#!/bin/bash
# Copyright (C) 2016 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.

cedit() {
  local help="Usage: [-h|--help ] [-v] [SECTION_NAME] FILE
Create/modify a section in a config file

Returns 1 if the file is modified by this command, 2 or higher
for other problems.

The section is #comment delimited. Reads STDIN for the contents of the
section. Without SECTION_NAME, it acts on a global unnamed
section. cedit is short for config edit.

-q         Quiet
-v         Verbose
-b         Keep backup file
-h|--help  Help"
  local s diff name init
  local file_dir="$(dirname "$file")"
  local exists=true
  local verbose=false
  local backup=false
  local quiet=false

  case $1 in
    -b) backup=true; shift ;;
    -v) verbose=true; shift ;;
    -q) quiet=true; shift ;;
    -h|--help) echo "$help"; return ;;
  esac

  if (( $# == 2 )); then
    name=": $1"
    shift
  fi

  local file="$1"
  local file_name="${file##*/}"

  local begin="#_#_# start delimiter of cedit section$name. do not modify. #_#_#"
  local end="#_#_# end delimiter of cedit section$name. do not modify. #_#_#"

  if [[ ! -e $file_dir ]]; then
    if ! mkdir -p $file_dir; then
      s=sudo
      $s mkdir -p $file_dir || return 2
    fi
  fi
  if [[ ! -e $file ]]; then
    exists=false
    if ! $s touch $file; then
      s=sudo
      $s touch $file || return 2
    fi
  fi

  [[ -w $file ]] || s=sudo


  local in_section=false
  if $exists; then
    local tailn=1
    local temp="$(mktemp -d)/$file_name"
    cp "$file" "$temp"
    cp /dev/null "$file"
    while IFS= read -r line; do
      tailn=$(( tailn + 1 ))
      if [[ $line == "$begin" ]]; then
        in_section=true;
        break
      fi
      printf '%s\n' "$line" >> $file
    done < "$temp"
  fi

  IFS= read -d '' -n 1 -r init
  if [[ $init ]]; then
    $s tee -a "$file" >/dev/null <<<"$begin"
    printf '%s' "$init" | $s tee -a "$file" >/dev/null
    $s tee -a "$file" >/dev/null
    $s tee -a "$file" >/dev/null <<<"$end"
  fi

  if $exists && $in_section; then
    while IFS= read -r line; do
      if [[ $line == "$begin" ]]; then
        in_section=true;
      fi
      if ! $in_section; then
        printf '%s\n' "$line" >> $file
      fi
      if [[ $line == $end ]]; then
        in_section=false;
      fi
    done < <(tail -n +$tailn "$temp")
  fi


  if ! $exists; then
    ret=1
    if $verbose; then
      echo "New file $file:"
      cat "$file"
    fi
  elif type -t diff &>/dev/null; then
    diff=$(diff -u "$temp" "$file")
    ret=$?
    if (( $ret )) && ! $quiet; then
      echo "backup of original at $temp"
      echo diff -u "$temp" "$file":
      echo "$diff"
      #elif $debug; then
      #  echo "No changes made to $file"
    fi
  else
    # for systems like openwrt which don't have diff
    diff=$(cmp "$temp" "$file")
    ret=$?
    if $verbose; then
      echo "$diff"
    fi
  fi
  if ! $backup && $exists; then
    rm -r "$temp"
  fi
  return $ret
}
cedit "$@"