import { DeleteItemCommand, DynamoDBClient, GetItemCommand, PutItemCommand } from '@aws-sdk/client-dynamodb';
import { OrchestratorInput } from './lambda-common';

/**
 * The set of jobs we started a runner for.
 *
 * This is the entire state behind stolen runner detection. One item per job, written before its runner can exist,
 * expiring on its own, and deleted only if its runner is gone without ever getting a job. One item per runner that
 * we know the fate of, so we only check each one once. Nothing is updated, nothing is counted, and nothing needs
 * cleaning up.
 *
 * A job in here is a job we control. A job that isn't is a job we never agreed to serve, so a runner of ours
 * running it was taken from whoever we did start it for.
 *
 * @internal
 */

const ddb = new DynamoDBClient();

/**
 * Default time-to-live for job records in DynamoDB. GitHub jobs can wait up to 24 hours to get a runner. This adds some margin.
 *
 * If we accidentally provision a runner, that's expensive. Keeping a small record in DynamoDB for a few days is cheaper.
 *
 * @internal
 */
export const DEFAULT_TRACKER_TTL_SECONDS = 3 * 24 * 60 * 60;

/**
 * A runner told us it picked up a job. Sent by the runners themselves, from a job started hook, and read out of
 * their logs. Also sent by the webhook handler for workflow_job.in_progress events.
 *
 * GitHub never tells a runner which job it's running, so this carries the workflow run instead. Combined with the
 * runner name it's enough to ask GitHub for the job id.
 *
 * @internal
 */
export interface RunnerReportMessage {
  readonly kind: 'report';
  readonly runnerName: string;
  readonly repo: string;
  readonly workflowId: number;
  readonly jobId?: number; // comes ONLY from workflow_job.in_progress webhook
}

function tableName(): string {
  const table = process.env.RUNNER_TRACKER_TABLE;
  if (!table) {
    throw new Error('Missing RUNNER_TRACKER_TABLE environment variable');
  }
  return table;
}

function expiry(): number {
  const seconds = parseInt(process.env.RUNNER_TRACKER_TTL_SECONDS ?? `${DEFAULT_TRACKER_TTL_SECONDS}`, 10);
  return Math.floor(Date.now() / 1000) + (isNaN(seconds) ? DEFAULT_TRACKER_TTL_SECONDS : seconds);
}

/**
 * Remember that we started a runner for this job. Written before the step function starts, so it's always there by
 * the time GitHub could possibly hand the runner a job.
 *
 * Runner labels tell whether that runner can run another job of ours instead. The job URL is for whoever is reading the table during an
 * incident. TTL is used for cleanup.
 *
 * @internal
 */
export async function recordControlledJob(input: OrchestratorInput) {
  await ddb.send(new PutItemCommand({
    TableName: tableName(),
    Item: {
      pk: { S: `job#${input.jobId}` },
      jobUrl: { S: input.jobUrl },
      runnerLabels: { S: input.labels },
      ttl: { N: `${expiry()}` },
    },
  }));
}

/**
 * Forget we started a runner for this job. Used when we take that runner away before it ever got the job, so the job
 * no longer has a runner of ours. If one of our other runners picks it up later, that runner was stolen.
 *
 * @internal
 */
export async function forgetControlledJob(jobId: number) {
  await ddb.send(new DeleteItemCommand({
    TableName: tableName(),
    Key: { pk: { S: `job#${jobId}` } },
  }));
}

/**
 * Remember that we know what happened to this runner's job. Either the runner reported a job, or the runner is gone and we already forgot
 * the job left without a runner because of it.
 *
 * @internal
 */
export async function recordRunnerAccounted(runnerName: string, jobId?: number) {
  await ddb.send(new PutItemCommand({
    TableName: tableName(),
    Item: {
      pk: { S: `runner#${runnerName}` },
      ttl: { N: `${expiry()}` },
      ...(jobId ? { jobId: { N: `${jobId}` } } : {}),
    },
  }));
}

/**
 * Do we know what happened to this runner's job?
 *
 * @internal
 */
export async function isRunnerAccounted(runnerName: string): Promise<boolean> {
  const result = await ddb.send(new GetItemCommand({
    TableName: tableName(),
    Key: { pk: { S: `runner#${runnerName}` } },
    ConsistentRead: true,
  }));

  return !!result.Item;
}

/**
 * Labels of the runner we started for this job, or undefined if we didn't start one.
 *
 * @internal
 */
export async function controlledJobRunnerLabels(jobId: number): Promise<string[] | undefined> {
  // consistent, because the job may have been recorded moments ago and reading a stale "no" would look like theft
  const result = await ddb.send(new GetItemCommand({
    TableName: tableName(),
    Key: { pk: { S: `job#${jobId}` } },
    ConsistentRead: true,
  }));

  return result.Item?.runnerLabels?.S?.split(',');
}