
+      intervalSeconds: interval,
+      lowerBound: tuesday,
+      upperBound: thursday
+    });
+    expect(result1[0].format("dd")).toEqual("Tu");
+    expect(result1[0].hour()).toEqual(4);
+    expect(result1.length).toEqual(16);
+    const EXPECTED = [
+      "04:00am Tu",
+      "08:00am Tu",
+      "12:00pm Tu",
+      "04:00pm Tu",
+      "08:00pm Tu",
+      "12:00am We",
+      "04:00am We",
+      "08:00am We",
+      "12:00pm We",
+      "04:00pm We",
+      "08:00pm We",
+      "12:00am Th",
+      "04:00am Th",
+      "08:00am Th",
+      "12:00pm Th",
+      "04:00pm Th"
+    ];
+    const REALITY = result1.map(x => x.format("hh:mma dd"));
+    EXPECTED.map(x => expect(REALITY).toContain(x));
+  });
+});

src/farm_designer/farm_events/calendar/scheduler.ts

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+import * as moment from "moment";
+import { Moment } from "moment";
+import { times, last } from "lodash";
+
+interface SchedulerProps {
+  originTime: Moment;
+  intervalSeconds: number;
+  lowerBound: Moment;
+  upperBound?: Moment;
+}
+
+export function scheduler({ originTime,
+  intervalSeconds,
+  lowerBound,
+  upperBound }: SchedulerProps): Moment[] {
+
+  upperBound = upperBound || moment(moment().add(1, "year"));
+  // # How many items must we skip to get to the first occurence?
+  let skip_intervals =
+    Math.ceil((lowerBound.unix() - originTime.unix()) / intervalSeconds);
+  // # At what time does the first event occur?
+  let first_item = originTime
+    .clone()
+    .add((skip_intervals * intervalSeconds), "seconds");
+  let list = [first_item];
+  times(60, () => {
+    let x = last(list);
+    if (x) {
+      let item = x.clone().add(intervalSeconds, "seconds");
+      if (item.isBefore(upperBound)) {
+        list.push(item);
+      }
+    }
+  });
+  return list;
+}