var aws4 = exports,
      url = require('url'),
      querystring = require('querystring'),
      crypto = require('crypto'),
      lru = require('./lru'),
      credentialsCache = lru(1000)
  
  // http://docs.amazonwebservices.com/general/latest/gr/signature-version-4.html
  
  function hmac(key, string, encoding) {
    return crypto.createHmac('sha256', key).update(string, 'utf8').digest(encoding)
  }
  
  function hash(string, encoding) {
    return crypto.createHash('sha256').update(string, 'utf8').digest(encoding)
  }
  
  // This function assumes the string has already been percent encoded
  function encodeRfc3986(urlEncodedString) {
    return urlEncodedString.replace(/[!'()*]/g, function(c) {
      return '%' + c.charCodeAt(0).toString(16).toUpperCase()
    })
  }
  
  // request: { path | body, [host], [method], [headers], [service], [region] }
  // credentials: { accessKeyId, secretAccessKey, [sessionToken] }
  function RequestSigner(request, credentials) {
  
    if (typeof request === 'string') request = url.parse(request)
  
    var headers = request.headers = (request.headers || {}),
        hostParts = this.matchHost(request.hostname || request.host || headers.Host || headers.host)
  
    this.request = request
    this.credentials = credentials || this.defaultCredentials()
  
    this.service = request.service || hostParts[0] || ''
    this.region = request.region || hostParts[1] || 'us-east-1'
  
    // SES uses a different domain from the service name
    if (this.service === 'email') this.service = 'ses'
  
    if (!request.method && request.body)
      request.method = 'POST'
  
    if (!headers.Host && !headers.host) {
      headers.Host = request.hostname || request.host || this.createHost()
  
      // If a port is specified explicitly, use it as is
      if (request.port)
        headers.Host += ':' + request.port
    }
    if (!request.hostname && !request.host)
      request.hostname = headers.Host || headers.host
  
    this.isCodeCommitGit = this.service === 'codecommit' && request.method === 'GIT'
  }
  
  RequestSigner.prototype.matchHost = function(host) {
    var match = (host || '').match(/([^\.]+)\.(?:([^\.]*)\.)?amazonaws\.com$/)
    var hostParts = (match || []).slice(1, 3)
  
    // ES's hostParts are sometimes the other way round, if the value that is expected
    // to be region equals ‘es’ switch them back
    // e.g. search-cluster-name-aaaa00aaaa0aaa0aaaaaaa0aaa.us-east-1.es.amazonaws.com
    if (hostParts[1] === 'es')
      hostParts = hostParts.reverse()
  
    return hostParts
  }
  
  // http://docs.aws.amazon.com/general/latest/gr/rande.html
  RequestSigner.prototype.isSingleRegion = function() {
    // Special case for S3 and SimpleDB in us-east-1
    if (['s3', 'sdb'].indexOf(this.service) >= 0 && this.region === 'us-east-1') return true
  
    return ['cloudfront', 'ls', 'route53', 'iam', 'importexport', 'sts']
      .indexOf(this.service) >= 0
  }
  
  RequestSigner.prototype.createHost = function() {
    var region = this.isSingleRegion() ? '' :
          (this.service === 's3' && this.region !== 'us-east-1' ? '-' : '.') + this.region,
        service = this.service === 'ses' ? 'email' : this.service
    return service + region + '.amazonaws.com'
  }
  
  RequestSigner.prototype.prepareRequest = function() {
    this.parsePath()
  
    var request = this.request, headers = request.headers, query
  
    if (request.signQuery) {
  
      this.parsedPath.query = query = this.parsedPath.query || {}
  
      if (this.credentials.sessionToken)
        query['X-Amz-Security-Token'] = this.credentials.sessionToken
  
      if (this.service === 's3' && !query['X-Amz-Expires'])
        query['X-Amz-Expires'] = 86400
  
      if (query['X-Amz-Date'])
        this.datetime = query['X-Amz-Date']
      else
        query['X-Amz-Date'] = this.getDateTime()
  
      query['X-Amz-Algorithm'] = 'AWS4-HMAC-SHA256'
      query['X-Amz-Credential'] = this.credentials.accessKeyId + '/' + this.credentialString()
      query['X-Amz-SignedHeaders'] = this.signedHeaders()
  
    } else {
  
      if (!request.doNotModifyHeaders && !this.isCodeCommitGit) {
        if (request.body && !headers['Content-Type'] && !headers['content-type'])
          headers['Content-Type'] = 'application/x-www-form-urlencoded; charset=utf-8'
  
        if (request.body && !headers['Content-Length'] && !headers['content-length'])
          headers['Content-Length'] = Buffer.byteLength(request.body)
  
        if (this.credentials.sessionToken && !headers['X-Amz-Security-Token'] && !headers['x-amz-security-token'])
          headers['X-Amz-Security-Token'] = this.credentials.sessionToken
  
        if (this.service === 's3' && !headers['X-Amz-Content-Sha256'] && !headers['x-amz-content-sha256'])
          headers['X-Amz-Content-Sha256'] = hash(this.request.body || '', 'hex')
  
        if (headers['X-Amz-Date'] || headers['x-amz-date'])
          this.datetime = headers['X-Amz-Date'] || headers['x-amz-date']
        else
          headers['X-Amz-Date'] = this.getDateTime()
      }
  
      delete headers.Authorization
      delete headers.authorization
    }
  }
  
  RequestSigner.prototype.sign = function() {
    if (!this.parsedPath) this.prepareRequest()
  
    if (this.request.signQuery) {
      this.parsedPath.query['X-Amz-Signature'] = this.signature()
    } else {
      this.request.headers.Authorization = this.authHeader()
    }
  
    this.request.path = this.formatPath()
  
    return this.request
  }
  
  RequestSigner.prototype.getDateTime = function() {
    if (!this.datetime) {
      var headers = this.request.headers,
        date = new Date(headers.Date || headers.date || new Date)
  
      this.datetime = date.toISOString().replace(/[:\-]|\.\d{3}/g, '')
  
      // Remove the trailing 'Z' on the timestamp string for CodeCommit git access
      if (this.isCodeCommitGit) this.datetime = this.datetime.slice(0, -1)
    }
    return this.datetime
  }
  
  RequestSigner.prototype.getDate = function() {
    return this.getDateTime().substr(0, 8)
  }
  
  RequestSigner.prototype.authHeader = function() {
    return [
      'AWS4-HMAC-SHA256 Credential=' + this.credentials.accessKeyId + '/' + this.credentialString(),
      'SignedHeaders=' + this.signedHeaders(),
      'Signature=' + this.signature(),
    ].join(', ')
  }
  
  RequestSigner.prototype.signature = function() {
    var date = this.getDate(),
        cacheKey = [this.credentials.secretAccessKey, date, this.region, this.service].join(),
        kDate, kRegion, kService, kCredentials = credentialsCache.get(cacheKey)
    if (!kCredentials) {
      kDate = hmac('AWS4' + this.credentials.secretAccessKey, date)
      kRegion = hmac(kDate, this.region)
      kService = hmac(kRegion, this.service)
      kCredentials = hmac(kService, 'aws4_request')
      credentialsCache.set(cacheKey, kCredentials)
    }
    return hmac(kCredentials, this.stringToSign(), 'hex')
  }
  
  RequestSigner.prototype.stringToSign = function() {
    return [
      'AWS4-HMAC-SHA256',
      this.getDateTime(),
      this.credentialString(),
      hash(this.canonicalString(), 'hex'),
    ].join('
  ')
  }
  
  RequestSigner.prototype.canonicalString = function() {
    if (!this.parsedPath) this.prepareRequest()
  
    var pathStr = this.parsedPath.path,
        query = this.parsedPath.query,
        headers = this.request.headers,
        queryStr = '',
        normalizePath = this.service !== 's3',
        decodePath = this.service === 's3' || this.request.doNotEncodePath,
        decodeSlashesInPath = this.service === 's3',
        firstValOnly = this.service === 's3',
        bodyHash
  
    if (this.service === 's3' && this.request.signQuery) {
      bodyHash = 'UNSIGNED-PAYLOAD'
    } else if (this.isCodeCommitGit) {
      bodyHash = ''
    } else {
      bodyHash = headers['X-Amz-Content-Sha256'] || headers['x-amz-content-sha256'] ||
        hash(this.request.body || '', 'hex')
    }
  
    if (query) {
      queryStr = encodeRfc3986(querystring.stringify(Object.keys(query).sort().reduce(function(obj, key) {
        if (!key) return obj
        obj[key] = !Array.isArray(query[key]) ? query[key] :
          (firstValOnly ? query[key][0] : query[key].slice().sort())
        return obj
      }, {})))
    }
    if (pathStr !== '/') {
      if (normalizePath) pathStr = pathStr.replace(/\/{2,}/g, '/')
      pathStr = pathStr.split('/').reduce(function(path, piece) {
        if (normalizePath && piece === '..') {
          path.pop()
        } else if (!normalizePath || piece !== '.') {
          if (decodePath) piece = querystring.unescape(piece)
          path.push(encodeRfc3986(querystring.escape(piece)))
        }
        return path
      }, []).join('/')
      if (pathStr[0] !== '/') pathStr = '/' + pathStr
      if (decodeSlashesInPath) pathStr = pathStr.replace(/%2F/g, '/')
    }
  
    return [
      this.request.method || 'GET',
      pathStr,
      queryStr,
      this.canonicalHeaders() + '
  ',
      this.signedHeaders(),
      bodyHash,
    ].join('
  ')
  }
  
  RequestSigner.prototype.canonicalHeaders = function() {
    var headers = this.request.headers
    function trimAll(header) {
      return header.toString().trim().replace(/\s+/g, ' ')
    }
    return Object.keys(headers)
      .sort(function(a, b) { return a.toLowerCase() < b.toLowerCase() ? -1 : 1 })
      .map(function(key) { return key.toLowerCase() + ':' + trimAll(headers[key]) })
      .join('
  ')
  }
  
  RequestSigner.prototype.signedHeaders = function() {
    return Object.keys(this.request.headers)
      .map(function(key) { return key.toLowerCase() })
      .sort()
      .join(';')
  }
  
  RequestSigner.prototype.credentialString = function() {
    return [
      this.getDate(),
      this.region,
      this.service,
      'aws4_request',
    ].join('/')
  }
  
  RequestSigner.prototype.defaultCredentials = function() {
    var env = process.env
    return {
      accessKeyId: env.AWS_ACCESS_KEY_ID || env.AWS_ACCESS_KEY,
      secretAccessKey: env.AWS_SECRET_ACCESS_KEY || env.AWS_SECRET_KEY,
      sessionToken: env.AWS_SESSION_TOKEN,
    }
  }
  
  RequestSigner.prototype.parsePath = function() {
    var path = this.request.path || '/',
        queryIx = path.indexOf('?'),
        query = null
  
    if (queryIx >= 0) {
      query = querystring.parse(path.slice(queryIx + 1))
      path = path.slice(0, queryIx)
    }
  
    // S3 doesn't always encode characters > 127 correctly and
    // all services don't encode characters > 255 correctly
    // So if there are non-reserved chars (and it's not already all % encoded), just encode them all
    if (/[^0-9A-Za-z!'()*\-._~%/]/.test(path)) {
      path = path.split('/').map(function(piece) {
        return querystring.escape(querystring.unescape(piece))
      }).join('/')
    }
  
    this.parsedPath = {
      path: path,
      query: query,
    }
  }
  
  RequestSigner.prototype.formatPath = function() {
    var path = this.parsedPath.path,
        query = this.parsedPath.query
  
    if (!query) return path
  
    // Services don't support empty query string keys
    if (query[''] != null) delete query['']
  
    return path + '?' + encodeRfc3986(querystring.stringify(query))
  }
  
  aws4.RequestSigner = RequestSigner
  
  aws4.sign = function(request, credentials) {
    return new RequestSigner(request, credentials).sign()
  }