package etw

// Channel represents the ETW logging channel that is used. It can be used by
// event consumers to give an event special treatment.
type Channel uint8

const (
	// ChannelTraceLogging is the default channel for TraceLogging events. It is
	// not required to be used for TraceLogging, but will prevent decoding
	// issues for these events on older operating systems.
	ChannelTraceLogging Channel = 11
)

// Level represents the ETW logging level. There are several predefined levels
// that are commonly used, but technically anything from 0-255 is allowed.
// Lower levels indicate more important events, and 0 indicates an event that
// will always be collected.
type Level uint8

// Predefined ETW log levels.
const (
	LevelAlways Level = iota
	LevelCritical
	LevelError
	LevelWarning
	LevelInfo
	LevelVerbose
)

// Event represents a single ETW event. It can have field metadata and data
// added to it, and then be logged via a provider to actually send it to ETW.
type Event struct {
	Descriptor *EventDescriptor
	Metadata   *EventMetadata
	Data       *EventData
}

// NewEvent returns a new instance of an event object.
func NewEvent(name string, descriptor *EventDescriptor) *Event {
	return &Event{
		Descriptor: descriptor,
		Metadata:   NewEventMetadata(name),
		Data:       &EventData{},
	}
}

// EventDescriptor represents various metadata for an ETW event.
type EventDescriptor struct {
	id      uint16
	version uint8
	Channel Channel
	Level   Level
	Opcode  uint8
	Task    uint16
	Keyword uint64
}

// NewEventDescriptor returns an EventDescriptor initialized for use with
// TraceLogging.
func NewEventDescriptor() *EventDescriptor {
	// Standard TraceLogging events default to the TraceLogging channel, and
	// verbose level.
	return &EventDescriptor{
		id:      0,
		version: 0,
		Channel: ChannelTraceLogging,
		Level:   LevelVerbose,
		Opcode:  0,
		Task:    0,
		Keyword: 0,
	}
}

// Identity returns the identity of the event. If the identity is not 0, it
// should uniquely identify the other event metadata (contained in
// EventDescriptor, and field metadata). Only the lower 24 bits of this value
// are relevant.
func (ed *EventDescriptor) Identity() uint32 {
	return (uint32(ed.version) << 16) & uint32(ed.id)
}

// SetIdentity sets the identity of the event. If the identity is not 0, it
// should uniquely identify the other event metadata (contained in
// EventDescriptor, and field metadata). Only the lower 24 bits of this value
// are relevant.
func (ed *EventDescriptor) SetIdentity(identity uint32) {
	ed.id = uint16(identity)
	ed.version = uint8(identity >> 16)
}