Pull in Star Helper cohort analysis work from DFG (#226)

I meant to build more on top of this before merging, but this is now
beginning to risk rework due to merge conflicts and it's in a workable
state, so I'm going to merge. Thank you @DanielFGray for the bulk of
this work!

The Star Hunter feature is going to be gated at launch as a future
premium feature — it currently relies on hardcoded channels from
Reactiflux, which obviously is not workable as a production feature, and
revising it to handle advance configuration/work delegation is more
effort than I want to gate further development on.

So tl;dr
- Star Hunter feature works for Reactiflux (only)
- Intended in the future as a premium add-on feature, available to paid
plans
- Merging this so it can continue to be built upon

---------

Co-authored-by: DanielFGray <danielfgray@gmail.com>

Author: vcarl

app/features/StarHunter/RangeForm.tsx

@@ -0,0 +1,239 @@
+import {
+  addDays,
+  addMonths,
+  addYears,
+  endOfQuarter,
+  endOfYear,
+  format,
+  startOfQuarter,
+  startOfYear,
+  subDays,
+} from "date-fns";
+import { useState, type LabelHTMLAttributes } from "react";
+
+const Label = (props: LabelHTMLAttributes<Element>) => (
+  <label {...props} className={`${props.className ?? ""} m-4`}>
+    {props.children}
+  </label>
+);
+
+const DATE_FORMAT = "yyyy-MM-dd";
+const DISPLAY_FORMAT = "MMM d, yyyy";
+
+export type PresetKey = "30d" | "quarter" | "half" | "year" | "custom";
+
+const presets: { key: PresetKey; label: string }[] = [
+  { key: "30d", label: "30 days" },
+  { key: "quarter", label: "Quarter" },
+  { key: "half", label: "6 months" },
+  { key: "year", label: "Year" },
+  { key: "custom", label: "Custom" },
+];
+
+// Get start of the half-year (H1: Jan-Jun, H2: Jul-Dec)
+function startOfHalf(date: Date): Date {
+  const month = date.getMonth();
+  const year = date.getFullYear();
+  return month < 6 ? new Date(year, 0, 1) : new Date(year, 6, 1);
+}
+
+function endOfHalf(date: Date): Date {
+  const month = date.getMonth();
+  const year = date.getFullYear();
+  return month < 6 ? new Date(year, 5, 30) : new Date(year, 11, 31);
+}
+
+function shiftDatesByInterval(
+  start: Date,
+  _end: Date,
+  interval: Exclude<PresetKey, "custom">,
+  direction: "back" | "forward",
+): { start: string; end: string } {
+  const shift = direction === "back" ? -1 : 1;
+
+  switch (interval) {
+    case "30d":
+      return {
+        start: format(addDays(start, shift * 30), DATE_FORMAT),
+        end: format(addDays(start, shift * 30 + 29), DATE_FORMAT),
+      };
+    case "quarter": {
+      const newStart = startOfQuarter(addMonths(start, shift * 3));
+      return {
+        start: format(newStart, DATE_FORMAT),
+        end: format(endOfQuarter(newStart), DATE_FORMAT),
+      };
+    }
+    case "half": {
+      const newStart = startOfHalf(addMonths(start, shift * 6));
+      return {
+        start: format(newStart, DATE_FORMAT),
+        end: format(endOfHalf(newStart), DATE_FORMAT),
+      };
+    }
+    case "year": {
+      const newStart = startOfYear(addYears(start, shift));
+      return {
+        start: format(newStart, DATE_FORMAT),
+        end: format(endOfYear(newStart), DATE_FORMAT),
+      };
+    }
+  }
+}
+
+function getPresetDates(key: Exclude<PresetKey, "custom">): {
+  start: string;
+  end: string;
+} {
+  const today = new Date();
+
+  switch (key) {
+    case "30d":
+      return {
+        start: format(subDays(today, 30), DATE_FORMAT),
+        end: format(today, DATE_FORMAT),
+      };
+    case "quarter":
+      return {
+        start: format(startOfQuarter(today), DATE_FORMAT),
+        end: format(endOfQuarter(today), DATE_FORMAT),
+      };
+    case "half":
+      return {
+        start: format(startOfHalf(today), DATE_FORMAT),
+        end: format(endOfHalf(today), DATE_FORMAT),
+      };
+    case "year":
+      return {
+        start: format(startOfYear(today), DATE_FORMAT),
+        end: format(endOfYear(today), DATE_FORMAT),
+      };
+  }
+}
+
+function navigateTo(start: string, end: string, interval?: PresetKey) {
+  const url = new URL(window.location.href);
+  url.searchParams.set("start", start);
+  url.searchParams.set("end", end);
+  if (interval) {
+    url.searchParams.set("interval", interval);
+  } else {
+    url.searchParams.delete("interval");
+  }
+  window.location.href = url.toString();
+}
+
+export function RangeForm({
+  values,
+  interval: currentInterval,
+}: {
+  values: { start?: string; end?: string };
+  interval?: PresetKey;
+}) {
+  const [showCustom, setShowCustom] = useState(currentInterval === "custom");
+  const [selectedInterval, setSelectedInterval] = useState<PresetKey>(
+    currentInterval ?? "30d",
+  );
+
+  const handlePresetChange = (e: React.ChangeEvent<HTMLSelectElement>) => {
+    const key = e.target.value as PresetKey;
+    setSelectedInterval(key);
+    if (key === "custom") {
+      setShowCustom(true);
+      return;
+    }
+    setShowCustom(false);
+    const { start, end } = getPresetDates(key);
+    navigateTo(start, end, key);
+  };
+
+  const handleNav = (direction: "back" | "forward") => {
+    if (!values.start || !values.end || selectedInterval === "custom") return;
+    const { start, end } = shiftDatesByInterval(
+      new Date(values.start),
+      new Date(values.end),
+      selectedInterval,
+      direction,
+    );
+    navigateTo(start, end, selectedInterval);
+  };
+
+  const rangeLabel =
+    values.start && values.end
+      ? `${format(new Date(values.start), DISPLAY_FORMAT)} – ${format(new Date(values.end), DISPLAY_FORMAT)}`
+      : null;
+
+  const canNavigate =
+    values.start && values.end && selectedInterval !== "custom";
+
+  return (
+    <div className="flex flex-col items-center gap-3">
+      <div className="flex items-center gap-3">
+        <select
+          onChange={handlePresetChange}
+          value={selectedInterval}
+          className="rounded border border-gray-300 px-3 py-1.5 text-gray-800"
+        >
+          {presets.map((p) => (
+            <option key={p.key} value={p.key}>
+              {p.label}
+            </option>
+          ))}
+        </select>
+
+        {canNavigate && (
+          <div className="flex items-center gap-1">
+            <button
+              type="button"
+              onClick={() => handleNav("back")}
+              className="rounded border border-gray-300 px-2 py-1 hover:bg-gray-100"
+              aria-label="Previous period"
+            >
+              ←
+            </button>
+            <button
+              type="button"
+              onClick={() => handleNav("forward")}
+              className="rounded border border-gray-300 px-2 py-1 hover:bg-gray-100"
+              aria-label="Next period"
+            >
+              →
+            </button>
+          </div>
+        )}
+      </div>
+
+      {rangeLabel && <div className="text-sm text-gray-600">{rangeLabel}</div>}
+
+      {showCustom && (
+        <form method="GET" className="flex items-end gap-2">
+          <Label className="m-0">
+            Start
+            <input
+              name="start"
+              type="date"
+              defaultValue={values.start}
+              className="ml-2 rounded border border-gray-300 px-2 py-1 text-gray-800"
+            />
+          </Label>
+          <Label className="m-0">
+            End
+            <input
+              name="end"
+              type="date"
+              defaultValue={values.end}
+              className="ml-2 rounded border border-gray-300 px-2 py-1 text-gray-800"
+            />
+          </Label>
+          <input type="hidden" name="interval" value="custom" />
+          <button
+            type="submit"
+            className="rounded bg-blue-600 px-4 py-1.5 text-white hover:bg-blue-700"
+          >
+            Apply
+          </button>
+        </form>
+      )}
+    </div>
+  );
+}