#!/bin/sh

# git-pk3-merge: Attempt a trivial merge of master in a bare repo.

set -x

# Helpers

die()
{
    echo "$(basename "$0"): error: $*" >&2
    exit 1
}

usage()
{
    cat <<EOF
Usage:

  # mandatory
  export GIT_DIR=/path/to/xonotic-maps.pk3dir.git # absolute path
  # optional
  export GIT_AUTHOR_NAME="Some Guy"
  export GIT_AUTHOR_EMAIL="someguy@example.com"

  $(basename $0) nick branch

EOF
}

# Check usage

[ $# -eq 2 ] || {
    usage
    die "wrong number of arguments"
}

[ -z "$GIT_DIR" ] && {
    usage
    die "GIT_DIR not set"
}

nick="$1"
branch=$(git check-ref-format --print "$nick/$2") ||
die "malformed branch name '$nick/$2'"

# Set up commit info

[ -z "$GIT_AUTHOR_NAME" ] && export GIT_AUTHOR_NAME="$nick"
[ -z "$GIT_AUTHOR_EMAIL" ] && export GIT_AUTHOR_EMAIL="${nick}@example.com"

message()
{
    echo "Merge branch 'master'"
}

# Clean up on exit

cleanup_index=

cleanup()
{
    [ "$cleanup_index" ] && rm -f "$GIT_INDEX_FILE"
}

trap cleanup EXIT

# Set up index file, makes testing easier
[ -z "$GIT_INDEX_FILE" ] && {
    export GIT_INDEX_FILE="$GIT_DIR/pk3-merge-index"
    cleanup_index=t
}

# Note the refs and the common ancestor
master=refs/heads/master
ref=refs/heads/$branch
base=$(git merge-base $master $ref 2> /dev/null) ||
die "couldn't determine the common ancestor"

# Figure out the parent commits
parent1=$(git rev-parse --verify -q $ref) &&
parent2=$(git rev-parse --verify -q $master) ||
die "couldn't determine parent commits"

# Attempt a trivial merge
git read-tree -i -m --aggressive --trivial $base $ref $master ||
die "couldn't do a trivial merge"

# Check if the index contains changes against parent
git diff-index --cached --quiet $parent1 &&
die "found no changes to commit"

# Commit the index and point the ref to the new commit
tree=$(git write-tree) &&
commit=$(message | git commit-tree $tree -p $parent1 -p $parent2) &&
git update-ref -m "pk3-merge" $ref $commit ||
die "couldn't commit merge"