clang-format pre-commit hook

#!/usr/bin/env bash
#
# Runs clang-format on changed regions before commit.
#
# To install this, copy it to .git/hooks/pre-commit in your repo.
# Remaining installation checks/instructions will be printed when you commit.
#

read -d '' help <<- EOF
  This repository requires you to install the git clang-format command.

  One-time setup steps:
    1) install the git-clang-format script in your \$PATH, for example:

      curl https://raw.githubusercontent.com/llvm-mirror/clang/master/tools/clang-format/git-clang-format > /usr/local/bin/git-clang-format

    2) make sure git-clang-format is executable:

      chmod u+x /usr/local/bin/git-clang-format

  In each repository where you use clang-format, add git config keys
  so that git clang-format finds your version and config:

      git config clangFormat.binary  node_modules/.bin/clang-format
      git config clangFormat.style   file
EOF

check_clang_format() {
  if hash git-clang-format 2>/dev/null; then
    return
  else
    echo "SETUP ERROR: no git-clang-format executable found, or it is not executable"
    echo "$help"
    exit 1
  fi
}

check_git_config() {
  if [[ "$(git config --get clangFormat.binary)" != "node_modules/.bin/clang-format" ]]; then
    echo "SETUP ERROR: git config clangFormat.binary is wrong."
    echo "$help"
    exit 1
  elif [[ "$(git config --get clangFormat.style)" != "file" ]]; then
    echo "SETUP ERROR: git config clangFormat.style is wrong."
    echo "$help"
    exit 1
  fi
}

check_clang_format
check_git_config

readonly out=$(git clang-format -v --diff)

if [[ "$out" == *"no modified files to format"* ]]; then exit 0; fi
if [[ "$out" == *"clang-format did not modify any files"* ]]; then exit 0; fi

echo "ERROR: you need to run git clang-format on your commit"
exit 1