go1.18-eventsource-poc-v0

stream.go

package stream

import (
	"fmt"

	"nimona.io/pkg/object"
)

type (
	Applicable[State any] interface {
		Apply(*State) error
	}
	Controller[State any] interface {
		NewStream() Stream[State]
	}
	Stream[State any] interface {
		ApplyObject(*object.Object) error
		ApplyEvent(Applicable[State]) error
		GetState() State
	}
	controller[State any] struct{}
	stream[State any]     struct {
		// lock sync.RWMutex // TODO add mutex
		LatestState *State
	}
)

func NewController[State any]() Controller[State] {
	c := &controller[State]{}
	return c
}

func (c *controller[State]) NewStream() Stream[State] {
	s := &stream[State]{
		LatestState: new(State),
	}
	return s
}

func (s *stream[State]) ApplyObject(o *object.Object) error {
	return nil
}

func (s *stream[State]) ApplyEvent(e Applicable[State]) error {
	err := e.Apply(s.LatestState)
	if err != nil {
		return fmt.Errorf("error applying state, %w", err)
	}
	return nil
}

func (s *stream[State]) GetState() State {
	return *s.LatestState
}

stream_test.go

package stream

import (
	"testing"

	"github.com/stretchr/testify/require"
	"nimona.io/pkg/object"
)

type (
	TestState struct {
		Foo      int
		Bar      int
		Comments []string
	}
	TestEventAddFoo struct {
		Metadata object.Metadata
	}
	TestEventAddBar struct {
		Metadata object.Metadata
	}
	TestEventAddComment struct {
		Metadata object.Metadata
		Comment  string
	}
)

func (e *TestEventAddFoo) Apply(s *TestState) error {
	s.Foo++
	return nil
}

func (e *TestEventAddBar) Apply(s *TestState) error {
	s.Bar++
	return nil
}

func (e *TestEventAddComment) Apply(s *TestState) error {
	s.Comments = append(s.Comments, e.Comment)
	return nil
}

func Test_Controller_Example(t *testing.T) {
	c := NewController[TestState]()
	require.NotNil(t, c)

	s := c.NewStream()

	err := s.ApplyEvent(&TestEventAddFoo{})
	require.NoError(t, err)

	err = s.ApplyEvent(&TestEventAddFoo{})
	require.NoError(t, err)

	err = s.ApplyEvent(&TestEventAddBar{})
	require.NoError(t, err)

	err = s.ApplyEvent(&TestEventAddComment{Comment: "hello"})
	require.NoError(t, err)

	err = s.ApplyEvent(&TestEventAddComment{Comment: "world"})
	require.NoError(t, err)

	require.Equal(t, TestState{
		Foo: 2,
		Bar: 1,
		Comments: []string{
			"hello",
			"world",
		},
	}, s.GetState())
}