package downloader

import "context"

// EventType identifies an observer event emitted by Queue.
type EventType string

const (
	EventStarted   EventType = "started"
	EventProgress  EventType = "progress"
	EventPaused    EventType = "paused"
	EventCompleted EventType = "completed"
	EventFailed    EventType = "failed"
	EventCanceled  EventType = "canceled"
)

// Event reports one generation of a download task. Done is monotonic within a
// RequestID+Attempt pair. A new Attempt permits a reset to zero when a server
// ignores Range or an entity cannot be safely resumed.
type Event struct {
	Type          EventType
	RequestID     string
	AppID         string
	Attempt       uint64
	Done          int64
	TotalKnown    bool
	Total         int64
	SpeedBytesSec int64
	CompletedPath string
	ErrorCode     string
}

// Observer receives queue events. Implementations must honor context
// cancellation so pause/cancel can wait for the old generation to exit.
type Observer interface {
	PublishDownload(context.Context, Event) error
}

type discardObserver struct{}

func (discardObserver) PublishDownload(context.Context, Event) error {
	return nil
}