#!/bin/bash
# Client for TAME daemon (tamed)
#
#   Copyright (C) 2014-2020 Ryan Specialty Group, LLC.
#
#   This program is free software: you can redistribute it and/or modify
#   it under the terms of the GNU General Public License as published by
#   the Free Software Foundation, either version 3 of the License, or
#   (at your option) any later version.
#
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU General Public License for more details.
#
#   You should have received a copy of the GNU General Public License
#   along with this program.  If not, see <http://www.gnu.org/licenses/>.
##

set -euo pipefail

declare -r mypath=$( dirname "$( readlink -f "$0" )" )

declare -ri EX_NOTAMED=1  # tried to start tamed or runner but failed
declare -ri EX_STALLED=2  # runner stalled and could not recover
declare -ri EX_NORUN=3    # no available runners
declare -ri EX_DLOCK=4    # failed to get a lock to start tamed
declare -ri EX_BLOCK=5    # failed to get a lock for busy runner check
declare -ri EX_NODONE=6   # tamed did not provide a DONE with exit code
declare -ri EX_USAGE=64   # incorrect usage; sysexits.h

# maximum amount of time in seconds to wait for runner to ack
# before forcibly restarting it
declare -ri TAME_CMD_WAITTIME="${TAME_CMD_WAITTIME:-3}"

# propagate to daemon
export TAMED_STALL_SECONDS
export TAMED_SPAWNER_PID
export TAMED_JAVA_OPTS


# Send a single command to the next available runner and
# observe the result
#
# See `command-runner' for more information.
command-available-runner()
{
  local -r root="${1?Missing root run path}"
  shift 1

  local -r id=$( reserve-runner "$root" )

  test -n "$id" || {
    echo "no available runners at $root" >&2
    exit $EX_NORUN
  }

  command-runner "$id" "$root" "$@" \
    | tee -a "run-$id.log"
}


# Send a single command to a runner and observe the result
#
# stdin will be directed to the runner.  stdout of the runner will be
# echoed until a line beginning with "DONE" is found, after which this
# procedure will return with the exit code indicated by the runner.
command-runner()
{
  local -ri id="${1?Missing id}"
  local -r root="${2?Missing root run path}"
  shift 2

  local -r base="$root/$id"
  local -ri pid=$( cat "$base/pid" )

  verify-runner "$base" "$pid"

  # forward signals to runner so that build is actually halted
  # (rather than continuing in background after we die)
  trap 'kill -TERM $pid &>/dev/null' INT TERM

  # all remaining arguments are passed to the runner
  echo "$*" > "$base/0"

  # we should immediately get a response from the runner;
  # if not, then it may have stalled for some reason
  verify-runner-ack "$*" < "$base/1" || {
    echo "warning: failed runner $id ack; requesting reload" >&2
    kill -HUP "$pid"

    # give some extra time in case the host is under high load
    sleep "$TAME_CMD_WAITTIME"

    # try one last time
    echo "$*" > "$base/0"
    verify-runner-ack "$*" < "$base/1" || {
      echo "error: runner $id still unresponsive; giving up" >&2
      exit "$EX_STALLED"
    }
  }

  # output lines from runner until we reach a line stating "DONE"
  while read line; do
    # don't parse words in the initial read because we may be
    # dealing with a lot of lines
    if [ "${line:0:5}" == "DONE " ]; then
      read _ code _ <<< "$line"

      mark-available "$base"
      return "$code"
    fi

    echo "$line"
  done < "$base/1"

  # We should have returned as soon as we received DONE.  If this was not
  # provided, then something probably went wrong (e.g. JVM crash).
  return "$EX_NODONE"
}


# Get id of the first available runner and mark it as busy
#
# If no runners are available, tamed is signalled to spawn a new one.
#
# This command calls `mark-busy' so that it can acquire a runner in an
# atomic manner.  The caller is responsible for invoking `mark-available'
# after processing is complete.
#
# If no runner is available, then the result will be empty.
reserve-runner()
{
  local -r root=${1?Missing root}

  local -r timeout=10

  (
    flock -w $timeout 7 || {
      echo "error: failed to acquire busy lock at $root" >&2
      exit $EX_BLOCK
    }

    # grab the first available or request a new one
    local id=$( get-available-runner-id "$root" )
    if [ -z "$id" ]; then
      id=$( spawn-runner-and-wait "$root" ) || {
        echo "error: failed to reserve runner at $root" >&2
        exit $EX_NORUN
      }
    fi

    # mark it as busy while we still have the lock
    mark-busy "$root/$id"

    echo "$id"
  ) 7>"$root/busy-lock"
}


# Get the id of the next available runner
#
# THIS FUNCTION MUST BE GUARDED BY A MUTEX!  Otherwise there is a race
# between acquiring the available id and then actually making use of it.
#
# If multiple runners are available, then the first available runner sorted
# numerically will be chosen.  This helps to give the same runners more
# work, since they're more likely to have source (and compiled) already
# parsed in memory.  As such, runners will have load disproportionately
# spread, and may exhibit large variances in resource consumption.
#
# Sorting numerically is done because globbing sorts lexically---if runner
# 10 is spawned, then it would find itself after "1" in the list rather than
# after runner "9".
#
# If all runners are visible, then nothing will be returned.
get-available-runner-id()
{
  local -r root=${1?Missing root}

  grep -l 0 "$root"/*/busy \
    | awk -F/ '{ print $(NF-1) }' \
    | sort -n \
    | head -n1
}


# Tell tamed to spawn a new runner and output the new runner id
#
# THIS FUNCTION MUST BE GUARDED BY A MUTEX!  Otherwise there is a race
# between signaling and reading from `maxid'.
#
# This sens USR1 to tamed indicating that the next available runner should
# be spawned, and then waits on that expected runner.  See `wait-for-runner'
# for more information on waiting.
spawn-runner-and-wait()
{
  local -r root=${1?Missing root}

  local -r pid=$( < "$root/pid" )
  local -ri maxid=$( < "$root/maxid" )

  # request runner
  kill -USR1 "$pid"

  # wait on the expected id
  local -ri nextid=$(( maxid + 1 ))
  wait-for-runner "$root" "$nextid"

  echo "$nextid"
}


# Mark a runner as busy (unable to accept new commands)
#
# Once work is done, use `mark-available' to undo this operation.
mark-busy()
{
  local -r base=${1?Missing runner base path}
  echo 1 > "$base/busy"
}


# Mark a runner as available (able to accept new commands)
#
# Once work is available, use `mark-busy' to undo this operation.
mark-available()
{
  local -r base=${1?Missing runner base path}
  echo 0 > "$base/busy"
}


# Verify that a runner is available
#
# If the runner is offline or not owned by $UID, then exit with
# a non-zero status.
verify-runner()
{
  local -r base="${1?Missing base}"
  local -ri pid="${2?Missing pid}"

  ps "$pid" &>/dev/null || {
    echo "error: runner $id ($pid) is offline!" >&2
    exit "$EX_NOTAMED"
  }

  test -O "$base/0" || {
    echo "error: runner $id ($pid) is not owned by $USER!" >&2
    exit "$EX_NOTAMED"
  }
}


# Wait for command acknowledgment from runner
#
# The runner must respond within TAME_CMD_WAITTIME seconds
# and must echo back the command that was given.  Otherwise,
# this function returns with a non-zero status.
verify-runner-ack()
{
  local -r cmd="${1?Missing command}"

  read -t"$TAME_CMD_WAITTIME" -r ack || return
  test "COMMAND $cmd" == "$ack" || {
    # TODO check for ack mismatch once output race condition is fixed
    :
  }
}


# Wait somewhat impatiently for a runner
#
# Assumes that the runner is ready once the pidfile becomes
# available.  Polls for a maximum of six seconds before giving up
# and exiting with a non-zero status.
wait-for-runner()
{
  local -r root=${1?Missing root}
  local -r id=${2?Missing runner id}

  # we could use inotify, but that is not installed by default
  # on Debian systems, so let's just poll rather than introduce
  # another dependency (give up after 6 seconds)
  local -i i=12
  while test $((i--)); do
    test ! -f "$root/$id/pid" || return 0
    sleep 0.5
  done

  # still not available
  echo "error: runner $id still unavailable; giving up" >&2
  exit "$EX_NOTAMED"
}


# Attempts to start tamed if it's not already running
#
# This is designed to be safe for parallel builds by allowing only the first
# process to start tamed and hanging the others until spawning is complete.
#
# See `_start-tamed' for more information.
start-tamed-safe()
{
  local -r root=${1?Missing root}

  local -ri timeout=5
  local -r guard="$root-guard"

  mkdir -p "$( dirname "$root" )"

  (
    flock -w $timeout 6 || {
      echo "error: failed to acquire tamed spawning lock at $root" >&2
      exit $EX_DLOCK
    }

    _start-tamed "$root"

    flock -u 6
    rm -f "$guard"
  ) 6>"$guard"
}


# Start tamed if it is not already running
#
# If tamed is already running, nothing will happen; otherwise, start
# tamed and wait impatiently for the runner to become available.
#
# Even if tamed is started, wait for runner 0 to become available;
# this ensures that tamed is initialized even if this script is run
# after tamed is started but before it has fully come online (e.g
# parallel make).
_start-tamed()
{
  local -r root="${1?Missing root}"

  local -ri pid=$( cat "$root/pid" 2>/dev/null )

  ps "$pid" &>/dev/null || {
    echo "starting tamed at $root..."

    # tell tamed to clean up so that we eliminate race conditions
    # with wait-for-tamed (this will also kill any stray processes
    # that a previous tamed may have spawned but didn't get the
    # chance to clean up)
    kill-tamed "$root" || true

    # start tamed and allow it to persist for future commands
    "$mypath/tamed" "$root" & disown
  }

  # wait for tamed even if it was already started (just in
  # case this script was executed right after tamed started
  # but before it is done initializing)
  wait-for-runner "$root" 0
}


# Kill tamed
#
# Ask tamed to kill itself.
kill-tamed()
{
  local -r root="${1?Missing root}"

  "$mypath/tamed" --kill "$root"
}


# Filter dslc output to essential information
#
# The original output of dslc is quite noisy; this filters it down
# to only errors and warnings.
#
# Eventually, dslc out to be modified to handle filtering its own
# output rather than wasting cycles doing this filtering.
saneout()
{
  awk ' \
    /^~~~~\[begin /,/^~~~~\[end / { next } \
    /^rm / { next } \
    /^COMMAND / { next } \
    /^Exception|^\t+at / { \
      if ( /^E/ ) { \
        print; \
        print "Stack trace written to run-*.log"; \
      } \
      next; \
     } \
    /([Ww]arning|[Nn]otice)[: ]/ { printf "\033[0;33m"; w++; out=1; } \
    /[Ff]atal:/ { printf "\033[0;31m"; out=1; } \
    /!|[Ee]rror:/ { printf "\033[0;31m"; e++; out=1; } \
    /internal:/ { printf "\033[0;35m"; out=1; } \
    /internal error:/ { printf "\033[1m"; out=1; } \
    /^[^[]/ || out { print; printf "\033[0;0m"; out=0; } \
  '
}


# Output usage information and exit
usage()
{
  cat <<EOF
Usage: $0 [-v|--verbose] cmdline
Or:    $0 --kill
Send command line CMDLINE to a tamed runner.  Start tamed if
not already running.

If a runner does not acknlowedge a request in TAME_CMD_WAITTIME
seconds, it will be reloaded and given TAME_CMD_WAITTIME seconds
to come online.  After that time has elapsed, the command will
be re-attempted, timing out again after TAME_CMD_WAITTIME and
and at that point giving up.

The first available runner sorted numerically will be
chosen.  This helps to give the same runners more work,
since they're more likely to have source (and compiled)
already parsed in memory.  As such, runners will have load
disproportionately spread, and may exhibit large variances
in resource consumption.

If all runners are busy, then a new runner will be spawned,
allowing for parallel builds.

Options:
  --help         show this message
  --kill         kill tamed
  -v, --verbose  show runner logs

Environment Variables:
  TAME_VERBOSE       when greater than zero, show runner logs
                       (see also --verbose)
  TAME_CMD_WAITTIME  number of seconds to wait for ack from
                       runner (default 3)
EOF

  exit $EX_USAGE
}


# Run tame
main()
{
  local -r root=/run/user/$UID/tamed

  local outcmd=saneout

  test $# -gt 0 || usage

  case "${1:-}" in
    --kill) kill-tamed "$root"; exit;;
    -v|--verbose) outcmd=cat; shift;;
    --help) usage;;
  esac

  # alternative to --verbose
  if [ "${TAME_VERBOSE:-0}" -ge 1 ]; then
    outcmd=cat
  fi

  start-tamed-safe "$root"

  # for now we only support a single runner
  command-available-runner "$root" "$@" \
    | "$outcmd"
}

main "$@"