refactor: give speed conversion a single home (#657)

Co-authored-by: Tarik Alani <tarik.nzl@gmail.com>

Author: CtrlAltDale

src/frontend/components/Battle/Battle.tsx

@@ -1,4 +1,6 @@
 import { memo, useMemo } from 'react';
+import { resolveSpeedUnit, speedFromKph } from '@irdashies/utils/units';
+import type { SpeedUnit } from '@irdashies/utils/units';
 import {
   useDrivingState,
   useSessionVisibility,
@@ -87,7 +89,7 @@ interface BattleRowProps {
   stintLaps?: number;
   lastTimeFormat?: import('@irdashies/types').TimeFormat;
   speedKph?: number;
-  isMetricSpeed?: boolean;
+  speedUnit?: SpeedUnit;
   rowIndex: number;
 }
 
@@ -107,7 +109,7 @@ const BattleRow = memo(
     stintLaps,
     lastTimeFormat = 'mixed',
     speedKph,
-    isMetricSpeed = true,
+    speedUnit = 'km/h',
     rowIndex,
   }: BattleRowProps) => {
     const onTrack = entry?.onTrack ?? true;
@@ -216,7 +218,7 @@ const BattleRow = memo(
       } else if (key === 'speed' && settings?.speed?.enabled) {
         const displaySpeed =
           speedKph != null && speedKph > 0
-            ? Math.round(isMetricSpeed ? speedKph : speedKph / 1.60934)
+            ? Math.round(speedFromKph(speedKph, speedUnit))
             : null;
         cols.push(
           <td
@@ -385,10 +387,11 @@ export const Battle = () => {
 
   // Speed: derived from CarIdxLapDistPct movement, in km/h.
   const carSpeeds = useCarIdxSpeed();
-  const displayUnits = useTelemetryValue('DisplayUnits'); // 0 = imperial, 1 = metric
-  const speedUnit = settings?.speed?.unit ?? 'auto';
-  const isMetricSpeed =
-    speedUnit === 'auto' ? displayUnits === 1 : speedUnit === 'km/h';
+  const displayUnits = useTelemetryValue('DisplayUnits');
+  const resolvedSpeedUnit = resolveSpeedUnit(
+    settings?.speed?.unit,
+    displayUnits
+  );
 
   const stintLaps = (carIdx: number) => {
     const currentLap = carLaps?.[carIdx] ?? 0;
@@ -449,7 +452,7 @@ export const Battle = () => {
             speedKph={
               aheadEntry != null ? carSpeeds[aheadEntry.carIdx] : undefined
             }
-            isMetricSpeed={isMetricSpeed}
+            speedUnit={resolvedSpeedUnit}
             rowIndex={0}
           />
           <BattleRow
@@ -468,7 +471,7 @@ export const Battle = () => {
             speedKph={
               playerEntry != null ? carSpeeds[playerEntry.carIdx] : undefined
             }
-            isMetricSpeed={isMetricSpeed}
+            speedUnit={resolvedSpeedUnit}
             rowIndex={1}
           />
           <BattleRow
@@ -496,7 +499,7 @@ export const Battle = () => {
             speedKph={
               behindEntry != null ? carSpeeds[behindEntry.carIdx] : undefined
             }
-            isMetricSpeed={isMetricSpeed}
+            speedUnit={resolvedSpeedUnit}
             rowIndex={2}
           />
         </tbody>

src/frontend/components/Input/InputGear/InputGear.tsx

@@ -1,4 +1,5 @@
 import { memo } from 'react';
+import { resolveSpeedUnit, speedFromMs } from '@irdashies/utils/units';
 
 export interface InputGearProps {
   gear?: number;
@@ -16,10 +17,14 @@ export interface InputGearProps {
 
 export const InputGear = memo(
   ({ gear, speedMs, unit, settings }: InputGearProps) => {
-    const isMetric =
-      (unit === 1 && settings.unit === 'auto') || settings.unit === 'km/h';
-    const speed = (speedMs ?? 0) * (isMetric ? 3.6 : 2.23694);
-    const displayUnit = isMetric ? 'km/h' : 'mph';
+    // 'none' is vestigial — the settings UI only offers auto/mph/km/h — but the
+    // type still permits it, and it previously fell through to mph. Kept that
+    // way rather than quietly changing behaviour for a hand-edited config.
+    const displayUnit = resolveSpeedUnit(
+      settings.unit === 'none' ? 'mph' : settings.unit,
+      unit
+    );
+    const speed = speedFromMs(speedMs ?? 0, displayUnit);
     let gearText;
     switch (gear) {
       case -1:

src/frontend/components/PitlaneHelper/hooks/usePitSpeed.tsx

@@ -1,5 +1,10 @@
 import { useMemo } from 'react';
 import { useTelemetryValue, useSessionStore } from '@irdashies/context';
+import {
+  kphFromSpeed,
+  speedFromKph,
+  speedFromMs,
+} from '@irdashies/utils/units';
 
 export interface PitSpeedResult {
   deltaKph: number;
@@ -24,13 +29,15 @@ export const usePitSpeed = (): PitSpeedResult => {
     const limitValue = parseFloat(limitString.split(' ')[0]);
     const limitUnit = limitString.split(' ')[1]?.toLowerCase();
 
-    // Determine limit in both units
-    const limitKph = limitUnit === 'mph' ? limitValue * 1.60934 : limitValue;
-    const limitMph = limitUnit === 'kph' ? limitValue / 1.60934 : limitValue;
+    // Determine limit in both units. iRacing writes the limit in whichever unit
+    // the track uses, so normalise via km/h rather than trusting one of them.
+    const limitKph =
+      limitUnit === 'mph' ? kphFromSpeed(limitValue, 'mph') : limitValue;
+    const limitMph = speedFromKph(limitKph, 'mph');
 
     // Current speed (convert m/s to km/h and mph)
-    const speedKph = speed * 3.6;
-    const speedMph = speed * 2.23694;
+    const speedKph = speedFromMs(speed, 'km/h');
+    const speedMph = speedFromMs(speed, 'mph');
 
     // Calculate deltas
     const deltaKph = speedKph - limitKph;

src/frontend/components/RejoinIndicator/RejoinIndicator.tsx

@@ -16,6 +16,7 @@ import { useDriverRelatives } from '../Standings/hooks/useDriverRelatives';
 import { useRejoinSettings } from './hooks/useRejoinSettings';
 import { getDemoRejoinData } from './demoData';
 import type { Standings } from '../Standings/createStandings';
+import { speedFromMs } from '@irdashies/utils/units';
 
 export const RejoinIndicator = () => {
   const { isDemoMode } = useDashboard();
@@ -78,7 +79,7 @@ export const RejoinIndicator = () => {
   }
 
   // Read telemetry and computed car speed for the focused car index
-  const speedKmH = (carSpeedForPlayer ?? 0) * 3.6;
+  const speedKmH = speedFromMs(carSpeedForPlayer ?? 0, 'km/h');
 
   const gap = Math.abs(carBehind?.delta ?? Number.POSITIVE_INFINITY);
   const gapLabel = Number.isFinite(gap) ? gap.toFixed(1) : '--';

src/frontend/components/Standings/components/SessionBar/components/TopSpeedItem/TopSpeedItem.tsx

@@ -5,6 +5,7 @@ import {
   useSessionBestTopSpeed,
   useTelemetryValue,
 } from '@irdashies/context';
+import { resolveSpeedUnit, speedFromMs } from '@irdashies/utils/units';
 import { sessionBarItemWrapperClass } from '../../sessionBarItemWrapperClass';
 import type { SessionBarItemProps } from '../../sessionBarItemTypes';
 
@@ -13,16 +14,14 @@ export const TopSpeedItem = memo(({ standalone }: SessionBarItemProps) => {
   const lastLapTopSpeedMs = useLastLapTopSpeed();
   const sessionBestTopSpeedMs = useSessionBestTopSpeed();
 
-  const isMetric = displayUnits === 1;
-  const factor = isMetric ? 3.6 : 2.23694;
-  const unit = isMetric ? 'km/h' : 'mph';
+  const unit = resolveSpeedUnit('auto', displayUnits);
   const last =
     lastLapTopSpeedMs !== null
-      ? `${(lastLapTopSpeedMs * factor).toFixed(0)} ${unit}`
+      ? `${speedFromMs(lastLapTopSpeedMs, unit).toFixed(0)} ${unit}`
       : '—';
   const best =
     sessionBestTopSpeedMs !== null
-      ? (sessionBestTopSpeedMs * factor).toFixed(0)
+      ? speedFromMs(sessionBestTopSpeedMs, unit).toFixed(0)
       : null;
 
   return (

src/frontend/components/Standings/components/SessionBar/components/WindItem/WindItem.tsx

@@ -1,5 +1,6 @@
 import { memo } from 'react';
 import { useTelemetryValue, useThrottledWeather } from '@irdashies/context';
+import { resolveSpeedUnit, speedFromMs } from '@irdashies/utils/units';
 import { WindArrow } from '../../../../../shared/WindArrow';
 import { sessionBarItemWrapperClass } from '../../sessionBarItemWrapperClass';
 import type { SessionBarItemProps } from '../../sessionBarItemTypes';
@@ -10,11 +11,11 @@ export const WindItem = memo(
     const { windDirection, windVelocity, windYaw } = useThrottledWeather();
     const relativeWindDirection = (windDirection ?? 0) - (windYaw ?? 0);
 
-    const isMetric = displayUnits === 1;
+    const speedUnit = resolveSpeedUnit('auto', displayUnits);
     const speedPosition = settings?.wind?.speedPosition ?? 'right';
     const speed =
       windVelocity !== undefined
-        ? Math.round(windVelocity * (isMetric ? 3.6 : 2.23694))
+        ? Math.round(speedFromMs(windVelocity, speedUnit))
         : '-';
     const speedEl = <span>{speed}</span>;
     const arrowEl = (

src/frontend/components/Weather/WindDirection/WindDirection.tsx

@@ -1,6 +1,7 @@
 import { WindIcon } from '@phosphor-icons/react';
 import { memo, useRef, useEffect, useState } from 'react';
 import { getWindIntensityClass } from '../../../domain/weather/wind';
+import { speedFromMs } from '@irdashies/utils/units';
 
 export interface WindDirectionProps {
   speedMs?: number;
@@ -46,7 +47,7 @@ export const WindDirection = memo(
     // Convert m/s to user's preferred unit
     const speed =
       speedMs !== undefined
-        ? speedMs * (metric ? 3.6 : 2.23694) // km/h or mph
+        ? speedFromMs(speedMs, metric ? 'km/h' : 'mph')
         : undefined;
 
     const [normalizedAngle, setNormalizedAngle] = useState<number>(0);

src/frontend/components/Wind/WindDirection/WindDirection.tsx

@@ -1,5 +1,6 @@
 import { memo, useEffect, useLayoutEffect, useRef, useState } from 'react';
 import { getWindIntensityClass } from '../../../domain/weather/wind';
+import { speedFromMs } from '@irdashies/utils/units';
 
 export interface WindDirectionProps {
   speedMs?: number;
@@ -10,7 +11,9 @@ export interface WindDirectionProps {
 export const WindDirection = memo(
   ({ speedMs, direction, metric = true }: WindDirectionProps) => {
     const speed =
-      speedMs !== undefined ? speedMs * (metric ? 3.6 : 2.23694) : undefined;
+      speedMs !== undefined
+        ? speedFromMs(speedMs, metric ? 'km/h' : 'mph')
+        : undefined;
     const [normalizedAngle, setNormalizedAngle] = useState(0);
     const prevAngleRef = useRef(0);
     const containerRef = useRef<HTMLDivElement | null>(null);

src/frontend/context/CarSpeedStore/CarSpeedsStore.tsx

@@ -1,5 +1,6 @@
 import type { Telemetry } from '@irdashies/types';
 import { create, useStore } from 'zustand';
+import { speedFromMs } from '@irdashies/utils/units';
 
 export interface CarSpeedBuffer {
   lastLapDistPct: number[];
@@ -65,7 +66,9 @@ export const useCarSpeedsStore = create<CarSpeedsState>((set, get) => ({
         if (wentBackwards && startedNewLap) distancePercent += 1.0;
 
         const distance = trackLength * distancePercent; // meters
-        const speed = deltaTime > 0 ? (distance / deltaTime) * 3.6 : 0; // m/s to km/h
+        // Stored in km/h throughout; converted here once from m/s.
+        const speed =
+          deltaTime > 0 ? speedFromMs(distance / deltaTime, 'km/h') : 0;
         if (!newHistory[idx]) newHistory[idx] = [];
         newHistory[idx].push(speed);
         if (newHistory[idx].length > SPEED_AVG_WINDOW) newHistory[idx].shift();

src/frontend/domain/weather/wind.ts

@@ -1,3 +1,5 @@
+import { msFromSpeed } from '@irdashies/utils/units';
+
 export interface WindDemoData {
   speedMs: number;
   direction: number;
@@ -18,7 +20,7 @@ export const getDemoWindData = (
   metric: boolean
 ): WindDemoData => {
   const demoValue = WIND_DEMO_VALUES[index % WIND_DEMO_VALUES.length];
-  const speedMs = demoValue.speed / (metric ? 3.6 : 2.23694);
+  const speedMs = msFromSpeed(demoValue.speed, metric ? 'km/h' : 'mph');
 
   return {
     speedMs,