text: 'use strict'
  
  const Buffer = require('safe-buffer').Buffer
  
  const crypto = require('crypto')
  const Transform = require('stream').Transform
  
  const SPEC_ALGORITHMS = ['sha256', 'sha384', 'sha512']
  
  const BASE64_REGEX = /^[a-z0-9+/]+(?:=?=?)$/i
  const SRI_REGEX = /^([^-]+)-([^?]+)([?\S*]*)$/
  const STRICT_SRI_REGEX = /^([^-]+)-([A-Za-z0-9+/]+(?:=?=?))([?\x21-\x7E]*)$/
  const VCHAR_REGEX = /^[\x21-\x7E]+$/
  
  class Hash {
    get isHash () { return true }
    constructor (hash, opts) {
      const strict = !!(opts && opts.strict)
      this.source = hash.trim()
      // 3.1. Integrity metadata (called "Hash" by ssri)
      // https://w3c.github.io/webappsec-subresource-integrity/#integrity-metadata-description
      const match = this.source.match(
        strict
        ? STRICT_SRI_REGEX
        : SRI_REGEX
      )
      if (!match) { return }
      if (strict && !SPEC_ALGORITHMS.some(a => a === match[1])) { return }
      this.algorithm = match[1]
      this.digest = match[2]
  
      const rawOpts = match[3]
      this.options = rawOpts ? rawOpts.slice(1).split('?') : []
    }
    hexDigest () {
      return this.digest && Buffer.from(this.digest, 'base64').toString('hex')
    }
    toJSON () {
      return this.toString()
    }
    toString (opts) {
      if (opts && opts.strict) {
        // Strict mode enforces the standard as close to the foot of the
        // letter as it can.
        if (!(
          // The spec has very restricted productions for algorithms.
          // https://www.w3.org/TR/CSP2/#source-list-syntax
          SPEC_ALGORITHMS.some(x => x === this.algorithm) &&
          // Usually, if someone insists on using a "different" base64, we
          // leave it as-is, since there's multiple standards, and the
          // specified is not a URL-safe variant.
          // https://www.w3.org/TR/CSP2/#base64_value
          this.digest.match(BASE64_REGEX) &&
          // Option syntax is strictly visual chars.
          // https://w3c.github.io/webappsec-subresource-integrity/#grammardef-option-expression
          // https://tools.ietf.org/html/rfc5234#appendix-B.1
          (this.options || []).every(opt => opt.match(VCHAR_REGEX))
        )) {
          return ''
        }
      }
      const options = this.options && this.options.length
      ? `?${this.options.join('?')}`
      : ''
      return `${this.algorithm}-${this.digest}${options}`
    }
  }
  
  class Integrity {
    get isIntegrity () { return true }
    toJSON () {
      return this.toString()
    }
    toString (opts) {
      opts = opts || {}
      let sep = opts.sep || ' '
      if (opts.strict) {
        // Entries must be separated by whitespace, according to spec.
        sep = sep.replace(/\S+/g, ' ')
      }
      return Object.keys(this).map(k => {
        return this[k].map(hash => {
          return Hash.prototype.toString.call(hash, opts)
        }).filter(x => x.length).join(sep)
      }).filter(x => x.length).join(sep)
    }
    concat (integrity, opts) {
      const other = typeof integrity === 'string'
      ? integrity
      : stringify(integrity, opts)
      return parse(`${this.toString(opts)} ${other}`, opts)
    }
    hexDigest () {
      return parse(this, {single: true}).hexDigest()
    }
    pickAlgorithm (opts) {
      const pickAlgorithm = (opts && opts.pickAlgorithm) || getPrioritizedHash
      const keys = Object.keys(this)
      if (!keys.length) {
        throw new Error(`No algorithms available for ${
          JSON.stringify(this.toString())
        }`)
      }
      return keys.reduce((acc, algo) => {
        return pickAlgorithm(acc, algo) || acc
      })
    }
  }
  
  module.exports.parse = parse
  function parse (sri, opts) {
    opts = opts || {}
    if (typeof sri === 'string') {
      return _parse(sri, opts)
    } else if (sri.algorithm && sri.digest) {
      const fullSri = new Integrity()
      fullSri[sri.algorithm] = [sri]
      return _parse(stringify(fullSri, opts), opts)
    } else {
      return _parse(stringify(sri, opts), opts)
    }
  }
  
  function _parse (integrity, opts) {
    // 3.4.3. Parse metadata
    // https://w3c.github.io/webappsec-subresource-integrity/#parse-metadata
    if (opts.single) {
      return new Hash(integrity, opts)
    }
    return integrity.trim().split(/\s+/).reduce((acc, string) => {
      const hash = new Hash(string, opts)
      if (hash.algorithm && hash.digest) {
        const algo = hash.algorithm
        if (!acc[algo]) { acc[algo] = [] }
        acc[algo].push(hash)
      }
      return acc
    }, new Integrity())
  }
  
  module.exports.stringify = stringify
  function stringify (obj, opts) {
    if (obj.algorithm && obj.digest) {
      return Hash.prototype.toString.call(obj, opts)
    } else if (typeof obj === 'string') {
      return stringify(parse(obj, opts), opts)
    } else {
      return Integrity.prototype.toString.call(obj, opts)
    }
  }
  
  module.exports.fromHex = fromHex
  function fromHex (hexDigest, algorithm, opts) {
    const optString = (opts && opts.options && opts.options.length)
    ? `?${opts.options.join('?')}`
    : ''
    return parse(
      `${algorithm}-${
        Buffer.from(hexDigest, 'hex').toString('base64')
      }${optString}`, opts
    )
  }
  
  module.exports.fromData = fromData
  function fromData (data, opts) {
    opts = opts || {}
    const algorithms = opts.algorithms || ['sha512']
    const optString = opts.options && opts.options.length
    ? `?${opts.options.join('?')}`
    : ''
    return algorithms.reduce((acc, algo) => {
      const digest = crypto.createHash(algo).update(data).digest('base64')
      const hash = new Hash(
        `${algo}-${digest}${optString}`,
         opts
      )
      if (hash.algorithm && hash.digest) {
        const algo = hash.algorithm
        if (!acc[algo]) { acc[algo] = [] }
        acc[algo].push(hash)
      }
      return acc
    }, new Integrity())
  }
  
  module.exports.fromStream = fromStream
  function fromStream (stream, opts) {
    opts = opts || {}
    const P = opts.Promise || Promise
    const istream = integrityStream(opts)
    return new P((resolve, reject) => {
      stream.pipe(istream)
      stream.on('error', reject)
      istream.on('error', reject)
      let sri
      istream.on('integrity', s => { sri = s })
      istream.on('end', () => resolve(sri))
      istream.on('data', () => {})
    })
  }
  
  module.exports.checkData = checkData
  function checkData (data, sri, opts) {
    opts = opts || {}
    sri = parse(sri, opts)
    if (!Object.keys(sri).length) { return false }
    const algorithm = sri.pickAlgorithm(opts)
    const digests = sri[algorithm] || []
    const digest = crypto.createHash(algorithm).update(data).digest('base64')
    return digests.find(hash => hash.digest === digest) || false
  }
  
  module.exports.checkStream = checkStream
  function checkStream (stream, sri, opts) {
    opts = opts || {}
    const P = opts.Promise || Promise
    const checker = integrityStream({
      integrity: sri,
      size: opts.size,
      strict: opts.strict,
      pickAlgorithm: opts.pickAlgorithm
    })
    return new P((resolve, reject) => {
      stream.pipe(checker)
      stream.on('error', reject)
      checker.on('error', reject)
      let sri
      checker.on('verified', s => { sri = s })
      checker.on('end', () => resolve(sri))
      checker.on('data', () => {})
    })
  }
  
  module.exports.integrityStream = integrityStream
  function integrityStream (opts) {
    opts = opts || {}
    // For verification
    const sri = opts.integrity && parse(opts.integrity, opts)
    const goodSri = sri && Object.keys(sri).length
    const algorithm = goodSri && sri.pickAlgorithm(opts)
    const digests = goodSri && sri[algorithm]
    // Calculating stream
    const algorithms = opts.algorithms || [algorithm || 'sha512']
    const hashes = algorithms.map(crypto.createHash)
    let streamSize = 0
    const stream = new Transform({
      transform (chunk, enc, cb) {
        streamSize += chunk.length
        hashes.forEach(h => h.update(chunk, enc))
        cb(null, chunk, enc)
      }
    }).on('end', () => {
      const optString = (opts.options && opts.options.length)
      ? `?${opts.options.join('?')}`
      : ''
      const newSri = parse(hashes.map((h, i) => {
        return `${algorithms[i]}-${h.digest('base64')}${optString}`
      }).join(' '), opts)
      const match = (
        // Integrity verification mode
        opts.integrity &&
        digests &&
        digests.find(hash => {
          return newSri[algorithm].find(newhash => {
            return hash.digest === newhash.digest
          })
        })
      )
      if (typeof opts.size === 'number' && streamSize !== opts.size) {
        const err = new Error(`stream size mismatch when checking ${sri}.\n  Wanted: ${opts.size}\n  Found: ${streamSize}`)
        err.code = 'EBADSIZE'
        err.found = streamSize
        err.expected = opts.size
        err.sri = sri
        stream.emit('error', err)
      } else if (opts.integrity && !match) {
        const err = new Error(`${sri} integrity checksum failed when using ${algorithm}: wanted ${digests} but got ${newSri}. (${streamSize} bytes)`)
        err.code = 'EINTEGRITY'
        err.found = newSri
        err.expected = digests
        err.algorithm = algorithm
        err.sri = sri
        stream.emit('error', err)
      } else {
        stream.emit('size', streamSize)
        stream.emit('integrity', newSri)
        match && stream.emit('verified', match)
      }
    })
    return stream
  }
  
  module.exports.create = createIntegrity
  function createIntegrity (opts) {
    opts = opts || {}
    const algorithms = opts.algorithms || ['sha512']
    const optString = opts.options && opts.options.length
    ? `?${opts.options.join('?')}`
    : ''
  
    const hashes = algorithms.map(crypto.createHash)
  
    return {
      update: function (chunk, enc) {
        hashes.forEach(h => h.update(chunk, enc))
        return this
      },
      digest: function (enc) {
        const integrity = algorithms.reduce((acc, algo) => {
          const digest = hashes.shift().digest('base64')
          const hash = new Hash(
            `${algo}-${digest}${optString}`,
            opts
          )
          if (hash.algorithm && hash.digest) {
            const algo = hash.algorithm
            if (!acc[algo]) { acc[algo] = [] }
            acc[algo].push(hash)
          }
          return acc
        }, new Integrity())
  
        return integrity
      }
    }
  }
  
  // This is a Best Effort™ at a reasonable priority for hash algos
  const DEFAULT_PRIORITY = [
    'md5', 'whirlpool', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512'
  ]
  function getPrioritizedHash (algo1, algo2) {
    return DEFAULT_PRIORITY.indexOf(algo1.toLowerCase()) >= DEFAULT_PRIORITY.indexOf(algo2.toLowerCase())
    ? algo1
    : algo2
  }
  