#!/usr/bin/env bash

DEF_TAG_RECENT="n.n.n"
GIT_LOG_OPTS="$(git config changelog.opts)"
GIT_LOG_FORMAT="$(git config changelog.format)"
[[ -z "$GIT_LOG_FORMAT" ]] && GIT_LOG_FORMAT='  * %s'
GIT_MERGELOG_FORMAT="$(git config changelog.mergeformat)"
[[ -z "$GIT_MERGELOG_FORMAT" ]] && GIT_MERGELOG_FORMAT='  * %s%n%w(64,4,4)%b'
GIT_EDITOR="$(git var GIT_EDITOR)"
PROGNAME="git-changelog"

_usage() {
cat << EOF
usage: $PROGNAME options [file]
usage: $PROGNAME -h|help|?

Generate a Changelog from git(1) tags (annotated or lightweight) and commit
messages. Existing Changelog files with filenames that begin with 'Change' or
'History' will be identified automatically and their content will be appended
to the new output generated (unless the -p|--prune-old option is used). If no
tags exist, then all commits are output; if tags exist, then only the most-
recent commits are output up to the last identified tag.

OPTIONS:
  -a, --all                 Retrieve all commits (ignores --start-tag/commit, --final-tag)
  -l, --list                Display commits as a list, with no titles
  -t, --tag                 Tag label to use for most-recent (untagged) commits
  -f, --final-tag           Newest tag to retrieve commits from in a range
  -s, --start-tag           Oldest tag to retrieve commits from in a range
      --start-commit        Like --start-tag but use commit instead of tag
  -n, --no-merges           Suppress commits from merged branches
  -m, --merges-only         Only uses merge commits (uses both subject and body of commit)
  -p, --prune-old           Replace existing Changelog entirely with new content
  -x, --stdout              Write output to stdout instead of to a Changelog file
  -h, --help, ?             Show this message
EOF
}

_error() {
  [ $# -eq 0 ] && _usage && exit 0

  echo
  echo "ERROR: " "$@"
  echo
}

# _setValueForKeyFakeAssocArray()
# /*!
# @abstract Set value for key from a fake associative array
# @discussion
# Iterates over target_ary (an indexed array), searching for target_key, if the
#   key is found its value is set to new_value otherwise the target_key and
#   new_value are appended to the array.
#
#   The indexed array values must conform to this format:
#     "key:value"
#   Where key and value are separated by a single colon character.
#
#   Specify empty values as an empty, quoted string.
#
#   So-called "fake" associative arrays are useful for environments where the
#   installed version of bash(1) precedes 4.0.
# @param target_key Key to retrieve
# @param new_value New or updated value
# @param target_ary Indexed array to scan
# @return Returns new array with updated key (status 0) or an empty array
#   (status 1) on failure.
# */
_setValueForKeyFakeAssocArray() {
  # parameter list supports empty arguments!
  local target_key="$1"; shift
  local new_value="$1"; shift
  local target_ary=()
  local defaultIFS="$IFS"
  local IFS="$defaultIFS"
  local found=false

  IFS=$' ' target_ary=( $1 ) IFS="$defaultIFS"

  [[ -z "${target_key}" || "${#target_ary[@]}" -eq 0 ]] && echo "${value}" && return 1

  local _target_ary_length="${#target_ary[@]}"
  local i
  for (( i=0; i<"${_target_ary_length}"; i++ )); do
    local __val="${target_ary[$i]}"

    if [[ "${__val%%:*}" == "${target_key}" ]]; then
      target_ary[$i]="${__val%%:*}:${new_value}"
      found=true
      break
    fi

    unset __val
  done
  unset i _target_ary_length

  # key not found, append
  [[ "$found" == false ]] && target_ary+=( "${target_key}:${new_value}" )

  printf "%s" "${target_ary[*]}"
}

# _valueForKeyFakeAssocArray()
# /*!
# @abstract Fetch value for key from a fake associative array
# @discussion
# Iterates over target_ary (an indexed array), searching for target_key, if the
#   key is found its value is returned.
#
#   The indexed array values must conform to this format:
#     "key:value"
#   Where key and value are separated by a single colon character.
#
#   So-called "fake" associative arrays are useful for environments where the
#   installed version of bash(1) precedes 4.0.
# @param target_key Key to retrieve
# @param target_ary Indexed array to scan
# @return Returns string containing value (status 0) or an empty string
#   (status 1) on failure.
# */
_valueForKeyFakeAssocArray() {
  local target_key="$1"
  local target_ary=()
  local defaultIFS="$IFS"
  local IFS="$defaultIFS"
  local value=""

  IFS=$' ' target_ary=( $2 ) IFS="$defaultIFS"

  [[ -z "${target_key}" || "${#target_ary[@]}" -eq 0 ]] && echo "${value}" && return 1

  local t
  for t in "${target_ary[@]}"; do
    if [[ "${t%%:*}" == "${target_key}" ]]; then
      value="${t#*:}"
      break
    fi
  done
  unset t

  echo -e "${value}"; return 0
}

_fetchCommitRange() {
  local list_all="${1:-false}"
  local start_tag="$2"
  local final_tag="$3"

  # This shellcheck disable is applied to the whole if-body
  # shellcheck disable=SC2086
  if [[ "$list_all" == true ]]; then
    git log $GIT_LOG_OPTS --pretty=format:"${CUR_GIT_LOG_FORMAT}"
  elif [[ -n "$final_tag" && "$start_tag" == "null" ]]; then
    git log $GIT_LOG_OPTS --pretty=format:"${CUR_GIT_LOG_FORMAT}" "${final_tag}"
  elif [[ -n "$final_tag" ]]; then
    git log $GIT_LOG_OPTS --pretty=format:"${CUR_GIT_LOG_FORMAT}" "${start_tag}"'..'"${final_tag}"
  elif [[ -n "$start_tag" ]]; then
    git log $GIT_LOG_OPTS --pretty=format:"${CUR_GIT_LOG_FORMAT}" "${start_tag}"'..'
  fi | sed 's/^  \* \*/  */g'
}

_formatCommitPlain() {
  local start_tag="$1"
  local final_tag="$2"

  printf "%s\n" "$(_fetchCommitRange "false" "$start_tag" "$final_tag")"
}

_formatCommitPretty() {
  local title_tag="$1"
  local title_date="$2"
  local start_tag="$3"
  local final_tag="$4"
  local title="$title_tag / $title_date"
  local title_underline=""

  local i
  for i in $(seq ${#title}); do
    title_underline+="="
  done
  unset i

  printf '\n%s\n%s\n' "$title" "$title_underline"
  printf "\n%s\n" "$(_fetchCommitRange "false" "$start_tag" "$final_tag")"
}

commitList() {
  # parameter list supports empty arguments!
  local list_all="${1:-false}"; shift
  local title_tag="$1"; shift
  local start_tag="$1"; shift
  local final_tag="$1"; shift
  local list_style="${1:-false}"; shift # enable/disable list format
  local start_commit="$1"; shift
  local changelog="$FILE"
  local title_date="$(date +'%Y-%m-%d')"
  local tags_list=()
  local tags_list_keys=()
  local defaultIFS="$IFS"
  local IFS="$defaultIFS"

  if [[ -n "$start_commit" && "$final_tag" == "null" \
      && "$start_tag" == "null" ]]; then
    # if there is not tag after $start_commit,
    # output directly without fetch all tags
    if [[ "$list_style" == true ]]; then
      _formatCommitPlain "${start_commit}~"
    else
      _formatCommitPretty "$title_tag" "$title_date" "$start_commit~"
    fi

    return
  fi

  #
  # Tags look like this:
  #
  # >git log --tags --simplify-by-decoration --date="short" --pretty="format:%h$%x09%ad$%x09%d"
  #
  # ecf1f2b$        2015-03-15$     (HEAD, tag: v1.0.1, origin/master, origin/HEAD, master, hotfix/1.0.2)
  # a473e9c$        2015-03-04$     (tag: v1.0.0)
  # f2cb562$        2015-02-19$     (tag: v0.9.2)
  # 6197c2b$        2015-02-19$     (tag: v0.9.1)
  # 1e5f5e6$        2015-02-16$     (tag: v0.9.0)
  # 3de8ab5$        2015-02-11$     (origin/feature/restore-auto)
  # a15afd1$        2015-02-02$     (origin/feature/versionable)
  # 38a44e0$        2015-02-02$     (origin/feature/save-auto)
  # 3244b80$        2015-01-16$     (origin/feature/silent-history, upstream)
  # 85e45f8$        2014-08-25$
  #
  # The most-recent tag will be preceded by "HEAD, " if there have been zero
  # commits since the tag. Also notice that with gitflow, we see features.
  #

  # fetch our tags
  local _ref _date _tag _tab='%x09'
  local _tag_regex='tag: *'
  while IFS=$'\t' read -r _ref _date _tag; do
    [[ -z "${_tag}" ]] && continue
    # strip out tags form ()
    # git v2.2.0+ supports '%D', like '%d' without the " (", ")" wrapping. One day we should use it instead.
    _tag="${_tag# }"; _tag="${_tag//[()]/}"
    # trap tag if it points to last commit (HEAD)
    _tag="${_tag#HEAD*, }"
    # strip out branches
    [[ ! "${_tag}" =~ ${_tag_regex} ]] && continue
    # strip out any additional tags pointing to same commit, remove tag label
    _tag="${_tag%%,*}"; _tag="${_tag#tag: }"
    # add tag to assoc array; copy tag to tag_list_keys for ordered iteration
    tags_list+=( "${_tag}:${_ref}=>${_date}" )
    tags_list_keys+=( "${_tag}" )
  done <<< "$(git log --tags --simplify-by-decoration --date="short" --pretty="format:%h${_tab}%ad${_tab}%d")"
  IFS="$defaultIFS"
  unset _tag_regex
  unset _ref _date _tag _tab

  local _tags_list_keys_length="${#tags_list_keys[@]}"
  if [[ "${_tags_list_keys_length}" -eq 0 ]]
  then
    unset _tags_list_keys_length
    if [[ "$list_style" == true ]]; then
      printf "%s" "$(_fetchCommitRange "true")"
    else
      local title="$title_tag / $title_date"
      local title_underline=""

      local i
      for i in $(seq ${#title}); do
        title_underline+="="
      done
      unset i

      printf '\n%s\n%s\n' "$title" "$title_underline"
      printf "\n%s\n" "$(_fetchCommitRange "true")"
    fi
    return
  fi

  local _final_tag_found=false
  local _start_tag_found=false
  local i
  for (( i=0; i<"${_tags_list_keys_length}"; i++ )); do
    local __curr_tag="${tags_list_keys[$i]}"
    local __prev_tag="${tags_list_keys[$i+1]:-null}"
    local __curr_date
    __curr_date="$(_valueForKeyFakeAssocArray "${__curr_tag}" "${tags_list[*]}")"
    __curr_date="${__curr_date##*=>}"

    # output latest commits, up until the most-recent tag, these are all
    # new commits made since the last tagged commit.
    if [[ $i -eq 0 && ( -z "$final_tag" || "$final_tag" == "null" ) ]]; then
      if [[ "$list_style" == true ]]; then
        _formatCommitPlain "${__curr_tag}" >> "$tmpfile"
      else
        _formatCommitPretty "$title_tag" "$title_date" "${__curr_tag}"
      fi
    fi

    # both final_tag and start_tag are "null", user just wanted recent commits
    [[ "$final_tag" == "null" && "$start_tag" == "null" ]] && break;

    # find the specified final tag, continue until found
    if [[ -n "$final_tag" && "$final_tag" != "null" ]]; then
      [[ "$final_tag" == "${__curr_tag}" ]] && _final_tag_found=true
      [[ "$final_tag" != "${__curr_tag}" && "${_final_tag_found}" == false ]] && continue
    fi

    # find the specified start tag, break when found
    if [[ -n "$start_tag" ]]; then
      [[ "$start_tag" == "${__curr_tag}" ]] && _start_tag_found=true
      if [[ "${_start_tag_found}" == true ]]; then
        if [[ -n "$start_commit" ]]; then

          # output commits after start_commit to its closest tag
          if [[ "$list_style" == true ]]; then
            _formatCommitPlain "$start_commit~" "${__curr_tag}"
          else
            _formatCommitPretty "${__curr_tag}" "${__curr_date}" \
              "$start_commit~" "${__curr_tag}"
          fi

          break
        fi

        [[ "$start_tag" != "${__curr_tag}" ]] && break

      fi
    fi

    # output commits made between prev_tag and curr_tag, these are all of the
    # commits related to the tag of interest.
    if [[ "$list_style" == true ]]; then
      _formatCommitPlain "${__prev_tag}" "${__curr_tag}"
    else
      _formatCommitPretty "${__curr_tag}" "${__curr_date}" "${__prev_tag}" "${__curr_tag}"
    fi
    unset __curr_date
    unset __prev_tag
    unset __curr_tag
  done
  unset i
  unset _start_tag_found
  unset _final_tag_found
  unset _tags_list_keys_length

  return
}

commitListPlain() {
  local list_all="${1:-false}"
  local start_tag="$2"
  local final_tag="$3"
  local start_commit="$4"

  commitList "$list_all" "" "$start_tag" "$final_tag" "true" "$start_commit"
}

commitListPretty() {
  local list_all="${1:-false}"
  local title_tag="$2"
  local start_tag="$3"
  local final_tag="$4"
  local start_commit="$5"
  local title_date="$(date +'%Y-%m-%d')"

  commitList "$list_all" "$title_tag" "$start_tag" "$final_tag" "false" \
    "$start_commit"
}

_exit() {
  local pid_list=()
  local defaultIFS="$IFS"
  local IFS="$defaultIFS"

  stty sane; echo; echo "caught signal, shutting down"

  IFS=$'\n'
  # The format of `ps` is different between Windows and other platforms,
  # so we need to calculate the total column number(COL_NUM) of header first.
  # Why don't we just use the last column?
  # Because the body of CMD column may contain space and be treated as multiple fields.
  pid_list=( $(ps -f |
    awk -v ppid=$$ 'NR == 1 {
      COL_NUM = NF
    }
    $3 == ppid {
      # filter out temp processes created in this subshell
      if ($COL_NUM != "ps" && $COL_NUM != "awk" && $COL_NUM !~ "bash$")
        print $2
    }')
  )
  IFS="$defaultIFS"

  local _pid
  for _pid in "${pid_list[@]}"; do
    echo "killing: ${_pid}"
    kill -TERM "${_pid}"
  done

  wait; stty sane; exit 1
}

trap '_exit' SIGINT SIGQUIT SIGTERM

main() {
  local start_tag="null" # empty string and "null" mean two different things!
  local final_tag="null"

  local option=(
    "list_all:false"
    "list_style:false"
    "title_tag:$DEF_TAG_RECENT"
    "start_tag:"
    "start_commit:"
    "final_tag:"
    "output_file:"
    "use_stdout:false"
    "prune_old:false"
  )

  #
  # We work chronologically backwards from NOW towards start_tag where NOW also
  # includes the most-recent (un-tagged) commits. If no start_tag has been
  # specified, we work back to the very first commit; if a final_tag has been
  # specified, we begin at the final_tag and work backwards towards start_tag.
  #

  # An existing ChangeLog/History file will be appended to the output unless the
  # prune old (-p | --prune-old) option has been enabled.

  while [ "$1" != "" ]; do
    case $1 in
      -a | --all )
        option=( $(_setValueForKeyFakeAssocArray "list_all" true "${option[*]}") )
        ;;
      -l | --list )
        option=( $(_setValueForKeyFakeAssocArray "list_style" true "${option[*]}") )
        ;;
      -t | --tag )
        option=( $(_setValueForKeyFakeAssocArray "title_tag" "$2" "${option[*]}") )
        shift
        ;;
      -f | --final-tag )
        option=( $(_setValueForKeyFakeAssocArray "final_tag" "$2" "${option[*]}") )
        shift
        ;;
      -s | --start-tag )
        option=( $(_setValueForKeyFakeAssocArray "start_tag" "$2" "${option[*]}") )
        shift
        ;;
      --start-commit )
        option=( $(_setValueForKeyFakeAssocArray "start_commit" "$2" "${option[*]}") )
        shift
        ;;
      -n | --no-merges )
        GIT_LOG_OPTS='--no-merges'
        CUR_GIT_LOG_FORMAT="$GIT_LOG_FORMAT"
        ;;
      -m | --merges-only )
        GIT_LOG_OPTS='--merges'
        CUR_GIT_LOG_FORMAT="$GIT_MERGELOG_FORMAT"
        ;;
      -p | --prune-old )
        option=( $(_setValueForKeyFakeAssocArray "prune_old" true "${option[*]}") )
        ;;
      -x | --stdout )
        option=( $(_setValueForKeyFakeAssocArray "use_stdout" true "${option[*]}") )
        ;;
      -h | ? | help | --help )
        _usage
        exit 1
        ;;
      * )
        [[ "${1:0:1}" == '-' ]] && _error "Invalid option: $1" && _usage && exit 1
        option=( $(_setValueForKeyFakeAssocArray "output_file" "$1" "${option[*]}") )
        ;;
    esac
    shift
  done

  # The default log format unless already set
  [[ -z "$CUR_GIT_LOG_FORMAT" ]] && CUR_GIT_LOG_FORMAT="$GIT_LOG_FORMAT"

  local _tag="$(_valueForKeyFakeAssocArray "start_tag" "${option[*]}")"
  local start_commit="$(_valueForKeyFakeAssocArray "start_commit" "${option[*]}")"

  if [[ -n "$start_commit" ]]; then
    if [[ -n "${_tag}" ]]; then
      _error "--start-tag could not use with --start-commit!"
      return 1
    fi

    start_tag="$(git describe --tags --contains "$start_commit" 2>/dev/null || echo 'null')"
    if [[ -z "$start_tag" ]]; then
      _error "Could find the associative tag for the start-commit!"
      return 1
    fi

    # remove suffix from the $start_tag when no tag matched exactly
    start_tag="${start_tag%%~*}"
    # also remove "^0" added sometimes when tag matched exactly
    start_tag="${start_tag%%^0}"

  elif [[ -n "${_tag}" ]]; then
    start_tag="$(git describe --tags --abbrev=0 "${_tag}" 2>/dev/null)"
    if [[ -z "$start_tag" ]]; then
      _error "Specified start-tag does not exist!"
      return 1
    fi
  fi

  if [[ -n "${_tag}" ]]; then
    if [[ -n "$start_commit" ]]; then
      _error "--start-tag could not use with --start-commit!"
      return 1
    fi

  fi
  unset _tag

  local _tag="$(_valueForKeyFakeAssocArray "final_tag" "${option[*]}")"
  if [[ -n "${_tag}" ]]; then
    final_tag="$(git describe --tags --abbrev=0 "${_tag}" 2>/dev/null)"
    if [[ -z "$final_tag" ]]; then
      _error "Specified final-tag does not exist!"
      return 1
    fi
  fi
  unset _tag

  #
  # generate changelog
  #
  local tmpfile changelog title_tag
  tmpfile="$(git_extra_mktemp)"
  changelog="$(_valueForKeyFakeAssocArray "output_file" "${option[*]}")"
  title_tag="$(_valueForKeyFakeAssocArray "title_tag" "${option[*]}")"

  if [[ "$(_valueForKeyFakeAssocArray "list_style" "${option[*]}")" == true ]]; then
    if [[ "$(_valueForKeyFakeAssocArray "list_all" "${option[*]}")" == true ]]; then
      commitListPlain "true" >> "$tmpfile"
    else
      commitListPlain "false" "$start_tag" "$final_tag" \
        "$start_commit" >> "$tmpfile"
    fi
  else
    if [[ "$(_valueForKeyFakeAssocArray "list_all" "${option[*]}")" == true ]]; then
      commitListPretty "true" "$title_tag" >> "$tmpfile"
    else
      commitListPretty "false" "$title_tag" "$start_tag" "$final_tag" \
        "$start_commit" >> "$tmpfile"
    fi
  fi

  if [[ -z "$changelog" ]]; then
    changelog="$(find . -mindepth 1 -maxdepth 1 \( -iname '*change*' -o -iname '*history*' \) | head -n1)"
    if [[ -z "$changelog" ]]; then
      changelog="History.md";
    fi
  fi

  # append existing changelog?
  if [[ -f "$changelog" \
    && "$(_valueForKeyFakeAssocArray "prune_old" "${option[*]}")" == false ]]; then
    cat "$changelog" >> "$tmpfile"
  fi

  # output file to stdout or move into place
  if [[ "$(_valueForKeyFakeAssocArray "use_stdout" "${option[*]}")" == true ]]; then
    cat "$tmpfile"
    rm -f "$tmpfile"
  else
    cp -f "$tmpfile" "$changelog"
    rm -f "$tmpfile"

    if [[ -n "$GIT_EDITOR" ]]; then
      $GIT_EDITOR "$changelog" || _exit
    else
      less "$changelog" || _exit
    fi
  fi

  return
}

main "$@"

exit 0