file-commons/src/isValidFileName.ts

const EXTENSION_DELIMITER = '.'
const MULTIPLE_VALID_EXTENSION_DELIMITER = ' '

export type IsValidFilenameConfig = {
  validExtensions: string | string[]
  allowMultipleExtensions?: boolean
}

type IsValidFileName = (config: IsValidFilenameConfig) => (maybeFileName: string) => boolean

const isValidFileName: IsValidFileName = config => {
  let validExtensionsArray: string[]
  const maybeValidExtensions = config.validExtensions as unknown
  if (typeof maybeValidExtensions === 'string') {
    validExtensionsArray = (config.validExtensions as string)
      .split(MULTIPLE_VALID_EXTENSION_DELIMITER)
      .filter(p => p.trim().length > 0)
  } else if (
    Array.isArray(maybeValidExtensions)
    && (config.validExtensions as unknown[]).every(s => typeof s === 'string')
  ) {
    if ((config.validExtensions as unknown[]).length < 1) {
      throw RangeError('There must be at least 1 valid extension defined.')
    }
    validExtensionsArray = config.validExtensions as string[]
  } else {
    throw TypeError('Valid extensions should be a space-delimited string or a string array.')
  }

  // strip . in valid extensions for easier matching
  const validExtensions = validExtensionsArray.map(e => (
    e.startsWith(EXTENSION_DELIMITER)
      ? e.slice(EXTENSION_DELIMITER.length)
      : e
  ))

  return maybeFileName => {
    if (typeof maybeFileName as unknown !== 'string') {
      throw TypeError('Argument should be a string.')
    }

    const fileName = maybeFileName as string
    const [, ...extensions] = fileName.split(EXTENSION_DELIMITER)

    if (config.allowMultipleExtensions) {
      return validExtensions.reduce<boolean>(
        (isValid, validExtension) => (
          isValid
          || extensions.includes(validExtension)
        ),
        false
      )
    }

    return validExtensions.reduce<boolean>(
      (isValid, validExtension) => (
        isValid
        || extensions.join(EXTENSION_DELIMITER).endsWith(validExtension)
      ),
      false
    )
  }
}

export default isValidFileName