import { safeFetchJson, SOURCE_LIMITS } from './safe-fetch.js'

/** Fully collect bounded cursor pages. Never accept an incomplete snapshot. */
export async function fetchEvobgpPages(base: string, token: string, path: string, limit: number): Promise<Record<string, unknown>[]> {
  const pages: Record<string, unknown>[] = []
  const seen = new Set<string>()
  let cursor: string | undefined
  let elements = 0
  let bytes = 0
  const deadline = Date.now() + SOURCE_LIMITS.timeoutMs
  for (let page = 0; page < SOURCE_LIMITS.pages; page++) {
    if (Date.now() >= deadline) throw new Error('EvoBGP snapshot deadline exceeded')
    if (bytes >= SOURCE_LIMITS.totalBytes) throw new Error('EvoBGP snapshot byte limit exceeded')
    const url = new URL(`${base.replace(/\/$/, '')}${path}`)
    url.searchParams.set('limit', String(limit))
    if (cursor) url.searchParams.set('cursor', cursor)
    const response = await safeFetchJson(url, {
      headers: { Authorization: `Bearer ${token}`, Accept: 'application/json' },
      timeoutMs: deadline - Date.now(),
      maxBytes: Math.min(SOURCE_LIMITS.bytes, SOURCE_LIMITS.totalBytes - bytes),
    })
    const data = response.data
    bytes += response.bytes
    if (bytes > SOURCE_LIMITS.totalBytes) throw new Error('EvoBGP snapshot byte limit exceeded')
    if (!data || typeof data !== 'object' || Array.isArray(data)) throw new Error('Invalid EvoBGP page')
    const body = data as Record<string, unknown>
    const items = body.prefixes ?? body.items
    if (!Array.isArray(items)) throw new Error('Invalid EvoBGP page items')
    elements += items.length
    if (elements > SOURCE_LIMITS.elements) throw new Error('EvoBGP snapshot element limit exceeded')
    if (body.has_more !== undefined && typeof body.has_more !== 'boolean') throw new Error('Invalid EvoBGP has_more')
    if (body.next_cursor !== undefined && body.next_cursor !== null && (typeof body.next_cursor !== 'string' || body.next_cursor.length > 2048)) throw new Error('Invalid EvoBGP next_cursor')
    pages.push(body)
    if (body.has_more !== true && !body.next_cursor) return pages
    const next = body.next_cursor
    if (typeof next !== 'string' || !next || seen.has(next)) throw new Error('Incomplete or repeated EvoBGP cursor')
    seen.add(next)
    cursor = next
  }
  throw new Error('EvoBGP page limit exceeded')
}