budibase/packages/client/src/api/workflow/orchestrator.js

import get from "lodash/fp/get";

/**
 * The workflow orhestrator is a class responsible for executing workflows.
 * It relies on the strategy pattern, which allows composable behaviour to be 
 * passed into its execute() function. This allows custom execution behaviour based
 * on where the orchestrator is run.
 * 
 */
export default class Orchestrator {
  constructor(api, instanceId) {
    this.api = api
    this.instanceId = instanceId
  }

  set strategy(strategy) {
    this._strategy = strategy
  }

  async execute(workflowId) {
    const EXECUTE_WORKFLOW_URL = `/api/${this.instanceId}/workflows/${workflowId}`;
    const workflow = await this.api.get({ url: EXECUTE_WORKFLOW_URL }) 
    this._strategy.run({
      workflow: workflow.definition,
      api: this.api,
      instanceId: this.instanceId
    });
  }
}

// Execute a workflow from a running budibase app
export const clientStrategy = {
  context: {},
  bindContextArgs: function(args) {
    const mappedArgs = { ...args };

    console.log("original args", args)

    // bind the workflow action args to the workflow context, if required
    for (let arg in args) {
      const argValue = args[arg];
      // Means that it's bound to state or workflow context
      if (argValue.startsWith("$")) {
        // if value is bound to workflow context.
        if (argValue.startsWith("$context")) {
          const path = argValue.replace("$context.", "");
          // pass in the value from context
          mappedArgs[arg] = get(path, this.context);  
        }

        // if the value is bound to state
        if (argValue.startsWith("$state")) {
          const path = argValue.match("$context.", "");
          // pass in the value from context
          mappedArgs[arg] = get(path, this.context);  
        }
      }
    }
    return Object.values(mappedArgs);
  },
  run: async function({ workflow, api, instanceId }) {
    const block = workflow.next;

    console.log("Executing workflow block", block);

    if (!block) return;

    // This code gets run in the browser
    if (block.type === "CLIENT") {
        if (block.actionId === "SET_STATE") {
          // get props from the workflow context if required
          api.setState(...this.bindContextArgs(block.args))
          // update the context with the data 
          this.context = {
            ...this.context,
            SET_STATE: block.args
          }
        }
    };

    // this workflow block gets executed on the server
    if (block.type === "SERVER") {
      const EXECUTE_WORKFLOW_URL = `/api/${instanceId}/workflows/action`
      const response = await api.post({ 
        url: EXECUTE_WORKFLOW_URL, 
        body: {
          action: block.actionId,
          args: block.args
        } 
      });

      this.context = {
        ...this.context,
        [block.actionId]: response 
      }
    }

    console.log("workflowContext", this.context)

    // TODO: clean this up, don't pass all those args
    this.run({ workflow: workflow.next, instanceId, api });
  }
}