import FlowNodeModel from "../models/FlowNode";
import JobModel from "../models/Job";
import Processor from "../Processor";
import { JOB_STATUS } from "../constants";

export const PARALLEL_MODE = {
  ALL: 'all',
  ANY: 'any',
  RACE: 'race'
} as const;

const Modes = {
  [PARALLEL_MODE.ALL]: {
    next(previous) {
      return previous.status !== JOB_STATUS.REJECTED;
    },
    getStatus(result) {
      if (result.some(status => status != null && status === JOB_STATUS.REJECTED)) {
        return JOB_STATUS.REJECTED;
      }
      if (result.every(status => status != null && status === JOB_STATUS.RESOLVED)) {
        return JOB_STATUS.RESOLVED;
      }
      return JOB_STATUS.PENDING;
    }
  },
  [PARALLEL_MODE.ANY]: {
    next(previous) {
      return previous.status !== JOB_STATUS.RESOLVED;
    },
    getStatus(result) {
      if (result.some(status => status != null && status === JOB_STATUS.RESOLVED)) {
        return JOB_STATUS.RESOLVED;
      }
      if (result.some(status => status != null ? status === JOB_STATUS.PENDING : true)) {
        return JOB_STATUS.PENDING;
      }
      return JOB_STATUS.REJECTED;
    }
  },
  [PARALLEL_MODE.RACE]: {
    next(previous) {
      return previous.status === JOB_STATUS.PENDING;
    },
    getStatus(result) {
      if (result.some(status => status != null && status === JOB_STATUS.RESOLVED)) {
        return JOB_STATUS.RESOLVED;
      }
      if (result.some(status => status != null && status === JOB_STATUS.REJECTED)) {
        return JOB_STATUS.REJECTED;
      }
      return JOB_STATUS.PENDING;
    }
  }
};

export default {
  async run(node: FlowNodeModel, prevJob: JobModel, processor: Processor) {
    const branches = processor.getBranches(node);

    const job = await processor.saveJob({
      status: JOB_STATUS.PENDING,
      result: Array(branches.length).fill(null),
      nodeId: node.id,
      upstreamId: prevJob?.id ?? null
    });

    // NOTE:
    // use `reduce` but not `Promise.all` here to avoid racing manupulating db.
    // for users, this is almost equivalent to `Promise.all`,
    // because of the delay is not significant sensible.
    // another benifit of this is, it could handle sequenced branches in future.
    const { mode = PARALLEL_MODE.ALL } = node.config;
    await branches.reduce((promise: Promise<any>, branch, i) =>
      promise.then((previous) => {
        if (i && !Modes[mode].next(previous)) {
          return Promise.resolve(previous);
        }
        return processor.run(branch, job);
      }), Promise.resolve());

    return processor.end(node, job);
  },

  async resume(node: FlowNodeModel, branchJob, processor: Processor) {
    const job = processor.findBranchParentJob(branchJob, node);

    const { result, status } = job;
    // if parallel has been done (resolved / rejected), do not care newly executed branch jobs.
    if (status !== JOB_STATUS.PENDING) {
      return null;
    }

    // find the index of the node which start the branch
    const jobNode = processor.nodesMap.get(branchJob.nodeId);
    const branchStartNode = processor.findBranchStartNode(jobNode, node);
    const branches = processor.getBranches(node);
    const branchIndex = branches.indexOf(branchStartNode);
    const { mode = PARALLEL_MODE.ALL } = node.config || {};

    const newResult = [...result.slice(0, branchIndex), branchJob.status, ...result.slice(branchIndex + 1)];
    job.set({
      result: newResult,
      status: Modes[mode].getStatus(newResult)
    });

    if (job.status === JOB_STATUS.PENDING) {
      await job.save({ transaction: processor.transaction });
      return processor.end(node, job);
    }

    return job;
  }
};