<?php

/**
 * Manages execution of `git pull` and `hg pull` commands for
 * @{class:PhabricatorRepository} objects. Used by
 * @{class:PhabricatorRepositoryPullLocalDaemon}.
 *
 * This class also covers initial working copy setup through `git clone`,
 * `git init`, `hg clone`, `hg init`, or `svnadmin create`.
 *
 * @task pull     Pulling Working Copies
 * @task git      Pulling Git Working Copies
 * @task hg       Pulling Mercurial Working Copies
 * @task svn      Pulling Subversion Working Copies
 * @task internal Internals
 */
final class PhabricatorRepositoryPullEngine
  extends PhabricatorRepositoryEngine {


/* -(  Pulling Working Copies  )--------------------------------------------- */


  public function pullRepository() {
    $repository = $this->getRepository();

    $lock = $this->newRepositoryLock($repository, 'repo.pull', true);

    try {
      $lock->lock();
    } catch (PhutilLockException $ex) {
      throw new DiffusionDaemonLockException(
        pht(
          'Another process is currently updating repository "%s", '.
          'skipping pull.',
          $repository->getDisplayName()));
    }

    try {
      $result = $this->pullRepositoryWithLock();
    } catch (Exception $ex) {
      $lock->unlock();
      throw $ex;
    }

    $lock->unlock();

    return $result;
  }

  private function pullRepositoryWithLock() {
    $repository = $this->getRepository();
    $viewer = PhabricatorUser::getOmnipotentUser();

    if ($repository->isReadOnly()) {
      $this->skipPull(
        pht(
          "Skipping pull on read-only repository.\n\n%s",
          $repository->getReadOnlyMessageForDisplay()));
    }

    $is_hg = false;
    $is_git = false;
    $is_svn = false;

    $vcs = $repository->getVersionControlSystem();

    switch ($vcs) {
      case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
        // We never pull a local copy of non-hosted Subversion repositories.
        if (!$repository->isHosted()) {
          $this->skipPull(
            pht(
              'Repository "%s" is a non-hosted Subversion repository, which '.
              'does not require a local working copy to be pulled.',
              $repository->getDisplayName()));
          return;
        }
        $is_svn = true;
        break;
      case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
        $is_git = true;
        break;
      case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
        $is_hg = true;
        break;
      default:
        $this->abortPull(pht('Unknown VCS "%s"!', $vcs));
        break;
    }

    $local_path = $repository->getLocalPath();
    if ($local_path === null) {
      $this->abortPull(
        pht(
          'No local path is configured for repository "%s".',
          $repository->getDisplayName()));
    }

    try {
      $dirname = dirname($local_path);
      if (!Filesystem::pathExists($dirname)) {
        Filesystem::createDirectory($dirname, 0755, $recursive = true);
      }

      if (!Filesystem::pathExists($local_path)) {
        $this->logPull(
          pht(
            'Creating a new working copy for repository "%s".',
            $repository->getDisplayName()));
        if ($is_git) {
          $this->executeGitCreate();
        } else if ($is_hg) {
          $this->executeMercurialCreate();
        } else {
          $this->executeSubversionCreate();
        }
      }

      id(new DiffusionRepositoryClusterEngine())
        ->setViewer($viewer)
        ->setRepository($repository)
        ->synchronizeWorkingCopyBeforeRead();

      if (!$repository->isHosted()) {
        $this->logPull(
          pht(
            'Updating the working copy for repository "%s".',
            $repository->getDisplayName()));

        if ($is_git) {
          $this->executeGitUpdate();
        } else if ($is_hg) {
          $this->executeMercurialUpdate();
        }
      }

      if ($repository->isHosted()) {
        if ($is_git) {
          $this->installGitHook();
        } else if ($is_svn) {
          $this->installSubversionHook();
        } else if ($is_hg) {
          $this->installMercurialHook();
        }

        foreach ($repository->getHookDirectories() as $directory) {
          $this->installHookDirectory($directory);
        }
      }

      if ($is_git) {
        $this->updateGitWorkingCopyConfiguration();
      }

    } catch (Exception $ex) {
      $this->abortPull(
        pht(
          "Pull of '%s' failed: %s",
          $repository->getDisplayName(),
          $ex->getMessage()),
        $ex);
    }

    $this->donePull();

    return $this;
  }

  private function skipPull($message) {
    $this->log($message);
    $this->donePull();
  }

  private function abortPull($message, ?Exception $ex = null) {
    $code_error = PhabricatorRepositoryStatusMessage::CODE_ERROR;
    $this->updateRepositoryInitStatus($code_error, $message);
    if ($ex) {
      throw $ex;
    } else {
      throw new Exception($message);
    }
  }

  private function logPull($message) {
    $this->log($message);
  }

  private function donePull() {
    $code_okay = PhabricatorRepositoryStatusMessage::CODE_OKAY;
    $this->updateRepositoryInitStatus($code_okay);
  }

  private function updateRepositoryInitStatus($code, $message = null) {
    $this->getRepository()->writeStatusMessage(
      PhabricatorRepositoryStatusMessage::TYPE_INIT,
      $code,
      array(
        'message' => $message,
      ));
  }

  private function installHook($path, array $hook_argv = array()) {
    $this->log(pht('Installing commit hook to "%s"...', $path));

    $repository = $this->getRepository();
    $identifier = $this->getHookContextIdentifier($repository);

    $root = dirname(phutil_get_library_root('phabricator'));
    $bin = $root.'/bin/commit-hook';

    $full_php_path = Filesystem::resolveBinary('php');
    $cmd = csprintf(
      'exec %s -f %s -- %s %Ls "$@"',
      $full_php_path,
      $bin,
      $identifier,
      $hook_argv);

    $hook = "#!/bin/sh\nexport TERM=dumb\n{$cmd}\n";

    Filesystem::writeFile($path, $hook);
    Filesystem::changePermissions($path, 0755);
  }

  private function installHookDirectory($path) {
    $readme = pht(
      "To add custom hook scripts to this repository, add them to this ".
      "directory.\n\n%s will run any executables in this directory ".
      "after running its own checks, as though they were normal hook ".
      "scripts.",
      PlatformSymbols::getPlatformServerName());

    Filesystem::createDirectory($path, 0755);
    Filesystem::writeFile($path.'/README', $readme);
  }

  private function getHookContextIdentifier(PhabricatorRepository $repository) {
    $identifier = $repository->getPHID();

    $instance = PhabricatorEnv::getEnvConfig('cluster.instance');
    if (phutil_nonempty_string($instance)) {
      $identifier = "{$identifier}:{$instance}";
    }

    return $identifier;
  }


/* -(  Pulling Git Working Copies  )----------------------------------------- */


  /**
   * @task git
   */
  private function executeGitCreate() {
    $repository = $this->getRepository();

    $path = rtrim($repository->getLocalPath(), '/');

    // See T13448. In all cases, we create repositories by using "git init"
    // to build a bare, empty working copy. If we try to use "git clone"
    // instead, we'll pull in too many refs if "Fetch Refs" is also
    // configured. There's no apparent way to make "git clone" behave narrowly
    // and no apparent reason to bother.

    $repository->execxRemoteCommand(
      'init --bare -- %s',
      $path);
  }


  /**
   * @task git
   */
  private function executeGitUpdate() {
    $repository = $this->getRepository();

    // See T13479. We previously used "--show-toplevel", but this stopped
    // working in Git 2.25.0 when run in a bare repository.

    // NOTE: As of Git 2.21.1, "git rev-parse" can not parse "--" in its
    // argument list, so we can not specify arguments unambiguously. Any
    // version of Git which does not recognize the "--git-dir" flag will
    // treat this as a request to parse the literal refname "--git-dir".

    list($err, $stdout) = $repository->execLocalCommand(
      'rev-parse --git-dir');

    $repository_root = null;
    $path = $repository->getLocalPath();

    if (!$err) {
      $repository_root = Filesystem::resolvePath(
        rtrim($stdout, "\n"),
        $path);

      // If we're in a bare Git repository, the "--git-dir" will be the
      // root directory. If we're in a working copy, the "--git-dir" will
      // be the ".git/" directory.

      // Test if the result is the root directory. If it is, we're in good
      // shape and appear to be inside a bare repository. If not, take the
      // parent directory to get out of the ".git/" folder.

      if (!Filesystem::pathsAreEquivalent($repository_root, $path)) {
        $repository_root = dirname($repository_root);
      }
    }

    $message = null;
    if ($err) {
      // Try to raise a more tailored error message in the more common case
      // of the user creating an empty directory. (We could try to remove it,
      // but might not be able to, and it's much simpler to raise a good
      // message than try to navigate those waters.)
      if (is_dir($path)) {
        $files = Filesystem::listDirectory($path, $include_hidden = true);
        if (!$files) {
          $message = pht(
            'Expected to find a Git repository at "%s", but there is an '.
            'empty directory there. Remove the directory. A daemon will '.
            'construct the working copy for you.',
            $path);
        } else {
          $message = pht(
            'Expected to find a Git repository at "%s", but there is '.
            'a non-repository directory (with other stuff in it) there. '.
            'Move or remove this directory. A daemon will construct '.
            'the working copy for you.',
            $path);
        }
      } else if (is_file($path)) {
        $message = pht(
          'Expected to find a Git repository at "%s", but there is a '.
          'file there instead. Move or remove this file. A daemon will '.
          'construct the working copy for you.',
          $path);
      } else {
        $message = pht(
          'Expected to find a git repository at "%s", but did not.',
          $path);
      }
    } else {

      // Prior to Git 2.25.0, we used "--show-toplevel", which had a weird
      // case here when the working copy was inside another working copy.
      // The switch to "--git-dir" seems to have resolved this; we now seem
      // to find the nearest git directory and thus the correct repository
      // root.

      if (!Filesystem::pathsAreEquivalent($repository_root, $path)) {
        $err = true;
        $message = pht(
          'Expected to find a Git repository at "%s", but the actual Git '.
          'repository root for this directory is "%s". Something is '.
          'misconfigured. This directory should be writable by the daemons '.
          'and not inside another Git repository.',
          $path,
          $repository_root);
      }
    }

    if ($err && $repository->canDestroyWorkingCopy()) {
      phlog(
        pht(
          "Repository working copy at '%s' failed sanity check; ".
          "destroying and re-cloning. %s",
          $path,
          $message));
      Filesystem::remove($path);
      $this->executeGitCreate();
    } else if ($err) {
      throw new Exception($message);
    }

    // Load the refs we're planning to fetch from the remote repository.
    $remote_refs = $this->loadGitRemoteRefs(
      $repository,
      $repository->getRemoteURIEnvelope(),
      $is_local = false);

    // Load the refs we're planning to fetch from the local repository, by
    // using the local working copy path as the "remote" repository URI.
    $local_refs = $this->loadGitRemoteRefs(
      $repository,
      new PhutilOpaqueEnvelope($path),
      $is_local = true);

    // See T13448. The "git fetch --prune ..." flag only prunes local refs
    // matching the refspecs we pass it. If "Fetch Refs" is configured, we'll
    // pass it a very narrow list of refspecs, and it won't prune older refs
    // that aren't currently subject to fetching.

    // Since we want to prune everything that isn't (a) on the fetch list and
    // (b) in the remote, handle pruning of any surplus leftover refs ourselves
    // before we fetch anything.

    // (We don't have to do this if "Fetch Refs" isn't set up, since "--prune"
    // will work in that case, but it's a little simpler to always go down the
    // same code path.)

    $surplus_refs = array();
    foreach ($local_refs as $local_ref => $local_hash) {
      $remote_hash = idx($remote_refs, $local_ref);
      if ($remote_hash === null) {
        $surplus_refs[] = $local_ref;
      }
    }

    if ($surplus_refs) {
      $this->log(
        pht(
          'Found %s surplus local ref(s) to delete.',
          phutil_count($surplus_refs)));
      foreach ($surplus_refs as $surplus_ref) {
        $this->log(
          pht(
            'Deleting surplus local ref "%s" ("%s").',
            $surplus_ref,
            $local_refs[$surplus_ref]));

        $repository->execLocalCommand(
          'update-ref -d %R --',
          $surplus_ref);

        unset($local_refs[$surplus_ref]);
      }
    }

    if ($remote_refs === $local_refs) {
      $this->log(
        pht(
          'Skipping fetch because local and remote refs are already '.
          'identical.'));
      return false;
    }

    $this->logRefDifferences($remote_refs, $local_refs);

    $fetch_rules = $this->getGitFetchRules($repository);

    // For very old non-bare working copies, we need to use "--update-head-ok"
    // to tell Git that it is allowed to overwrite whatever is currently
    // checked out. See T13280.

    $future = $repository->getRemoteCommandFuture(
      'fetch --no-tags --update-head-ok -- %P %Ls',
      $repository->getRemoteURIEnvelope(),
      $fetch_rules);

    $future
      ->setCWD($path)
      ->resolvex();
  }

  private function getGitRefRules(PhabricatorRepository $repository) {
    $ref_rules = $repository->getFetchRules();

    if (!$ref_rules) {
      $ref_rules = array(
        'refs/*',
      );
    }

    return $ref_rules;
  }

  private function getGitFetchRules(PhabricatorRepository $repository) {
    $ref_rules = $this->getGitRefRules($repository);

    // Rewrite each ref rule "X" into "+X:X".

    // The "X" means "fetch ref X".
    // The "...:X" means "...and copy it into local ref X".
    // The "+..." means "...and overwrite the local ref if it already exists".

    $fetch_rules = array();
    foreach ($ref_rules as $key => $ref_rule) {
      $fetch_rules[] = sprintf(
        '+%s:%s',
        $ref_rule,
        $ref_rule);
    }

    return $fetch_rules;
  }

  /**
   * @task git
   */
  private function installGitHook() {
    $repository = $this->getRepository();
    $root = $repository->getLocalPath();

    if ($repository->isWorkingCopyBare()) {
      $path = '/hooks/pre-receive';
    } else {
      $path = '/.git/hooks/pre-receive';
    }

    $this->installHook($root.$path);
  }

  private function updateGitWorkingCopyConfiguration() {
    $repository = $this->getRepository();

    // See T5963. When you "git clone" from a remote with no "master", the
    // client warns you that it isn't sure what it should check out as an
    // initial state:

    //   warning: remote HEAD refers to nonexistent ref, unable to checkout

    // We can tell the client what it should check out by making "HEAD"
    // point somewhere. However:
    //
    // (1) If we don't set "receive.denyDeleteCurrent" to "ignore" and a user
    // tries to delete the default branch, Git raises an error and refuses.
    // We want to allow this; we already have sufficient protections around
    // dangerous changes and do not need to special case the default branch.
    //
    // (2) A repository may have a nonexistent default branch configured.
    // For now, we just respect configuration. This will raise a warning when
    // users clone the repository.
    //
    // In any case, these changes are both advisory, so ignore any errors we
    // may encounter.

    // We do this for both hosted and observed repositories. Although it is
    // not terribly common to clone from Phabricator's copy of an observed
    // repository, it works fine and makes sense occasionally.

    if ($repository->isWorkingCopyBare()) {
      $repository->execLocalCommand(
        'config -- receive.denyDeleteCurrent ignore');
      $repository->execLocalCommand(
        'symbolic-ref HEAD %s',
        'refs/heads/'.$repository->getDefaultBranch());
    }
  }

  private function loadGitRemoteRefs(
    PhabricatorRepository $repository,
    PhutilOpaqueEnvelope $remote_envelope,
    $is_local) {

    // See T13448. When listing local remotes, we want to list everything,
    // not just refs we expect to fetch. This allows us to detect that we have
    // undesirable refs (which have been deleted in the remote, but are still
    // present locally) so we can update our state to reflect the correct
    // remote state.

    if ($is_local) {
      $ref_rules = array();
    } else {
      $ref_rules = $this->getGitRefRules($repository);

      // NOTE: "git ls-remote" does not support "--" until circa January 2016.
      // See T12416. None of the flags to "ls-remote" appear dangerous, but
      // refuse to list any refs beginning with "-" just in case.

      foreach ($ref_rules as $ref_rule) {
        if (preg_match('/^-/', $ref_rule)) {
          throw new Exception(
            pht(
              'Refusing to list potentially dangerous ref ("%s") beginning '.
              'with "-".',
              $ref_rule));
        }
      }
    }

    list($stdout) = $repository->execxRemoteCommand(
      'ls-remote %P %Ls',
      $remote_envelope,
      $ref_rules);

    // Empty repositories don't have any refs.
    if (!strlen(rtrim($stdout))) {
      return array();
    }

    $map = array();
    $lines = phutil_split_lines($stdout, false);
    foreach ($lines as $line) {
      list($hash, $name) = preg_split('/\s+/', $line, 2);

      // If the remote has a HEAD, just ignore it.
      if ($name == 'HEAD') {
        continue;
      }

      // If the remote ref is itself a remote ref, ignore it.
      if (preg_match('(^refs/remotes/)', $name)) {
        continue;
      }

      $map[$name] = $hash;
    }

    ksort($map);

    return $map;
  }

  private function logRefDifferences(array $remote, array $local) {
    $all = $local + $remote;

    $differences = array();
    foreach ($all as $key => $ignored) {
      $remote_ref = idx($remote, $key, pht('<null>'));
      $local_ref = idx($local, $key, pht('<null>'));
      if ($remote_ref !== $local_ref) {
        $differences[] = pht(
          '%s (remote: "%s", local: "%s")',
          $key,
          $remote_ref,
          $local_ref);
      }
    }

    $this->log(
      pht(
        "Updating repository after detecting ref differences:\n%s",
        implode("\n", $differences)));
  }


/* -(  Pulling Mercurial Working Copies  )----------------------------------- */


  /**
   * @task hg
   */
  private function executeMercurialCreate() {
    $repository = $this->getRepository();

    $path = rtrim($repository->getLocalPath(), '/');

    if ($repository->isHosted()) {
      $repository->execxRemoteCommand(
        'init -- %s',
        $path);
    } else {
      $remote = $repository->getRemoteURIEnvelope();

      // NOTE: Mercurial prior to 3.2.4 has an severe command injection
      // vulnerability. See: <http://bit.ly/19B58E9>

      // On vulnerable versions of Mercurial, we refuse to clone remotes which
      // contain characters which may be interpreted by the shell.
      $hg_binary = PhutilBinaryAnalyzer::getForBinary('hg');
      $is_vulnerable = $hg_binary->isMercurialVulnerableToInjection();
      if ($is_vulnerable) {
        $cleartext = $remote->openEnvelope();
        // The use of "%R" here is an attempt to limit collateral damage
        // for normal URIs because it isn't clear how long this vulnerability
        // has been around for.

        $escaped = csprintf('%R', $cleartext);
        if ((string)$escaped !== (string)$cleartext) {
          throw new Exception(
            pht(
              'You have an old version of Mercurial (%s) which has a severe '.
              'command injection security vulnerability. The remote URI for '.
              'this repository (%s) is potentially unsafe. Upgrade Mercurial '.
              'to at least 3.2.4 to clone it.',
              $hg_binary->getBinaryVersion(),
              $repository->getMonogram()));
        }
      }

      try {
        $repository->execxRemoteCommand(
          'clone --noupdate -- %P %s',
          $remote,
          $path);
      } catch (Exception $ex) {
        $message = $ex->getMessage();
        $message = $this->censorMercurialErrorMessage($message);
        throw new Exception($message);
      }
    }
  }


  /**
   * @task hg
   */
  private function executeMercurialUpdate() {
    $repository = $this->getRepository();
    $path = $repository->getLocalPath();

    // This is a local command, but needs credentials.
    $remote = $repository->getRemoteURIEnvelope();
    $future = $repository->getRemoteCommandFuture('pull -- %P', $remote);
    $future->setCWD($path);

    try {
      $future->resolvex();
    } catch (CommandException $ex) {
      $err = $ex->getError();
      $stdout = $ex->getStdout();

      // NOTE: Between versions 2.1 and 2.1.1, Mercurial changed the behavior
      // of "hg pull" to return 1 in case of a successful pull with no changes.
      // This behavior has been reverted, but users who updated between Feb 1,
      // 2012 and Mar 1, 2012 will have the erroring version. Do a dumb test
      // against stdout to check for this possibility.

      // NOTE: Mercurial has translated versions, which translate this error
      // string. In a translated version, the string will be something else,
      // like "aucun changement trouve". There didn't seem to be an easy way
      // to handle this (there are hard ways but this is not a common problem
      // and only creates log spam, not application failures). Assume English.

      // TODO: Remove this once we're far enough in the future that deployment
      // of 2.1 is exceedingly rare?
      if ($err == 1 && preg_match('/no changes found/', $stdout)) {
        return;
      } else {
        $message = $ex->getMessage();
        $message = $this->censorMercurialErrorMessage($message);
        throw new Exception($message);
      }
    }
  }


  /**
   * Censor response bodies from Mercurial error messages.
   *
   * When Mercurial attempts to clone an HTTP repository but does not
   * receive a response it expects, it emits the response body in the
   * command output.
   *
   * This represents a potential SSRF issue, because an attacker with
   * permission to create repositories can create one which points at the
   * remote URI for some local service, then read the response from the
   * error message. To prevent this, censor response bodies out of error
   * messages.
   *
   * @param string $message Uncensored Mercurial command output.
   * @return string Censored Mercurial command output.
   */
  private function censorMercurialErrorMessage($message) {
    return preg_replace(
      '/^---%<---.*/sm',
      pht('<Response body omitted from Mercurial error message.>')."\n",
      $message);
  }


  /**
   * @task hg
   */
  private function installMercurialHook() {
    $repository = $this->getRepository();
    $path = $repository->getLocalPath().'/.hg/hgrc';

    $identifier = $this->getHookContextIdentifier($repository);

    $root = dirname(phutil_get_library_root('phabricator'));
    $bin = $root.'/bin/commit-hook';

    $data = array();
    $data[] = '[hooks]';

    // This hook handles normal pushes.
    $data[] = csprintf(
      'pretxnchangegroup.phabricator = TERM=dumb %s %s %s',
      $bin,
      $identifier,
      'pretxnchangegroup');

    // This one handles creating bookmarks.
    $data[] = csprintf(
      'prepushkey.phabricator = TERM=dumb %s %s %s',
      $bin,
      $identifier,
      'prepushkey');

    $data[] = null;

    $data = implode("\n", $data);

    $this->log('%s', pht('Installing commit hook config to "%s"...', $path));

    Filesystem::writeFile($path, $data);
  }


/* -(  Pulling Subversion Working Copies  )---------------------------------- */


  /**
   * @task svn
   */
  private function executeSubversionCreate() {
    $repository = $this->getRepository();

    $path = rtrim($repository->getLocalPath(), '/');
    execx('svnadmin create -- %s', $path);
  }


  /**
   * @task svn
   */
  private function installSubversionHook() {
    $repository = $this->getRepository();
    $root = $repository->getLocalPath();

    $path = '/hooks/pre-commit';
    $this->installHook($root.$path);

    $revprop_path = '/hooks/pre-revprop-change';

    $revprop_argv = array(
      '--hook-mode',
      'svn-revprop',
    );

    $this->installHook($root.$revprop_path, $revprop_argv);
  }


}