#!/bin/sh

# Copy a Git hook into the user's .git/hooks/ directory.
# If a different hook of that name is already present, back it up first.
#
# Usage:
#   install-hook <hook-file>
# Example:
#   install-hook ${PENCIL_HOME}/utils/git/hooks/prepare-commit-msg


# Require exactly one argument that does not start with a '-'
if [ "$#" != '1' -o "$(echo "$1" | cut -c1)" = '-' ]; then
    echo "install-hook: Copy a Git hook into the user's .git/hooks/ directory."
    echo 'Usage:'
    echo '  install-hook <hook-file>'
    exit 1
fi


hash_content() {
    # Print a hash of a file's content
    filename="$1"
    md5sum "${filename}" | cut -d ' ' -f 1
}


back_up() {
    # Make a backup copy of a given file
    file="$1"
    backup="${file}.bak"
    echo "Backing up ${file} -> ${backup}"
    cp "${file}" "${backup}"
}


find_git_root() {
    # Find the directory containing our .git directory.
    # Resolves 'git worktree' indirection.
    # Prints nothing if the cwd is not under Git
    git_root="$(git rev-parse --show-toplevel 2>/dev/null)"
    if [ ! "${git_root}" ]; then
        return
    fi
    dot_git="${git_root}/.git"
    if [ -d $dot_git ]; then
        echo $git_root
    else
        # 'git worktree': .git points to the true root dir
        cat $dot_git \
            | grep -E '^gitdir:' \
            | sed -r -e 's/^gitdir:\s*//;' -e 's|/\.git/worktrees/.*||;'
    fi
}


hook="$1"
if [ ! -e "${hook}" ]; then echo "Hook ${hook} does not exist"; exit 1; fi
if [ ! -r "${hook}" ]; then echo "Hook ${hook} is not readable"; exit 1; fi
hook_name="$(basename "${hook}")"

git_root="$(find_git_root)"
if [ ! "${git_root}" ]; then
    echo "Not a Git repository -- not attempting to install hook"
    exit 0
fi

destination="${git_root}/.git/hooks/${hook_name}"

# Check if a hook is already present
if [ -e "${destination}" ]; then
    if [ "$(hash_content ${hook})" = "$(hash_content $destination)" ]; then
        echo "Git hook .git/hooks/${hook_name} already in place"
        exit 0
    else
        # A different hook exists: back it up
        back_up "${destination}" "${hook}"
    fi
fi

# Install the new hook
echo "Installing Git hook ${destination}"
cp "${hook}" "${destination}"