feat: experiment conversion rate chart

frontend/common/types/responses.ts

@@ -727,6 +727,16 @@ export type ExposuresSummary = {
   timeseries: ExposuresTimeseries
 }
 
+export type ConversionsTimeseriesPoint = {
+  bucket: string
+  converted_identities: Record<string, number>
+}
+
+export type ConversionsTimeseries = {
+  granularity: ExposureGranularity
+  points: ConversionsTimeseriesPoint[]
+}
+
 export type ExperimentExposures = {
   as_of: string | null
   last_error_at: string | null
@@ -760,11 +770,19 @@ export type BayesianMetricResult = {
   metric_id: number
   variants: Record<string, VariantStats>
   inference: Record<string, Inference | null>
+  // Occurrence metrics only; null for value metrics. Absent from payloads
+  // stored before the backend shipped it (finalised experiments never gain it).
+  conversions_timeseries?: ConversionsTimeseries | null
 }
 
 export type BayesianResultsSummary = {
   srm_p_value: number | null
   metrics: BayesianMetricResult[]
+  // Denominator for the conversion-rate charts, same warehouse run as the
+  // metrics. Exposures bucket by first exposure and conversions by first
+  // conversion, so only running totals may be divided — a per-bucket division
+  // can exceed 100%. Absent from payloads stored before the backend shipped it.
+  exposures_timeseries?: ExposuresTimeseries
 }
 
 export enum TagStrategy {

frontend/web/components/charts/BarChart.tsx

@@ -35,20 +35,100 @@ type BarChartProps = {
   barSize?: number
   /** Render vertical grid lines (one per x tick). Default `true`. */
   verticalGrid?: boolean
+  /** Chart height in pixels. Default 400. */
+  height?: number
+  /**
+   * Render series side by side instead of stacked. Required for non-additive
+   * values (rates, percentages) where stacking would be meaningless.
+   */
+  grouped?: boolean
+  /**
+   * dataKey → stack id, for part-of-whole bars: series sharing a stack id
+   * stack together, distinct ids sit side by side (e.g. converted/remainder
+   * segments stacked per variant, variants grouped). Overrides `grouped`.
+   */
+  stackMap?: Record<string, string>
+  /**
+   * dataKey → fill opacity (0–1). Colours are CSS `var()` strings, so
+   * transparency must come from SVG fill-opacity, not an alpha channel.
+   */
+  opacityMap?: Record<string, number>
+  /** Left axis overrides, e.g. a `%` tick formatter. */
+  yAxis?: {
+    tickFormatter?: (value: number) => string
+    domain?: [number, number]
+  }
+  /**
+   * Per-entry tooltip value renderer, threaded to ChartTooltip. Skipped for
+   * missing or non-numeric values, which render blank.
+   */
+  tooltipValueFormatter?: (
+    value: number,
+    seriesKey: string,
+    label: string,
+  ) => string
+  /**
+   * Hide the tooltip's total row — required when `tooltipValueFormatter`
+   * renders a non-additive unit such as a percentage.
+   */
+  tooltipHideTotal?: boolean
 }
 
+type FadedSwatchLegendProps = {
+  opacityMap: Record<string, number>
+  seriesLabels?: Record<string, string>
+  // Injected by recharts' <Legend content={...}>.
+  payload?: { value?: string | number; color?: string }[]
+}
+
+const FadedSwatchLegend: FC<FadedSwatchLegendProps> = ({
+  opacityMap,
+  payload,
+  seriesLabels,
+}) => (
+  <div className='d-flex justify-content-center flex-wrap gap-3'>
+    {payload?.map((entry) => {
+      const key = String(entry.value)
+      return (
+        <span className='d-flex align-items-center gap-1' key={key}>
+          <span
+            style={{
+              backgroundColor: entry.color,
+              display: 'inline-block',
+              height: 10,
+              opacity: opacityMap[key] ?? 1,
+              width: 10,
+            }}
+          />
+          <span style={{ color: entry.color, fontSize: 12 }}>
+            {seriesLabels?.[key] ?? key}
+          </span>
+        </span>
+      )
+    })}
+  </div>
+)
+
 const BarChart: FC<BarChartProps> = ({
   barSize,
   colorMap,
   data,
+  grouped = false,
+  height = 400,
+  opacityMap,
   series,
   seriesLabels,
   showLegend = false,
+  stackMap,
+  tooltipHideTotal,
+  tooltipValueFormatter,
   verticalGrid = true,
   xAxisInterval = 0,
+  yAxis,
 }) => {
+  const defaultStackId = grouped ? undefined : 'series'
   return (
-    <ResponsiveContainer height={400} width='100%'>
+    <ResponsiveContainer height={height} width='100%'>
       <RawBarChart data={data}>
         <CartesianGrid
           strokeDasharray='3 5'
@@ -69,28 +149,48 @@ const BarChart: FC<BarChartProps> = ({
         <YAxis
           tick={{ fill: colorTextSecondary, fontSize: 11 }}
           axisLine={{ stroke: colorTextSecondary }}
-          tickFormatter={(value) =>
-            value >= 1000 ? `${(value / 1000).toFixed(0)}k` : value
+          domain={yAxis?.domain}
+          tickFormatter={
+            yAxis?.tickFormatter ??
+            ((value) =>
+              value >= 1000 ? `${(value / 1000).toFixed(0)}k` : value)
           }
         />
         <Tooltip
           cursor={{ fill: 'transparent' }}
-          content={<ChartTooltip seriesLabels={seriesLabels} />}
+          content={
+            <ChartTooltip
+              hideTotal={tooltipHideTotal}
+              seriesLabels={seriesLabels}
+              valueFormatter={tooltipValueFormatter}
+            />
+          }
         />
         {showLegend && (
           <Legend
             wrapperStyle={{ paddingTop: 16 }}
             formatter={(value) =>
               seriesLabels?.[String(value)] ?? String(value)
             }
+            content={
+              // The default legend swatch ignores fillOpacity, so faded
+              // series need their own renderer to match the bars.
+              opacityMap ? (
+                <FadedSwatchLegend
+                  opacityMap={opacityMap}
+                  seriesLabels={seriesLabels}
+                />
+              ) : undefined
+            }
           />
         )}
         {series.map((label, index) => (
           <Bar
             key={label}
             dataKey={label}
-            stackId='series'
+            stackId={stackMap ? stackMap[label] : defaultStackId}
             fill={colorMap[label]}
+            fillOpacity={opacityMap?.[label]}
             barSize={barSize}
             animationBegin={index * 80}
             animationDuration={600}

frontend/web/components/charts/ChartTooltip.tsx

@@ -25,9 +25,16 @@ type ChartTooltipProps = TooltipProps<ValueType, NameType> & {
   /**
    * Hide the total row at the bottom. Useful for single-entry payloads
    * (e.g. a pie-slice hover) where the total just repeats the entry value.
+   * Also required when `valueFormatter` renders a non-additive unit such as a
+   * percentage, since the total row stays plain-number formatted.
    * Default: false.
    */
   hideTotal?: boolean
+  /**
+   * Optional per-entry value renderer, e.g. to append units ("8.3%") or
+   * counts ("120 of 1,450"). Falls back to localised number formatting.
+   */
+  valueFormatter?: (value: number, seriesKey: string, label: string) => string
 }
 
 const ChartTooltip: FC<ChartTooltipProps> = ({
@@ -36,6 +43,7 @@ const ChartTooltip: FC<ChartTooltipProps> = ({
   label,
   payload,
   seriesLabels,
+  valueFormatter,
 }) => {
   if (!active || !payload || payload.length === 0) return null
   const total = payload.reduce<number>(
@@ -66,7 +74,9 @@ const ChartTooltip: FC<ChartTooltipProps> = ({
             <ColorSwatch color={entry.color ?? ''} size='sm' />
             <span className='text-default'>{displayName}:</span>
             <span className='fw-semibold text-default'>
-              {formatNumber(entry.value)}
+              {typeof entry.value === 'number' && valueFormatter
+                ? valueFormatter(entry.value, key, String(label ?? ''))
+                : formatNumber(entry.value)}
             </span>
           </div>
         )

frontend/web/components/experiments/results/ExperimentConversionRateCard/ExperimentConversionRateCard.tsx

@@ -0,0 +1,146 @@
+import { FC, useCallback, useMemo, useState } from 'react'
+import moment from 'moment'
+import { BarChart } from 'components/charts'
+import ContentCard from 'components/base/grid/ContentCard'
+import InlinePillToggle from 'components/base/forms/InlinePillToggle'
+import { BayesianResultsSummary, Experiment } from 'common/types/responses'
+import { getPrimaryMetric } from 'components/experiments/constants'
+import {
+  getMetricResult,
+  getVariantIdentities,
+} from 'components/experiments/results/derive'
+import {
+  ConversionStackMode,
+  REST_SUFFIX,
+  buildConversionRateChartData,
+  buildConversionStackChartData,
+} from 'components/experiments/results/deriveConversionRate'
+
+type ExperimentConversionRateCardProps = {
+  experiment: Experiment
+  results?: BayesianResultsSummary
+  asOf: string | null
+}
+
+const ExperimentConversionRateCard: FC<ExperimentConversionRateCardProps> = ({
+  asOf,
+  experiment,
+  results,
+}) => {
+  const [mode, setMode] = useState<ConversionStackMode>('cumulative')
+  const metric = getPrimaryMetric(experiment)
+  const identities = useMemo(
+    () => getVariantIdentities(experiment.feature),
+    [experiment.feature],
+  )
+  const chart = useMemo(
+    () =>
+      metric && results
+        ? buildConversionStackChartData(
+            results,
+            metric.metric,
+            identities,
+            mode,
+          )
+        : null,
+    [metric, results, identities, mode],
+  )
+  // Running counts and rates, for the cumulative tooltip ("x of y (z%)").
+  const rateChart = useMemo(
+    () =>
+      metric && results
+        ? buildConversionRateChartData(results, metric.metric, identities)
+        : null,
+    [metric, results, identities],
+  )
+
+  const formatTooltipValue = useCallback(
+    (value: number, seriesKey: string, label: string) => {
+      if (mode === 'daily') return value.toLocaleString()
+      if (seriesKey.endsWith(REST_SUFFIX)) {
+        // The faded segment is labelled "exposures", so report the full bar
+        // total rather than the plotted remainder (exposures − conversions).
+        const variantKey = seriesKey.slice(0, -REST_SUFFIX.length)
+        const counts = rateChart?.countsByDay[label]?.[variantKey]
+        return (counts?.exposed ?? value).toLocaleString()
+      }
+      const counts = rateChart?.countsByDay[label]?.[seriesKey]
+      if (!counts) return value.toLocaleString()
+      const rate = rateChart?.points.find((p) => p.day === label)?.[seriesKey]
+      return `${counts.converted.toLocaleString()} of ${counts.exposed.toLocaleString()}${
+        typeof rate === 'number' ? ` (${rate}%)` : ''
+      }`
+    },
+    [mode, rateChart],
+  )
+
+  // Hidden entirely when no rate can be charted: value metrics, and
+  // payloads stored before the backend shipped the timeseries.
+  if (!metric || !results || !chart) return null
+
+  const conversions = getMetricResult(
+    results,
+    metric.metric,
+  )?.conversions_timeseries
+  const hasConversions = !!conversions && conversions.points.length > 0
+
+  return (
+    <ContentCard
+      action={
+        hasConversions ? (
+          // Single metric today — disabled until multi-metric ships.
+          <div style={{ minWidth: 180 }}>
+            <Select
+              isDisabled
+              size='select-sm'
+              value={{ label: metric.metric_name, value: metric.metric }}
+              options={[{ label: metric.metric_name, value: metric.metric }]}
+            />
+          </div>
+        ) : undefined
+      }
+      className='experiment-results__conversion-rate-card'
+      title='Conversion rate over time'
+    >
+      {hasConversions ? (
+        <>
+          {/* mt-n2 halves the card's 16px child gap after the title. */}
+          <div className='d-flex mt-n2'>
+            <InlinePillToggle<ConversionStackMode>
+              size='small'
+              options={[
+                { label: 'Cumulative', value: 'cumulative' },
+                { label: 'Daily', value: 'daily' },
+              ]}
+              value={mode}
+              onChange={setMode}
+            />
+          </div>
+          <BarChart
+            colorMap={chart.colorMap}
+            data={chart.points}
+            height={260}
+            opacityMap={chart.opacityMap}
+            series={chart.series}
+            seriesLabels={chart.seriesLabels}
+            showLegend
+            stackMap={chart.stackMap}
+            tooltipHideTotal
+            tooltipValueFormatter={formatTooltipValue}
+          />
+          <span className='text-muted fs-caption'>
+            {asOf
+              ? `As of ${moment.utc(asOf).format('D MMM YYYY, HH:mm')} UTC`
+              : ''}
+          </span>
+        </>
+      ) : (
+        <div className='text-muted text-center py-5'>
+          No conversions recorded yet.
+        </div>
+      )}
+    </ContentCard>
+  )
+}
+
+export default ExperimentConversionRateCard

frontend/web/components/experiments/results/ExperimentConversionRateCard/index.ts

@@ -0,0 +1 @@
+export { default } from './ExperimentConversionRateCard'