#!/bin/bash

# Suggested by Github actions to be strict
set -e
set -o pipefail

################################################################################
# Global Variables (we can't use GITHUB_ prefix)
################################################################################

API_VERSION=v3
BASE=https://api.github.com
AUTH_HEADER="Authorization: token ${GITHUB_TOKEN}"
HEADER="Accept: application/vnd.github.${API_VERSION}+json"
HEADER="${HEADER}; application/vnd.github.antiope-preview+json; application/vnd.github.shadow-cat-preview+json"

# URLs
REPO_URL="${BASE}/repos/${GITHUB_REPOSITORY}"
PULLS_URL=$REPO_URL/pulls

################################################################################
# Helper Functions
################################################################################


check_credentials() {

    if [[ -z "${GITHUB_TOKEN}" ]]; then
        printf "You must include the GITHUB_TOKEN as an environment variable.\n"
        exit 1
    fi

}

check_events_json() {

    if [[ ! -f "${GITHUB_EVENT_PATH}" ]]; then
        printf "Cannot find Github events file at ${GITHUB_EVENT_PATH}\n";
        exit 1;
    fi
    printf "Found ${GITHUB_EVENT_PATH}\n";

}

create_pull_request() {

    # JSON strings
    SOURCE="$(echo -n "${1}" | jq --raw-input --slurp ".")"  # from this branch
    TARGET="$(echo -n "${2}" | jq --raw-input --slurp ".")"  # pull request TO this target
    BODY="$(echo -n "${3}" | jq --raw-input --slurp ".")"    # this is the content of the message
    TITLE="$(echo -n "${4}" | jq --raw-input --slurp ".")"   # pull request title
    DRAFT="${5}"                                             # pull request draft?
    MODIFY="${6}"                                            # maintainer can modify

    # Check if the branch already has a pull request open
    DATA="{\"base\":${TARGET}, \"head\":${SOURCE}, \"body\":${BODY}}"
    RESPONSE=$(curl -sSL -H "${AUTH_HEADER}" -H "${HEADER}" --user "${GITHUB_ACTOR}" -X GET --data "${DATA}" ${PULLS_URL})
    PR=$(echo "${RESPONSE}" | jq --raw-output '.[] | .head.ref')
    printf "Response ref: ${PR}\n"

    # Option 1: The pull request is already open
    if [[ "${PR}" == "${SOURCE}" ]]; then
        printf "Pull request from ${SOURCE} to ${TARGET} is already open!\n"

    # Option 2: Open a new pull request
    else
        # Post the pull request
        DATA="{\"title\":${TITLE}, \"body\":${BODY}, \"base\":${TARGET}, \"head\":${SOURCE}, \"draft\":${DRAFT}, \"maintainer_can_modify\":${MODIFY}}"
        printf "curl --user ${GITHUB_ACTOR} -X POST --data ${DATA} ${PULLS_URL}\n"
        curl -sSL -H "${AUTH_HEADER}" -H "${HEADER}" --user "${GITHUB_ACTOR}" -X POST --data "${DATA}" ${PULLS_URL}
        echo $?
    fi
}


main () {

    # path to file that contains the POST response of the event
    # Example: https://github.com/actions/bin/tree/master/debug
    # Value: /github/workflow/event.json
    check_events_json;

    # User specified branch to PR to, and check
    if [ -z "${BRANCH_PREFIX}" ]; then
        printf "No branch prefix is set, all branches will be used.\n"
        BRANCH_PREFIX=""
        printf "Branch prefix is $BRANCH_PREFIX\n"
    fi

    if [ -z "${PULL_REQUEST_BRANCH}" ]; then
        PULL_REQUEST_BRANCH=master
    fi
    printf "Pull requests will go to ${PULL_REQUEST_BRANCH}\n"

    # Pull request draft
    if [ -z "${PULL_REQUEST_DRAFT}" ]; then
        printf "No explicit preference for draft PR: created PRs will be normal PRs.\n"
        PULL_REQUEST_DRAFT="false"
    else
        printf "Environment variable PULL_REQUEST_DRAFT set to a value: created PRs will be draft PRs.\n"
        PULL_REQUEST_DRAFT="true"
    fi

    # Maintainer can modify, defaults to CAN, unless user sets MAINTAINER_CANT_MODIFY
    if [ -z "${MAINTAINER_CANT_MODIFY}" ]; then
        printf "No explicit preference for maintainer being able to modify: default is true.\n"
        MODIFY="true"
    else
        printf "Environment variable MAINTAINER_CANT_MODIFY set to a value: maintainer will not be able to modify.\n"
        MODIFY="false"
    fi

    # The user is allowed to explicitly set the name of the branch
    if [ -z "${PULL_REQUEST_FROM_BRANCH}" ]; then
        printf "PULL_REQUEST_FROM_BRANCH is not set, checking branch in payload.\n"
        BRANCH=$(jq --raw-output .ref "${GITHUB_EVENT_PATH}");
        BRANCH=$(echo "${BRANCH/refs\/heads\//}")
    else
        printf "PULL_REQUEST_FROM_BRANCH is set.\n"
        BRANCH="${PULL_REQUEST_FROM_BRANCH}"        
    fi

    # At this point, we must have a branch
    if [[ "$BRANCH" != "null" ]]; then
        printf "Found branch $BRANCH to open PR from\n"
    else
        printf "No branch in payload, you are required to define PULL_REQUEST_FROM_BRANCH in the environment.\n"
        exit 1
    fi

    # If it's to the target branch, ignore it
    if [[ "${BRANCH}" == "${PULL_REQUEST_BRANCH}" ]]; then
        printf "Target and current branch are identical (${BRANCH}), skipping.\n"
    else

        # If the prefix for the branch matches
        if  [[ $BRANCH == ${BRANCH_PREFIX}* ]]; then

            # Ensure we have a GitHub token
            check_credentials

            # Pull request body (optional)
            if [ -z "${PULL_REQUEST_BODY}" ]; then
                echo "No pull request body is set, will use default."
                PULL_REQUEST_BODY="This is an automated pull request to update the container collection ${BRANCH}"
            fi
            printf "Pull request body is ${PULL_REQUEST_BODY}\n"

            # Pull request title (optional)
            if [ -z "${PULL_REQUEST_TITLE}" ]; then
                printf "No pull request title is set, will use default.\n"
                PULL_REQUEST_TITLE="Update container ${BRANCH}"
            fi
            printf "Pull request title is ${PULL_REQUEST_TITLE}\n"

            create_pull_request "${BRANCH}" "${PULL_REQUEST_BRANCH}" "${PULL_REQUEST_BODY}" \
                                "${PULL_REQUEST_TITLE}" "${PULL_REQUEST_DRAFT}" "${MODIFY}"

        fi

    fi
}

echo "==========================================================================
START: Running Pull Request on Branch Update Action!";
main;
echo "==========================================================================
END: Finished";