#!/bin/sh
#
# Copyright (c) 2006 Johannes E. Schindelin

# SHORT DESCRIPTION
#
# This script makes it easy to fix up commits in the middle of a series,
# and rearrange commits.
#
# The original idea comes from Eric W. Biederman, in
# http://article.gmane.org/gmane.comp.version-control.git/22407

USAGE='(--continue | --abort | --skip | [--preserve-merges] [--verbose]
        [--onto <branch>] <upstream> [<branch>])'

OPTIONS_SPEC=
. git-sh-setup
require_work_tree

DOTEST="$GIT_DIR/.dotest-merge"
TODO="$DOTEST"/git-rebase-todo
DONE="$DOTEST"/done
MSG="$DOTEST"/message
SQUASH_MSG="$DOTEST"/message-squash
REWRITTEN="$DOTEST"/rewritten
PRESERVE_MERGES=
STRATEGY=
VERBOSE=
test -d "$REWRITTEN" && PRESERVE_MERGES=t
test -f "$DOTEST"/strategy && STRATEGY="$(cat "$DOTEST"/strategy)"
test -f "$DOTEST"/verbose && VERBOSE=t

GIT_CHERRY_PICK_HELP="  After resolving the conflicts,
mark the corrected paths with 'git add <paths>', and
run 'git rebase --continue'"
export GIT_CHERRY_PICK_HELP

warn () {
        echo "$*" >&2
}

output () {
        case "$VERBOSE" in
        '')
                output=$("$@" 2>&1 )
                status=$?
                test $status != 0 && printf "%s\n" "$output"
                return $status
                ;;
        *)
                "$@"
                ;;
        esac
}

require_clean_work_tree () {
        # test if working tree is dirty
        git rev-parse --verify HEAD > /dev/null &&
        git update-index --refresh &&
        git diff-files --quiet &&
        git diff-index --cached --quiet HEAD -- ||
        die "Working tree is dirty"
}

ORIG_REFLOG_ACTION="$GIT_REFLOG_ACTION"

comment_for_reflog () {
        case "$ORIG_REFLOG_ACTION" in
        ''|rebase*)
                GIT_REFLOG_ACTION="rebase -i ($1)"
                export GIT_REFLOG_ACTION
                ;;
        esac
}

last_count=
mark_action_done () {
        sed -e 1q < "$TODO" >> "$DONE"
        sed -e 1d < "$TODO" >> "$TODO".new
        mv -f "$TODO".new "$TODO"
        count=$(($(grep -ve '^$' -e '^#' < "$DONE" | wc -l)))
        total=$(($count+$(grep -ve '^$' -e '^#' < "$TODO" | wc -l)))
        if test "$last_count" != "$count"
        then
                last_count=$count
                printf "Rebasing (%d/%d)\r" $count $total
                test -z "$VERBOSE" || echo
        fi
}

make_patch () {
        parent_sha1=$(git rev-parse --verify "$1"^) ||
                die "Cannot get patch for $1^"
        git diff-tree -p "$parent_sha1".."$1" > "$DOTEST"/patch
        test -f "$DOTEST"/message ||
                git cat-file commit "$1" | sed "1,/^$/d" > "$DOTEST"/message
        test -f "$DOTEST"/author-script ||
                get_author_ident_from_commit "$1" > "$DOTEST"/author-script
}

die_with_patch () {
        make_patch "$1"
        git rerere
        die "$2"
}

die_abort () {
        rm -rf "$DOTEST"
        die "$1"
}

has_action () {
        grep -vqe '^$' -e '^#' "$1"
}

pick_one () {
        no_ff=
        case "$1" in -n) sha1=$2; no_ff=t ;; *) sha1=$1 ;; esac
        output git rev-parse --verify $sha1 || die "Invalid commit name: $sha1"
        test -d "$REWRITTEN" &&
                pick_one_preserving_merges "$@" && return
        parent_sha1=$(git rev-parse --verify $sha1^) ||
                die "Could not get the parent of $sha1"
        current_sha1=$(git rev-parse --verify HEAD)
        if test "$no_ff$current_sha1" = "$parent_sha1"; then
                output git reset --hard $sha1
                test "a$1" = a-n && output git reset --soft $current_sha1
                sha1=$(git rev-parse --short $sha1)
                output warn Fast forward to $sha1
        else
                output git cherry-pick "$@"
        fi
}

pick_one_preserving_merges () {
        case "$1" in -n) sha1=$2 ;; *) sha1=$1 ;; esac
        sha1=$(git rev-parse $sha1)

        if test -f "$DOTEST"/current-commit
        then
                current_commit=$(cat "$DOTEST"/current-commit) &&
                git rev-parse HEAD > "$REWRITTEN"/$current_commit &&
                rm "$DOTEST"/current-commit ||
                die "Cannot write current commit's replacement sha1"
        fi

        # rewrite parents; if none were rewritten, we can fast-forward.
        fast_forward=t
        preserve=t
        new_parents=
        for p in $(git rev-list --parents -1 $sha1 | cut -d' ' -f2-)
        do
                if test -f "$REWRITTEN"/$p
                then
                        preserve=f
                        new_p=$(cat "$REWRITTEN"/$p)
                        test $p != $new_p && fast_forward=f
                        case "$new_parents" in
                        *$new_p*)
                                ;; # do nothing; that parent is already there
                        *)
                                new_parents="$new_parents $new_p"
                                ;;
                        esac
                fi
        done
        case $fast_forward in
        t)
                output warn "Fast forward to $sha1"
                test $preserve = f || echo $sha1 > "$REWRITTEN"/$sha1
                ;;
        f)
                test "a$1" = a-n && die "Refusing to squash a merge: $sha1"

                first_parent=$(expr "$new_parents" : ' \([^ ]*\)')
                # detach HEAD to current parent
                output git checkout $first_parent 2> /dev/null ||
                        die "Cannot move HEAD to $first_parent"

                echo $sha1 > "$DOTEST"/current-commit
                case "$new_parents" in
                ' '*' '*)
                        # redo merge
                        author_script=$(get_author_ident_from_commit $sha1)
                        eval "$author_script"
                        msg="$(git cat-file commit $sha1 | sed -e '1,/^$/d')"
                        # No point in merging the first parent, that's HEAD
                        new_parents=${new_parents# $first_parent}
                        if ! GIT_AUTHOR_NAME="$GIT_AUTHOR_NAME" \
                                GIT_AUTHOR_EMAIL="$GIT_AUTHOR_EMAIL" \
                                GIT_AUTHOR_DATE="$GIT_AUTHOR_DATE" \
                                output git merge $STRATEGY -m "$msg" \
                                        $new_parents
                        then
                                git rerere
                                printf "%s\n" "$msg" > "$GIT_DIR"/MERGE_MSG
                                die Error redoing merge $sha1
                        fi
                        ;;
                *)
                        output git cherry-pick "$@" ||
                                die_with_patch $sha1 "Could not pick $sha1"
                        ;;
                esac
                ;;
        esac
}

nth_string () {
        case "$1" in
        *1[0-9]|*[04-9]) echo "$1"th;;
        *1) echo "$1"st;;
        *2) echo "$1"nd;;
        *3) echo "$1"rd;;
        esac
}

make_squash_message () {
        if test -f "$SQUASH_MSG"; then
                COUNT=$(($(sed -n "s/^# This is [^0-9]*\([1-9][0-9]*\).*/\1/p" \
                        < "$SQUASH_MSG" | tail -n 1)+1))
                echo "# This is a combination of $COUNT commits."
                sed -e 1d -e '2,/^./{
                        /^$/d
                }' <"$SQUASH_MSG"
        else
                COUNT=2
                echo "# This is a combination of two commits."
                echo "# The first commit's message is:"
                echo
                git cat-file commit HEAD | sed -e '1,/^$/d'
        fi
        echo
        echo "# This is the $(nth_string $COUNT) commit message:"
        echo
        git cat-file commit $1 | sed -e '1,/^$/d'
}

peek_next_command () {
        sed -n "1s/ .*$//p" < "$TODO"
}

do_next () {
        rm -f "$DOTEST"/message "$DOTEST"/author-script \
                "$DOTEST"/amend || exit
        read command sha1 rest < "$TODO"
        case "$command" in
        '#'*|'')
                mark_action_done
                ;;
        pick|p)
                comment_for_reflog pick

                mark_action_done
                pick_one $sha1 ||
                        die_with_patch $sha1 "Could not apply $sha1... $rest"
                ;;
        edit|e)
                comment_for_reflog edit

                mark_action_done
                pick_one $sha1 ||
                        die_with_patch $sha1 "Could not apply $sha1... $rest"
                make_patch $sha1
                : > "$DOTEST"/amend
                warn
                warn "You can amend the commit now, with"
                warn
                warn "  git commit --amend"
                warn
                exit 0
                ;;
        squash|s)
                comment_for_reflog squash

                has_action "$DONE" ||
                        die "Cannot 'squash' without a previous commit"

                mark_action_done
                make_squash_message $sha1 > "$MSG"
                case "$(peek_next_command)" in
                squash|s)
                        EDIT_COMMIT=
                        USE_OUTPUT=output
                        cp "$MSG" "$SQUASH_MSG"
                        ;;
                *)
                        EDIT_COMMIT=-e
                        USE_OUTPUT=
                        rm -f "$SQUASH_MSG" || exit
                        ;;
                esac

                failed=f
                author_script=$(get_author_ident_from_commit HEAD)
                output git reset --soft HEAD^
                pick_one -n $sha1 || failed=t
                echo "$author_script" > "$DOTEST"/author-script
                if test $failed = f
                then
                        # This is like --amend, but with a different message
                        eval "$author_script"
                        GIT_AUTHOR_NAME="$GIT_AUTHOR_NAME" \
                        GIT_AUTHOR_EMAIL="$GIT_AUTHOR_EMAIL" \
                        GIT_AUTHOR_DATE="$GIT_AUTHOR_DATE" \
                        $USE_OUTPUT git commit --no-verify -F "$MSG" $EDIT_COMMIT || failed=t
                fi
                if test $failed = t
                then
                        cp "$MSG" "$GIT_DIR"/MERGE_MSG
                        warn
                        warn "Could not apply $sha1... $rest"
                        die_with_patch $sha1 ""
                fi
                ;;
        *)
                warn "Unknown command: $command $sha1 $rest"
                die_with_patch $sha1 "Please fix this in the file $TODO."
                ;;
        esac
        test -s "$TODO" && return

        comment_for_reflog finish &&
        HEADNAME=$(cat "$DOTEST"/head-name) &&
        OLDHEAD=$(cat "$DOTEST"/head) &&
        SHORTONTO=$(git rev-parse --short $(cat "$DOTEST"/onto)) &&
        if test -d "$REWRITTEN"
        then
                test -f "$DOTEST"/current-commit &&
                        current_commit=$(cat "$DOTEST"/current-commit) &&
                        git rev-parse HEAD > "$REWRITTEN"/$current_commit
                if test -f "$REWRITTEN"/$OLDHEAD
                then
                        NEWHEAD=$(cat "$REWRITTEN"/$OLDHEAD)
                else
                        NEWHEAD=$OLDHEAD
                fi
        else
                NEWHEAD=$(git rev-parse HEAD)
        fi &&
        case $HEADNAME in
        refs/*)
                message="$GIT_REFLOG_ACTION: $HEADNAME onto $SHORTONTO)" &&
                git update-ref -m "$message" $HEADNAME $NEWHEAD $OLDHEAD &&
                git symbolic-ref HEAD $HEADNAME
                ;;
        esac && {
                test ! -f "$DOTEST"/verbose ||
                        git diff-tree --stat $(cat "$DOTEST"/head)..HEAD
        } &&
        rm -rf "$DOTEST" &&
        git gc --auto &&
        warn "Successfully rebased and updated $HEADNAME."

        exit
}

do_rest () {
        while :
        do
                do_next
        done
}

while test $# != 0
do
        case "$1" in
        --continue)
                comment_for_reflog continue

                test -d "$DOTEST" || die "No interactive rebase running"

                # Sanity check
                git rev-parse --verify HEAD >/dev/null ||
                        die "Cannot read HEAD"
                git update-index --refresh && git diff-files --quiet ||
                        die "Working tree is dirty"

                # do we have anything to commit?
                if git diff-index --cached --quiet HEAD --
                then
                        : Nothing to commit -- skip this
                else
                        . "$DOTEST"/author-script ||
                                die "Cannot find the author identity"
                        if test -f "$DOTEST"/amend
                        then
                                git reset --soft HEAD^ ||
                                die "Cannot rewind the HEAD"
                        fi
                        export GIT_AUTHOR_NAME GIT_AUTHOR_EMAIL GIT_AUTHOR_DATE &&
                        git commit --no-verify -F "$DOTEST"/message -e ||
                        die "Could not commit staged changes."
                fi

                require_clean_work_tree
                do_rest
                ;;
        --abort)
                comment_for_reflog abort

                git rerere clear
                test -d "$DOTEST" || die "No interactive rebase running"

                HEADNAME=$(cat "$DOTEST"/head-name)
                HEAD=$(cat "$DOTEST"/head)
                case $HEADNAME in
                refs/*)
                        git symbolic-ref HEAD $HEADNAME
                        ;;
                esac &&
                output git reset --hard $HEAD &&
                rm -rf "$DOTEST"
                exit
                ;;
        --skip)
                comment_for_reflog skip

                git rerere clear
                test -d "$DOTEST" || die "No interactive rebase running"

                output git reset --hard && do_rest
                ;;
        -s|--strategy)
                case "$#,$1" in
                *,*=*)
                        STRATEGY="-s "$(expr "z$1" : 'z-[^=]*=\(.*\)') ;;
                1,*)
                        usage ;;
                *)
                        STRATEGY="-s $2"
                        shift ;;
                esac
                ;;
        --merge)
                # we use merge anyway
                ;;
        -C*)
                die "Interactive rebase uses merge, so $1 does not make sense"
                ;;
        -v|--verbose)
                VERBOSE=t
                ;;
        -p|--preserve-merges)
                PRESERVE_MERGES=t
                ;;
        -i|--interactive)
                # yeah, we know
                ;;
        ''|-h)
                usage
                ;;
        *)
                test -d "$DOTEST" &&
                        die "Interactive rebase already started"

                git var GIT_COMMITTER_IDENT >/dev/null ||
                        die "You need to set your committer info first"

                comment_for_reflog start

                ONTO=
                case "$1" in
                --onto)
                        ONTO=$(git rev-parse --verify "$2") ||
                                die "Does not point to a valid commit: $2"
                        shift; shift
                        ;;
                esac

                require_clean_work_tree

                if test ! -z "$2"
                then
                        output git show-ref --verify --quiet "refs/heads/$2" ||
                                die "Invalid branchname: $2"
                        output git checkout "$2" ||
                                die "Could not checkout $2"
                fi

                HEAD=$(git rev-parse --verify HEAD) || die "No HEAD?"
                UPSTREAM=$(git rev-parse --verify "$1") || die "Invalid base"

                mkdir "$DOTEST" || die "Could not create temporary $DOTEST"

                test -z "$ONTO" && ONTO=$UPSTREAM

                : > "$DOTEST"/interactive || die "Could not mark as interactive"
                git symbolic-ref HEAD > "$DOTEST"/head-name 2> /dev/null ||
                        echo "detached HEAD" > "$DOTEST"/head-name

                echo $HEAD > "$DOTEST"/head
                echo $UPSTREAM > "$DOTEST"/upstream
                echo $ONTO > "$DOTEST"/onto
                test -z "$STRATEGY" || echo "$STRATEGY" > "$DOTEST"/strategy
                test t = "$VERBOSE" && : > "$DOTEST"/verbose
                if test t = "$PRESERVE_MERGES"
                then
                        # $REWRITTEN contains files for each commit that is
                        # reachable by at least one merge base of $HEAD and
                        # $UPSTREAM. They are not necessarily rewritten, but
                        # their children might be.
                        # This ensures that commits on merged, but otherwise
                        # unrelated side branches are left alone. (Think "X"
                        # in the man page's example.)
                        mkdir "$REWRITTEN" &&
                        for c in $(git merge-base --all $HEAD $UPSTREAM)
                        do
                                echo $ONTO > "$REWRITTEN"/$c ||
                                        die "Could not init rewritten commits"
                        done
                        MERGES_OPTION=
                else
                        MERGES_OPTION=--no-merges
                fi

                SHORTUPSTREAM=$(git rev-parse --short $UPSTREAM)
                SHORTHEAD=$(git rev-parse --short $HEAD)
                SHORTONTO=$(git rev-parse --short $ONTO)
                git rev-list $MERGES_OPTION --pretty=oneline --abbrev-commit \
                        --abbrev=7 --reverse --left-right --cherry-pick \
                        $UPSTREAM...$HEAD | \
                        sed -n "s/^>/pick /p" > "$TODO"
                cat >> "$TODO" << EOF

# Rebase $SHORTUPSTREAM..$SHORTHEAD onto $SHORTONTO
#
# Commands:
#  pick = use commit
#  edit = use commit, but stop for amending
#  squash = use commit, but meld into previous commit
#
# If you remove a line here THAT COMMIT WILL BE LOST.
# However, if you remove everything, the rebase will be aborted.
#
EOF

                has_action "$TODO" ||
                        die_abort "Nothing to do"

                cp "$TODO" "$TODO".backup
                git_editor "$TODO" ||
                        die "Could not execute editor"

                has_action "$TODO" ||
                        die_abort "Nothing to do"

                output git checkout $ONTO && do_rest
                ;;
        esac
        shift
done