#!/usr/bin/env bash

# git pre-commit hook that runs a black stylecheck.
# Based on pre-commit-clang-format.

##################################################################
# SETTINGS
# Set path to black binary.
BLACK=`which black`
BLACK_OPTIONS="-l 120"

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

# File types to parse.
FILE_NAMES="SConstruct SCsub"
FILE_EXTS="py"

# Use pygmentize instead of cat to parse diff with highlighting.
# Install it with `pip install pygments` (Linux) or `easy_install Pygments` (Mac)
# READER="pygmentize -l diff"
READER=cat

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

. "$(dirname -- "$0")/canonicalize_filename.sh"

# exit on error
set -e

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

    for name in $FILE_NAMES; do [[ "$name" == "$filename" ]] && return 0; done
    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 "$BLACK" ] ; then
    printf "Error: black executable not found.\n"
    printf "Set the correct path in $(canonicalize_filename "$0").\n"
    exit 1
fi

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

# clean up any older black 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 thirdparty files
    if grep -q "thirdparty" <<< $file; then
        continue;
    fi

    # ignore file if not one of the names or extensions we handle
    if ! matches_name_or_extension "$file"; then
        continue;
    fi

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

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

# Allows us to read user input below, assigns stdin to keyboard
exec < /dev/tty

while true; do
    read -p "Do you want to apply that patch (Y - Apply, N - Do not apply, S - Apply and stage files)? [Y/N/S] " yn
    case $yn in
        [Yy] ) git apply $patch;
        printf "The patch was applied. You can now stage the changes and commit again.\n\n";
        break
        ;;
        [Nn] ) 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";
        printf "Aborting commit. Apply changes and commit again or skip checking with";
        printf " --no-verify (not recommended).\n\n";
        break
        ;;
        [Ss] ) git apply $patch;
        git diff-index --cached --diff-filter=ACMR --name-only $against -- | while read file;
        do git add $file;
        done
        printf "The patch was applied and the changed files staged. You can now commit.\n\n";
        break
        ;;
        * ) echo "Please answer yes or no."
        ;;
    esac
done
exit 1 # we don't commit in any case