import {PullRequestSchema, ConfigurationOptions} from './schemas'

export function getRefs(
  config: ConfigurationOptions,
  context: {payload: {pull_request?: unknown}; eventName: string}
): {base: string; head: string} {
  let base_ref = config.base_ref
  let head_ref = config.head_ref

  // If possible, source default base & head refs from the GitHub event.
  // The base/head ref from the config take priority, if provided.
  if (
    context.eventName === 'pull_request' ||
    context.eventName === 'pull_request_target'
  ) {
    const pull_request = PullRequestSchema.parse(context.payload.pull_request)
    base_ref = base_ref || pull_request.base.sha
    head_ref = head_ref || pull_request.head.sha
  }

  if (!base_ref && !head_ref) {
    throw new Error(
      'Both a base ref and head ref must be provided, either via the `base_ref`/`head_ref` ' +
        'config options, or by running a `pull_request`/`pull_request_target` workflow.'
    )
  } else if (!base_ref) {
    throw new Error(
      'A base ref must be provided, either via the `base_ref` config option, ' +
        'or by running a `pull_request`/`pull_request_target` workflow.'
    )
  } else if (!head_ref) {
    throw new Error(
      'A head ref must be provided, either via the `head_ref` config option, ' +
        'or by running a `pull_request`/`pull_request_target` workflow.'
    )
  }

  return {
    base: base_ref,
    head: head_ref
  }
}