#!/usr/bin/env sh
## Amends your staged changes as a fixup (keeping the pre-existing commit message) to the specified commit, or HEAD if no revision is specified.
## Source: git-extra-commands

#
# Copied from Danielle Sucher's blog post at
# http://www.daniellesucher.com/2014/05/08/git-shamend/
# source: https://github.com/DanielleSucher/dotfiles/blob/master/git/git-shamend

set -o nounset

# Copyright (c) 2014 Danielle E. Sucher <dsucher@gmail.com>

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

PrintGitShamendUsage() {
  echo "Usage: git shamend [options] [<revision>]"
  echo "Amends your staged changes as a fixup (keeping the pre-existing commit"
  echo "message) to the specified commit, or HEAD if no revision is specified."
  echo
  echo "Options:"
  echo "    -a, --all             Commit unchanged files, same as git commit."
  echo "    -h, --help            Print this help."
}

ALL=""
SHA_TO_AMEND=""

# parse arguments
while [ "$#" -gt 0 ]; do
  case $1 in
    -h | --help)
      PrintGitShamendUsage
      exit 0
      ;;
    -a | --all)
      ALL="--all"
      ;;
    *)
      if [ -n "$SHA_TO_AMEND" ]; then
        echo "ERROR: unknown parameter \"$1\""
        PrintGitShamendUsage
        exit 1
      fi
      SHA_TO_AMEND=$(git rev-parse "$1")
      if [ ! $? ]; then
        echo "ERROR: unparsable revision \"$1\""
        PrintGitShamendUsage
        exit 1
      fi
      ;;
  esac
  shift
done

# fall back to HEAD if no SHA was given
if [ -z "$SHA_TO_AMEND" ]; then
  SHA_TO_AMEND="HEAD"
fi

# shortcut the HEAD case for simplicity
if [ "$SHA_TO_AMEND" = "HEAD" ]; then
  git commit --amend --no-edit $ALL
  exit 0
fi

BOLD=$(tput bold)
RED=$(tput setaf 1)
NORMAL=$(tput sgr0)

if git merge-base --is-ancestor $SHA_TO_AMEND HEAD
then

  if [ -z "$ALL" ]; then
    echo "${BOLD}Warning: your unstaged changes will be stashed during this process${NORMAL}"
  fi

  git commit $ALL --fixup $SHA_TO_AMEND > /dev/null

  git diff-index --quiet HEAD
  NOTHING_TO_STASH=$?
  if [ $NOTHING_TO_STASH -ne 0 ]
  then
    git stash > /dev/null
  fi

  GIT_EDITOR=true git rebase -i --autosquash "$SHA_TO_AMEND^"

  if [ $? -ne 0 ]
  then
    git rebase --abort
    git reset --soft HEAD^
    echo "${RED}${BOLD}Whoops, that didn't work! Cleaning up after this attempt now, but"
    echo "it looks like you'll have to interactive rebase this one manually.${NORMAL}"
  fi

  if [ $NOTHING_TO_STASH -ne 0 ]
  then
    git stash pop > /dev/null
  fi
else
  echo "${RED}${BOLD}${SHA_TO_AMEND} is not an ancestor of HEAD.${NORMAL}"
  PrintGitShamendUsage
  exit 1
fi