backend

type ActivityTask struct {
	ID string

	WorkflowInstance *core.WorkflowInstance

	Event *history.Event
}

type Backend interface {
	// CreateWorkflowInstance creates a new workflow instance
	CreateWorkflowInstance(ctx context.Context, instance *workflow.Instance, event *history.Event) error

	// CancelWorkflowInstance cancels a running workflow instance
	CancelWorkflowInstance(ctx context.Context, instance *workflow.Instance, cancelEvent *history.Event) error

	// RemoveWorkflowInstance removes a workflow instance
	RemoveWorkflowInstance(ctx context.Context, instance *workflow.Instance) error

	// GetWorkflowInstanceState returns the state of the given workflow instance
	GetWorkflowInstanceState(ctx context.Context, instance *workflow.Instance) (core.WorkflowInstanceState, error)

	// GetWorkflowInstanceHistory returns the workflow history for the given instance. When lastSequenceID
	// is given, only events after that event are returned. Otherwise the full history is returned.
	GetWorkflowInstanceHistory(ctx context.Context, instance *workflow.Instance, lastSequenceID *int64) ([]*history.Event, error)

	// SignalWorkflow signals a running workflow instance
	//
	// If the given instance does not exist, it will return an error
	SignalWorkflow(ctx context.Context, instanceID string, event *history.Event) error

	// GetWorkflowTask returns a pending workflow task or nil if there are no pending workflow executions
	GetWorkflowTask(ctx context.Context) (*WorkflowTask, error)

	// ExtendWorkflowTask extends the lock of a workflow task
	ExtendWorkflowTask(ctx context.Context, taskID string, instance *core.WorkflowInstance) error

	// CompleteWorkflowTask checkpoints a workflow task retrieved using GetWorkflowTask
	//
	// This checkpoints the execution. events are new events from the last workflow execution
	// which will be added to the workflow instance history. workflowEvents are new events for the
	// completed or other workflow instances.
	CompleteWorkflowTask(
		ctx context.Context, task *WorkflowTask, instance *workflow.Instance, state core.WorkflowInstanceState,
		executedEvents, activityEvents, timerEvents []*history.Event, workflowEvents []history.WorkflowEvent) error

	// GetActivityTask returns a pending activity task or nil if there are no pending activities
	GetActivityTask(ctx context.Context) (*ActivityTask, error)

	// CompleteActivityTask completes an activity task retrieved using GetActivityTask
	CompleteActivityTask(ctx context.Context, instance *workflow.Instance, activityID string, event *history.Event) error

	// ExtendActivityTask extends the lock of an activity task
	ExtendActivityTask(ctx context.Context, activityID string) error

	// GetStats returns stats about the backend
	GetStats(ctx context.Context) (*Stats, error)

	// Logger returns the configured logger for the backend
	Logger() *slog.Logger

	// Tracer returns the configured trace provider for the backend
	Tracer() trace.Tracer

	// Metrics returns the configured metrics client for the backend
	Metrics() metrics.Client

	// Converter returns the configured converter for the backend
	Converter() converter.Converter

	// ContextPropagators returns the configured context propagators for the backend
	ContextPropagators() []workflow.ContextPropagator

	// Close closes any underlying resources
	Close() error
}

type BackendOption func(*Options)

type MockBackend struct {
	mock.Mock
}

type Options struct {
	Logger *slog.Logger

	Metrics metrics.Client

	TracerProvider trace.TracerProvider

	// Converter is the converter to use for serializing and deserializing inputs and results. If not explicitly set
	// converter.DefaultConverter is used.
	Converter converter.Converter

	// ContextPropagators is a list of context propagators to use for passing context into workflows and activities.
	ContextPropagators []workflow.ContextPropagator

	StickyTimeout time.Duration

	// WorkflowLockTimeout determines how long a workflow task can be locked for. If the workflow task is not completed
	// by that timeframe, it's considered abandoned and another worker might pick it up.
	//
	// For long running workflow tasks, combine this with heartbearts.
	WorkflowLockTimeout time.Duration

	// ActivityLockTimeout determines how long an activity task can be locked for. If the activity task is not completed
	// by that timeframe, it's considered abandoned and another worker might pick it up
	ActivityLockTimeout time.Duration
}

type Stats struct {
	ActiveWorkflowInstances int64

	// PendingWorkflowTasks are the number of workflow tasks that are currently in the queue,
	// waiting to be processed by a worker
	PendingWorkflowTasks int64

	// PendingActivities are the number of activities that are currently in the queue,
	// waiting to be processed by a worker
	PendingActivities int64
}

type WorkflowTask struct {
	// ID is an identifier for this task. It's set by the backend
	ID string

	// WorkflowInstance is the workflow instance that this task is for
	WorkflowInstance *core.WorkflowInstance

	WorkflowInstanceState core.WorkflowInstanceState

	Metadata *metadata.WorkflowMetadata

	// LastSequenceID is the sequence ID of the newest event in the workflow instances's history
	LastSequenceID int64

	// NewEvents are new events since the last task execution
	NewEvents []*history.Event

	// Backend specific data, only the producer of the task should rely on this.
	CustomData any
}