package telemetry

import (
	"context"
	"fmt"
	"net"
	"net/http"
	"reflect"

	"github.com/gorilla/mux"
	prometheus2 "github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	log "github.com/sirupsen/logrus"
	"go.opentelemetry.io/otel/exporters/prometheus"
	metric2 "go.opentelemetry.io/otel/metric"
	"go.opentelemetry.io/otel/sdk/metric"
)

const defaultEndpoint = "/metrics"

// MockAppMetrics mocks the AppMetrics interface
type MockAppMetrics struct {
	GetMeterFunc       func() metric2.Meter
	CloseFunc          func() error
	ExposeFunc         func(port int, endpoint string) error
	IDPMetricsFunc     func() *IDPMetrics
	HTTPMiddlewareFunc func() *HTTPMiddleware
	GRPCMetricsFunc    func() *GRPCMetrics
	StoreMetricsFunc   func() *StoreMetrics
}

// GetMeter mocks the GetMeter function of the AppMetrics interface
func (mock *MockAppMetrics) GetMeter() metric2.Meter {
	if mock.GetMeterFunc != nil {
		return mock.GetMeterFunc()
	}
	return nil
}

// Close mocks the Close function of the AppMetrics interface
func (mock *MockAppMetrics) Close() error {
	if mock.CloseFunc != nil {
		return mock.CloseFunc()
	}
	return fmt.Errorf("unimplemented")
}

// Expose mocks the Expose function of the AppMetrics interface
func (mock *MockAppMetrics) Expose(port int, endpoint string) error {
	if mock.ExposeFunc != nil {
		return mock.ExposeFunc(port, endpoint)
	}
	return fmt.Errorf("unimplemented")
}

// IDPMetrics mocks the IDPMetrics function of the IDPMetrics interface
func (mock *MockAppMetrics) IDPMetrics() *IDPMetrics {
	if mock.IDPMetricsFunc != nil {
		return mock.IDPMetricsFunc()
	}
	return nil
}

// HTTPMiddleware mocks the HTTPMiddleware function of the IDPMetrics interface
func (mock *MockAppMetrics) HTTPMiddleware() *HTTPMiddleware {
	if mock.HTTPMiddlewareFunc != nil {
		return mock.HTTPMiddlewareFunc()
	}
	return nil
}

// GRPCMetrics mocks the GRPCMetrics function of the IDPMetrics interface
func (mock *MockAppMetrics) GRPCMetrics() *GRPCMetrics {
	if mock.GRPCMetricsFunc != nil {
		return mock.GRPCMetricsFunc()
	}
	return nil
}

// StoreMetrics mocks the MockAppMetrics function of the StoreMetrics interface
func (mock *MockAppMetrics) StoreMetrics() *StoreMetrics {
	if mock.StoreMetricsFunc != nil {
		return mock.StoreMetricsFunc()
	}
	return nil
}

// AppMetrics is metrics interface
type AppMetrics interface {
	GetMeter() metric2.Meter
	Close() error
	Expose(port int, endpoint string) error
	IDPMetrics() *IDPMetrics
	HTTPMiddleware() *HTTPMiddleware
	GRPCMetrics() *GRPCMetrics
	StoreMetrics() *StoreMetrics
}

// defaultAppMetrics are core application metrics based on OpenTelemetry https://opentelemetry.io/
type defaultAppMetrics struct {
	// Meter can be used by different application parts to create counters and measure things
	Meter          metric2.Meter
	listener       net.Listener
	ctx            context.Context
	idpMetrics     *IDPMetrics
	httpMiddleware *HTTPMiddleware
	grpcMetrics    *GRPCMetrics
	storeMetrics   *StoreMetrics
}

// IDPMetrics returns metrics for the idp package
func (appMetrics *defaultAppMetrics) IDPMetrics() *IDPMetrics {
	return appMetrics.idpMetrics
}

// HTTPMiddleware returns metrics for the http api package
func (appMetrics *defaultAppMetrics) HTTPMiddleware() *HTTPMiddleware {
	return appMetrics.httpMiddleware
}

// GRPCMetrics returns metrics for the gRPC api
func (appMetrics *defaultAppMetrics) GRPCMetrics() *GRPCMetrics {
	return appMetrics.grpcMetrics
}

// StoreMetrics returns metrics for the store
func (appMetrics *defaultAppMetrics) StoreMetrics() *StoreMetrics {
	return appMetrics.storeMetrics
}

// Close stop application metrics HTTP handler and closes listener.
func (appMetrics *defaultAppMetrics) Close() error {
	if appMetrics.listener == nil {
		return nil
	}
	return appMetrics.listener.Close()
}

// Expose metrics on a given port and endpoint. If endpoint is empty a defaultEndpoint one will be used.
// Exposes metrics in the Prometheus format https://prometheus.io/
func (appMetrics *defaultAppMetrics) Expose(port int, endpoint string) error {
	if endpoint == "" {
		endpoint = defaultEndpoint
	}
	rootRouter := mux.NewRouter()
	rootRouter.Handle(endpoint, promhttp.HandlerFor(
		prometheus2.DefaultGatherer,
		promhttp.HandlerOpts{EnableOpenMetrics: true}))
	listener, err := net.Listen("tcp4", fmt.Sprintf(":%d", port))
	if err != nil {
		return err
	}
	appMetrics.listener = listener
	go func() {
		err := http.Serve(listener, rootRouter)
		if err != nil {
			return
		}
	}()

	log.Infof("enabled application metrics and exposing on http://%s", listener.Addr().String())

	return nil
}

// GetMeter returns metrics meter that can be used to add various counters
func (appMetrics *defaultAppMetrics) GetMeter() metric2.Meter {
	return appMetrics.Meter
}

// NewDefaultAppMetrics and expose them via defaultEndpoint on a given HTTP port
func NewDefaultAppMetrics(ctx context.Context) (AppMetrics, error) {
	exporter, err := prometheus.New()
	if err != nil {
		return nil, err
	}

	provider := metric.NewMeterProvider(metric.WithReader(exporter))
	pkg := reflect.TypeOf(defaultEndpoint).PkgPath()
	meter := provider.Meter(pkg)

	idpMetrics, err := NewIDPMetrics(ctx, meter)
	if err != nil {
		return nil, err
	}

	middleware, err := NewMetricsMiddleware(ctx, meter)
	if err != nil {
		return nil, err
	}

	grpcMetrics, err := NewGRPCMetrics(ctx, meter)
	if err != nil {
		return nil, err
	}

	storeMetrics, err := NewStoreMetrics(ctx, meter)
	if err != nil {
		return nil, err
	}

	return &defaultAppMetrics{Meter: meter, ctx: ctx, idpMetrics: idpMetrics, httpMiddleware: middleware,
		grpcMetrics: grpcMetrics, storeMetrics: storeMetrics}, nil
}