Limit study time to hours in reviews graph (#4086)

* Add maxUnit argument to naturalUnit

* Limit study time to hours in reviews graph

Relevant discussions:
- https://forums.ankiweb.net/t/reviews-graph-units-of-total-time-studied-suggestion/61237
- https://forums.ankiweb.net/t/why-does-anki-display-study-time-in-months/37722
- https://forums.ankiweb.net/t/poll-use-hours-in-total-time-stats/62076
- https://github.com/ankitects/anki/pull/3901#issuecomment-2973161601

* Use the new approach for native stability in Card Info

* Use a simpler approach

ts/lib/tslib/time.ts

@@ -7,8 +7,8 @@ export const SECOND = 1.0;
 export const MINUTE = 60.0 * SECOND;
 export const HOUR = 60.0 * MINUTE;
 export const DAY = 24.0 * HOUR;
-export const MONTH = 30.417 * DAY; // 365/12 ≈ 30.417
 export const YEAR = 365.0 * DAY;
+export const MONTH = YEAR / 12;
 
 export enum TimespanUnit {
     Seconds,
@@ -146,8 +146,13 @@ function i18nFuncForUnit(
 If precise is true, show to two decimal places, eg
 eg 70 seconds -> "1.17 minutes"
 If false, seconds and days are shown without decimals. */
-export function timeSpan(seconds: number, short = false, precise = true): string {
+export function timeSpan(
-    const unit = naturalUnit(seconds);
+    seconds: number,
+    short = false,
+    precise = true,
+    maxUnit: TimespanUnit = TimespanUnit.Years,
+): string {
+    const unit = Math.min(naturalUnit(seconds), maxUnit);
     let amount = unitAmount(unit, seconds);
     if (!precise && unit < TimespanUnit.Months) {
         amount = Math.round(amount);

ts/routes/card-info/CardStats.svelte

@@ -5,7 +5,7 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 <script lang="ts">
     import type { CardStatsResponse } from "@generated/anki/stats_pb";
     import * as tr2 from "@generated/ftl";
-    import { DAY, timeSpan, Timestamp } from "@tslib/time";
+    import { DAY, timeSpan, TimespanUnit, Timestamp } from "@tslib/time";
 
     export let stats: CardStatsResponse;
 
@@ -58,7 +58,12 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
         if (stats.memoryState) {
             let stability = timeSpan(stats.memoryState.stability * 86400, false, false);
             if (stats.memoryState.stability > 31) {
-                const nativeStability = stats.memoryState.stability.toFixed(0);
+                const nativeStability = timeSpan(
+                    stats.memoryState.stability * 86400,
+                    false,
+                    false,
+                    TimespanUnit.Days,
+                );
                 stability += ` (${nativeStability})`;
             }
             statsRows.push({

ts/routes/graphs/reviews.ts

@@ -8,7 +8,7 @@
 import type { GraphsResponse } from "@generated/anki/stats_pb";
 import * as tr from "@generated/ftl";
 import { localizedNumber } from "@tslib/i18n";
-import { dayLabel, timeSpan } from "@tslib/time";
+import { dayLabel, timeSpan, TimespanUnit } from "@tslib/time";
 import type { Bin, ScaleSequential } from "d3";
 import {
     area,
@@ -141,7 +141,7 @@ export function renderReviews(
 
     const yTickFormat = (n: number): string => {
         if (showTime) {
-            return timeSpan(n / 1000, true);
+            return timeSpan(n / 1000, true, false, TimespanUnit.Hours);
         } else {
             if (Math.round(n) != n) {
                 return "";
@@ -205,7 +205,7 @@ export function renderReviews(
 
     function valueLabel(n: number): string {
         if (showTime) {
-            return timeSpan(n / 1000);
+            return timeSpan(n / 1000, false, true, TimespanUnit.Hours);
         } else {
             return tr.statisticsReviews({ reviews: n });
         }
@@ -340,7 +340,7 @@ export function renderReviews(
         averageAnswerTime: string,
         averageAnswerTimeLabel: string;
     if (showTime) {
-        totalString = timeSpan(total / 1000, false);
+        totalString = timeSpan(total / 1000, false, true, TimespanUnit.Hours);
         averageForDaysStudied = tr.statisticsMinutesPerDay({
             count: Math.round(studiedAvg / 1000 / 60),
         });