Focus Line

"use client"import * as React from "react"import {  ResponsiveContainer,  LineChart,  Line,  XAxis,  YAxis,  Tooltip,  CartesianGrid,  Legend,  ReferenceLine,} from "recharts"import { HugeiconsIcon } from "@hugeicons/react"import { LockKeyIcon } from "@hugeicons/core-free-icons"import { useChartReducedMotion } from "../shared/use-chart-reduced-motion"import { ChartContainer } from "../shared/chart-container"import {  ChartLoadingState,  ChartEmptyState,  ChartErrorState,  ChartUnavailableState,} from "../shared/chart-state"import { cn } from "@/lib/utils"/* -------------------------------------------------------------------------- *//*  Type Definitions                                                          *//* -------------------------------------------------------------------------- *//** * Semantic representation of an actively inspected or locked observation. */export interface ActiveDatum<  TData extends Record<string, unknown> = Record<string, unknown>,  XVal extends string | number = string | number> {  /** 0-based index within the normalized observation dataset */  index: number  /** Domain coordinate along the horizontal axis */  x: XVal  /** Numeric quantitative metric value (null if missing/unrecorded) */  value: number | null  /** Original raw observation record from caller */  raw: TData  /** Alias for raw observation record */  datum?: TData  /** Whether this observation is actively pinned/locked */  isLocked: boolean  /** Whether this observation has a missing or unrecorded value */  isMissing: boolean}export interface FocusSeriesConfig<TData extends Record<string, unknown> = Record<string, unknown>> {  key?: keyof TData & string  label?: string  valueFormatter?: (value: number) => string  color?: string}export interface FocusLineProps<  TData extends Record<string, unknown> = Record<string, unknown>,  XVal extends string | number = string | number> {  /** Readonly array of observation records. Caller data is never mutated. */  data: readonly TData[]  /** Key for the horizontal axis domain (e.g. time, date, timestamp, sprint). */  xKey: keyof TData & string  /** Direct property name for the active quantitative numeric metric series. */  seriesKey?: keyof TData & string  /** Semantic series descriptor combining key, label, valueFormatter, and color. */  series?: FocusSeriesConfig<TData>  /** Human-readable label for the primary metric series. */  label?: string  /** Primary stroke color for the continuous signal line and active indicator. */  color?: string  /** Accent color for locked selection marker, concentric double-ring, and persistent tooltip. */  selectionColor?: string  /** Container height in pixels or CSS dimension string. (default: 320) */  height?: number | string  /** Curve interpolation for the continuous signal line: "linear", "monotone", or "step". (default: "monotone") */  curve?: "linear" | "monotone" | "step"  /** Explicit Y-axis numeric domain, or "auto" calculation. (default: "auto") */  domain?: [number, number] | ["auto", "auto"] | "auto"  /** Animation mode: "draw", "fade", or "none". (default: "draw") */  animation?: "draw" | "fade" | "none"  /** Handling of null or undefined values in the series: "gap" (truthful break) or "carry" (last known). */  missingValuePolicy?: "gap" | "carry"  /** Whether clicking or pressing Enter/Space pins the currently inspected datum. (default: true) */  lockableTooltip?: boolean  /** Default observation index to pin/lock on initial mount. (default: null) */  defaultLockedIndex?: number | null  /** Initial inspection position upon keyboard focus entry: "none", "first", or "last". (default: "none") */  initialFocus?: "none" | "first" | "last"  /** Horizontal inspection resolution algorithm: "nearest-x". (default: "nearest-x") */  scrubMode?: "nearest-x"  /** Tooltip inspection behavior: "nearest-x". (default: "nearest-x") */  tooltipMode?: "nearest-x"  /** Whether to render subtle horizontal background reference gridlines. (default: true) */  showGrid?: boolean  /** Whether to render the horizontal category scale. (default: true) */  showXAxis?: boolean  /** Whether to render the vertical numeric scale. (default: true) */  showYAxis?: boolean  /** Whether to render the chart legend. (default: false) */  showLegend?: boolean  /** Custom formatter for Y-axis scale numbers and tooltip metric values. */  valueFormatter?: (value: number) => string  /** Custom formatter for X-axis coordinate labels. */  xFormatter?: (value: string | number) => string  /** Animation configuration or boolean toggle. Respects prefers-reduced-motion. */  motion?: boolean | { duration?: number }  /** Callback fired whenever the active inspected observation changes. */  onActiveDatumChange?: (datum: ActiveDatum<TData, XVal> | null) => void  /** Callback fired whenever the persistent locked observation changes. */  onLockedDatumChange?: (datum: ActiveDatum<TData, XVal> | null) => void  /** Optional heading announced to assistive technologies. */  title?: string  /** Optional descriptive explanation announced to assistive technologies. */  description?: string  /** Optional CSS class name passed to the root figure element. */  className?: string  /** Display neutral skeleton loading state. */  loading?: boolean  /** Display actionable error banner. */  error?: Error | string | null  /** Display metric unavailability notice. */  unavailable?: boolean | string | null}/* -------------------------------------------------------------------------- *//*  Pure Algorithmic Helpers                                                  *//* -------------------------------------------------------------------------- */export function isFiniteNumber(val: unknown): val is number {  return typeof val === "number" && Number.isFinite(val)}export interface NormalizedFocusDatum {  __x: string | number  __value: number | null  __raw: Record<string, unknown>  __index: number}/** * Safely normalizes input observation records: * 1. Missing values are preserved as null under "gap" policy (no null-to-zero coercion). * 2. Non-finite values (NaN, Infinity) are treated as missing. * 3. Never mutates caller array or objects. */export function normalizeFocusData<TData extends Record<string, unknown>>(  data: readonly TData[],  xKey: keyof TData & string,  seriesKey: string,  missingValuePolicy: "gap" | "carry" = "gap"): NormalizedFocusDatum[] {  if (!Array.isArray(data) || data.length === 0) return []  let lastKnownValid: number | null = null  return data.map((d, idx) => {    const rawX = d[xKey]    const xVal = typeof rawX === "string" || typeof rawX === "number" ? rawX : String(rawX ?? "")    const rawV = d[seriesKey]    const isDirectFinite = isFiniteNumber(rawV)    let finalVal: number | null = null    if (isDirectFinite) {      finalVal = rawV      lastKnownValid = rawV    } else if (missingValuePolicy === "carry" && lastKnownValid !== null) {      finalVal = lastKnownValid    } else {      finalVal = null      if (missingValuePolicy === "gap") {        lastKnownValid = null      }    }    return {      __x: xVal,      __value: finalVal,      __raw: d,      __index: idx,    }  })}/** * Calculates a safe Cartesian Y-domain covering observation extrema. * Guarantees: * 1. If explicit numeric domain [min, max] is provided, respects it verbatim. * 2. Auto domain calculates series min/max with protective 8% padding. * 3. Handles empty, single-value, and constant data without collapsing. * 4. Handles negative, zero-span, and mixed-sign coordinates. */export function calculateFocusDomain(  normalized: readonly NormalizedFocusDatum[],  explicitDomain?: [number, number] | ["auto", "auto"] | "auto"): [number, number] {  if (    Array.isArray(explicitDomain) &&    typeof explicitDomain[0] === "number" &&    typeof explicitDomain[1] === "number" &&    Number.isFinite(explicitDomain[0]) &&    Number.isFinite(explicitDomain[1])  ) {    return explicitDomain  }  const values: number[] = []  for (const item of normalized) {    if (item.__value !== null && Number.isFinite(item.__value)) {      values.push(item.__value)    }  }  if (values.length === 0) {    return [0, 100]  }  const min = Math.min(...values)  const max = Math.max(...values)  if (min === max) {    if (min === 0) return [-10, 10]    const delta = Math.abs(min) * 0.15 || 10    return [Math.floor(min - delta), Math.ceil(max + delta)]  }  const span = max - min  const pad = span * 0.08  return [Math.floor(min - pad), Math.ceil(max + pad)]}/* -------------------------------------------------------------------------- *//*  Synchronized Custom Tooltip                                               *//* -------------------------------------------------------------------------- */interface FocusTooltipContentProps {  active?: boolean  payload?: readonly { dataKey?: string | number; value?: any; payload?: any; [key: string]: any }[]  label?: React.ReactNode  activeDatum: ActiveDatum | null  seriesLabel: string  primaryColor: string  selectionColor: string  valueFormatter?: (value: number) => string  xFormatter?: (value: string | number) => string  lockableTooltip: boolean  isLocked?: boolean}function FocusTooltipContent({  active,  payload,  label: _label,  activeDatum,  seriesLabel,  primaryColor,  selectionColor,  valueFormatter,  xFormatter,  lockableTooltip,  isLocked = false,}: FocusTooltipContentProps) {  // Extract observation from payload (Recharts hover) OR activeDatum (keyboard/locked state)  const payloadItem = payload?.[0]?.payload as NormalizedFocusDatum | undefined  const hasPayload = Boolean(payloadItem)  if (!activeDatum && (!active || !hasPayload)) {    return null  }  const fmt = valueFormatter ?? ((n: number) => n.toLocaleString())  const rawX = activeDatum ? activeDatum.x : (payloadItem?.__x ?? "")  const xDisplay = xFormatter ? xFormatter(rawX) : String(rawX)  const val = activeDatum ? activeDatum.value : (payloadItem?.__value ?? null)  const isMissing = val === null  const lockedState = activeDatum ? activeDatum.isLocked : isLocked  const isCustomHex = typeof selectionColor === "string" && selectionColor.startsWith("#")  return (    <div      className={cn(        "rounded-xl border bg-zinc-950/95 p-3.5 shadow-2xl backdrop-blur-md min-w-[180px] max-w-[260px] text-left transition-all duration-150 pointer-events-none select-none z-50",        lockedState          ? "border-amber-500/40 shadow-[0_12px_32px_-4px_rgba(0,0,0,0.6),0_0_16px_rgba(245,158,11,0.15)] ring-1 ring-amber-500/25"          : "border-white/[0.12] ring-1 ring-white/[0.04]"      )}      style={        lockedState && isCustomHex          ? {              borderColor: `${selectionColor}66`,              boxShadow: `0 12px 32px -4px rgba(0,0,0,0.6), 0 0 16px ${selectionColor}26, 0 0 0 1px ${selectionColor}40`,            }          : undefined      }    >      {/* Header: Coordinate + Lock Badge */}      <div className="flex items-center justify-between gap-2 border-b border-white/[0.08] pb-2 mb-2.5">        <span className="font-mono text-xs font-semibold text-zinc-200 tracking-wide truncate">          {xDisplay}        </span>        {lockedState && (          <span            className="inline-flex items-center gap-1 rounded-md px-1.5 py-0.5 text-[10px] font-mono font-semibold tracking-tight border bg-amber-500/15 border-amber-500/40 text-amber-300 dark:bg-amber-400/15 dark:border-amber-400/40 dark:text-amber-200 shadow-2xs"            style={              isCustomHex                ? {                    backgroundColor: `${selectionColor}20`,                    borderColor: `${selectionColor}55`,                    color: selectionColor,                  }                : undefined            }          >            <HugeiconsIcon icon={LockKeyIcon} size={11} strokeWidth={2.2} className="shrink-0" />            Locked          </span>        )}      </div>      {/* Series Metric Row */}      <div className="flex items-center justify-between gap-3">        <div className="flex items-center gap-2 min-w-0">          <span className="relative flex size-2 shrink-0 items-center justify-center">            {lockedState && (              <span                className="absolute size-3.5 rounded-full opacity-30 animate-pulse"                style={{ backgroundColor: primaryColor }}              />            )}            <span              className="size-2 rounded-full ring-1 ring-white/20 shadow-xs"              style={{ backgroundColor: primaryColor }}            />          </span>          <span className="text-xs font-medium text-zinc-300 font-sans truncate">            {seriesLabel}          </span>        </div>        <span className="font-mono text-xs font-bold text-white shrink-0 tabular-nums">          {isMissing ? "—" : fmt(val)}        </span>      </div>      {/* Interaction Hint Footer */}      {lockableTooltip && (        <div className="mt-2.5 pt-2 border-t border-white/[0.08] flex items-center justify-between text-[10px] font-mono text-zinc-400">          {lockedState ? (            <span className="flex items-center gap-1.5">              <kbd className="inline-flex items-center justify-center px-1.5 py-0.5 rounded bg-zinc-800/90 border border-white/15 text-[9px] font-mono font-semibold text-zinc-200 shadow-2xs">                Esc              </kbd>              <span className="text-zinc-400">or click to release</span>            </span>          ) : (            <span className="flex items-center gap-1.5 text-zinc-500">              <kbd className="inline-flex items-center justify-center px-1.5 py-0.5 rounded bg-zinc-800/60 border border-white/10 text-[9px] font-mono font-medium text-zinc-400">                Click              </kbd>              <span>to lock</span>            </span>          )}        </div>      )}    </div>  )}/* -------------------------------------------------------------------------- *//*  Main FocusLine Component                                                  *//* -------------------------------------------------------------------------- */export function FocusLine<  TData extends Record<string, unknown> = Record<string, unknown>,  XVal extends string | number = string | number>({  data,  xKey,  seriesKey: propSeriesKey,  series,  label: propLabel,  color: propColor,  selectionColor: propSelectionColor,  height = 320,  curve = "monotone",  domain = "auto",  animation = "draw",  missingValuePolicy = "gap",  lockableTooltip = true,  defaultLockedIndex = null,  initialFocus = "none",  scrubMode = "nearest-x",  tooltipMode = "nearest-x",  showGrid = true,  showXAxis = true,  showYAxis = true,  showLegend = false,  valueFormatter,  xFormatter,  motion = true,  onActiveDatumChange,  onLockedDatumChange,  title,  description,  className,  loading = false,  error = null,  unavailable = false,}: FocusLineProps<TData, XVal>) {  // Container & Motion hooks  const reducedMotion = useChartReducedMotion()  const uid = React.useId()  const titleId = `plotcn-focus-title-${uid}`  const descId = `plotcn-focus-desc-${uid}`  // Resolved series metadata & colors  const activeSeriesKey = series?.key ?? propSeriesKey ?? "value"  const seriesLabel = series?.label ?? propLabel ?? "Metric"  const primaryColor = series?.color ?? propColor ?? "var(--chart-1, #3b82f6)"  const selectionColor = propSelectionColor ?? "var(--chart-selection, #f59e0b)"  // Normalized observation dataset  const normalizedData = React.useMemo(    () => normalizeFocusData(data, xKey, activeSeriesKey, missingValuePolicy),    [data, xKey, activeSeriesKey, missingValuePolicy]  )  // Safe Y-axis domain  const safeDomain = React.useMemo(    () => calculateFocusDomain(normalizedData, domain),    [normalizedData, domain]  )  // Explicit interaction state model  const [lockedIndex, setLockedIndex] = React.useState<number | null>(() => {    if (      typeof defaultLockedIndex === "number" &&      defaultLockedIndex >= 0 &&      defaultLockedIndex < normalizedData.length    ) {      return defaultLockedIndex    }    return null  })  const [activeIndex, setActiveIndex] = React.useState<number | null>(() => {    if (      typeof defaultLockedIndex === "number" &&      defaultLockedIndex >= 0 &&      defaultLockedIndex < normalizedData.length    ) {      return defaultLockedIndex    }    if (normalizedData.length === 0) return null    if (initialFocus === "first") return 0    if (initialFocus === "last") return normalizedData.length - 1    return null  })  const [isChartFocused, setIsChartFocused] = React.useState(false)  // Ensure lockedIndex is safely cleared if underlying datum disappears after data update  React.useEffect(() => {    if (lockedIndex !== null && (lockedIndex >= normalizedData.length || normalizedData.length === 0)) {      setLockedIndex(null)      if (onLockedDatumChange) onLockedDatumChange(null)    }  }, [normalizedData.length, lockedIndex, onLockedDatumChange])  // Effective currently visible inspected index: lockedIndex takes priority over transient activeIndex  const effectiveIndex = lockedIndex !== null ? lockedIndex : activeIndex  // Construct active datum object for callbacks and tooltip  const activeDatum = React.useMemo<ActiveDatum<TData, XVal> | null>(() => {    if (effectiveIndex === null || effectiveIndex < 0 || effectiveIndex >= normalizedData.length) {      return null    }    const item = normalizedData[effectiveIndex]    return {      index: effectiveIndex,      x: item.__x as XVal,      value: item.__value,      raw: item.__raw as TData,      datum: item.__raw as TData,      isLocked: lockedIndex !== null && lockedIndex === effectiveIndex,      isMissing: item.__value === null,    }  }, [effectiveIndex, lockedIndex, normalizedData])  // Notify consumer callbacks when state changes  React.useEffect(() => {    if (onActiveDatumChange) {      onActiveDatumChange(activeDatum)    }  }, [activeDatum, onActiveDatumChange])  React.useEffect(() => {    if (onLockedDatumChange) {      if (lockedIndex !== null && activeDatum && activeDatum.isLocked) {        onLockedDatumChange(activeDatum)      } else {        onLockedDatumChange(null)      }    }  }, [lockedIndex, activeDatum, onLockedDatumChange])  /* -------------------------------------------------------------------------- */  /*  Keyboard Navigation Handlers (Single entry point on root <figure>)        */  /* -------------------------------------------------------------------------- */  const handleKeyDown = (e: React.KeyboardEvent<HTMLElement>) => {    if (normalizedData.length === 0) return    switch (e.key) {      case "ArrowRight": {        e.preventDefault()        const nextIdx = activeIndex === null ? 0 : Math.min(activeIndex + 1, normalizedData.length - 1)        setActiveIndex(nextIdx)        break      }      case "ArrowLeft": {        e.preventDefault()        const prevIdx =          activeIndex === null            ? normalizedData.length - 1            : Math.max(activeIndex - 1, 0)        setActiveIndex(prevIdx)        break      }      case "Home": {        e.preventDefault()        setActiveIndex(0)        break      }      case "End": {        e.preventDefault()        setActiveIndex(normalizedData.length - 1)        break      }      case "Enter":      case " ": {        if (!lockableTooltip) return        e.preventDefault()        const targetIndex = activeIndex !== null ? activeIndex : 0        if (lockedIndex === targetIndex) {          setLockedIndex(null)        } else {          setLockedIndex(targetIndex)          setActiveIndex(targetIndex)        }        break      }      case "Escape": {        e.preventDefault()        setLockedIndex(null)        setActiveIndex(null)        break      }    }  }  /* -------------------------------------------------------------------------- */  /*  Pointer / Mouse Scrubbing Handlers                                        */  /* -------------------------------------------------------------------------- */  const handleChartMouseMove = (state: any) => {    if (!state || typeof state.activeTooltipIndex !== "number") return    const idx = state.activeTooltipIndex    if (idx < 0 || idx >= normalizedData.length) return    // If a datum is locked, pointer movement does not override locked datum until unlocked    if (lockedIndex === null) {      if (activeIndex !== idx) {        setActiveIndex(idx)      }    }  }  const handleChartMouseLeave = () => {    // When unlocked, pointer leave clears active transient inspection    if (lockedIndex === null) {      setActiveIndex(null)    }  }  const handleChartClick = (state: any) => {    if (!lockableTooltip || normalizedData.length === 0) return    const clickedIdx = typeof state?.activeTooltipIndex === "number" ? state.activeTooltipIndex : activeIndex    if (clickedIdx === null || clickedIdx < 0 || clickedIdx >= normalizedData.length) return    if (lockedIndex === clickedIdx) {      // Clicking locked datum again unlocks it      setLockedIndex(null)    } else {      // Lock newly clicked datum      setLockedIndex(clickedIdx)      setActiveIndex(clickedIdx)    }  }  // Animation settings  const isAnimated = animation !== "none" && motion !== false && !reducedMotion  const animationDuration =    typeof motion === "object" && motion?.duration !== undefined ? motion.duration * 1000 : 350  // Screen reader factual summary  const factualSummary = React.useMemo(() => {    if (normalizedData.length === 0) return "No observations recorded."    const count = normalizedData.length    const activeInfo = activeDatum      ? ` Currently ${activeDatum.isLocked ? "locked on" : "inspecting"} observation ${activeDatum.index + 1} of ${count} at ${String(activeDatum.x)}${activeDatum.isMissing ? " (value unavailable)" : ` with value ${activeDatum.value}`}.`      : " Use Left and Right Arrow keys to inspect observations along the timeline."    return `Interactive time-series line chart depicting ${count} observations for ${seriesLabel}.${activeInfo}`  }, [normalizedData.length, activeDatum, seriesLabel])  /* -------------------------------------------------------------------------- */  /*  Early Return Exception States                                             */  /* -------------------------------------------------------------------------- */  if (error) {    return (      <figure        role="region"        aria-label={title || `${seriesLabel} chart error state`}        className={cn("plotcn-focus-line relative w-full overflow-hidden rounded-xl border border-white/10 bg-zinc-950 p-4", className)}        style={{ height }}      >        <ChartErrorState          title="Unable to load focus visualization"          description={            typeof error === "string"              ? error              : error?.message || "An unexpected error occurred while loading trend and inspection data."          }        />      </figure>    )  }  if (loading) {    return (      <figure        role="region"        aria-label={title || `${seriesLabel} chart loading state`}        className={cn("plotcn-focus-line relative w-full overflow-hidden rounded-xl border border-white/10 bg-zinc-950 p-4", className)}        style={{ height }}      >        <ChartLoadingState          title="Loading focus chart…"          description="Preparing timeline observations for inspection"        />      </figure>    )  }  if (unavailable) {    return (      <figure        role="region"        aria-label={title || `${seriesLabel} chart unavailable state`}        className={cn("plotcn-focus-line relative w-full overflow-hidden rounded-xl border border-white/10 bg-zinc-950 p-4", className)}        style={{ height }}      >        <ChartUnavailableState          title="Inspection metrics unavailable"          description={            typeof unavailable === "string"              ? unavailable              : "Timeline inspection metrics are unavailable for this view."          }        />      </figure>    )  }  if (normalizedData.length === 0) {    return (      <figure        role="region"        aria-label={title || `${seriesLabel} chart empty state`}        className={cn("plotcn-focus-line relative w-full overflow-hidden rounded-xl border border-white/10 bg-zinc-950 p-4", className)}        style={{ height }}      >        <ChartEmptyState          title="No data available"          description="Provide ordered observations to inspect latency and series metrics."        />      </figure>    )  }  /* -------------------------------------------------------------------------- */  /*  Active Coordinate Crosshair & Point Calculation                           */  /* -------------------------------------------------------------------------- */  const activeXCoordinate = effectiveIndex !== null ? normalizedData[effectiveIndex].__x : null  const isCurrentlyLocked = lockedIndex !== null  return (    <figure      role="region"      aria-labelledby={titleId}      aria-describedby={descId}      tabIndex={0}      onKeyDown={handleKeyDown}      onFocus={() => setIsChartFocused(true)}      onBlur={() => setIsChartFocused(false)}      className={cn(        "plotcn-focus-line relative w-full outline-none select-none transition-all duration-150 rounded-xl",        "focus-visible:ring-2 focus-visible:ring-[var(--chart-focus,#38bdf8)] focus-visible:ring-offset-2 focus-visible:ring-offset-zinc-950",        className      )}      style={{        height,        minHeight: typeof height === "number" ? height : 320,        touchAction: "pan-y", // Preserve vertical page scroll while allowing horizontal inspection      }}    >      {/* Accessible Name & Screen Reader Description */}      <div className="sr-only">        <h3 id={titleId}>{title || `${seriesLabel} Interactive Focus Line Chart`}</h3>        <p id={descId}>{description ? `${description} ${factualSummary}` : factualSummary}</p>      </div>      <ChartContainer className="w-full h-full min-w-0 max-w-full overflow-hidden">        <ResponsiveContainer          width="100%"          height="100%"          minWidth={0}          minHeight={0}          initialDimension={{ width: 320, height: typeof height === "number" ? height : 320 }}        >          <LineChart            data={normalizedData as any}            margin={{ top: 12, right: 16, bottom: 8, left: 8 }}            onMouseMove={handleChartMouseMove}            onMouseLeave={handleChartMouseLeave}            onClick={handleChartClick}          >            {/* 1. Subtle Reference Grid */}            {showGrid && (              <CartesianGrid                stroke="var(--chart-grid, rgba(255, 255, 255, 0.08))"                strokeDasharray="3 3"                vertical={false}              />            )}            {/* 2. Horizontal Category Scale */}            <XAxis              hide={!showXAxis}              dataKey="__x"              tickLine={false}              axisLine={false}              tick={{ fontSize: 11, fill: "var(--chart-axis, #71717a)" }}              tickFormatter={xFormatter as any}              dy={6}            />            {/* 3. Vertical Numeric Scale */}            <YAxis              hide={!showYAxis}              domain={safeDomain as any}              tickLine={false}              axisLine={false}              tick={{ fontSize: 11, fill: "var(--chart-axis, #71717a)" }}              tickFormatter={valueFormatter ? (v) => valueFormatter(Number(v)) : undefined}              dx={-4}            />            {/* 4. Persistent Inspection Crosshair when Locked */}            {activeXCoordinate !== null && isCurrentlyLocked && (              <ReferenceLine                x={activeXCoordinate}                stroke={selectionColor}                strokeDasharray="3 3"                strokeWidth={1.5}              />            )}            {/* 5. Synchronized Tooltip */}            <Tooltip              active={isCurrentlyLocked || (isChartFocused && activeIndex !== null) ? true : undefined}              defaultIndex={typeof defaultLockedIndex === "number" ? defaultLockedIndex : undefined}              content={                <FocusTooltipContent                  activeDatum={activeDatum}                  seriesLabel={seriesLabel}                  primaryColor={primaryColor}                  selectionColor={selectionColor}                  valueFormatter={valueFormatter}                  xFormatter={xFormatter}                  lockableTooltip={lockableTooltip}                  isLocked={isCurrentlyLocked}                />              }              cursor={{                stroke: isCurrentlyLocked ? selectionColor : "var(--chart-crosshair, rgba(255, 255, 255, 0.28))",                strokeDasharray: "3 3",                strokeWidth: isCurrentlyLocked ? 1.5 : 1.2,              }}            />            {/* 6. Optional Legend */}            {showLegend && (              <Legend                content={() => (                  <div className="flex items-center justify-center gap-2 pt-2 text-xs font-mono text-zinc-400">                    <span className="size-2.5 rounded-full" style={{ backgroundColor: primaryColor }} />                    <span>{seriesLabel}</span>                  </div>                )}              />            )}            {/* 7. Primary Continuous Signal Line with Custom Active / Locked Dot */}            <Line              type={curve === "step" ? "stepAfter" : curve}              dataKey="__value"              name={seriesLabel}              stroke={primaryColor}              strokeWidth={2.2}              connectNulls={false}              isAnimationActive={isAnimated}              animationDuration={animationDuration}              // Active / Locked Marker rendering              dot={(dotProps: any) => {                const { cx, cy, index, payload } = dotProps                if (typeof cx !== "number" || typeof cy !== "number" || payload.__value === null) {                  return <React.Fragment key={`dot-frag-${index}`} />                }                // Render special marker for active / locked observation                if (index === effectiveIndex) {                  if (index === lockedIndex) {                    // Concentric Double-Ring Marker for Locked Datum (───◎───)                    return (                      <g key={`locked-marker-${index}`} className="pointer-events-none">                        {/* Outer concentric selection ring */}                        <circle                          cx={cx}                          cy={cy}                          r={8}                          fill="none"                          stroke={selectionColor}                          strokeWidth={2.5}                        />                        {/* Inner selection dot */}                        <circle                          cx={cx}                          cy={cy}                          r={4}                          fill={selectionColor}                          stroke="var(--chart-background, #09090b)"                          strokeWidth={1.5}                        />                      </g>                    )                  }                  // Active Dot for transient inspection (───●───)                  return (                    <circle                      key={`active-dot-${index}`}                      cx={cx}                      cy={cy}                      r={5.5}                      fill={primaryColor}                      stroke="var(--chart-background, #09090b)"                      strokeWidth={2}                      className="pointer-events-none"                    />                  )                }                // If dataset has only 1 observation, render single static dot                if (normalizedData.length === 1) {                  return (                    <circle                      key={`single-dot-${index}`}                      cx={cx}                      cy={cy}                      r={4}                      fill={primaryColor}                      stroke="var(--chart-background, #09090b)"                      strokeWidth={1.5}                      className="pointer-events-none"                    />                  )                }                // Subtle baseline observation dot so points are clearly discoverable                if (normalizedData.length <= 40) {                  return (                    <circle                      key={`dot-base-${index}`}                      cx={cx}                      cy={cy}                      r={3}                      fill={primaryColor}                      fillOpacity={0.5}                      stroke="var(--chart-background, #09090b)"                      strokeWidth={1}                      className="pointer-events-none transition-all duration-150"                    />                  )                }                return <React.Fragment key={`dot-empty-${index}`} />              }}              activeDot={(activeProps: any) => {                const { cx, cy, index, payload } = activeProps                if (typeof cx !== "number" || typeof cy !== "number" || payload?.__value === null) {                  return <React.Fragment key={`active-dot-empty-${index}`} />                }                if (index === lockedIndex) {                  return (                    <g key={`locked-active-${index}`} className="pointer-events-none">                      <circle cx={cx} cy={cy} r={8} fill="none" stroke={selectionColor} strokeWidth={2} />                      <circle cx={cx} cy={cy} r={4} fill={selectionColor} stroke="var(--chart-background, #09090b)" strokeWidth={1.5} />                    </g>                  )                }                return (                  <circle                    key={`active-hover-dot-${index}`}                    cx={cx}                    cy={cy}                    r={5}                    fill={primaryColor}                    stroke="var(--chart-background, #09090b)"                    strokeWidth={2}                    className="pointer-events-none"                  />                )              }}            />          </LineChart>        </ResponsiveContainer>      </ChartContainer>    </figure>  )}