"use client"

import { createContext, useContext, useEffect, useState, useCallback, useMemo, useRef } from "react"
import {
  configuredBackendUrl,
  defaultDataSourceMode,
  isBackendUrlLocked,
  isMockDataSourceAvailable,
  LOCAL_DEFAULT_BACKEND_URL,
  resolveStoredBackendUrl,
} from "@/lib/backend-url"
import { getBackendHealth } from "@/shared/api/backend-health"

// ── types ─────────────────────────────────────────────────────────────────────

export type DataSourceMode = "mock" | "live"

/** Режим «Живые» в настройках: моковые данные не подставлять. */
export function isLiveDataSourceMode(mode: DataSourceMode): boolean {
  return mode === "live"
}

interface DataSourceContextValue {
  mode:          DataSourceMode
  setMode:       (m: DataSourceMode) => void
  backendUrl:    string
  setBackendUrl: (url: string) => void
  backendUrlLocked: boolean
  mockModeAvailable: boolean
  /** localStorage для mode/backendUrl применён на клиенте (после первого paint). */
  prefsHydrated: boolean
  /** undefined = не проверялось, true = OK, false = недоступен */
  backendStatus: boolean | undefined
  backendChecking: boolean
  checkBackend:  () => Promise<void>
}

// ── context ───────────────────────────────────────────────────────────────────

const DataSourceContext = createContext<DataSourceContextValue | null>(null)

const LS_MODE    = "routerlists:data-source"
const LS_BACKEND = "routerlists:backend-url"

function readStoredMode(): DataSourceMode {
  if (!isMockDataSourceAvailable()) return "live"
  if (typeof window === "undefined") return defaultDataSourceMode()
  const stored = localStorage.getItem(LS_MODE) as DataSourceMode | null
  if (stored === "live") return "live"
  if (stored === "mock") return "mock"
  return defaultDataSourceMode()
}

function initialBackendUrl(): string {
  if (typeof window === "undefined") {
    const cfg = configuredBackendUrl()
    if (cfg.kind === "same-origin") return ""
    if (cfg.kind === "fixed") return cfg.url
    return LOCAL_DEFAULT_BACKEND_URL
  }
  return resolveStoredBackendUrl(localStorage.getItem(LS_BACKEND))
}

function normalizeBackendUrl(url: string): string {
  return url.trim().replace(/\/$/, "")
}

export function DataSourceProvider({ children }: { children: React.ReactNode }) {
  const [mode, setModeState] = useState<DataSourceMode>(defaultDataSourceMode)
  const [backendUrl, setBackendUrlState] = useState(initialBackendUrl)
  const [prefsHydrated, setPrefsHydrated] = useState(false)
  const healthToken = useMemo(() => Symbol(backendUrl), [backendUrl])
  const [health, setHealth] = useState<{ token: symbol; value: boolean | undefined; checking: boolean }>(() => ({ token: healthToken, value: undefined, checking: false }))
  const backendStatus = health.token === healthToken ? health.value : undefined
  const backendChecking = health.token === healthToken && health.checking
  const healthSession = useRef<{token:symbol;active:boolean;revision:number;controller?:AbortController}>({token:healthToken,active:true,revision:0})
  useEffect(() => {
    const scope = {token:healthToken,active:true,revision:0,controller:undefined as AbortController | undefined}
    healthSession.current = scope
    return () => { scope.active = false; scope.controller?.abort() }
  }, [healthToken])
  const backendUrlLocked = isBackendUrlLocked()
  const mockModeAvailable = isMockDataSourceAvailable()

  useEffect(() => {
    let active = true
    queueMicrotask(() => {
      if (!active) return
      const storedMode = readStoredMode()
      const url = resolveStoredBackendUrl(localStorage.getItem(LS_BACKEND))
      setModeState(storedMode)
      setBackendUrlState(url)
      setPrefsHydrated(true)
    })
    return () => { active = false }
  }, [])

  const setMode = useCallback((m: DataSourceMode) => {
    if (!mockModeAvailable && m === "mock") return
    setModeState(m)
    localStorage.setItem(LS_MODE, m)
  }, [mockModeAvailable])

  const setBackendUrl = useCallback((url: string) => {
    if (backendUrlLocked) return
    const normalized = normalizeBackendUrl(url)
    setBackendUrlState(normalized)
    localStorage.setItem(LS_BACKEND, normalized)
  }, [backendUrlLocked])

  const checkBackend = useCallback(async () => {
    const scope = healthSession.current
    if (!scope.active || scope.token !== healthToken) return
    const revision = ++scope.revision
    scope.controller?.abort()
    const controller = new AbortController(); scope.controller = controller
    const current = () => scope.active && scope.revision === revision && !controller.signal.aborted
    setHealth({token:healthToken,value:undefined,checking:true})
    try {
      await getBackendHealth(backendUrl, controller.signal)
      if (current()) setHealth({token:healthToken,value:true,checking:false})
    } catch {
      if (current()) setHealth({token:healthToken,value:false,checking:false})
    }
  }, [backendUrl, healthToken])

  useEffect(() => {
    if (!prefsHydrated || mode !== "live") return
    queueMicrotask(() => { void checkBackend() })
  }, [prefsHydrated, mode, checkBackend])

  return (
    <DataSourceContext.Provider
      value={{ mode, setMode, backendUrl, setBackendUrl, backendUrlLocked, mockModeAvailable, prefsHydrated, backendStatus, backendChecking, checkBackend }}
    >
      {children}
    </DataSourceContext.Provider>
  )
}

export function useDataSource(): DataSourceContextValue {
  const ctx = useContext(DataSourceContext)
  if (!ctx) throw new Error("useDataSource must be used inside <DataSourceProvider>")
  return ctx
}