text: module.exports = exports = configure
  module.exports.test = {
    PythonFinder: PythonFinder,
    findAccessibleSync: findAccessibleSync,
    findPython: findPython,
  }
  
  /**
   * Module dependencies.
   */
  
  var fs = require('graceful-fs')
    , path = require('path')
    , log = require('npmlog')
    , osenv = require('osenv')
    , which = require('which')
    , semver = require('semver')
    , mkdirp = require('mkdirp')
    , cp = require('child_process')
    , extend = require('util')._extend
    , processRelease = require('./process-release')
    , win = process.platform === 'win32'
    , findNodeDirectory = require('./find-node-directory')
    , msgFormat = require('util').format
  if (win)
    var findVS2017 = require('./find-vs2017')
  
  exports.usage = 'Generates ' + (win ? 'MSVC project files' : 'a Makefile') + ' for the current module'
  
  function configure (gyp, argv, callback) {
  
    var python = gyp.opts.python || process.env.PYTHON || 'python2'
      , buildDir = path.resolve('build')
      , configNames = [ 'config.gypi', 'common.gypi' ]
      , configs = []
      , nodeDir
      , release = processRelease(argv, gyp, process.version, process.release)
  
    findPython(python, function (err, found) {
      if (err) {
        callback(err)
      } else {
        python = found
        getNodeDir()
      }
    })
  
    function getNodeDir () {
  
      // 'python' should be set by now
      process.env.PYTHON = python
  
      if (gyp.opts.nodedir) {
        // --nodedir was specified. use that for the dev files
        nodeDir = gyp.opts.nodedir.replace(/^~/, osenv.home())
  
        log.verbose('get node dir', 'compiling against specified --nodedir dev files: %s', nodeDir)
        createBuildDir()
  
      } else {
        // if no --nodedir specified, ensure node dependencies are installed
        if ('v' + release.version !== process.version) {
          // if --target was given, then determine a target version to compile for
          log.verbose('get node dir', 'compiling against --target node version: %s', release.version)
        } else {
          // if no --target was specified then use the current host node version
          log.verbose('get node dir', 'no --target version specified, falling back to host node version: %s', release.version)
        }
  
        if (!release.semver) {
          // could not parse the version string with semver
          return callback(new Error('Invalid version number: ' + release.version))
        }
  
        // ensure that the target node version's dev files are installed
        gyp.opts.ensure = true
        gyp.commands.install([ release.version ], function (err, version) {
          if (err) return callback(err)
          log.verbose('get node dir', 'target node version installed:', release.versionDir)
          nodeDir = path.resolve(gyp.devDir, release.versionDir)
          createBuildDir()
        })
      }
    }
  
    function createBuildDir () {
      log.verbose('build dir', 'attempting to create "build" dir: %s', buildDir)
      mkdirp(buildDir, function (err, isNew) {
        if (err) return callback(err)
        log.verbose('build dir', '"build" dir needed to be created?', isNew)
        if (win && (!gyp.opts.msvs_version || gyp.opts.msvs_version === '2017')) {
          findVS2017(function (err, vsSetup) {
            if (err) {
              log.verbose('Not using VS2017:', err.message)
              createConfigFile()
            } else {
              createConfigFile(null, vsSetup)
            }
          })
        } else {
          createConfigFile()
        }
      })
    }
  
    function createConfigFile (err, vsSetup) {
      if (err) return callback(err)
  
      var configFilename = 'config.gypi'
      var configPath = path.resolve(buildDir, configFilename)
  
      log.verbose('build/' + configFilename, 'creating config file')
  
      var config = process.config || {}
        , defaults = config.target_defaults
        , variables = config.variables
  
      // default "config.variables"
      if (!variables) variables = config.variables = {}
  
      // default "config.defaults"
      if (!defaults) defaults = config.target_defaults = {}
  
      // don't inherit the "defaults" from node's `process.config` object.
      // doing so could cause problems in cases where the `node` executable was
      // compiled on a different machine (with different lib/include paths) than
      // the machine where the addon is being built to
      defaults.cflags = []
      defaults.defines = []
      defaults.include_dirs = []
      defaults.libraries = []
  
      // set the default_configuration prop
      if ('debug' in gyp.opts) {
        defaults.default_configuration = gyp.opts.debug ? 'Debug' : 'Release'
      }
      if (!defaults.default_configuration) {
        defaults.default_configuration = 'Release'
      }
  
      // set the target_arch variable
      variables.target_arch = gyp.opts.arch || process.arch || 'ia32'
  
      // set the node development directory
      variables.nodedir = nodeDir
  
      // don't copy dev libraries with nodedir option
      variables.copy_dev_lib = !gyp.opts.nodedir
  
      // disable -T "thin" static archives by default
      variables.standalone_static_library = gyp.opts.thin ? 0 : 1
  
      if (vsSetup) {
        // GYP doesn't (yet) have support for VS2017, so we force it to VS2015
        // to avoid pulling a floating patch that has not landed upstream.
        // Ref: https://chromium-review.googlesource.com/#/c/433540/
        gyp.opts.msvs_version = '2015'
        process.env['GYP_MSVS_VERSION'] = 2015
        process.env['GYP_MSVS_OVERRIDE_PATH'] = vsSetup.path
        defaults['msbuild_toolset'] = 'v141'
        defaults['msvs_windows_target_platform_version'] = vsSetup.sdk
        variables['msbuild_path'] = path.join(vsSetup.path, 'MSBuild', '15.0',
                                              'Bin', 'MSBuild.exe')
      }
  
      // loop through the rest of the opts and add the unknown ones as variables.
      // this allows for module-specific configure flags like:
      //
      //   $ node-gyp configure --shared-libxml2
      Object.keys(gyp.opts).forEach(function (opt) {
        if (opt === 'argv') return
        if (opt in gyp.configDefs) return
        variables[opt.replace(/-/g, '_')] = gyp.opts[opt]
      })
  
      // ensures that any boolean values from `process.config` get stringified
      function boolsToString (k, v) {
        if (typeof v === 'boolean')
          return String(v)
        return v
      }
  
      log.silly('build/' + configFilename, config)
  
      // now write out the config.gypi file to the build/ dir
      var prefix = '# Do not edit. File was generated by node-gyp\'s "configure" step'
        , json = JSON.stringify(config, boolsToString, 2)
      log.verbose('build/' + configFilename, 'writing out config file: %s', configPath)
      configs.push(configPath)
      fs.writeFile(configPath, [prefix, json, ''].join('\n'), findConfigs)
    }
  
    function findConfigs (err) {
      if (err) return callback(err)
      var name = configNames.shift()
      if (!name) return runGyp()
      var fullPath = path.resolve(name)
      log.verbose(name, 'checking for gypi file: %s', fullPath)
      fs.stat(fullPath, function (err, stat) {
        if (err) {
          if (err.code == 'ENOENT') {
            findConfigs() // check next gypi filename
          } else {
            callback(err)
          }
        } else {
          log.verbose(name, 'found gypi file')
          configs.push(fullPath)
          findConfigs()
        }
      })
    }
  
    function runGyp (err) {
      if (err) return callback(err)
  
      if (!~argv.indexOf('-f') && !~argv.indexOf('--format')) {
        if (win) {
          log.verbose('gyp', 'gyp format was not specified; forcing "msvs"')
          // force the 'make' target for non-Windows
          argv.push('-f', 'msvs')
        } else {
          log.verbose('gyp', 'gyp format was not specified; forcing "make"')
          // force the 'make' target for non-Windows
          argv.push('-f', 'make')
        }
      }
  
      function hasMsvsVersion () {
        return argv.some(function (arg) {
          return arg.indexOf('msvs_version') === 0
        })
      }
  
      if (win && !hasMsvsVersion()) {
        if ('msvs_version' in gyp.opts) {
          argv.push('-G', 'msvs_version=' + gyp.opts.msvs_version)
        } else {
          argv.push('-G', 'msvs_version=auto')
        }
      }
  
      // include all the ".gypi" files that were found
      configs.forEach(function (config) {
        argv.push('-I', config)
      })
  
      // for AIX we need to set up the path to the exp file
      // which contains the symbols needed for linking.
      // The file will either be in one of the following
      // depending on whether it is an installed or
      // development environment:
      //  - the include/node directory
      //  - the out/Release directory
      //  - the out/Debug directory
      //  - the root directory
      var node_exp_file = undefined
      if (process.platform === 'aix') {
        var node_root_dir = findNodeDirectory()
        var candidates = ['include/node/node.exp',
                          'out/Release/node.exp',
                          'out/Debug/node.exp',
                          'node.exp']
        var logprefix = 'find exports file'
        node_exp_file = findAccessibleSync(logprefix, node_root_dir, candidates)
        if (node_exp_file !== undefined) {
          log.verbose(logprefix, 'Found exports file: %s', node_exp_file)
        } else {
          var msg = msgFormat('Could not find node.exp file in %s', node_root_dir)
          log.error(logprefix, 'Could not find exports file')
          return callback(new Error(msg))
        }
      }
  
      // this logic ported from the old `gyp_addon` python file
      var gyp_script = path.resolve(__dirname, '..', 'gyp', 'gyp_main.py')
      var addon_gypi = path.resolve(__dirname, '..', 'addon.gypi')
      var common_gypi = path.resolve(nodeDir, 'include/node/common.gypi')
      fs.stat(common_gypi, function (err, stat) {
        if (err)
          common_gypi = path.resolve(nodeDir, 'common.gypi')
  
        var output_dir = 'build'
        if (win) {
          // Windows expects an absolute path
          output_dir = buildDir
        }
        var nodeGypDir = path.resolve(__dirname, '..')
  
        argv.push('-I', addon_gypi)
        argv.push('-I', common_gypi)
        argv.push('-Dlibrary=shared_library')
        argv.push('-Dvisibility=default')
        argv.push('-Dnode_root_dir=' + nodeDir)
        if (process.platform === 'aix') {
          argv.push('-Dnode_exp_file=' + node_exp_file)
        }
        argv.push('-Dnode_gyp_dir=' + nodeGypDir)
        argv.push('-Dnode_lib_file=' + release.name + '.lib')
        argv.push('-Dmodule_root_dir=' + process.cwd())
        argv.push('-Dnode_engine=' +
          (gyp.opts.node_engine || process.jsEngine || 'v8'))
        argv.push('--depth=.')
        argv.push('--no-parallel')
  
        // tell gyp to write the Makefile/Solution files into output_dir
        argv.push('--generator-output', output_dir)
  
        // tell make to write its output into the same dir
        argv.push('-Goutput_dir=.')
  
        // enforce use of the "binding.gyp" file
        argv.unshift('binding.gyp')
  
        // execute `gyp` from the current target nodedir
        argv.unshift(gyp_script)
  
        // make sure python uses files that came with this particular node package
        var pypath = [path.join(__dirname, '..', 'gyp', 'pylib')]
        if (process.env.PYTHONPATH) {
          pypath.push(process.env.PYTHONPATH)
        }
        process.env.PYTHONPATH = pypath.join(win ? ';' : ':')
  
        var cp = gyp.spawn(python, argv)
        cp.on('exit', onCpExit)
      })
    }
  
    /**
     * Called when the `gyp` child process exits.
     */
  
    function onCpExit (code, signal) {
      if (code !== 0) {
        callback(new Error('`gyp` failed with exit code: ' + code))
      } else {
        // we're done
        callback()
      }
    }
  
  }
  
  /**
   * Returns the first file or directory from an array of candidates that is
   * readable by the current user, or undefined if none of the candidates are
   * readable.
   */
  function findAccessibleSync (logprefix, dir, candidates) {
    for (var next = 0; next < candidates.length; next++) {
       var candidate = path.resolve(dir, candidates[next])
       try {
         var fd = fs.openSync(candidate, 'r')
       } catch (e) {
         // this candidate was not found or not readable, do nothing
         log.silly(logprefix, 'Could not open %s: %s', candidate, e.message)
         continue
       }
       fs.closeSync(fd)
       log.silly(logprefix, 'Found readable %s', candidate)
       return candidate
    }
  
    return undefined
  }
  
  function PythonFinder(python, callback) {
    this.callback = callback
    this.python = python
  }
  
  PythonFinder.prototype = {
    checkPythonLauncherDepth: 0,
    env: process.env,
    execFile: cp.execFile,
    log: log,
    stat: fs.stat,
    which: which,
    win: win,
  
    checkPython: function checkPython () {
      this.log.verbose('check python',
                       'checking for Python executable "%s" in the PATH',
                       this.python)
      this.which(this.python, function (err, execPath) {
        if (err) {
          this.log.verbose('`which` failed', this.python, err)
          if (this.python === 'python2') {
            this.python = 'python'
            return this.checkPython()
          }
          if (this.win) {
            this.checkPythonLauncher()
          } else {
            this.failNoPython()
          }
        } else {
          this.log.verbose('`which` succeeded', this.python, execPath)
          // Found the `python` executable, and from now on we use it explicitly.
          // This solves #667 and #750 (`execFile` won't run batch files
          // (*.cmd, and *.bat))
          this.python = execPath
          this.checkPythonVersion()
        }
      }.bind(this))
    },
  
    // Distributions of Python on Windows by default install with the "py.exe"
    // Python launcher which is more likely to exist than the Python executable
    // being in the $PATH.
    // Because the Python launcher supports all versions of Python, we have to
    // explicitly request a Python 2 version. This is done by supplying "-2" as
    // the first command line argument. Since "py.exe -2" would be an invalid
    // executable for "execFile", we have to use the launcher to figure out
    // where the actual "python.exe" executable is located.
    checkPythonLauncher: function checkPythonLauncher () {
      this.checkPythonLauncherDepth += 1
  
      this.log.verbose(
          'could not find "' + this.python + '". checking python launcher')
      var env = extend({}, this.env)
      env.TERM = 'dumb'
  
      var launcherArgs = ['-2', '-c', 'import sys; print sys.executable']
      this.execFile('py.exe', launcherArgs, { env: env }, function (err, stdout) {
        if (err) {
          this.guessPython()
        } else {
          this.python = stdout.trim()
          this.log.verbose('check python launcher',
                           'python executable found: %j',
                           this.python)
          this.checkPythonVersion()
        }
        this.checkPythonLauncherDepth -= 1
      }.bind(this))
    },
  
    checkPythonVersion: function checkPythonVersion () {
      var args = ['-c', 'import platform; print(platform.python_version());']
      var env = extend({}, this.env)
      env.TERM = 'dumb'
  
      this.execFile(this.python, args, { env: env }, function (err, stdout) {
        if (err) {
          return this.callback(err)
        }
        this.log.verbose('check python version',
                         '`%s -c "' + args[1] + '"` returned: %j',
                         this.python, stdout)
        var version = stdout.trim()
        if (~version.indexOf('+')) {
          this.log.silly('stripping "+" sign(s) from version')
          version = version.replace(/\+/g, '')
        }
        if (~version.indexOf('rc')) {
          this.log.silly('stripping "rc" identifier from version')
          version = version.replace(/rc(.*)$/ig, '')
        }
        var range = semver.Range('>=2.5.0 <3.0.0')
        var valid = false
        try {
          valid = range.test(version)
        } catch (e) {
          this.log.silly('range.test() error', e)
        }
        if (valid) {
          this.callback(null, this.python)
        } else if (this.win && this.checkPythonLauncherDepth === 0) {
          this.checkPythonLauncher()
        } else {
          this.failPythonVersion(version)
        }
      }.bind(this))
    },
  
    failNoPython: function failNoPython () {
      var errmsg =
          'Can\'t find Python executable "' + this.python +
          '", you can set the PYTHON env variable.'
      this.callback(new Error(errmsg))
    },
  
    failPythonVersion: function failPythonVersion (badVersion) {
      var errmsg =
          'Python executable "' + this.python +
          '" is v' + badVersion + ', which is not supported by gyp.\n' +
          'You can pass the --python switch to point to ' +
          'Python >= v2.5.0 & < 3.0.0.'
      this.callback(new Error(errmsg))
    },
  
    // Called on Windows when "python" isn't available in the current $PATH.
    // We are going to check if "%SystemDrive%\python27\python.exe" exists.
    guessPython: function guessPython () {
      this.log.verbose('could not find "' + this.python + '". guessing location')
      var rootDir = this.env.SystemDrive || 'C:\\'
      if (rootDir[rootDir.length - 1] !== '\\') {
        rootDir += '\\'
      }
      var resolve = path.win32 && path.win32.resolve || path.resolve
      var pythonPath = resolve(rootDir, 'Python27', 'python.exe')
      this.log.verbose('ensuring that file exists:', pythonPath)
      this.stat(pythonPath, function (err, stat) {
        if (err) {
          if (err.code == 'ENOENT') {
            this.failNoPython()
          } else {
            this.callback(err)
          }
          return
        }
        this.python = pythonPath
        this.checkPythonVersion()
      }.bind(this))
    },
  }
  
  function findPython (python, callback) {
    var finder = new PythonFinder(python, callback)
    finder.checkPython()
  }
  