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

USAGE='[-n] [--no-commit] [--squash] [-s <strategy>] [-m=<merge-message>] <commit>+'

. git-sh-setup
set_reflog_action "merge $*"

LF='
'

all_strategies='recur recursive octopus resolve stupid ours'
default_twohead_strategies='recursive'
default_octopus_strategies='octopus'
no_trivial_merge_strategies='ours'
use_strategies=

index_merge=t

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

savestate() {
        # Stash away any local modifications.
        git-diff-index -z --name-only $head |
        cpio -0 -o >"$GIT_DIR/MERGE_SAVE"
}

restorestate() {
        if test -f "$GIT_DIR/MERGE_SAVE"
        then
                git reset --hard $head >/dev/null
                cpio -iuv <"$GIT_DIR/MERGE_SAVE"
                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 ^"$head" $remote
}

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
                        ;;
                esac
                ;;
        esac
        case "$1" in
        '')
                ;;
        ?*)
                case "$no_summary" in
                '')
                        git-diff-tree --stat --summary -M "$head" "$1"
                        ;;
                esac
                ;;
        esac
}

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 ."
        else
                echo "$rh               commit '$remote'"
        fi
}

case "$#" in 0) usage ;; esac

have_message=
while case "$#" in 0) break ;; esac
do
        case "$1" in
        -n|--n|--no|--no-|--no-s|--no-su|--no-sum|--no-summ|\
                --no-summa|--no-summar|--no-summary)
                no_summary=t ;;
        --sq|--squ|--squa|--squas|--squash)
                squash=t no_commit=t ;;
        --no-c|--no-co|--no-com|--no-comm|--no-commi|--no-commit)
                no_commit=t ;;
        -s=*|--s=*|--st=*|--str=*|--stra=*|--strat=*|--strate=*|\
                --strateg=*|--strategy=*|\
        -s|--s|--st|--str|--stra|--strat|--strate|--strateg|--strategy)
                case "$#,$1" in
                *,*=*)
                        strategy=`expr "z$1" : 'z-[^=]*=\(.*\)'` ;;
                1,*)
                        usage ;;
                *)
                        strategy="$2"
                        shift ;;
                esac
                case " $all_strategies " in
                *" $strategy "*)
                        use_strategies="$use_strategies$strategy " ;;
                *)
                        die "available strategies are: $all_strategies" ;;
                esac
                ;;
        -m=*|--m=*|--me=*|--mes=*|--mess=*|--messa=*|--messag=*|--message=*)
                merge_msg=`expr "z$1" : 'z-[^=]*=\(.*\)'`
                have_message=t
                ;;
        -m|--m|--me|--mes|--mess|--messa|--messag|--message)
                shift
                case "$#" in
                1)      usage ;;
                esac
                merge_msg="$1"
                have_message=t
                ;;
        -*)     usage ;;
        *)      break ;;
        esac
        shift
done

# 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
        )
        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.

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)
                use_strategies="$default_twohead_strategies" ;;
        *)
                use_strategies="$default_octopus_strategies" ;;
        esac
        ;;
esac

for s in $use_strategies
do
        case " $s " in
        *" $no_trivial_merge_strategies "*)
                index_merge=f
                break
                ;;
        esac
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 "$index_merge,$#,$common,$no_commit" in
f,*)
        # We've been told not to try anything clever.  Skip to real merge.
        ;;
?,*,'',*)
        # No common ancestors found. We need a real merge.
        ;;
?,1,"$1",*)
        # If head can reach all the merge then we are up to date.
        # but first the most common case of merging one remote.
        finish_up_to_date "Already up-to-date."
        exit 0
        ;;
?,1,"$head",*)
        # Again the most common case of merging one remote.
        echo "Updating $(git-rev-parse --short $head)..$(git-rev-parse --short $1)"
        git-update-index --refresh 2>/dev/null
        new_head=$(git-rev-parse --verify "$1^0") &&
        git-read-tree -v -m -u --exclude-per-directory=.gitignore $head "$new_head" &&
        finish "$new_head" "Fast forward"
        dropsave
        exit 0
        ;;
?,1,?*"$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.  See if it is really trivial.
        git var GIT_COMMITTER_IDENT >/dev/null || exit

        echo "Trying really trivial in-index merge..."
        git-update-index --refresh 2>/dev/null
        if git-read-tree --trivial -m -u -v $common $head "$1" &&
           result_tree=$(git-write-tree)
        then
            echo "Wonderful."
            result_commit=$(
                echo "$merge_msg" |
                git-commit-tree $result_tree -p HEAD -p "$1"
            ) || exit
            finish "$result_commit" "In-index merge"
            dropsave
            exit 0
        fi
        echo "Nope."
        ;;
*)
        # 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_SAVE"
    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 '' != "$result_tree"
then
    parents=$(git-show-branch --independent "$head" "$@" | sed -e 's/^/-p /')
    result_commit=$(echo "$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"
        echo "$merge_msg" >"$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"
        if test -d "$GIT_DIR/rr-cache"
        then
                git-rerere
        fi
        die "Automatic merge failed; fix conflicts and then commit the result."
fi