#!/bin/bash
# Copyright 2018 Ian Kelling

# Licensed 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.


# Commentary: Bash stack trace and error handling functions. This file
# is meant to be sourced. It loads some functions which you may want to
# call manually (see the comments at the start of each one), and then
# runs err-catch. See the README file for a slightly longer explanation.


#######################################
# Undoes err-catch. turns off exit and stack trace on error.
#######################################
err-allow() {
  set +E +o pipefail; trap ERR
}


#######################################
# Print stack trace
#
# usage: err-bash-trace [FRAME_START]
#
# It does not show function args unless you first run:
# shopt -s extdebug
# which err-catch & err-print does for you.
#
# FRAME_START   The frame to start printing on. default=0. Useful when
#               printing from an ERR trap function to avoid printing
#               that function.
#######################################
err-bash-trace() {
  local -i argc_index=0 frame i start=${1:-0} max_indent=8 indent
  local source
  local extdebug=false
  if [[ $(shopt -p extdebug) == *-s* ]]; then
    extdebug=true
  fi
  for ((frame=0; frame < ${#FUNCNAME[@]}-1; frame++)); do
    argc=${BASH_ARGC[frame]}
    argc_index+=$argc
    ((frame < start)) && continue
    if (( ${#BASH_SOURCE[@]} > 1 )); then
      source="${BASH_SOURCE[frame+1]}:${BASH_LINENO[frame]}:"
    fi
    indent=$((frame-start + 1))
    indent=$((indent < max_indent ? indent : max_indent))
    printf "%${indent}s↳%sin \`%s" '' "$source" "${FUNCNAME[frame]}"
    if $extdebug; then
      for ((i=argc_index-1; i >= argc_index-argc; i--)); do
        printf " %s" "${BASH_ARGV[i]}"
      done
    fi
    echo \'
  done
  return 0
}

#######################################
# On error print stack trace and exit
#
# Globals:
#   ${_errcatch_cleanup[@]}  Optional command & args that will run before exiting
#######################################
err-catch() {
  set -E; shopt -s extdebug
  _err-trap() {
    err=$?
    exec >&2
    set +x
    echo "${BASH_SOURCE[1]}:${BASH_LINENO[0]}: \`$BASH_COMMAND' returned $err"
    err-bash-trace 2
    set -e # err trap does not work within an error trap
    "${_errcatch_cleanup[@]:-:}" # note :-: is to be compatible with set -u
    echo "$0: exiting with code $err"
    exit $err
  }
  trap _err-trap ERR
  set -o pipefail
}

#######################################
# On error, print stack trace
#######################################
err-print() {
  # help: on errors: print stack trace
  #
  # This function depends on err-bash-trace.

  set -E; shopt -s extdebug
  _err-trap() {
    err=$?
    exec >&2
    set +x
    echo "${BASH_SOURCE[1]}:${BASH_LINENO[0]}: \`$BASH_COMMAND' returned $err"
    err-bash-trace 2
  }
  trap _err-trap ERR
  set -o pipefail
}


#######################################
# On error, print stack trace
#
# Use this instead of the exit command to be more informative.
#
# usage: err-exit [EXIT_CODE] [MESSAGE]
#
# EXIT_CODE  Default is 1.
# MESSAGE    Print MESSAGE to stderr. If only one of EXIT_CODE
#            and MESSAGE is given, we consider it to be an
#            exit code if it is a number.
#######################################
err-exit() {
  exec >&2
  code=1
  if [[ "$*" ]]; then
    if [[ ${1/[^0-9]/} == "$1" ]]; then
      code=$1
      if [[ $2 ]]; then
        printf '%s\n' "$2" >&2
      fi
    else
      printf '%s\n' "$0: $1" >&2
    fi
  fi
  echo "${BASH_SOURCE[1]}:${BASH_LINENO[0]}"
  err-bash-trace 2
  echo "$0: exiting with code $code"
  exit $err
}

# We want this more often than not, so run it now.
err-catch