const (
	// Queue Group name used across all services
	DefaultQueueGroup = "q"

	// APIPrefix is the root of all control subjects
	APIPrefix = "$SRV"
)

const (
	ErrorHeader     = "Nats-Service-Error"
	ErrorCodeHeader = "Nats-Service-Error-Code"
)

const (
	InfoResponseType  = "io.nats.micro.v1.info_response"
	PingResponseType  = "io.nats.micro.v1.ping_response"
	StatsResponseType = "io.nats.micro.v1.stats_response"
)

var (
	ErrRespond         = errors.New("NATS error when sending response")
	ErrMarshalResponse = errors.New("marshaling response")
	ErrArgRequired     = errors.New("argument required")
)

var (
	// ErrConfigValidation is returned when service configuration is invalid
	ErrConfigValidation = errors.New("validation")

	// ErrVerbNotSupported is returned when invalid [Verb] is used (PING, INFO, STATS)
	ErrVerbNotSupported = errors.New("unsupported verb")

	// ErrServiceNameRequired is returned when attempting to generate control subject with ID but empty name
	ErrServiceNameRequired = errors.New("service name is required to generate ID control subject")
)

type Config struct {
	// Name represents the name of the service.
	Name string `json:"name"`

	// Endpoint is an optional endpoint configuration.
	// More complex, multi-endpoint services can be configured using
	// Service.AddGroup and Service.AddEndpoint methods.
	Endpoint *EndpointConfig `json:"endpoint"`

	// Version is a SemVer compatible version string.
	Version string `json:"version"`

	// Description of the service.
	Description string `json:"description"`

	// Metadata annotates the service
	Metadata map[string]string `json:"metadata,omitempty"`

	// QueueGroup can be used to override the default queue group name.
	QueueGroup string `json:"queue_group"`

	// QueueGroupDisabled disables the queue group for the service.
	QueueGroupDisabled bool `json:"queue_group_disabled"`

	// StatsHandler is a user-defined custom function.
	// used to calculate additional service stats.
	StatsHandler StatsHandler

	// DoneHandler is invoked when all service subscription are stopped.
	DoneHandler DoneHandler

	// ErrorHandler is invoked on any nats-related service error.
	ErrorHandler ErrHandler
}

type DoneHandler func(Service)

type Endpoint struct {
	EndpointConfig
	Name string
	// contains filtered or unexported fields
}

type EndpointConfig struct {
	// Subject on which the endpoint is registered.
	Subject string

	// Handler used by the endpoint.
	Handler Handler

	// Metadata annotates the service
	Metadata map[string]string `json:"metadata,omitempty"`

	// QueueGroup can be used to override the default queue group name.
	QueueGroup string `json:"queue_group"`

	// QueueGroupDisabled disables the queue group for the endpoint.
	QueueGroupDisabled bool `json:"queue_group_disabled"`
}

type EndpointInfo struct {
	Name       string            `json:"name"`
	Subject    string            `json:"subject"`
	QueueGroup string            `json:"queue_group"`
	Metadata   map[string]string `json:"metadata"`
}

type EndpointOpt func(*endpointOpts) error

type EndpointStats struct {
	Name                  string          `json:"name"`
	Subject               string          `json:"subject"`
	QueueGroup            string          `json:"queue_group"`
	NumRequests           int             `json:"num_requests"`
	NumErrors             int             `json:"num_errors"`
	LastError             string          `json:"last_error"`
	ProcessingTime        time.Duration   `json:"processing_time"`
	AverageProcessingTime time.Duration   `json:"average_processing_time"`
	Data                  json.RawMessage `json:"data,omitempty"`
}

type ErrHandler func(Service, *NATSError)

type Group interface {
	// AddGroup creates a new group, prefixed by this group's prefix.
	AddGroup(string, ...GroupOpt) Group

	// AddEndpoint registers new endpoints on a service.
	// The endpoint's subject will be prefixed with the group prefix.
	AddEndpoint(string, Handler, ...EndpointOpt) error
}

type GroupOpt func(*groupOpts)

type Handler interface {
	Handle(Request)
}

type HandlerFunc func(Request)

type Headers nats.Header

type Info struct {
	ServiceIdentity
	Type        string         `json:"type"`
	Description string         `json:"description"`
	Endpoints   []EndpointInfo `json:"endpoints"`
}

type NATSError struct {
	Subject     string
	Description string
}

type Ping struct {
	ServiceIdentity
	Type string `json:"type"`
}

type Request interface {
	// Respond sends the response for the request.
	// Additional headers can be passed using [WithHeaders] option.
	Respond([]byte, ...RespondOpt) error

	// RespondJSON marshals the given response value and responds to the request.
	// Additional headers can be passed using [WithHeaders] option.
	RespondJSON(any, ...RespondOpt) error

	// Error prepares and publishes error response from a handler.
	// A response error should be set containing an error code and description.
	// Optionally, data can be set as response payload.
	Error(code, description string, data []byte, opts ...RespondOpt) error

	// Data returns request data.
	Data() []byte

	// Headers returns request headers.
	Headers() Headers

	// Subject returns underlying NATS message subject.
	Subject() string

	// Reply returns underlying NATS message reply subject.
	Reply() string
}

type RespondOpt func(*nats.Msg)

type Service interface {
	// AddEndpoint registers endpoint with given name on a specific subject.
	AddEndpoint(string, Handler, ...EndpointOpt) error

	// AddGroup returns a Group interface, allowing for more complex endpoint topologies.
	// A group can be used to register endpoints with given prefix.
	AddGroup(string, ...GroupOpt) Group

	// Info returns the service info.
	Info() Info

	// Stats returns statistics for the service endpoint and all monitoring endpoints.
	Stats() Stats

	// Reset resets all statistics (for all endpoints) on a service instance.
	Reset()

	// Stop drains the endpoint subscriptions and marks the service as stopped.
	Stop() error

	// Stopped informs whether [Stop] was executed on the service.
	Stopped() bool
}

type ServiceIdentity struct {
	Name     string            `json:"name"`
	ID       string            `json:"id"`
	Version  string            `json:"version"`
	Metadata map[string]string `json:"metadata"`
}

type Stats struct {
	ServiceIdentity
	Type      string           `json:"type"`
	Started   time.Time        `json:"started"`
	Endpoints []*EndpointStats `json:"endpoints"`
}

type StatsHandler func(*Endpoint) any

type Verb int64

const (
	PingVerb Verb = iota
	StatsVerb
	InfoVerb
)