#!/bin/bash
#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

_usage() {
  echo -e "Usage: ${0} {classpath} {mainclass} [dir]\n\n\
Runs a Java application while saving its stdout to dir/mainclass.out, its stderr to dir/mainclass.err, and its process id to dir/mainclass.pid.\n\
\n\
This script starts a Java application only if it cannot find its pid. If the process id specified by dir/mainclass.pid exists, then the script will not start the application.\n\
\n\
    classpath The application's class path.\n\
    classname The name of the class to be launched.\n\
    dir       The directory where the process stdout, stderr and pid files are\n\
              written. If dir is not specified, then the files are saved into\n\
              the current directory.\n\
"
}

# _get_pid program [pidfile]
# Set $pid to pids from /tmp* for {program}.
# $pid should be declared local in the caller.
_get_pid() {
  local base=${1##*/}
  local pid_file=${2:-/tmp/$base.pid}

  pid=
  if [ -f "$pid_file" ] ; then
    local p

    [ ! -r "$pid_file" ] && return 1 # "Cannot access pid file"

    p=$(cat "$pid_file")
    [ -z "${p//[0-9]/}" ] && [ -d "/proc/$p" ] && pid="$p"
    if [ -n "$pid" ]; then
        return 0
    fi
    return 2 # "Program is not running but pid file exists"
  fi
  return 3 # "Program pid file does not exist"
}

# _readlink path
# Output the full path, replacement for readlink -f
_readlink() {
  (
  pushd ${1%/*} > /dev/null 2>&1
  echo $PWD/${1##*/}
  popd > /dev/null 2>&1
  )
}

# _dirname path
# Get the directory name, replacement for dirname.
_dirname() {
  echo ${1%/*}
}

_error() {
  echo $1; exit 1
}


## Main script
#[ ! -n "${EDGENT:-}" ] && EDGENT=../..
[ ! -n "${JAVA_HOME:-}" ] && _error "JAVA_HOME must be set"

if [ $# -lt 2 ]; then
  _usage
  exit 1
fi

classpath=${1}
main_class=${2}
out_dir=${3:-.}

# Command to start the application.
command="${JAVA_HOME}/bin/java -cp ${classpath} ${main_class}"

if [[ ! -d ${out_dir} || ${out_dir:0:1} != '/' ]]; then
  ## out_dir as absolute path
  out_dir=$(_readlink ${out_dir})
  out_dir=$(_dirname ${out_dir})
fi

pid_file=${out_dir}/${main_class}.pid
out_file=${out_dir}/${main_class}.out
err_file=${out_dir}/${main_class}.err
pid=

_get_pid $main_class $pid_file
RC="$?"
[ $RC == "1" ] && _error "Cannot access pid file $pid_file"

if [ -z "$pid" ]; then
  $command >> $out_file 2>> $err_file &
  pid="$!"
  echo $pid >| $pid_file
  echo -e "The program was restarted with command:\n\
${command}\n\
Process id: $pid"
else
  echo "The program's process id is $pid"
fi