#!/bin/bash

SUBDIRECTORY_OK=Yes
OPTIONS_SPEC=
. git-sh-setup
require_work_tree
cd_to_toplevel

DATE="$(date +'%Y%m%d_%H%M%S')"
USE_COLORS="yes"

usage () {
    echo "Usage: $(basename $0) [-C] [-c] [-m message]"
    exit 1
}

info () {
    if [ "x$USE_COLORS" == "xyes" ]; then
        echo -en "\033[32m"
    fi
    echo -n "** "
    if [ "x$USE_COLORS" == "xyes" ]; then
        echo -en "\033[0m"
    fi
    echo "$@"
}

error () {
    if [ "x$USE_COLORS" == "xyes" ]; then
        echo -en "\033[31m"
    fi
    echo -n "!! "
    if [ "x$USE_COLORS" == "xyes" ]; then
        echo -en "\033[0m"
    fi
    echo "$@"
    exit 1
}

main () {
    commit_message=""
    temporary_branch="svn.merge.$DATE"
    verbose="no"
    while getopts "hCm:v" opt; do
        case "$opt" in
            C) USE_COLORS="no"
            ;;
            v) verbose="yes"
            ;;
            m) commit_message="$OPTARG"
            ;;
            *) usage
            ;;
        esac
    done
    shift $((OPTIND - 1))

    # attempt a rebase against the latest revision in subversion
    [ "$verbose" == "yes" ] && info "attempting to rebase"

    git svn rebase >/dev/null 2>&1 ||
        error "rebase failed: this is probably due to conflicts"

    # determine the active branch, the checksum of the most recent
    # dcommit to subversion, and the checksom of HEAD
    active_branch="$(git branch --no-color |
        awk '/^[*]\s*/ { print $0 }' |
        sed -e 's/^[*]\s//g')"

    last_dcommit_revision="$(git svn info |
        awk '/^Revision:\s*/ { print $0; }' |
        sed -e 's/^Revision:\s*//g')"
    [ -z $last_dcommit_revision ] &&
        error "could not determine most recent dcommit"

    last_dcommit="$(git svn find-rev r$last_dcommit_revision)"
    [ -z $last_dcommit ] &&
        error "could not determine most recent dcommit"

    last_revision="$(git rev-parse HEAD)"
    [ -z $last_revision ] &&
        error "could not determine HEAD checksum"

    # has anything changed from our last subversion commit?
    if [ "x$last_dcommit" == "x$last_revision" ]; then
        [ "$verbose" == "yes" ] &&
            info "no local changes to $active_branch"
        exit 0
    fi

    # create a temporary branch for merging our local changes
    [ "$verbose" == "yes" ] && info "creating temporary branch for merging"

    git branch "$temporary_branch" >/dev/null 2>&1 ||
        error "could not create temporary branch"

    # wind the active branch back to the most recent dcommit
    [ "$verbose" == "yes" ] && info "resetting $active_branch to $last_dcommit"

    git reset --hard "$last_dcommit" >/dev/null 2>&1 ||
        error "reset to $last_dcommit failed"

    # merge the changes from the temporary branch into the active branch
    [ "$verbose" == "yes" ] && info "merging with $temporary_branch"

    merge_opts=(--no-ff)
    if [ ! -z "$commit_message" ]; then
        merge_opts=(${merge_opts[@]} --no-summary "-m $commit_message")
    fi

    git merge "${merge_opts[@]}" "$temporary_branch" ||
        error "could not merge with $temporary_branch"

    [ "$verbose" == "yes" ] &&
        info "merge complete: local changes merged into $active_branch"
}

main "$@"