text: 'use strict'
  
  const path = require('path')
  const log = require('npmlog')
  const semver = require('semver')
  const cp = require('child_process')
  const extend = require('util')._extend // eslint-disable-line
  const win = process.platform === 'win32'
  const logWithPrefix = require('./util').logWithPrefix
  
  function PythonFinder (configPython, callback) {
    this.callback = callback
    this.configPython = configPython
    this.errorLog = []
  }
  
  PythonFinder.prototype = {
    log: logWithPrefix(log, 'find Python'),
    argsExecutable: ['-c', 'import sys; print(sys.executable);'],
    argsVersion: ['-c', 'import sys; print("%s.%s.%s" % sys.version_info[:3]);'],
    semverRange: '^2.6.0 || >=3.5.0',
  
    // These can be overridden for testing:
    execFile: cp.execFile,
    env: process.env,
    win: win,
    pyLauncher: 'py.exe',
    winDefaultLocations: [
      path.join(process.env.SystemDrive || 'C:', 'Python27', 'python.exe'),
      path.join(process.env.SystemDrive || 'C:', 'Python37', 'python.exe')
    ],
  
    // Logs a message at verbose level, but also saves it to be displayed later
    // at error level if an error occurs. This should help diagnose the problem.
    addLog: function addLog (message) {
      this.log.verbose(message)
      this.errorLog.push(message)
    },
  
    // Find Python by trying a sequence of possibilities.
    // Ignore errors, keep trying until Python is found.
    findPython: function findPython () {
      const SKIP = 0; const FAIL = 1
      var toCheck = getChecks.apply(this)
  
      function getChecks () {
        if (this.env.NODE_GYP_FORCE_PYTHON) {
          return [{
            before: () => {
              this.addLog(
                'checking Python explicitly set from NODE_GYP_FORCE_PYTHON')
              this.addLog('- process.env.NODE_GYP_FORCE_PYTHON is ' +
                `"${this.env.NODE_GYP_FORCE_PYTHON}"`)
            },
            check: this.checkCommand,
            arg: this.env.NODE_GYP_FORCE_PYTHON
          }]
        }
  
        var checks = [
          {
            before: () => {
              if (!this.configPython) {
                this.addLog(
                  'Python is not set from command line or npm configuration')
                return SKIP
              }
              this.addLog('checking Python explicitly set from command line or ' +
                'npm configuration')
              this.addLog('- "--python=" or "npm config get python" is ' +
                `"${this.configPython}"`)
            },
            check: this.checkCommand,
            arg: this.configPython
          },
          {
            before: () => {
              if (!this.env.PYTHON) {
                this.addLog('Python is not set from environment variable ' +
                  'PYTHON')
                return SKIP
              }
              this.addLog('checking Python explicitly set from environment ' +
                'variable PYTHON')
              this.addLog(`- process.env.PYTHON is "${this.env.PYTHON}"`)
            },
            check: this.checkCommand,
            arg: this.env.PYTHON
          },
          {
            before: () => { this.addLog('checking if "python" can be used') },
            check: this.checkCommand,
            arg: 'python'
          },
          {
            before: () => { this.addLog('checking if "python2" can be used') },
            check: this.checkCommand,
            arg: 'python2'
          },
          {
            before: () => { this.addLog('checking if "python3" can be used') },
            check: this.checkCommand,
            arg: 'python3'
          }
        ]
  
        if (this.win) {
          checks.push({
            before: () => {
              this.addLog(
                'checking if the py launcher can be used to find Python 2')
            },
            check: this.checkPyLauncher
          })
          for (var i = 0; i < this.winDefaultLocations.length; ++i) {
            const location = this.winDefaultLocations[i]
            checks.push({
              before: () => {
                this.addLog('checking if Python is ' +
                  `${location}`)
              },
              check: this.checkExecPath,
              arg: location
            })
          }
        }
  
        return checks
      }
  
      function runChecks (err) {
        this.log.silly('runChecks: err = %j', (err && err.stack) || err)
  
        const check = toCheck.shift()
        if (!check) {
          return this.fail()
        }
  
        const before = check.before.apply(this)
        if (before === SKIP) {
          return runChecks.apply(this)
        }
        if (before === FAIL) {
          return this.fail()
        }
  
        const args = [runChecks.bind(this)]
        if (check.arg) {
          args.unshift(check.arg)
        }
        check.check.apply(this, args)
      }
  
      runChecks.apply(this)
    },
  
    // Check if command is a valid Python to use.
    // Will exit the Python finder on success.
    // If on Windows, run in a CMD shell to support BAT/CMD launchers.
    checkCommand: function checkCommand (command, errorCallback) {
      var exec = command
      var args = this.argsExecutable
      var shell = false
      if (this.win) {
        // Arguments have to be manually quoted
        exec = `"${exec}"`
        args = args.map(a => `"${a}"`)
        shell = true
      }
  
      this.log.verbose(`- executing "${command}" to get executable path`)
      this.run(exec, args, shell, function (err, execPath) {
        // Possible outcomes:
        // - Error: not in PATH, not executable or execution fails
        // - Gibberish: the next command to check version will fail
        // - Absolute path to executable
        if (err) {
          this.addLog(`- "${command}" is not in PATH or produced an error`)
          return errorCallback(err)
        }
        this.addLog(`- executable path is "${execPath}"`)
        this.checkExecPath(execPath, errorCallback)
      }.bind(this))
    },
  
    // Check if the py launcher can find a valid Python to use.
    // Will exit the Python finder on success.
    // 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 $PATH.
    // Because the Python launcher supports all versions of Python, we have to
    // explicitly request a Python 2 version. This is done by supplying "-2" as
    // the first command line argument. Since "py.exe -2" would be an invalid
    // executable for "execFile", we have to use the launcher to figure out
    // where the actual "python.exe" executable is located.
    checkPyLauncher: function checkPyLauncher (errorCallback) {
      this.log.verbose(
        `- executing "${this.pyLauncher}" to get Python 2 executable path`)
      this.run(this.pyLauncher, ['-2', ...this.argsExecutable], false,
        function (err, execPath) {
        // Possible outcomes: same as checkCommand
          if (err) {
            this.addLog(
              `- "${this.pyLauncher}" is not in PATH or produced an error`)
            return errorCallback(err)
          }
          this.addLog(`- executable path is "${execPath}"`)
          this.checkExecPath(execPath, errorCallback)
        }.bind(this))
    },
  
    // Check if a Python executable is the correct version to use.
    // Will exit the Python finder on success.
    checkExecPath: function checkExecPath (execPath, errorCallback) {
      this.log.verbose(`- executing "${execPath}" to get version`)
      this.run(execPath, this.argsVersion, false, function (err, version) {
        // Possible outcomes:
        // - Error: executable can not be run (likely meaning the command wasn't
        //   a Python executable and the previous command produced gibberish)
        // - Gibberish: somehow the last command produced an executable path,
        //   this will fail when verifying the version
        // - Version of the Python executable
        if (err) {
          this.addLog(`- "${execPath}" could not be run`)
          return errorCallback(err)
        }
        this.addLog(`- version is "${version}"`)
  
        const range = semver.Range(this.semverRange)
        var valid = false
        try {
          valid = range.test(version)
        } catch (err) {
          this.log.silly('range.test() threw:\n%s', err.stack)
          this.addLog(`- "${execPath}" does not have a valid version`)
          this.addLog('- is it a Python executable?')
          return errorCallback(err)
        }
  
        if (!valid) {
          this.addLog(`- version is ${version} - should be ${this.semverRange}`)
          this.addLog('- THIS VERSION OF PYTHON IS NOT SUPPORTED')
          return errorCallback(new Error(
            `Found unsupported Python version ${version}`))
        }
        this.succeed(execPath, version)
      }.bind(this))
    },
  
    // Run an executable or shell command, trimming the output.
    run: function run (exec, args, shell, callback) {
      var env = extend({}, this.env)
      env.TERM = 'dumb'
      const opts = { env: env, shell: shell }
  
      this.log.silly('execFile: exec = %j', exec)
      this.log.silly('execFile: args = %j', args)
      this.log.silly('execFile: opts = %j', opts)
      try {
        this.execFile(exec, args, opts, execFileCallback.bind(this))
      } catch (err) {
        this.log.silly('execFile: threw:\n%s', err.stack)
        return callback(err)
      }
  
      function execFileCallback (err, stdout, stderr) {
        this.log.silly('execFile result: err = %j', (err && err.stack) || err)
        this.log.silly('execFile result: stdout = %j', stdout)
        this.log.silly('execFile result: stderr = %j', stderr)
        if (err) {
          return callback(err)
        }
        const execPath = stdout.trim()
        callback(null, execPath)
      }
    },
  
    succeed: function succeed (execPath, version) {
      this.log.info(`using Python version ${version} found at "${execPath}"`)
      process.nextTick(this.callback.bind(null, null, execPath))
    },
  
    fail: function fail () {
      const errorLog = this.errorLog.join('\n')
  
      const pathExample = this.win ? 'C:\\Path\\To\\python.exe'
        : '/path/to/pythonexecutable'
      // For Windows 80 col console, use up to the column before the one marked
      // with X (total 79 chars including logger prefix, 58 chars usable here):
      //                                                           X
      const info = [
        '**********************************************************',
        'You need to install the latest version of Python.',
        'Node-gyp should be able to find and use Python. If not,',
        'you can try one of the following options:',
        `- Use the switch --python="${pathExample}"`,
        '  (accepted by both node-gyp and npm)',
        '- Set the environment variable PYTHON',
        '- Set the npm configuration variable python:',
        `  npm config set python "${pathExample}"`,
        'For more information consult the documentation at:',
        'https://github.com/nodejs/node-gyp#installation',
        '**********************************************************'
      ].join('\n')
  
      this.log.error(`\n${errorLog}\n\n${info}\n`)
      process.nextTick(this.callback.bind(null, new Error(
        'Could not find any Python installation to use')))
    }
  }
  
  function findPython (configPython, callback) {
    var finder = new PythonFinder(configPython, callback)
    finder.findPython()
  }
  
  module.exports = findPython
  module.exports.test = {
    PythonFinder: PythonFinder,
    findPython: findPython
  }
  