package listener

import (
	"context"
	"fmt"
	"time"

	"github.com/synapsecns/sanguine/core/metrics"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/metric"
)

const meterName = "github.com/synapsecns/sanguine/ethergo/listener"

// generate an interface for otelRecorder that exports the public method.
// this allows us to avoid using recordX externally anad makes the package less confusing.
//
// =============================================================================
// =============================================================================
// IMPORTANT: DO NOT REMOVE THIS COMMENT.
// NOTICE: PLEASE MAKE SURE YOU UPDATE BOTH THE DOCS AND THE GRAFANA DASHBOARD (IF NEEDED) AFTER UPDATING METRICS.
// =============================================================================
// =============================================================================
//
//go:generate go run github.com/vburenin/ifacemaker -f otel.go -s otelRecorder -i iOtelRecorder -p listener -o otel_generated.go -c "autogenerated file"
type otelRecorder struct {
	metrics metrics.Handler
	// meter is the metrics meter.
	meter metric.Meter
	// lastBlockGauge is the gauge for the last block.
	lastBlockGauge metric.Int64ObservableGauge
	// lastFetchedBlockAgeGauge is the gauge for the last block age.
	lastFetchedBlockAgeGauge metric.Float64ObservableGauge
	// lastBlock is the last block processed by the listener.
	lastBlock *uint64
	// lastBlockFetchTime is the time the last block was fetched (used to calculate last block age).
	lastBlockFetchTime *time.Time
	// chainID is the chain ID for the listener.
	chainID int
	// listenerName is the name of the listener.
	listenerName string
}

func newOtelRecorder(meterHandler metrics.Handler, chainID int, name string) (_ iOtelRecorder, err error) {
	or := otelRecorder{
		metrics:            meterHandler,
		meter:              meterHandler.Meter(meterName),
		lastBlock:          nil,
		lastBlockFetchTime: nil,
		chainID:            chainID,
		listenerName:       name,
	}

	or.lastBlockGauge, err = or.meter.Int64ObservableGauge("last_block")
	if err != nil {
		return nil, fmt.Errorf("could not create last block gauge")
	}

	or.lastFetchedBlockAgeGauge, err = or.meter.Float64ObservableGauge("last_block_age")
	if err != nil {
		return nil, fmt.Errorf("could not create last block age gauge")
	}

	_, err = or.meter.RegisterCallback(or.recordLastBlock, or.lastBlockGauge)
	if err != nil {
		return nil, fmt.Errorf("could not register callback for last block gauge")
	}

	_, err = or.meter.RegisterCallback(or.recordLastFetchedBlockAge, or.lastFetchedBlockAgeGauge)
	if err != nil {
		return nil, fmt.Errorf("could not register callback for last block age gauge")
	}

	return &or, nil
}

func (o *otelRecorder) recordLastBlock(_ context.Context, observer metric.Observer) (err error) {
	if o.metrics == nil || o.lastBlockGauge == nil || o.lastBlock == nil {
		return nil
	}

	opts := metric.WithAttributes(
		attribute.Int(metrics.ChainID, o.chainID),
		attribute.String("listener_name", o.listenerName),
	)
	observer.ObserveInt64(o.lastBlockGauge, int64(*o.lastBlock), opts)

	return nil
}

func (o *otelRecorder) recordLastFetchedBlockAge(_ context.Context, observer metric.Observer) (err error) {
	if o.metrics == nil || o.lastFetchedBlockAgeGauge == nil || o.lastBlockFetchTime == nil {
		return nil
	}

	age := time.Since(*o.lastBlockFetchTime).Seconds()
	opts := metric.WithAttributes(
		attribute.Int(metrics.ChainID, o.chainID),
		attribute.String("listener_name", o.listenerName),
	)
	observer.ObserveFloat64(o.lastFetchedBlockAgeGauge, age, opts)

	return nil
}

// RecordLastBlock records the last block processed by the listener.
func (o *otelRecorder) RecordLastBlock(lastBlock uint64) {
	// verify if the last block has changed
	var hasChanged bool
	if o.lastBlock == nil {
		hasChanged = true
	} else {
		hasChanged = *o.lastBlock != lastBlock
	}
	if !hasChanged {
		return
	}

	// record the block
	o.lastBlock = &lastBlock
	fetchTime := time.Now()
	o.lastBlockFetchTime = &fetchTime
}