// file      : bbot/agent.cxx -*- C++ -*-
// copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
// license   : TBC; see accompanying LICENSE file

#include <bbot/agent>

#include <pwd.h>    // getpwuid()
#include <limits.h> // PATH_MAX
#include <signal.h> // signal()
#include <unistd.h> // sleep(), realink(), getuid()

#include <net/if.h>     // ifreq
#include <netinet/in.h> // sockaddr_in
#include <arpa/inet.h>  // inet_ntop()
#include <sys/ioctl.h>
#include <sys/socket.h>

#include <iostream>

#include <butl/pager>
#include <butl/filesystem> // dir_iterator

#include <bbot/manifest>

#include <bbot/types>
#include <bbot/utility>
#include <bbot/diagnostics>

#include <bbot/tftp>
#include <bbot/machine>
#include <bbot/bootstrap-manifest>

using namespace std;
using namespace butl;
using namespace bbot;

namespace bbot
{
  agent_options ops;

  const string bs_prot ("1");

  string tc_name;
  string tc_num;
  string tc_id;

  uid_t  uid;
  string uname;

  // Note: Linux-specific implementation.
  //
  string
  iface_addr (const string& i)
  {
    if (i.size () >= IFNAMSIZ)
      throw invalid_argument ("interface nama too long");

    auto_fd fd (socket (AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0));

    if (fd.get () == -1)
      throw_system_error (errno);

    ifreq ifr;
    ifr.ifr_addr.sa_family = AF_INET;
    strcpy (ifr.ifr_name, i.c_str ());

    if (ioctl (fd.get (), SIOCGIFADDR, &ifr) == -1)
      throw_system_error (errno);

    char buf[3 * 4 + 3 + 1]; // IPv4 address.
    if (inet_ntop (AF_INET,
                   &reinterpret_cast<sockaddr_in*> (&ifr.ifr_addr)->sin_addr,
                   buf,
                   sizeof (buf)) == nullptr)
      throw_system_error (errno);

    return buf;
  }
}

// The btrfs tool likes to print informational messages, like "Created
// snapshot such and such". Luckily, it writes them to stdout while proper
// diagnostics to stderr.
//
template <typename... A>
inline void
btrfs (tracer& t, A&&... a)
{
  if (verb >= 3)
    run_io (t, fdnull (), 2, 2, "btrfs", forward<A> (a)...);
  else
    run_io (t, fdnull (), fdnull (), 2, "btrfs", forward<A> (a)...);
}

template <typename... A>
inline butl::process_exit::code_type
btrfs_exit (tracer& t, A&&... a)
{
  return verb >= 3
    ? run_io_exit (t, fdnull (), 2, 2, "btrfs", forward<A> (a)...)
    : run_io_exit (t, fdnull (), fdnull (), 2, "btrfs", forward<A> (a)...);
}

// Bootstrap the machine. Return the bootstrapped machine manifest if
// successful and nullopt otherwise (in which case the machine directory
// should be cleaned and the machine ignored for now).
//
static optional<bootstrapped_machine_manifest>
bootstrap_machine (const dir_path& md,
                   const machine_manifest& mm,
                   optional<bootstrapped_machine_manifest> obmm)
{
  tracer trace ("bootstrap_machine");

  bootstrapped_machine_manifest r {
    mm,
    toolchain_manifest {tc_id},
    bootstrap_manifest {
      bootstrap_manifest::versions_type {
        {"bbot",    BBOT_VERSION},
        {"libbbot", LIBBBOT_VERSION},
        {"libbpkg", LIBBPKG_VERSION},
        {"libbutl", LIBBUTL_VERSION}
      }
    }
  };

  if (ops.fake_bootstrap ())
  {
    r.machine.mac = "de:ad:be:ef:de:ad";
  }
  else
  try
  {
    string br ("br1"); // Using private bridge for now.

    // Start the TFTP server (server chroot is /build/tftp). Map:
    //
    // GET requests to /build/tftp/toolchain/<name>/*
    // PUT requests to /build/tftp/bootstrap/<name>/*
    //
    auto_rmdir arm (dir_path ("/build/tftp/bootstrap/" + tc_name));
    try_mkdir_p (arm.path ());

    // Bootstrap result manifest.
    //
    path mf (arm.path () / "manifest");
    try_rmfile (mf);

    tftp_server tftpd ("Gr  ^/?(.+)$  /toolchain/" + tc_name + "/\\1\n" +
                       "Pr  ^/?(.+)$  /bootstrap/" + tc_name + "/\\1\n");

    l2 ([&]{trace << "tftp server on port " << tftpd.port ();});

    // Start the machine.
    //
    unique_ptr<machine> m (
      start_machine (md,
                     mm,
                     obmm ? obmm->machine.mac : nullopt,
                     br,
                     tftpd.port ()));

    {
      // If we are terminating with an exception then force the machine down.
      // Failed that, the machine's destructor will block waiting for its
      // completion.
      //
      auto mg (
        make_exception_guard (
          [&m, &md] ()
          {
            info << "trying to force machine " << md << " down";
            try {m->forcedown ();} catch (const failed&) {}
          }));

      // What happens if the bootstrap process hangs? The simple thing would
      // be to force the machine down after some timeout and then fail. But
      // that won't be very helpful for investigating the cause. So instead
      // the plan is to suspend it after some timeout, issue diagnostics
      // (without failing and which Build OS monitor will relay to the admin),
      // and wait for the external intervention.
      //
      auto soft_fail = [&md, &m] (const char* msg)
      {
        {
          diag_record dr (error);
          dr << msg << " for machine " << md << ", suspending";
          m->print_info (dr);
        }
        m->suspend ();
        m->wait ();
        return nullopt;
      };

      // The first request should be the toolchain download. Wait for up to 60
      // seconds for that to arrive. In a sense we use it as an indication
      // that the machine has booted and the bootstrap process has started.
      //
      size_t to;
      const size_t startup_to   (60);
      const size_t bootstrap_to (ops.bootstrap_timeout ());
      const size_t shutdown_to  (60);

      if (!tftpd.serve ((to = startup_to)))
        return soft_fail ("bootstrap startup timeout");

      l2 ([&]{trace << "completed startup in " << startup_to - to << "s";});

      // Next the bootstrap process may download additional toolchain
      // archives, build things, and then upload the result manifest. So on
      // our side we serve TFTP requests while periodically checking for the
      // manifest file.
      //
      for (to = bootstrap_to; to != 0 && !file_exists (mf); tftpd.serve (to)) ;

      if (to == 0)
        return soft_fail ("bootstrap timeout");

      l2 ([&]{trace << "completed bootstrap in " << bootstrap_to - to << "s";});

      // Shut the machine down cleanly.
      //
      if (!m->shutdown ((to = shutdown_to)))
        return soft_fail ("bootstrap shutdown timeout");

      l2 ([&]{trace << "completed shutdown in " << shutdown_to - to << "s";});
    }

    // Parse the result manifest.
    //
    try
    {
      r.bootstrap = parse_manifest<bootstrap_manifest> (mf, "bootstrap");
    }
    catch (const failed&)
    {
      error << "invalid bootstrap manifest for machine " << md;
      return nullopt;
    }

    r.machine.mac = m->mac; // Save the MAC address.
  }
  catch (const system_error& e)
  {
    fail << "tftp server error: " << e;
  }

  serialize_manifest (r, md / "manifest", "bootstrapped machine");
  return r;
}

static machine_header_manifests
enumerate_machines (const dir_path& rd)
try
{
  tracer trace ("enumerate_machines");

  machine_header_manifests r;

  // The first level are machine volumes.
  //
  for (const dir_entry& ve: dir_iterator (rd))
  {
    const string vn (ve.path ().string ());

    // Ignore hidden directories.
    //
    if (ve.type () != entry_type::directory || vn[0] == '.')
      continue;

    const dir_path vd (dir_path (rd) /= vn);

    // Inside we have machines.
    //
    try
    {
      for (const dir_entry& me: dir_iterator (vd))
      {
        const string mn (me.path ().string ());

        if (me.type () != entry_type::directory || mn[0] == '.')
          continue;

        const dir_path md (dir_path (vd) /= mn);

        // Our endgoal here is to obtain a bootstrapped snapshot of this
        // machine while watching out for potential race conditions (machines
        // being added/upgraded/removed; see the manual for details).
        //
        // So here is our overall plan:
        //
        // 1. Resolve current subvolume link for our bootstrap protocol.
        //
        // 2. If there is no link, cleanup and ignore this machine.
        //
        // 3. Try to create a snapshot of current subvolume (this operation is
        //    atomic). If failed (e.g., someone changed the link and removed
        //    the subvolume in the meantime), retry from #1.
        //
        // 4. Compare the snapshot to the already bootstrapped version (if
        //    any) and see if we need to re-bootstrap. If so, use the snapshot
        //    as a starting point. Rename to bootstrapped at the end (atomic).
        //
        const dir_path lp (dir_path (md) /= (mn + '-' + bs_prot)); // -<P>
        const dir_path tp (dir_path (md) /= (mn + '-' + tc_name)); // -<too...>
        bool te (dir_exists (tp));

        auto delete_t = [&tp, &trace] ()
        {
          btrfs (trace, "property", "set", "-ts", tp, "ro", "false");
          btrfs (trace, "subvolume", "delete", tp);
        };

        for (size_t retry (0);; ++retry)
        {
          if (retry != 0)
            sleep (1);

          // Resolve the link to subvolume path.
          //
          dir_path sp; // <name>-<P>.<R>
          try
          {
            char b [PATH_MAX + 1];
            ssize_t r (readlink (lp.string ().c_str (), b, sizeof (b)));

            if (r == -1)
            {
              if (errno != ENOENT)
                throw_generic_error (errno);
            }
            else if (static_cast<size_t> (r) >= sizeof (b))
              throw_generic_error (EINVAL);
            else
            {
              b[r] = '\0';
              sp = dir_path (b);
              if (sp.relative ())
                sp = md / sp;
            }
          }
          catch (const system_error& e)
          {
            fail << "unable to read subvolume link " << lp << ": " << e;
          }

          // If the resolution fails, then this means there is no current
          // machine subvolume (for this bootstrap protocol). In this case we
          // clean up our toolchain subvolume (<name>-<toolchain>) and ignore
          // this machine.
          //
          if (sp.empty ())
          {
            if (te)
              delete_t ();

            l2 ([&]{trace << "skipping " << md << ": no subvolume link";});
            break;
          }

          // <name>-<toolchain>-<xxx>
          //
          const dir_path xp (dir_path (md) /=
                             path::traits::temp_name (mn + '-' + tc_name));

          if (btrfs_exit (trace, "subvolume", "snapshot", sp, xp) != 0)
          {
            if (retry >= 10)
              fail << "unable to snapshot subvolume " << sp;

            continue;
          }

          // Load the (original) machine manifest.
          //
          auto mm (
            parse_manifest<machine_manifest> (sp / "manifest", "machine"));

          // If we already have <name>-<toolchain>, see if it needs to be re-
          // bootstrapped. Things that render it obsolete:
          //
          // 1. New machine revision  (compare machine ids).
          // 2. New toolchain         (compare toolchain ids).
          // 3. New bbot/libbbot      (compare versions).
          //
          // The last case has a complication: what should we do if we have
          // bootstrapped a newer version of bbot? This would mean that we are
          // about to be stopped and upgraded (and the upgraded version will
          // probably be able to use the result). So we simply ignore this
          // machine for this run.

          // Return -1 if older, 0 if the same, and +1 if newer.
          //
          auto compare_bbot = [] (const bootstrap_manifest& m) -> int
          {
            auto cmp = [&m] (const string& n, uint64_t v) -> int
            {
              auto i = m.versions.find (n);
              return
                i == m.versions.end () || i->second < v
                ? -1
                : i->second > v ? 1 : 0;
            };

            // Start from the top assuming a new dependency cannot be added
            // without changing the dependent's version.
            //
            int r;
            return
              (r = cmp ("bbot",       BBOT_VERSION)) != 0 ? r :
              (r = cmp ("libbbot", LIBBBOT_VERSION)) != 0 ? r :
              (r = cmp ("libbpkg", LIBBPKG_VERSION)) != 0 ? r :
              (r = cmp ("libbutl", LIBBUTL_VERSION)) != 0 ? r : 0;
          };

          optional<bootstrapped_machine_manifest> bmm;
          if (te)
          {
            bmm = parse_manifest<bootstrapped_machine_manifest> (
              tp / "manifest", "bootstrapped machine");

            if (bmm->machine.id != mm.id)
            {
              l2 ([&]{trace << "re-bootstrapping " << tp << ": new machine";});
              te = false;
            }

            if (bmm->toolchain.id != tc_id)
            {
              l2 ([&]{trace << "re-bootstrapping " << tp << ": new toolchain";});
              te = false;
            }

            if (int i = compare_bbot (bmm->bootstrap))
            {
              if (i < 0)
              {
                l2 ([&]{trace << "re-bootstrapping " << tp << ": new bbot";});
                te = false;
              }
              else
              {
                l2 ([&]{trace << "ignoring " << tp << ": old bbot";});
                btrfs (trace, "subvolume", "delete", xp);
                break;
              }
            }

            if (!te)
              delete_t ();
          }
          else
            l2 ([&]{trace << "bootstrapping " << tp;});

          if (!te)
          {
            // Use the <name>-<toolchain>-<xxx> snapshot that we have made to
            // bootstrap the new machine. Then atomically rename it to
            // <name>-<toolchain>.
            //
            bmm = bootstrap_machine (xp, mm, move (bmm));

            if (!bmm)
            {
              l2 ([&]{trace << "ignoring " << tp << ": failed to bootstrap";});
              btrfs (trace, "subvolume", "delete", xp);
              break;
            }

            try
            {
              mvdir (xp, tp);
            }
            catch (const system_error& e)
            {
              fail << "unable to rename " << xp << " to " << tp;
            }

            // Check the boostrapped bbot version as above and ignore this
            // machine if it's newer than us.
            //
            if (int i = compare_bbot (bmm->bootstrap))
            {
              assert (i > 0);
              l2 ([&]{trace << "ignoring " << tp << ": old bbot";});
              break;
            }
          }
          else
            btrfs (trace, "subvolume", "delete", xp);

          // Add the machine to the list.
          //
          r.push_back (
            machine_header_manifest (move (mm.id),
                                     move (mm.name),
                                     move (mm.summary)));

          break;
        }
      }
    }
    catch (const system_error& e)
    {
      fail << "unable to iterate over " << vd << ": " << e << endf;
    }
  }

  return r;
}
catch (const system_error& e)
{
  fail << "unable to iterate over " << rd << ": " << e << endf;
}

extern "C" void
handle_signal (int sig)
{
  switch (sig)
  {
  case SIGHUP:  exit (3); // Unimplemented feature.
  case SIGTERM: exit (0);
  default:      assert (false);
  }
}

// Right arrow followed by newline.
//
const char systemd_indent[] = "\xE2\x86\xB2\n";

int
main (int argc, char* argv[])
try
{
  cli::argv_scanner scan (argc, argv, true);
  ops.parse (scan);

  verb = ops.verbose ();

  uid = getuid ();
  uname = getpwuid (uid)->pw_name;

  if (ops.systemd_daemon ())
  {
    // Map to systemd severity prefixes (see sd-daemon(3) for details). Note
    // that here we assume we will never have location (like file name which
    // would end up being before the prefix).
    //
    trace_indent    =
      fail.indent_  =
      error.indent_ =
      warn.indent_  =
      info.indent_  =
      text.indent_  = systemd_indent;

    fail.type_  = "<3>";
    error.type_ = "<3>";
    warn.type_  = "<4>";
    info.type_  = "<6>";
    trace_type  = "<7>";

    info << "bbot agent for " << tc_name << '/' << tc_num <<
      info << "toolchain id " << tc_id <<
      info << "CPU(s)       " << ops.cpu () <<
      info << "RAM(kB)      " << ops.ram ();
  }

  tracer trace ("main");

  // On POSIX ignore SIGPIPE which is signaled to a pipe-writing process if
  // the pipe reading end is closed. Note that by default this signal
  // terminates a process. Also note that there is no way to disable this
  // behavior on a file descriptor basis or for the write() function call.
  //
  if (signal (SIGPIPE, SIG_IGN) == SIG_ERR)
    fail << "unable to ignore broken pipe (SIGPIPE) signal: "
         << system_error (errno, generic_category ()); // Sanitize.

  // Version.
  //
  if (ops.version ())
  {
    cout << "bbot-agent " << BBOT_VERSION_STR << endl
         << "libbbot " << LIBBBOT_VERSION_STR << endl
         << "libbutl " << LIBBUTL_VERSION_STR << endl
         << "Copyright (c) 2014-2017 Code Synthesis Ltd" << endl
         << "TBC; All rights reserved" << endl;

    return 0;
  }

  // Help.
  //
  if (ops.help ())
  {
    pager p ("bbot-agent help", false);
    print_bbot_agent_usage (p.stream ());

    // If the pager failed, assume it has issued some diagnostics.
    //
    return p.wait () ? 0 : 1;
  }

  if (argc != 4)
    fail << "toolchain name/id/num excected" <<
      info << "run " << argv[0] << " --help for details";

  tc_name = argv[1];
  tc_num  = argv[2];
  tc_id   = argv[3];

  // Handle SIGHUP and SIGTERM.
  //
  if (signal (SIGHUP,  &handle_signal) == SIG_ERR ||
      signal (SIGTERM, &handle_signal) == SIG_ERR)
    fail << "unable to set signal handler: "
         << system_error (errno, generic_category ()); // Sanitize.

  // The work loop. The steps we go through are:
  //
  // 1. Enumerate the available machines, (re-)bootstrapping any of necessary.
  //
  // 2. Poll controller(s) for build tasks.
  //
  // 3. If no build tasks are available, go to #1 after sleeping a bit.
  //
  // 4. If a build task is returned, do it, upload the result, and go to #1
  //    immediately.
  //
  for (unsigned int s; (s = 60); sleep (s))
  {
    machine_header_manifests mms (enumerate_machines (ops.machines ()));

    if (ops.dump_machines ())
    {
      for (const machine_header_manifest& mm: mms)
        serialize_manifest (mm, cout, "stdout", "machine manifest");

      return 0;
    }
  }
}
catch (const failed&)
{
  return 1; // Diagnostics has already been issued.
}
catch (const cli::exception& e)
{
  error << e;
  return 1;
}