#!/bin/sh
#
# Copyright (c) 2005 Junio C Hamano
#

OPTIONS_KEEPDASHDASH=
OPTIONS_SPEC="\
git merge [options] <remote>...
git merge [options] <msg> HEAD <remote>
--
stat                 show a diffstat at the end of the merge
n                    don't show a diffstat at the end of the merge
summary              (synonym to --stat)
log                  add list of one-line log to merge commit message
squash               create a single commit instead of doing a merge
commit               perform a commit if the merge succeeds (default)
ff                   allow fast forward (default)
s,strategy=          merge strategy to use
m,message=           message to be used for the merge commit (if any)
"

SUBDIRECTORY_OK=Yes
. git-sh-setup
require_work_tree
cd_to_toplevel

test -z "$(git ls-files -u)" ||
        die "You are in the middle of a conflicted merge."

LF='
'

all_strategies='recur recursive octopus resolve stupid ours subtree'
default_twohead_strategies='recursive'
default_octopus_strategies='octopus'
no_fast_forward_strategies='subtree ours'
no_trivial_strategies='recursive recur subtree ours'
use_strategies=

allow_fast_forward=t
allow_trivial_merge=t
squash= no_commit= log_arg=

dropsave() {
        rm -f -- "$GIT_DIR/MERGE_HEAD" "$GIT_DIR/MERGE_MSG" \
                 "$GIT_DIR/MERGE_STASH" || exit 1
}

savestate() {
        # Stash away any local modifications.
        git stash create >"$GIT_DIR/MERGE_STASH"
}

restorestate() {
        if test -f "$GIT_DIR/MERGE_STASH"
        then
                git reset --hard $head >/dev/null
                git stash apply $(cat "$GIT_DIR/MERGE_STASH")
                git update-index --refresh >/dev/null
        fi
}

finish_up_to_date () {
        case "$squash" in
        t)
                echo "$1 (nothing to squash)" ;;
        '')
                echo "$1" ;;
        esac
        dropsave
}

squash_message () {
        echo Squashed commit of the following:
        echo
        git log --no-merges --pretty=medium ^"$head" $remoteheads
}

finish () {
        if test '' = "$2"
        then
                rlogm="$GIT_REFLOG_ACTION"
        else
                echo "$2"
                rlogm="$GIT_REFLOG_ACTION: $2"
        fi
        case "$squash" in
        t)
                echo "Squash commit -- not updating HEAD"
                squash_message >"$GIT_DIR/SQUASH_MSG"
                ;;
        '')
                case "$merge_msg" in
                '')
                        echo "No merge message -- not updating HEAD"
                        ;;
                *)
                        git update-ref -m "$rlogm" HEAD "$1" "$head" || exit 1
                        git gc --auto
                        ;;
                esac
                ;;
        esac
        case "$1" in
        '')
                ;;
        ?*)
                if test "$show_diffstat" = t
                then
                        # We want color (if set), but no pager
                        GIT_PAGER='' git diff --stat --summary -M "$head" "$1"
                fi
                ;;
        esac

        # Run a post-merge hook
        if test -x "$GIT_DIR"/hooks/post-merge
        then
            case "$squash" in
            t)
                "$GIT_DIR"/hooks/post-merge 1
                ;;
            '')
                "$GIT_DIR"/hooks/post-merge 0
                ;;
            esac
        fi
}

merge_name () {
        remote="$1"
        rh=$(git rev-parse --verify "$remote^0" 2>/dev/null) || return
        bh=$(git show-ref -s --verify "refs/heads/$remote" 2>/dev/null)
        if test "$rh" = "$bh"
        then
                echo "$rh               branch '$remote' of ."
        elif truname=$(expr "$remote" : '\(.*\)~[1-9][0-9]*$') &&
                git show-ref -q --verify "refs/heads/$truname" 2>/dev/null
        then
                echo "$rh               branch '$truname' (early part) of ."
        elif test "$remote" = "FETCH_HEAD" -a -r "$GIT_DIR/FETCH_HEAD"
        then
                sed -e 's/      not-for-merge   /               /' -e 1q \
                        "$GIT_DIR/FETCH_HEAD"
        else
                echo "$rh               commit '$remote'"
        fi
}

parse_config () {
        while test $# != 0; do
                case "$1" in
                -n|--no-stat|--no-summary)
                        show_diffstat=false ;;
                --stat|--summary)
                        show_diffstat=t ;;
                --log|--no-log)
                        log_arg=$1 ;;
                --squash)
                        test "$allow_fast_forward" = t ||
                                die "You cannot combine --squash with --no-ff."
                        squash=t no_commit=t ;;
                --no-squash)
                        squash= no_commit= ;;
                --commit)
                        no_commit= ;;
                --no-commit)
                        no_commit=t ;;
                --ff)
                        allow_fast_forward=t ;;
                --no-ff)
                        test "$squash" != t ||
                                die "You cannot combine --squash with --no-ff."
                        allow_fast_forward=f ;;
                -s|--strategy)
                        shift
                        case " $all_strategies " in
                        *" $1 "*)
                                use_strategies="$use_strategies$1 " ;;
                        *)
                                die "available strategies are: $all_strategies" ;;
                        esac
                        ;;
                -m|--message)
                        shift
                        merge_msg="$1"
                        have_message=t
                        ;;
                --)
                        shift
                        break ;;
                *)      usage ;;
                esac
                shift
        done
        args_left=$#
}

test $# != 0 || usage

have_message=

if branch=$(git-symbolic-ref -q HEAD)
then
        mergeopts=$(git config "branch.${branch#refs/heads/}.mergeoptions")
        if test -n "$mergeopts"
        then
                parse_config $mergeopts --
        fi
fi

parse_config "$@"
while test $args_left -lt $#; do shift; done

if test -z "$show_diffstat"; then
    test "$(git config --bool merge.diffstat)" = false && show_diffstat=false
    test "$(git config --bool merge.stat)" = false && show_diffstat=false
    test -z "$show_diffstat" && show_diffstat=t
fi

# This could be traditional "merge <msg> HEAD <commit>..."  and the
# way we can tell it is to see if the second token is HEAD, but some
# people might have misused the interface and used a committish that
# is the same as HEAD there instead.  Traditional format never would
# have "-m" so it is an additional safety measure to check for it.

if test -z "$have_message" &&
        second_token=$(git rev-parse --verify "$2^0" 2>/dev/null) &&
        head_commit=$(git rev-parse --verify "HEAD" 2>/dev/null) &&
        test "$second_token" = "$head_commit"
then
        merge_msg="$1"
        shift
        head_arg="$1"
        shift
elif ! git rev-parse --verify HEAD >/dev/null 2>&1
then
        # If the merged head is a valid one there is no reason to
        # forbid "git merge" into a branch yet to be born.  We do
        # the same for "git pull".
        if test 1 -ne $#
        then
                echo >&2 "Can merge only exactly one commit into empty head"
                exit 1
        fi

        rh=$(git rev-parse --verify "$1^0") ||
                die "$1 - not something we can merge"

        git update-ref -m "initial pull" HEAD "$rh" "" &&
        git read-tree --reset -u HEAD
        exit

else
        # We are invoked directly as the first-class UI.
        head_arg=HEAD

        # All the rest are the commits being merged; prepare
        # the standard merge summary message to be appended to
        # the given message.  If remote is invalid we will die
        # later in the common codepath so we discard the error
        # in this loop.
        merge_name=$(for remote
                do
                        merge_name "$remote"
                done | git fmt-merge-msg $log_arg
        )
        merge_msg="${merge_msg:+$merge_msg$LF$LF}$merge_name"
fi
head=$(git rev-parse --verify "$head_arg"^0) || usage

# All the rest are remote heads
test "$#" = 0 && usage ;# we need at least one remote head.
set_reflog_action "merge $*"

remoteheads=
for remote
do
        remotehead=$(git rev-parse --verify "$remote"^0 2>/dev/null) ||
            die "$remote - not something we can merge"
        remoteheads="${remoteheads}$remotehead "
        eval GITHEAD_$remotehead='"$remote"'
        export GITHEAD_$remotehead
done
set x $remoteheads ; shift

case "$use_strategies" in
'')
        case "$#" in
        1)
                var="`git config --get pull.twohead`"
                if test -n "$var"
                then
                        use_strategies="$var"
                else
                        use_strategies="$default_twohead_strategies"
                fi ;;
        *)
                var="`git config --get pull.octopus`"
                if test -n "$var"
                then
                        use_strategies="$var"
                else
                        use_strategies="$default_octopus_strategies"
                fi ;;
        esac
        ;;
esac

for s in $use_strategies
do
        for ss in $no_fast_forward_strategies
        do
                case " $s " in
                *" $ss "*)
                        allow_fast_forward=f
                        break
                        ;;
                esac
        done
        for ss in $no_trivial_strategies
        do
                case " $s " in
                *" $ss "*)
                        allow_trivial_merge=f
                        break
                        ;;
                esac
        done
done

case "$#" in
1)
        common=$(git merge-base --all $head "$@")
        ;;
*)
        common=$(git show-branch --merge-base $head "$@")
        ;;
esac
echo "$head" >"$GIT_DIR/ORIG_HEAD"

case "$allow_fast_forward,$#,$common,$no_commit" in
?,*,'',*)
        # No common ancestors found. We need a real merge.
        ;;
?,1,"$1",*)
        # If head can reach all the merge then we are up to date.
        # but first the most common case of merging one remote.
        finish_up_to_date "Already up-to-date."
        exit 0
        ;;
t,1,"$head",*)
        # Again the most common case of merging one remote.
        echo "Updating $(git rev-parse --short $head)..$(git rev-parse --short $1)"
        git update-index --refresh 2>/dev/null
        msg="Fast forward"
        if test -n "$have_message"
        then
                msg="$msg (no commit created; -m option ignored)"
        fi
        new_head=$(git rev-parse --verify "$1^0") &&
        git read-tree -v -m -u --exclude-per-directory=.gitignore $head "$new_head" &&
        finish "$new_head" "$msg" || exit
        dropsave
        exit 0
        ;;
?,1,?*"$LF"?*,*)
        # We are not doing octopus and not fast forward.  Need a
        # real merge.
        ;;
?,1,*,)
        # We are not doing octopus, not fast forward, and have only
        # one common.
        git update-index --refresh 2>/dev/null
        case "$allow_trivial_merge" in
        t)
                # See if it is really trivial.
                git var GIT_COMMITTER_IDENT >/dev/null || exit
                echo "Trying really trivial in-index merge..."
                if git read-tree --trivial -m -u -v $common $head "$1" &&
                   result_tree=$(git write-tree)
                then
                        echo "Wonderful."
                        result_commit=$(
                                printf '%s\n' "$merge_msg" |
                                git commit-tree $result_tree -p HEAD -p "$1"
                        ) || exit
                        finish "$result_commit" "In-index merge"
                        dropsave
                        exit 0
                fi
                echo "Nope."
        esac
        ;;
*)
        # An octopus.  If we can reach all the remote we are up to date.
        up_to_date=t
        for remote
        do
                common_one=$(git merge-base --all $head $remote)
                if test "$common_one" != "$remote"
                then
                        up_to_date=f
                        break
                fi
        done
        if test "$up_to_date" = t
        then
                finish_up_to_date "Already up-to-date. Yeeah!"
                exit 0
        fi
        ;;
esac

# We are going to make a new commit.
git var GIT_COMMITTER_IDENT >/dev/null || exit

# At this point, we need a real merge.  No matter what strategy
# we use, it would operate on the index, possibly affecting the
# working tree, and when resolved cleanly, have the desired tree
# in the index -- this means that the index must be in sync with
# the $head commit.  The strategies are responsible to ensure this.

case "$use_strategies" in
?*' '?*)
    # Stash away the local changes so that we can try more than one.
    savestate
    single_strategy=no
    ;;
*)
    rm -f "$GIT_DIR/MERGE_STASH"
    single_strategy=yes
    ;;
esac

result_tree= best_cnt=-1 best_strategy= wt_strategy=
merge_was_ok=
for strategy in $use_strategies
do
    test "$wt_strategy" = '' || {
        echo "Rewinding the tree to pristine..."
        restorestate
    }
    case "$single_strategy" in
    no)
        echo "Trying merge strategy $strategy..."
        ;;
    esac

    # Remember which strategy left the state in the working tree
    wt_strategy=$strategy

    git-merge-$strategy $common -- "$head_arg" "$@"
    exit=$?
    if test "$no_commit" = t && test "$exit" = 0
    then
        merge_was_ok=t
        exit=1 ;# pretend it left conflicts.
    fi

    test "$exit" = 0 || {

        # The backend exits with 1 when conflicts are left to be resolved,
        # with 2 when it does not handle the given merge at all.

        if test "$exit" -eq 1
        then
            cnt=`{
                git diff-files --name-only
                git ls-files --unmerged
            } | wc -l`
            if test $best_cnt -le 0 -o $cnt -le $best_cnt
            then
                best_strategy=$strategy
                best_cnt=$cnt
            fi
        fi
        continue
    }

    # Automerge succeeded.
    result_tree=$(git write-tree) && break
done

# If we have a resulting tree, that means the strategy module
# auto resolved the merge cleanly.
if test '' != "$result_tree"
then
    if test "$allow_fast_forward" = "t"
    then
        parents=$(git show-branch --independent "$head" "$@")
    else
        parents=$(git rev-parse "$head" "$@")
    fi
    parents=$(echo "$parents" | sed -e 's/^/-p /')
    result_commit=$(printf '%s\n' "$merge_msg" | git commit-tree $result_tree $parents) || exit
    finish "$result_commit" "Merge made by $wt_strategy."
    dropsave
    exit 0
fi

# Pick the result from the best strategy and have the user fix it up.
case "$best_strategy" in
'')
        restorestate
        case "$use_strategies" in
        ?*' '?*)
                echo >&2 "No merge strategy handled the merge."
                ;;
        *)
                echo >&2 "Merge with strategy $use_strategies failed."
                ;;
        esac
        exit 2
        ;;
"$wt_strategy")
        # We already have its result in the working tree.
        ;;
*)
        echo "Rewinding the tree to pristine..."
        restorestate
        echo "Using the $best_strategy to prepare resolving by hand."
        git-merge-$best_strategy $common -- "$head_arg" "$@"
        ;;
esac

if test "$squash" = t
then
        finish
else
        for remote
        do
                echo $remote
        done >"$GIT_DIR/MERGE_HEAD"
        printf '%s\n' "$merge_msg" >"$GIT_DIR/MERGE_MSG"
fi

if test "$merge_was_ok" = t
then
        echo >&2 \
        "Automatic merge went well; stopped before committing as requested"
        exit 0
else
        {
            echo '
Conflicts:
'
                git ls-files --unmerged |
                sed -e 's/^[^   ]*      /       /' |
                uniq
        } >>"$GIT_DIR/MERGE_MSG"
        git rerere
        die "Automatic merge failed; fix conflicts and then commit the result."
fi