import { writable } from 'svelte/store'

export interface OikosEvent {
  id: number
  ts: string
  type: string
  entity_id?: string | null
  severity: 'info' | 'warning' | 'critical'
  source: string
  data?: unknown
  correlation_id?: string | null
}

const MAX_BUFFERED = 200

export const liveEvents = writable<OikosEvent[]>([])
export const connectionState = writable<'connecting' | 'open' | 'closed'>('connecting')

let source: EventSource | null = null
let subscriberCount = 0

function connect() {
  if (source) return
  connectionState.set('connecting')
  // The browser's EventSource sends Last-Event-ID automatically on reconnect.
  source = new EventSource('/api/v1/events/stream')

  source.onopen = () => connectionState.set('open')

  source.onmessage = (ev) => {
    try {
      const parsed: OikosEvent = JSON.parse(ev.data)
      liveEvents.update((events) => [parsed, ...events].slice(0, MAX_BUFFERED))
    } catch {
      // skip malformed
    }
  }

  source.onerror = () => {
    connectionState.set('closed')
  }
}

function disconnect() {
  source?.close()
  source = null
}

// Reference-counted: the stream stays open as long as at least one page subscribes.
export function subscribeEvents(): () => void {
  subscriberCount++
  if (subscriberCount === 1) connect()
  return () => {
    subscriberCount--
    if (subscriberCount === 0) disconnect()
  }
}