#!/bin/bash
set -e

NOGIT_DIR=.nogit
NOGIT_DIR_TMP=$NOGIT_DIR-tmp

usage_brief()
{
    echo "Usage: nogit <command>"
    echo ""
    echo "Available commands are:"
    echo ""
    echo "    nogit clone"
    echo "    nogit sync"
    echo ""
    echo "See 'nogit help' for more details"
}

usage()
{
    echo "Usage: nogit <command>"
    echo ""
    echo "Possible commands are described below:"
    echo ""
    echo "nogit clone <command>"
    echo ""
    echo "    Clone a nogit repository into the current directory."
    echo "    This differs from 'git clone' in that it will not create"
    echo "    a new top-level directory but will instead clone the"
    echo "    resulting files into the current directory (which may"
    echo "    already be a local git repository). The object store for"
    echo "    this newly-cloned repository will be a directory named"
    echo "    .nogit rather than .git."
    echo ""
    echo "    The repository to be cloned should be a nogit repository"
    echo "    in the sense that its files are intended to be managed"
    echo "    according to nogit semantics. But other than that, the"
    echo "    repository to be cloned is an actual git repository."
    echo ""
    echo "nogit sync"
    echo ""
    echo "    Synchronize local and remote changes"
    echo ""
    echo "    For all files managed by a previously-cloned nogit repository"
    echo "    this command will:"
    echo ""
    echo "        * Commit local changes (auto-generated commit message)"
    echo ""
    echo "        * Pull down any new commits from the remote"
    echo ""
    echo "        * Auto-merge local and remote (keeping both sides and"
    echo "          with an auto-generated commit message)"
    echo ""
    echo "        * Push out any new commits generated locally"
    echo ""
    echo "nogit log"
    echo ""
    echo "    Display a log of changes"
}

nogit_clone()
{
    url="$1"

    if [ -e $NOGIT_DIR ]; then
        echo "Error: $NOGIT_DIR already exists. Cowardly refusing to re-clone."
        return 1
    fi

    if [ -e $NOGIT_DIR_TMP ]; then
        echo "Error: $NOGIT_DIR_TMP already exists. Was a previous clone interrupted?"
        echo "You'll want to clean that up before trying again."
        return 1
    fi

    # Clone the repository into a temporary directory
    mkdir $NOGIT_DIR_TMP
    cd $NOGIT_DIR_TMP
    git clone "$url" tmp >/dev/null 2>&1

    # Sanity check that we won't be overwriting any files
    EXISTING=()
    cd tmp
    for file in $(find . -mindepth 1 -a -path ./.git -prune -o -print); do
        if [ -e "../../$file" ]; then
            EXISTING+=($(echo "$file" | sed -s 's,^\./,,'))
        fi
    done
    cd ..

    if [ ${#EXISTING[@]} -gt 0 ]; then
        echo "Error: The following existing files would be overwritten:" >&2
        echo "" >&2
        for file in ${EXISTING[@]}; do
            echo "    $file" >&2
        done
        echo "" >&2
        echo "Cowardly refusing to clone" >&2
        cd ..
        rm -rf $NOGIT_DIR_TMP
        false
    fi

    # Install the info/atttributes file that forces the "union" merge
    # driver for all files, giving us the semantics of "keep both sides
    # of all conflicts" that is at the heart of nogit.
    mkdir -p tmp/.git/info
    echo '* merge=union' > tmp/.git/info/attributes

    # Install the config entry for the pretty format for "nogit log"
    (cd tmp; git config pretty.nogit "format:%Cblue%h %an (%ad)%Creset")

    # Now that we've passed the sanity check, install the cloned .git
    # object store into $NOGIT_DIR, cleanup our temporary files, and
    # checkout the (known to not be conflicting) files.
    mv tmp/.git ../$NOGIT_DIR
    cd ..
    rm -rf $NOGIT_DIR_TMP
    GIT_DIR=$NOGIT_DIR git reset --hard >/dev/null 2>&1

    echo "Completed nogit clone of $url"
}

nogit_sync()
{
    # First commit any locally modified nogit files
    GIT_DIR=$NOGIT_DIR git commit -a -m "nogit-sync commit" >/dev/null 2>&1 || true

    # Then, fetch and merge any upstream changes
    GIT_DIR=$NOGIT_DIR git fetch >/dev/null 2>&1
    GIT_DIR=$NOGIT_DIR git merge -m "nogit-sync merge" >/dev/null 2>&1

    # Finally, push any new commits up to the upstream repository
    GIT_DIR=$NOGIT_DIR git push >/dev/null 2>&1

    echo "Completed nogit sync"
}

nogit_log()
{
    GIT_DIR=$NOGIT_DIR git log -p --pretty=nogit
}

if [ $# -lt 1 ]; then
    echo "Error: missing command name." >&2
    echo ""
    usage_brief >&2
    exit 1
fi

cmd="$1"

case "$cmd" in
    clone)
        if [ $# -lt 2 ]; then
            echo "Error: 'nogit clone' requires the URL of a repository to clone"
            false;
        fi
        nogit_clone "$2"
	;;
    sync)
        nogit_sync
	;;
    log)
        nogit_log
        ;;
    help)
        usage
        true
	;;
    *)
        echo "Error: Unknown command: $cmd" >&2
        echo ""
        usage_brief >&2
        false
        ;;
esac

exit $?