module.exports = async function ({ github, context, core }) {
  for (const retryInterval of [5, 10, 20, 40, 80]) {
    console.log("Checking whether the pull request can be merged...")
    const prInfo = (await github.rest.pulls.get({
      owner: context.repo.owner,
      repo: context.repo.repo,
      pull_number: context.payload.pull_request.number
    })).data

    if (prInfo.state != 'open') throw new Error ("PR is not open anymore.")

    if (prInfo.mergeable == null) {
      console.log(`GitHub is still computing whether this PR can be merged, waiting ${retryInterval} seconds before trying again...`)
      await new Promise(resolve => setTimeout(resolve, retryInterval * 1000))
      continue
    }

    let mergedSha, targetSha

    if (prInfo.mergeable) {
      console.log("The PR can be merged.")

      mergedSha = prInfo.merge_commit_sha
      targetSha = (await github.rest.repos.getCommit({
        owner: context.repo.owner,
        repo: context.repo.repo,
        ref: prInfo.merge_commit_sha
      })).data.parents[0].sha
    } else {
      console.log("The PR has a merge conflict.")

      mergedSha = prInfo.head.sha
      targetSha = (await github.rest.repos.compareCommitsWithBasehead({
        owner: context.repo.owner,
        repo: context.repo.repo,
        basehead: `${prInfo.base.sha}...${prInfo.head.sha}`
      })).data.merge_base_commit.sha
    }

    console.log(`Checking the commits:\nmerged:${mergedSha}\ntarget:${targetSha}`)
    core.setOutput('mergedSha', mergedSha)
    core.setOutput('targetSha', targetSha)
    return
  }
  throw new Error("Not retrying anymore. It's likely that GitHub is having internal issues: check https://www.githubstatus.com.")
}