#!/usr/bin/env bash


init_variables() {
  COMMAND=${0#*-}

  CONFIG=false
  ALL=false
  unset OLD_EMAIL
  unset CORRECT_EMAIL
  unset CORRECT_NAME
  TYPE='both'
}


usage() {
  cat << EOF
usage: git ${COMMAND} [<options>]

Options
    -a, --all                     rewrite all identities in commits and tags
    -c, --use-config              define correct values from user Git config
    -e, --correct-email  <email>  define the correct email to set
    -n, --correct-name   <name>   define the correct name to set
    -o, --old-email      <email>  rewrite identities matching old email in commits and tags
    -t, --type           <id>     define the type of identities affected by the rewrite
                                  author, committer, both (default)
EOF
}


error() {
  if [[ -n "$1" ]]; then
    local msg=$( echo "error: $1" | sed 's/\\n/\\n       /g' )
    echo -e "${msg}" >&2
  fi
  usage
  exit 1
}


reauthor() {
  local author='
    if ${ALL} || [ "${GIT_AUTHOR_EMAIL}" = "${OLD_EMAIL}" ]; then
      [ -z "${CORRECT_EMAIL+x}" ] || export GIT_AUTHOR_EMAIL="${CORRECT_EMAIL}"
      [ -z "${CORRECT_NAME+x}" ] || export GIT_AUTHOR_NAME="${CORRECT_NAME}"
    fi
  '
  local committer='
    if ${ALL} || [ "${GIT_COMMITTER_EMAIL}" = "${OLD_EMAIL}" ]; then
      [ -z "${CORRECT_EMAIL+x}" ] || export GIT_COMMITTER_EMAIL="${CORRECT_EMAIL}"
      [ -z "${CORRECT_NAME+x}" ] || export GIT_COMMITTER_NAME="${CORRECT_NAME}"
    fi
  '
  local filter

  case "${TYPE}" in
    author) filter="${author}" ;;
    committer) filter="${committer}" ;;
    both) filter="${author} ${committer}" ;;
  esac

  export ALL
  export OLD_EMAIL
  export CORRECT_EMAIL
  export CORRECT_NAME

  git filter-branch --force --env-filter "${filter}" \
  --tag-name-filter cat -- --branches --tags
}


parse_options() {
  while [[ "$#" -gt 0 ]]; do
    case "$1" in
      --all|-a)
        ALL=true
        shift
        ;;
      --correct-email|-e)
        [[ -n "${2+x}" ]] || error 'Missing correct-email value'
        CORRECT_EMAIL="$2"
        shift 2
        ;;
      -h)
        usage
        exit 0
        ;;
      --correct-name|-n)
        [[ -n "${2+x}" ]] || error 'Missing correct-name value'
        CORRECT_NAME="$2"
        shift 2
        ;;
      --old-email|-o)
        [[ -n "${2+x}" ]] || error 'Missing old-email value'
        OLD_EMAIL="$2"
        shift 2
        ;;
      --type|-t)
        [[ -n "${2+x}" ]] || error 'Missing type value'
        TYPE="$2"
        shift 2
        ;;
      --use-config|-c)
        CONFIG=true
        shift
        ;;
      *)
        error "invalid option '$1'"
        ;;
    esac
  done

  if ${CONFIG}; then
    # use config values if not explicitly already defined
    [[ -n "${CORRECT_EMAIL+x}" ]] || CORRECT_EMAIL=$( git config user.email )
    [[ -n "${CORRECT_NAME+x}" ]] || CORRECT_NAME=$( git config user.name )
  fi
}


validate_options() {
  # Either OLD_EMAIL should be set or ALL should be true
  if [[ -z "${OLD_EMAIL+x}" ]] && ! ${ALL}; then
    msg="missing target of the rewrite"
    msg="${msg}\nuse either --old-email option or --all flag"
    error "${msg}"
  fi

  # OLD_EMAIL shouldn't be set if ALL is true as well to prevent misuse
  if [[ -n "${OLD_EMAIL+x}" ]] && ${ALL}; then
    msg="ambiguous target of the rewrite"
    msg="${msg}\nuse either --old-email option or --all flag"
    error "${msg}"
  fi

  # CORRECT_NAME should be either unset or set to non-empty string
  [[ -n "${CORRECT_NAME-x}" ]] || error "empty name is not allowed"

  # Either CORRECT_EMAIL or CORRECT_NAME should be set
  if [[ -z "${CORRECT_EMAIL+x}" ]] && [[ -z "${CORRECT_NAME+x}" ]]; then
    msg="missing correct email and/or name to set"
    msg="${msg}\nuse --correct-email and/or --correct-name options"
    msg="${msg}\nor --use-config flag with user values set in Git config"
    error "${msg}"
  fi

  # TYPE should be a valid identifier
  if [[ "${TYPE}" != 'both' ]] \
     && [[ "${TYPE}" != 'author' ]] \
     && [[ "${TYPE}" != 'committer' ]]; then
    error "invalid type '${TYPE}'"
  fi
}


init_variables
parse_options "$@"
validate_options

reauthor