var path = require('path');
var fs = require('fs');
var child = require('child_process');
var common = require('./common');
var _tempDir = require('./tempdir').tempDir;
var _pwd = require('./pwd');

var DEFAULT_MAXBUFFER_SIZE = 20 * 1024 * 1024;
var DEFAULT_ERROR_CODE = 1;

common.register('exec', _exec, {
  unix: false,
  canReceivePipe: true,
  wrapOutput: false,
  handlesFatalDynamically: true,
});

// We use this function to run `exec` synchronously while also providing realtime
// output.
function execSync(cmd, opts, pipe) {
  if (!common.config.execPath) {
    try {
        common.error('Unable to find a path to the node binary. Please manually set config.execPath');
    } catch (e) {
      if (opts.fatal) {
        throw e;
      }

      return;
    }
  }

  var tempDir = _tempDir();
  var paramsFile = path.join(tempDir, common.randomFileName());
  var stderrFile = path.join(tempDir, common.randomFileName());
  var stdoutFile = path.join(tempDir, common.randomFileName());

  opts = common.extend({
    silent: common.config.silent,
    fatal: common.config.fatal, // TODO(nfischer): this and the line above are probably unnecessary
    cwd: _pwd().toString(),
    env: process.env,
    maxBuffer: DEFAULT_MAXBUFFER_SIZE,
    encoding: 'utf8',
  }, opts);

  if (fs.existsSync(paramsFile)) common.unlinkSync(paramsFile);
  if (fs.existsSync(stderrFile)) common.unlinkSync(stderrFile);
  if (fs.existsSync(stdoutFile)) common.unlinkSync(stdoutFile);

  opts.cwd = path.resolve(opts.cwd);

  var paramsToSerialize = {
    command: cmd,
    execOptions: opts,
    pipe,
    stdoutFile,
    stderrFile,
  };

  // Create the files and ensure these are locked down (for read and write) to
  // the current user. The main concerns here are:
  //
  // * If we execute a command which prints sensitive output, then
  //   stdoutFile/stderrFile must not be readable by other users.
  // * paramsFile must not be readable by other users, or else they can read it
  //   to figure out the path for stdoutFile/stderrFile and create these first
  //   (locked down to their own access), which will crash exec() when it tries
  //   to write to the files.
  function writeFileLockedDown(filePath, data) {
    fs.writeFileSync(filePath, data, {
      encoding: 'utf8',
      mode: parseInt('600', 8),
    });
  }
  writeFileLockedDown(stdoutFile, '');
  writeFileLockedDown(stderrFile, '');
  writeFileLockedDown(paramsFile, JSON.stringify(paramsToSerialize));

  var execArgs = [
    path.join(__dirname, 'exec-child.js'),
    paramsFile,
  ];

  /* istanbul ignore else */
  if (opts.silent) {
    opts.stdio = 'ignore';
  } else {
    opts.stdio = [0, 1, 2];
  }

  var code = 0;

  // Welcome to the future
  try {
    // Bad things if we pass in a `shell` option to child_process.execFileSync,
    // so we need to explicitly remove it here.
    delete opts.shell;

    child.execFileSync(common.config.execPath, execArgs, opts);
  } catch (e) {
    // Commands with non-zero exit code raise an exception.
    code = e.status || DEFAULT_ERROR_CODE;
  }

  // fs.readFileSync uses buffer encoding by default, so call
  // it without the encoding option if the encoding is 'buffer'.
  // Also, if the exec timeout is too short for node to start up,
  // the files will not be created, so these calls will throw.
  var stdout = '';
  var stderr = '';
  if (opts.encoding === 'buffer') {
    stdout = fs.readFileSync(stdoutFile);
    stderr = fs.readFileSync(stderrFile);
  } else {
    stdout = fs.readFileSync(stdoutFile, opts.encoding);
    stderr = fs.readFileSync(stderrFile, opts.encoding);
  }

  // No biggie if we can't erase the files now -- they're in a temp dir anyway
  // and we locked down permissions (see the note above).
  try { common.unlinkSync(paramsFile); } catch (e) {}
  try { common.unlinkSync(stderrFile); } catch (e) {}
  try { common.unlinkSync(stdoutFile); } catch (e) {}

  if (code !== 0) {
    // Note: `silent` should be unconditionally true to avoid double-printing
    // the command's stderr, and to avoid printing any stderr when the user has
    // set `shell.config.silent`.
    common.error(stderr, code, { continue: true, silent: true, fatal: opts.fatal });
  }
  var obj = common.ShellString(stdout, stderr, code);
  return obj;
} // execSync()

// Wrapper around exec() to enable echoing output to console in real time
function execAsync(cmd, opts, pipe, callback) {
  opts = common.extend({
    silent: common.config.silent,
    fatal: common.config.fatal, // TODO(nfischer): this and the line above are probably unnecessary
    cwd: _pwd().toString(),
    env: process.env,
    maxBuffer: DEFAULT_MAXBUFFER_SIZE,
    encoding: 'utf8',
  }, opts);

  var c = child.exec(cmd, opts, function (err, stdout, stderr) {
    if (callback) {
      if (!err) {
        callback(0, stdout, stderr);
      } else if (err.code === undefined) {
        // See issue #536
        /* istanbul ignore next */
        callback(1, stdout, stderr);
      } else {
        callback(err.code, stdout, stderr);
      }
    }
  });

  if (pipe) c.stdin.end(pipe);

  if (!opts.silent) {
    c.stdout.pipe(process.stdout);
    c.stderr.pipe(process.stderr);
  }

  return c;
}

//@
//@ ### exec(command [, options] [, callback])
//@
//@ Available options:
//@
//@ + `async`: Asynchronous execution. If a callback is provided, it will be set to
//@   `true`, regardless of the passed value (default: `false`).
//@ + `fatal`: Exit upon error (default: `false`).
//@ + `silent`: Do not echo program output to console (default: `false`).
//@ + `encoding`: Character encoding to use. Affects the values returned to stdout and stderr, and
//@   what is written to stdout and stderr when not in silent mode (default: `'utf8'`).
//@ + and any option available to Node.js's
//@   [`child_process.exec()`](https://nodejs.org/api/child_process.html#child_process_child_process_exec_command_options_callback)
//@
//@ Examples:
//@
//@ ```javascript
//@ var version = exec('node --version', {silent:true}).stdout;
//@
//@ var child = exec('some_long_running_process', {async:true});
//@ child.stdout.on('data', function(data) {
//@   /* ... do something with data ... */
//@ });
//@
//@ exec('some_long_running_process', function(code, stdout, stderr) {
//@   console.log('Exit code:', code);
//@   console.log('Program output:', stdout);
//@   console.log('Program stderr:', stderr);
//@ });
//@ ```
//@
//@ Executes the given `command` _synchronously_, unless otherwise specified.
//@ When in synchronous mode, this returns a [ShellString](#shellstringstr).
//@ Otherwise, this returns the child process object, and the `callback`
//@ receives the arguments `(code, stdout, stderr)`.
//@
//@ Not seeing the behavior you want? `exec()` runs everything through `sh`
//@ by default (or `cmd.exe` on Windows), which differs from `bash`. If you
//@ need bash-specific behavior, try out the `{shell: 'path/to/bash'}` option.
//@
//@ **Security note:** as `shell.exec()` executes an arbitrary string in the
//@ system shell, it is **critical** to properly sanitize user input to avoid
//@ **command injection**. For more context, consult the [Security
//@ Guidelines](https://github.com/shelljs/shelljs/wiki/Security-guidelines).
function _exec(command, options, callback) {
  options = options || {};

  var pipe = common.readFromPipe();

  // Callback is defined instead of options.
  if (typeof options === 'function') {
    callback = options;
    options = { async: true };
  }

  // Callback is defined with options.
  if (typeof options === 'object' && typeof callback === 'function') {
    options.async = true;
  }

  options = common.extend({
    silent: common.config.silent,
    fatal: common.config.fatal,
    async: false,
  }, options);

  if (!command) {
    try {
      common.error('must specify command');
    } catch (e) {
      if (options.fatal) {
        throw e;
      }

      return;
    }
  }

  if (options.async) {
    return execAsync(command, options, pipe, callback);
  } else {
    return execSync(command, options, pipe);
  }
}
module.exports = _exec;
