import { useEffect, useState } from 'react'
import { useAuthStore } from '@/store/authStore'

const SOON_MS = 5 * 60 * 1000 // 5 minutes

export type ExpiryWarning = 'none' | 'soon' | 'now'
export type ExpiryReason = 'idle' | 'absolute'

interface ExpiryState {
  idleExpiresAt: Date | null
  absoluteExpiresAt: Date | null
  warning: ExpiryWarning
  /**
   * Which window is the closer (and therefore the active) deadline. Used by
   * SessionExpiryToast to pick the right copy + action button: idle gets
   * "Stay signed in" (calls /auth/refresh); absolute is informational only.
   */
  reason: ExpiryReason | null
}

function computeState(token: ReturnType<typeof useAuthStore.getState>['token']): ExpiryState {
  const idleStr = token?.idle_expires_at
  const absStr = token?.absolute_expires_at
  if (!idleStr || !absStr) {
    return { idleExpiresAt: null, absoluteExpiresAt: null, warning: 'none', reason: null }
  }
  const idle = new Date(idleStr)
  const abs = new Date(absStr)
  const now = Date.now()
  const idleMs = idle.getTime() - now
  const absMs = abs.getTime() - now

  // Closer window wins.
  const reason: ExpiryReason = idleMs <= absMs ? 'idle' : 'absolute'
  const closestMs = Math.min(idleMs, absMs)

  let warning: ExpiryWarning = 'none'
  if (closestMs <= 0) warning = 'now'
  else if (closestMs <= SOON_MS) warning = 'soon'

  return { idleExpiresAt: idle, absoluteExpiresAt: abs, warning, reason }
}

/**
 * Track how close the active session is to its idle/absolute deadline.
 *
 * Returns `warning: "soon"` within 5 min of whichever window comes first,
 * and `reason: "idle" | "absolute"` so callers can choose the right UX
 * (idle is recoverable via /auth/refresh; absolute is not). Re-evaluates
 * every 30 seconds while authenticated; cheap (single Date subtraction).
 *
 * See docs/plans/2026-05-13-session-expiration-policy.md §4.8.
 */
export function useAuthSessionExpiry(): ExpiryState {
  const token = useAuthStore((s) => s.token)
  const [state, setState] = useState<ExpiryState>(() => computeState(token))

  useEffect(() => {
    setState(computeState(token))
    if (!token?.idle_expires_at || !token?.absolute_expires_at) return
    const interval = window.setInterval(() => setState(computeState(token)), 30_000)
    return () => window.clearInterval(interval)
  }, [token])

  return state
}