app/frontend/src/components/Flow/MessageSparkline.tsx

import { useQuery } from "@tanstack/react-query"
import { useEffect, useState } from "react"

import type { DType, HistoryPoint } from "@/client"
import { Sparkline } from "@/components/Common/Sparkline"
import {
  Tooltip,
  TooltipContent,
  TooltipTrigger,
} from "@/components/ui/tooltip"
import { qualify } from "./deriveEdges"
import { useLiveValue } from "./liveStore"
import { messageHistoryQueryOptions } from "./queries"
import { ValuePreview } from "./ValuePreview"

/** The same bound the server keeps, so the live tail cannot outgrow the window. */
const WINDOW = 120

/** A stretch of time in the coarsest unit that still says it. */
function span(seconds: number): string {
  if (seconds < 90) return `${Math.round(seconds)}s`
  if (seconds < 5400) return `${Math.round(seconds / 60)}m`
  return `${Math.round(seconds / 3600)}h`
}

/**
 * What the curve is actually showing.
 *
 * These are a ring of the last `WINDOW` values per message, not a window of
 * time — a message that fires twice an hour and one that fires at 10 Hz draw
 * the same width for wildly different spans. The readings themselves are what
 * says which, so the caption reads it off them rather than claiming a range.
 */
function caption(points: HistoryPoint[]): string {
  const readings = `The last ${points.length} reading${points.length === 1 ? "" : "s"}`
  const covered = points[points.length - 1].ts - points[0].ts
  return covered > 0 ? `${readings}, over ${span(covered)}.` : `${readings}.`
}

/**
 * The name only settles once typing stops. Without this, every keystroke in the
 * message field would ask the server for a history.
 */
function useSettled(value: string): string {
  const [settled, setSettled] = useState(value)
  useEffect(() => {
    const timer = setTimeout(() => setSettled(value), 400)
    return () => clearTimeout(timer)
  }, [value])
  return settled
}

/**
 * How one message has been moving, as a sparkline with a live end.
 *
 * The panel already knows the current value, so the three silences stay
 * distinct: nothing has run yet, the message carries something a chart cannot
 * say anything about, or there is a series to draw.
 */
export function MessageSparkline({
  flow,
  name,
  dtype,
}: {
  flow: string
  name: string
  /** What the port declares, so a value that never arrived still says what it would be. */
  dtype?: DType
}) {
  const message = useSettled(name)
  const live = useLiveValue(qualify(flow, message))
  const { data } = useQuery(messageHistoryQueryOptions(flow, message))
  const [tail, setTail] = useState<HistoryPoint[]>([])

  // Pointing the field at another message makes the collected tail meaningless.
  // biome-ignore lint/correctness/useExhaustiveDependencies: the name is what invalidates the tail, not anything the effect reads.
  useEffect(() => {
    setTail((previous) => (previous.length ? [] : previous))
  }, [message])

  // Values keep arriving over the socket while the panel is open. Appending
  // them beats refetching the whole series on every emission.
  const ts = live?.ts
  const value = live?.value
  useEffect(() => {
    if (typeof value !== "number" || !ts) return
    setTail((previous) =>
      previous[previous.length - 1]?.ts === ts
        ? previous
        : [...previous, { ts, value }].slice(-WINDOW),
    )
  }, [ts, value])

  const fetched = data?.points ?? []
  // The fetch and the socket overlap; only what the server had not yet seen.
  const since = fetched[fetched.length - 1]?.ts ?? 0
  const points = [
    ...fetched,
    ...tail.filter((point) => point.ts > since),
  ].slice(-WINDOW)

  if (points.length === 0) {
    // Three silences, kept apart: nothing has run, or something arrived that
    // no curve can say anything about. The second is worth showing; the first
    // is worth admitting to in as few words as the row can spare.
    if (live === undefined) {
      // A dash rather than a sentence: one of these sits under every port, and
      // nine ports of "nothing has come through yet" is a panel of prose about
      // the absence of values. The row keeps its height either way, so nothing
      // shifts when the first one arrives.
      return (
        <p
          className="text-xs leading-5 text-muted-foreground"
          title="Nothing has come through yet"
        >
          —
        </p>
      )
    }
    return <ValuePreview value={live.value} dtype={dtype} />
  }

  // The value is live here, so the dot on the newest reading is earned. The
  // caption is on hover rather than beside the curve: these sit one per port
  // in a dense panel, and a line of prose each would crowd it out.
  return (
    <Tooltip>
      <TooltipTrigger asChild>
        <div>
          <Sparkline points={points} />
        </div>
      </TooltipTrigger>
      <TooltipContent>{caption(points)}</TooltipContent>
    </Tooltip>
  )
}