import escapeStringRegexp from 'escape-string-regexp'

export function exampleMatchesRegex(example, regex) {
  const { title, keywords } = example
  const haystack = [title].concat(keywords).join(' ')
  return regex.test(haystack)
}

export function predicateFromQuery(query) {
  if (query) {
    const escaped = escapeStringRegexp(query)
    const regex = new RegExp(escaped, 'i') // Case-insensitive.
    return example => exampleMatchesRegex(example, regex)
  } else {
    return () => true
  }
}

export function mapExamples(categories, iteratee) {
  return (
    categories
      .map(({ category, examples }) => ({
        category,
        examples: iteratee(examples),
      }))
      // Remove empty categories.
      .filter(({ category, examples }) => examples.length > 0)
  )
}

export function prepareExamples(categories, predicateProvider) {
  let nextKey = 0
  return mapExamples(categories, examples =>
    examples.map(example =>
      Object.assign(
        {
          shouldDisplay: () => predicateProvider()(example),
          // Assign each example a unique ID.
          key: nextKey++,
        },
        example
      )
    )
  )
}