package journal

import (
	"time"

	logging "github.com/ipfs/go-log"
)

var log = logging.Logger("journal")

var (
	// DefaultDisabledEvents lists the journal events disabled by
	// default, usually because they are considered noisy.
	DefaultDisabledEvents = DisabledEvents{
		EventType{System: "mpool", Event: "add"},
		EventType{System: "mpool", Event: "remove"},
	}
)

// DisabledEvents is the set of event types whose journaling is suppressed.
type DisabledEvents []EventType

// EventType represents the signature of an event.
type EventType struct {
	System string
	Event  string

	// enabled stores whether this event type is enabled.
	enabled bool

	// safe is a sentinel marker that's set to true if this EventType was
	// constructed correctly (via Journal#RegisterEventType).
	safe bool
}

func (et EventType) String() string {
	return et.System + ":" + et.Event
}

// Enabled returns whether this event type is enabled in the journaling
// subsystem. Users are advised to check this before actually attempting to
// add a journal entry, as it helps bypass object construction for events that
// would be discarded anyway.
//
// All event types are enabled by default, and specific event types can only
// be disabled at Journal construction time.
func (et EventType) Enabled() bool {
	return et.safe && et.enabled
}

// Journal represents an audit trail of system actions.
//
// Every entry is tagged with a timestamp, a system name, and an event name.
// The supplied data can be any type, as long as it is JSON serializable,
// including structs, map[string]interface{}, or primitive types.
//
// For cleanliness and type safety, we recommend to use typed events. See the
// *Evt struct types in this package for more info.
type Journal interface {
	EventTypeRegistry

	// RecordEvent records this event to the journal, if and only if the
	// EventType is enabled. If so, it calls the supplier function to obtain
	// the payload to record.
	//
	// Implementations MUST recover from panics raised by the supplier function.
	RecordEvent(evtType EventType, supplier func() interface{})

	// Close closes this journal for further writing.
	Close() error
}

// Event represents a journal entry.
//
// See godocs on Journal for more information.
type Event struct {
	EventType

	Timestamp time.Time
	Data      interface{}
}