snap-shot/src/file-system.js

'use strict'

const fs = require('fs')
const path = require('path')
const diff = require('variable-diff')
const disparity = require('disparity')
const debug = require('debug')('snap-shot')
const la = require('lazy-ass')
const is = require('check-more-types')
const mkdirp = require('mkdirp')
const vm = require('vm')

const cwd = process.cwd()
const fromCurrentFolder = path.relative.bind(null, cwd)
const snapshotsFolder = fromCurrentFolder('__snapshots__')

function loadSnaps (snapshotPath) {
  const full = require.resolve(snapshotPath)
  if (!fs.existsSync(snapshotPath)) {
    return {}
  }

  const sandbox = {
    exports: {}
  }
  const source = fs.readFileSync(full, 'utf8')
  try {
    vm.runInNewContext(source, sandbox)
    return sandbox.exports
  } catch (e) {
    console.error('Could not load file', full)
    console.error(source)
    console.error(e)
    return {}
  }
}

function fileForSpec (specFile) {
  const specName = path.basename(specFile)
  const filename = path.join(snapshotsFolder, specName + '.snap-shot')
  return path.resolve(filename)
}

function loadSnapshots (specFile) {
  la(is.unemptyString(specFile), 'missing specFile name', specFile)
  const filename = fileForSpec(specFile)
  debug('loading snapshots from %s', filename)
  let snapshots = {}
  if (fs.existsSync(filename)) {
    snapshots = loadSnaps(filename)
  } else {
    debug('could not find snapshots file %s', filename)
  }
  return snapshots
}

function saveSnapshots (specFile, snapshots) {
  mkdirp.sync(snapshotsFolder)
  const filename = fileForSpec(specFile)
  const specRelativeName = fromCurrentFolder(specFile)
  debug('saving snapshots into %s for %s', filename, specRelativeName)

  let s = ''
  Object.keys(snapshots).forEach(testName => {
    const value = snapshots[testName]
    const serialized = JSON.stringify(value, null, 2)
    s += `exports['${testName}'] = ${serialized}\n\n`
  })
  fs.writeFileSync(filename, s, 'utf8')
  return snapshots
}

const isMultiLineText = s => is.string(s) && s.includes('\n')
const areStrings = (s, t) => is.string(s) && is.string(t)
const compareAsStrings = (s, t) => areStrings(s, t) &&
  (isMultiLineText(s) || isMultiLineText(t))

function compareText (expected, value) {
  const textDiff = disparity.unified(expected, value)
  if (!textDiff) {
    return {changed: false}
  }
  return {
    changed: true,
    text: textDiff
  }
}

const compareObjects = diff

function raiseIfDifferent ({value, expected, specName}) {
  const diffed = compareAsStrings(value, expected)
    ? compareText(expected + '\n', value + '\n')
    : compareObjects(expected, value)
  if (diffed.changed) {
    const text = diffed.text
    debug('Test "%s" snapshot difference', specName)
    const msg = `snapshot difference\n${text}`
    console.log(msg)
    throw new Error(msg)
  }
}

module.exports = {
  readFileSync: fs.readFileSync,
  fromCurrentFolder,
  loadSnapshots,
  saveSnapshots,
  raiseIfDifferent
}