![Statebox Logo](/images/statebox-logo.png)

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> Orchestrate Node functions using [Amazon States Language](https://states-language.net/spec.html)

## Useful links

* [AWS Step Functions](https://aws.amazon.com/step-functions/) - overview of Amazon States Language, use cases, etc
* [statelint](https://npmjs.com/package/@wmfs/statelint) - a validator for Amazon States Language JSON files
* https://docs.aws.amazon.com/step-functions/latest/dg/concepts-amazon-states-language.html
* https://docs.aws.amazon.com/step-functions/latest/apireference/API_SendTaskSuccess.html

## <a name='install'></a>Install
```bash
$ npm install @wmfs/statebox --save
```

## <a name='usage'></a>Usage

```javascript
const Statebox = require('@wmfs/statebox')
const statebox = new Statebox({})

const main = async

function() {

  // STEP 1:
  // Create some 'module' resources (i.e. Javascript
  // classes with 'run' and optional 'init' methods)
  // that state machines can then refer to...
  // -------------------------------------------------
  await statebox.ready
  statebox.createModuleResources({
    // Simple module to add two numbers together
    add: class Add {
      run(event, context) {
        context.sendTaskSuccess(event.number1 + event.number2)
      }
    },
    // Simple module to subtract one number from another
    subtract: class Subtract {
      // Init methods are optional, but all allow
      // resource-instances to be configured...
      init(resourceConfig, env, callback) {
        callback(null)
      }
      run(event, context) {
        context.sendTaskSuccess(event.number1 - event.number2)
      }
    }
  })

  // STEP 2:
  // Next create a new 'calculator' state
  // machine using Amazon States Language...
  // ---------------------------------------
  await statebox.createStateMachines({
      'calculator': {
        Comment: 'A simple calculator',
        StartAt: 'OperatorChoice',
        States: {
          OperatorChoice: {
            Type: 'Choice',
            Choices: [{
              Variable: '$.operator',
              StringEquals: '+',
              Next: 'Add'
            }, {
              Variable: '$.operator',
              StringEquals: '-',
              Next: 'Subtract'
            }]
          },
          Add: {
            Type: 'Task',
            InputPath: '$.numbers',
            Resource: 'module:add', // See createModuleResources()
            ResultPath: '$.result',
            End: true
          },
          Subtract: {
            Type: 'Task',
            InputPath: '$.numbers',
            Resource: 'module:subtract',
            ResultPath: '$.result',
            End: true
          }
        }
      }
    }, {}, // 'env': An environment/context/sandbox
  )

  // STEP 3:
  // Start a new execution on a state machine
  // ----------------------------------------
  const executionDescription = await statebox.startExecution({
      numbers: {
        number1: 3,
        number2: 2
      },
      operator: '-'
    }, // input
    'calculator', // state machine name
    {} // options
  )

  // STEP 4:
  // Look at the results...
  // ----------------------
  console.log(executionDescription)
  //  Result object
  //  -------------
  // {
  //   executionName: '...',
  //   ctx: {
  //     numbers': {
  //       number1: 3,
  //       number2: 2
  //     },
  //     operator: '-',
  //     result: 1 <--- The important bit :-)
  //   },
  //   currentStateName:'Subtract',
  //   currentResource:'module:subtract',
  //   stateMachineName:'calculator',
  //   startDate: '2018-09-03T21:58:04.287Z'
  // }
}

if (require.main === module) {
  main();
}
```

## <a name='test'></a>Testing

```bash
$ npm test
```

## <a name='license'></a>License
[MIT](https://github.com/wmfs/tymly/packages/statebox/blob/master/LICENSE)