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

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

#include <iostream>

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

#include <bbot/manifest>

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

#include <bbot/diagnostics>
#include <bbot/agent-options>

#include <bbot/bootstrap-manifest>

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

// 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 (t, fdnull (), 2, 2, "btrfs", forward<A> (a)...);
  else
    run (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_exit (t, fdnull (), 2, 2, "btrfs", forward<A> (a)...)
    : run_exit (t, fdnull (), fdnull (), 2, "btrfs", forward<A> (a)...);
}

agent_options ops;

const string bs_prot ("1"); // Bootstrap protocol version.

string tc_name; // Toolchain name.
string tc_num;  // Toolchain number.
string tc_id;   // Toolchain id.

static bootstrapped_machine_manifest
bootstrap_machine (const dir_path& md, const machine_manifest& mm)
{
  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 ())
  {
  }

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

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

  machine_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;
          };

          if (te)
          {
            auto 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>.
            //
            bootstrapped_machine_manifest bmm (bootstrap_machine (xp, mm));

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

            te = true;

            // 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.
          //
          // In order not to forget to clear new fields, we are instead going
          // to create a new instance with just the required fields.
          //
          r.push_back (machine_manifest (mm.id, mm.name, 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 ();

  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
         << "MIT; see accompanying LICENSE file" << 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_manifests mms (enumerate_machines (ops.machines ()));

    if (ops.dump_machines ())
    {
      for (const machine_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;
}