package beater

import (
	"time"

	"github.com/elastic/beats/libbeat/common"
	"github.com/elastic/beats/libbeat/logp"
	"github.com/elastic/beats/libbeat/processors"
	"github.com/elastic/beats/metricbeat/mb"
)

const (
	defaultType = "metricsets"
)

// EventBuilder is used for building MetricSet events. MetricSets generate a
// data in the form of a common.MapStr. This builder transforms that data into
// a complete event and applies any Module-level filtering.
type EventBuilder struct {
	ModuleName    string
	MetricSetName string
	Host          string
	StartTime     time.Time
	FetchDuration time.Duration
	Event         common.MapStr
	fetchErr      error
	filters       *processors.Processors
	metadata      common.EventMetadata
}

// Build builds an event from MetricSet data and applies the Module-level
// filters.
func (b EventBuilder) Build() (common.MapStr, error) {
	// event may be nil when there was an error fetching.
	event := b.Event
	if event == nil {
		event = common.MapStr{} // TODO (akroh): do we want to send an empty event field?
	}

	// Get and remove meta fields from the event created by the MetricSet.
	indexName := getIndex(event, "")
	typeName := getType(event, defaultType)
	timestamp := getTimestamp(event, common.Time(b.StartTime))

	// Apply filters.
	if b.filters != nil {
		if event = b.filters.Run(event); event == nil {
			return nil, nil
		}
	}

	// Checks if additional meta information is provided by the MetricSet under the key ModuleData
	// This is based on the convention that each MetricSet can provide module data under the key ModuleData
	moduleData, moudleDataExists := event[mb.ModuleData]
	if moudleDataExists {
		delete(event, mb.ModuleData)
	}

	metricsetData := common.MapStr{
		"module": b.ModuleName,
		"name":   b.MetricSetName,
		"rtt":    b.FetchDuration.Nanoseconds() / int64(time.Microsecond),
	}

	namespace := b.MetricSetName
	if n, ok := event["_namespace"]; ok {
		delete(event, "_namespace")
		namespace = n.(string)
		// TODO: check if namespace does not already exist
		metricsetData["namespace"] = namespace
	}

	event = common.MapStr{
		"@timestamp":            timestamp,
		"type":                  typeName,
		common.EventMetadataKey: b.metadata,
		b.ModuleName: common.MapStr{
			namespace: event,
		},
		"metricset": metricsetData,
	}

	// In case meta data exists, it is added on the module level
	if moudleDataExists {
		if _, ok := moduleData.(common.MapStr); ok {
			event[b.ModuleName].(common.MapStr).Update(moduleData.(common.MapStr))
		}
	}

	// Overwrite default index if set.
	if indexName != "" {
		event["beat"] = common.MapStr{
			"index": indexName,
		}
	}

	// Adds host name to event.
	if b.Host != "" {
		event["metricset"].(common.MapStr)["host"] = b.Host
	}

	// Adds error to event in case error happened
	if b.fetchErr != nil {
		event["error"] = b.fetchErr.Error()
	}

	return event, nil
}

func getIndex(event common.MapStr, indexName string) string {
	// Set index from event if set

	if _, ok := event["index"]; ok {
		indexName, ok = event["index"].(string)
		if !ok {
			logp.Err("Index couldn't be overwritten because event index is not string")
		}
		delete(event, "index")
	}
	return indexName
}

func getType(event common.MapStr, typeName string) string {

	// Set type from event if set
	if _, ok := event["type"]; ok {
		typeName, ok = event["type"].(string)
		if !ok {
			logp.Err("Type couldn't be overwritten because event type is not string")
		}
		delete(event, "type")
	}

	return typeName
}

func getTimestamp(event common.MapStr, timestamp common.Time) common.Time {

	// Set timestamp from event if set, move it to the top level
	// If not set, timestamp is created
	if _, ok := event["@timestamp"]; ok {
		timestamp, ok = event["@timestamp"].(common.Time)
		if !ok {
			logp.Err("Timestamp couldn't be overwritten because event @timestamp is not common.Time")
		}
		delete(event, "@timestamp")
	}
	return timestamp
}

// createEvent creates a new event from the fetched MetricSet data.
func createEvent(
	msw *metricSetWrapper,
	event common.MapStr,
	fetchErr error,
	start time.Time,
	elapsed time.Duration,
) (common.MapStr, error) {
	return EventBuilder{
		ModuleName:    msw.Module().Name(),
		MetricSetName: msw.Name(),
		Host:          msw.Host(),
		StartTime:     start,
		FetchDuration: elapsed,
		Event:         event,
		fetchErr:      fetchErr,
		filters:       msw.module.filters,
		metadata:      msw.module.Config().EventMetadata,
	}.Build()
}