"use client"

import { useEffect, useState } from "react"
import { resolveApiUrl, withAuthHeaders } from "@/shared/api/http-client"

export interface TrafficLiveSample {
  rxMbps: number
  txMbps: number
  at: string
  timestampKind?: "backend-receipt"
}

function parseSseBlock(block: string): { event: string; data: string } {
  let event = "message"
  const dataLines: string[] = []
  for (const line of block.split(/\r?\n/)) {
    if (line.startsWith("event:")) event = line.slice(6).trim()
    else if (line.startsWith("data:")) dataLines.push(line.slice(5).trim())
  }
  return { event, data: dataLines.join("\n") }
}

export function useTrafficLive(opts: {
  enabled: boolean
  backendUrl: string
  serverId: string
  iface: string
  reloadKey?: number
}): { sample: TrafficLiveSample | null; error: string | null; receivedAt: number | null } {
  const scope = JSON.stringify([opts.backendUrl, opts.serverId, opts.iface])
  const key = JSON.stringify([opts.enabled, scope, opts.reloadKey ?? 0])
  const [result, setResult] = useState<{ key: string; scope: string; sample: TrafficLiveSample | null; receivedAt: number | null; error: string | null } | null>(null)

  useEffect(() => {
    if (!opts.enabled || !opts.serverId) return
    const ac = new AbortController()
    let lastStreamError: string | null = null
    // A new connection owns the status; the same device's previous sample remains historical.
    // eslint-disable-next-line react-hooks/set-state-in-effect
    setResult(previous => ({ key, scope, sample: previous?.scope === scope ? previous.sample : null,
      receivedAt: previous?.scope === scope ? previous.receivedAt : null, error: "Ожидание нового live-измерения" }))
    let sampleTimer: ReturnType<typeof setTimeout> | undefined
    const stopTimer = () => clearTimeout(sampleTimer)
    const setError = (error: string) => {
      lastStreamError = error
      stopTimer()
      if (!ac.signal.aborted) setResult(previous => ({ key, scope, sample: previous?.scope === scope ? previous.sample : null, receivedAt: previous?.scope === scope ? previous.receivedAt : null, error }))
    }
    const ifaceQ =
      opts.iface && opts.iface !== "__all__"
        ? `?iface=${encodeURIComponent(opts.iface)}`
        : ""
    const path = `/api/traffic/servers/${encodeURIComponent(opts.serverId)}/live${ifaceQ}`
    const url = resolveApiUrl(opts.backendUrl, path)
    // Backend ticks every 1.5–2s; tolerate several missed samples. Heartbeats do not reset this timer.
    const awaitSample = () => {
      stopTimer()
      sampleTimer = setTimeout(() => setError("Нет обновлений live более 15 секунд"), 15_000)
    }
    awaitSample()

    let buf = ""

    void (async () => {
      try {
        const res = await fetch(url, {
          headers: withAuthHeaders({ Accept: "text/event-stream" }),
          signal: ac.signal,
          credentials: "include",
        })
        if (ac.signal.aborted) return
        if (!res.ok || !res.body) {
          const body = await res.json().catch(() => null) as { error?: unknown } | null
          setError(`${typeof body?.error === "string" ? body.error : "Live-поток недоступен"} (HTTP ${res.status})`)
          return
        }
        const reader = res.body.getReader()
        const decoder = new TextDecoder()
        while (!ac.signal.aborted) {
          const { done, value } = await reader.read()
          if (ac.signal.aborted) return
          if (done) {
            setError(lastStreamError ?? "Поток live завершён")
            break
          }
          buf += decoder.decode(value, { stream: true })
          const parts = buf.split(/\r?\n\r?\n/)
          buf = parts.pop() ?? ""
          for (const raw of parts) {
            if (!raw.trim()) continue
            const ev = parseSseBlock(raw)
            if (ev.event === "sample" && ev.data) {
              const parsed = JSON.parse(ev.data) as TrafficLiveSample
              if (!parsed || !Number.isFinite(parsed.rxMbps) || !Number.isFinite(parsed.txMbps) || parsed.rxMbps < 0 || parsed.txMbps < 0 || typeof parsed.at !== "string" || !Number.isFinite(Date.parse(parsed.at)) || parsed.timestampKind !== undefined && parsed.timestampKind !== "backend-receipt") {
                throw new Error("Некорректные данные live-потока")
              }
              awaitSample()
              lastStreamError = null
              setResult({ key, scope, sample: parsed, receivedAt: Date.now(), error: null })
            } else if (ev.event === "error" && ev.data) {
              const parsed = JSON.parse(ev.data) as { error?: unknown } | null
              setError(typeof parsed?.error === "string" ? parsed.error : "Некорректный ответ об ошибке live-потока")
            }
          }
        }
      } catch (e) {
        if (ac.signal.aborted) return
        setError(e instanceof Error ? e.message : "live error")
      } finally {
        stopTimer()
        ac.abort()
      }
    })()

    return () => { stopTimer(); ac.abort() }
  }, [opts.enabled, opts.backendUrl, opts.serverId, opts.iface, key, scope])

  return opts.enabled && result?.scope === scope ? { sample: result.sample, error: result.key === key ? result.error : "Ожидание нового live-измерения", receivedAt: result.receivedAt } : { sample: null, error: null, receivedAt: null }
}