#!/usr/bin/env bash
# git pre-commit hook that runs an clang-format stylecheck.
# Features:
#  - abort commit when commit does not comply with the style guidelines
#  - create a patch of the proposed style changes
#
# modifications for clang-format by rene.milk@wwu.de
# Link:    https://github.com/githubbrowser/Pre-commit-hooks
# Contact: David Martin, david.martin.mailbox@googlemail.com

# DESCR: Checking that VCS 'staged' source conforms to coding style

##################################################################
# SETTINGS
# set path to clang-format binary
CLANG_FORMAT="$(command -v clang-format)"

# remove any older patches from previous commits. Set to true or false.
# DELETE_OLD_PATCHES=false
DELETE_OLD_PATCHES=false

# only parse files with the extensions in FILE_EXTS. Set to true or false.
# if false every changed file in the commit will be parsed with clang-format.
# if true only files matching one of the extensions are parsed with clang-format.
# PARSE_EXTS=true
PARSE_EXTS=true

# file types to parse. Only effective when PARSE_EXTS is true.
# FILE_EXTS=".c .h .cpp .hpp"
FILE_EXTS=".c .h .cpp .hpp .cc .hh .cxx"

##################################################################
# There should be no need to change anything below this line.

# Reference: http://stackoverflow.com/questions/1055671/how-can-i-get-the-behavior-of-gnus-readlink-f-on-a-mac
canonicalize_filename () {
    local target_file=$1
    local physical_directory=""
    local result=""

    # Need to restore the working directory after work.
    pushd `pwd` > /dev/null

    cd "$(dirname "$target_file")"
    target_file=`basename $target_file`

    # Iterate down a (possible) chain of symlinks
    while [ -L "$target_file" ]
    do
        target_file=$(readlink "$target_file")
        cd "$(dirname "$target_file")"
        target_file=$(basename "$target_file")
    done

    # Compute the canonicalized name by finding the physical path
    # for the directory we're in and appending the target file.
    physical_directory=`pwd -P`
    result="$physical_directory"/"$target_file"

    # restore the working directory after work.
    popd > /dev/null

    echo "$result"
}

# exit on error
set -e

# check whether the given file matches any of the set extensions
matches_extension() {
    local filename=$(basename "$1")
    local extension=".${filename##*.}"
    local ext

    for ext in $FILE_EXTS; do [[ "$ext" == "$extension" ]] && return 0; done

    return 1
}

# necessary check for initial commit
if git rev-parse --verify HEAD >/dev/null 2>&1 ; then
    against=HEAD
else
    # Initial commit: diff against an empty tree object
    against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

if [ ! -x "$CLANG_FORMAT" ] ; then
    printf "Warning: clang-format executable not found.\n"
    printf "Set the correct path in $(canonicalize_filename "$0").\n"
    printf "Skipping clang-format style check test.\n"
#    exit 1
    exit 0
fi

# create a random filename to store our generated patch
prefix="pre-commit-clang-format"
suffix="$(date +%s)"
patch="/tmp/$prefix-$suffix.patch"

# clean up any older clang-format patches
$DELETE_OLD_PATCHES && rm -f /tmp/$prefix*.patch

# create one patch containing all changes to the files
git diff-index --cached --diff-filter=ACMR --name-only $against -- | while read file;
do
    # ignore file if we do check for file extensions and the file
    # does not match any of the extensions specified in $FILE_EXTS
    if $PARSE_EXTS && ! matches_extension "$file"; then
        continue;
    fi

    # clang-format our sourcefile, create a patch with diff and append it to our $patch
    # The sed call is necessary to transform the patch from
    #    --- $file timestamp
    #    +++ - timestamp
    # to both lines working on the same file and having a a/ and b/ prefix.
    # Else it can not be applied with 'git apply'.
    "$CLANG_FORMAT" -style=file "$file" | \
        diff -u "$file" - | \
        sed -e "1s|--- |--- a/|" -e "2s|+++ -|+++ b/$file|" >> "$patch"
done

# if no patch has been generated all is ok, clean up the file stub and exit
if [ ! -s "$patch" ] ; then
    printf "Files in this commit comply with the clang-format rules.\n"
    rm -f "$patch"
    exit 0
fi

# a patch has been created, notify the user and exit
printf "\nThe following differences were found between the code to commit "
printf "and the clang-format rules:\n\n"
cat "$patch"

printf "\nYou can apply these changes with:\n git apply $patch\n"
printf "(may need to be called from the root directory of your repository)\n"

# FIXME: clang-format is currently unusable, so don't abort the commit.
# printf "Aborting commit. Apply changes and commit again or skip checking with"
# printf " --no-verify (not recommended).\n"
# exit 1

exit 0