import type {SanityDocument} from '../types.js'

interface IdAccumulator {
  seen: string[]
  duplicates: string[]
}

function reduceDuplicateIds(ids: IdAccumulator, doc: SanityDocument): IdAccumulator {
  if (!doc._id) {
    return ids
  }

  if (ids.seen.includes(doc._id)) {
    ids.duplicates.push(doc._id)
  } else {
    ids.seen.push(doc._id)
  }

  return ids
}

export function ensureUniqueIds(documents: SanityDocument[]): void {
  const {duplicates} = documents.reduce(reduceDuplicateIds, {
    seen: [],
    duplicates: [],
  })

  const numDupes = duplicates.length
  if (numDupes === 0) {
    return
  }

  throw new Error(
    `Found ${numDupes} duplicate IDs in the source file:\n- ${duplicates.join('\n- ')}`,
  )
}