update-production

#!/usr/bin/env nix-shell
#!nix-shell -i bash -p git curl python3

set -eux -o pipefail

main() {
    local TOKEN=$1
    shift
    local SERVER_URL=$1
    shift
    local PROJECT_ID=$1
    shift
    local SOURCE_BRANCH=$1
    shift
    local TARGET_BRANCH=$1
    shift

    # Make sure the things we want to talk about are locally known.  GitLab
    # seems to prefer to know about as few refs as possible.
    checkout_git_ref "$SOURCE_BRANCH"
    checkout_git_ref "$TARGET_BRANCH"

    # If there have been no changes we'll just abandon this update.
    if ! ensure_changes "$SOURCE_BRANCH" "$TARGET_BRANCH"; then
	echo "No changes."
	exit 0
    fi

    local NOTES=$(describe_update "$SOURCE_BRANCH" "$TARGET_BRANCH")

    create_merge_request "$TOKEN" "$SERVER_URL" "$PROJECT_ID" "$SOURCE_BRANCH" "$TARGET_BRANCH" "$NOTES"
}

checkout_git_ref() {
    local REF=$1
    shift

    git fetch origin "$REF"
}

ensure_changes() {
    local SOURCE_BRANCH=$1
    shift
    local TARGET_BRANCH=$1
    shift

    if [ "$(git rev-parse origin/"$SOURCE_BRANCH")" = "$(git rev-parse origin/"$TARGET_BRANCH")" ]; then
	return 1
    fi
}

describe_merge_request() {
    git show $rev | grep 'See merge request' | sed -e 's/See merge request //' | tr -d '[:space:]'
}

describe_merge_requests() {
    local RANGE=$1
    shift
    local TARGET=$1
    shift

    # Find all of the relevant merge revisions
    local onelines=$(git log --merges --first-parent -m --oneline "$RANGE" | grep "into '$TARGET'")

    # Describe each merge revision
    local IFS=$'\n'
    for line in $onelines; do
	local rev=$(echo "$line" | cut -d ' ' -f 1)
	echo -n "* "
	describe_merge_request $rev