#!/usr/bin/env bash

set -e

if [[ $# == 0 ]]; then
    echo "Usage: $0 [--no-conflict] [--no-signature-check] [--stop-before-merging] prnum"
    exit 1
fi

while [[ $# -gt 0 ]]; do
    case "$1" in
        --no-conflict)
            NO_CONFLICTS="true"
            shift
            ;;
        --no-signature-check)
            NO_SIGNATURE_CHECK="true"
            shift
            ;;
        --stop-before-merging)
            STOP_BEFORE_MERGING="true"
            shift
            ;;
        *)
            if [[ "$PRNUM" != "" ]]; then
                echo "PRNUM was already set to $PRNUM and is now being overridden with $1."
            fi
            PRNUM="$1"
            shift
    esac
done

if ! git log master --grep "Merge PR #${PRNUM}" | grep "." > /dev/null; then
    echo "PR #${PRNUM} does not exist."
    exit 1
fi

SIGNATURE_STATUS=$(git log master --grep "Merge PR #${PRNUM}" --format="%G?")
git log master --grep "Merge PR #${PRNUM}" --format="%GG"
if [[ "$NO_SIGNATURE_CHECK" != "true" && "$SIGNATURE_STATUS" != "G" ]]; then
    echo
    read -p "Merge commit does not have a good (valid) signature. Bypass? [y/N] " -n 1 -r
    echo
    if [[ ! $REPLY =~ ^[Yy]$ ]]; then
        exit 1
    fi
fi

BRANCH=backport-pr-${PRNUM}
RANGE=$(git log master --grep "Merge PR #${PRNUM}" --format="%P" | sed 's/ /../')
MESSAGE=$(git log master --grep "Merge PR #${PRNUM}" --format="%s" | sed 's/Merge/Backport/')

if git checkout -b "${BRANCH}"; then

    if ! git cherry-pick -x "${RANGE}"; then
        if [[ "$NO_CONFLICTS" == "true" ]]; then
            git status
            echo "Conflicts! Aborting..."
            git cherry-pick --abort
            git checkout -
            git branch -d "$BRANCH"
            exit 1
        fi
        echo "Please fix the conflicts, then exit."
        bash
        while ! git cherry-pick --continue; do
            echo "Please fix the conflicts, then exit."
            bash
        done
    fi
    git checkout -

else

    echo
    read -p "Skip directly to merging phase? [y/N] " -n 1 -r
    echo
    if [[ ! $REPLY =~ ^[Yy]$ ]]; then
        exit 1
    fi

fi

if ! git diff --exit-code HEAD "${BRANCH}" -- "*.mli"; then
    echo
    read -p "Some mli files are modified. Bypass? [y/N] " -n 1 -r
    echo
    if [[ ! $REPLY =~ ^[Yy]$ ]]; then
        exit 1
    fi
fi

if [[ "$STOP_BEFORE_MERGING" == "true" ]]; then
    exit 0
fi

git merge -S --no-ff "${BRANCH}" -m "${MESSAGE}"
git branch -d "${BRANCH}"

# To-Do:
# - Support for backporting a PR before it is merged
# - Automatically backport all PRs in the "Waiting to be backported" column using a command like:
# $ curl -s -H "Authorization: token ${GITHUB_TOKEN}" -H "Accept: application/vnd.github.inertia-preview+json" https://api.github.com/projects/columns/1358120/cards | jq -r '.[].content_url' | grep issue | sed 's/^.*issues\/\([0-9]*\)$/\1/' | tac
# (The ID of the column must first be obtained through https://api.github.com/repos/coq/coq/projects then https://api.github.com/projects/819866/columns.)
# - Then move each of the backported PR to the subsequent columns automatically as well...