export const checkFiles = (images: string[], metadata: string[]) => {
  // Check images length is equal to metadata length
  if (images.length !== metadata.length) {
    throw Error('Images files must have matching number of metadata files')
  }

  function parseFileName(path: string | null): number {
    // Check file name is not null
    if (!path) {
      throw Error('File cannot be null')
    }

    // Extract fileName from path
    const fileName = path.match(
      /([a-zA-Z0-9\s_\\.\-:]+)(.png|.jpg|.gif|.json)?$/i
    )![1]

    // Check that file name is an Integer
    if (isNaN(parseInt(fileName, 10))) {
      throw Error('Filenames must be numbers. Invalid fileName: ' + fileName)
    }
    return parseInt(fileName, 10)
  }

  // We need to ensure that the files are numerically sorted (as opposed to lexicographically)
  const sortedImages = [...images.map(parseFileName)].sort(function (a, b) {
    return a - b
  })
  const sortedMetadata = [...metadata.map(parseFileName)].sort(function (a, b) {
    return a - b
  })
  let lastValue
  // Check each image is sequentially named with a number and has a matching metadata file
  for (let i = 0; i < sortedImages.length; i++) {
    const image = sortedImages[i]
    const json = sortedMetadata[i]
    if (image !== json) {
      throw Error('Images must have matching JSON files')
    }
    if (lastValue && lastValue + 1 !== image) {
      throw Error('Images must be sequential')
    }
    lastValue = image
  }
}