mutation.js

const chalk = require('chalk')
const jsdiff = require('diff')
const fs = require('fs')
const sha1 = require('sha1')
const config = require('./config')

const baselineDir = config.baselineDir
const contractsDir = config.contractsDir

function splice(str, start, length, replacement) {
  return str.substring(0, start) + replacement + str.substring(start + length)
}

function Mutation(file, start, end, replace) {
  this.file = file
  this.start = start
  this.end = end
  this.replace = replace
}

Mutation.prototype.hash = function() {
  const input = [this.file, this.start, this.end, this.replace].join(':')
  return sha1(input).slice(0, 8)
}

Mutation.prototype.apply = function() {
  const original = fs.readFileSync(this.file, 'utf8')
  const mutated = this.applyToString(original)

  fs.writeFileSync(this.file, mutated, 'utf8')
}

Mutation.prototype.applyToString = function(original) {
  return splice(original, this.start, this.end - this.start, this.replace)
}

Mutation.prototype.restore = function() {
  const baseline = this.baseline()

  console.log('Restoring ' + this.file)

  const original = fs.readFileSync(baseline, 'utf8')
  fs.writeFileSync(this.file, original, 'utf8')
}

Mutation.prototype.baseline = function() {
  return baselineDir + this.file.substr(contractsDir.length)
}

Mutation.prototype.diff = function() {
  const original = fs.readFileSync(this.baseline(), 'utf8')
  const mutated = this.applyToString(original)

  let diff = jsdiff.diffLines(original, mutated)
  const lineNumber = this.getLineNumber()
  const context = 2

  diff = diff
    .filter(part => part.added || part.removed)
    .map(function(part) {
      // green for additions, red for deletions
      // grey for common parts
      const color = part.added ? 'green' : part.removed ? 'red' : 'grey'

      let num
      if (part.removed) {
        num = lineNumber.toString().padStart(4)
        num = chalk.gray(num + ' | ')
      } else {
        num = chalk.gray('     | ')
      }

      return num + chalk[color](part.value.replace(/\n$/, ''))
    })

  let lines = mutated.split('\n').map((line, i) => {
    const num = (i + 1).toString().padStart(4)
    return chalk.gray(num + ' | ' + line)
  })

  lines.splice(lineNumber - 1, 1, diff[0], diff[1])

  lines = lines.slice(Math.max(0, lineNumber - context - 1), lineNumber + context + 1)

  return lines.join('\n') + '\n'
}

Mutation.prototype.getLineNumber = function() {
  const source = fs.readFileSync(this.baseline(), 'utf8')
  const indexes = []

  for (let i = 0; i < source.length; i++) {
    if (source[i] == '\n') {
      indexes.push(i)
    }
  }

  return indexes.findIndex(idx => idx > this.start) + 1
}

Mutation.prototype.patch = function() {
  const original = fs.readFileSync(this.baseline(), 'utf8')
  const mutated = this.applyToString(original)

  return jsdiff.createPatch(this.file, original, mutated)
}

module.exports = Mutation