package apiserver

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/http"

	"github.com/grafana/grafana-plugin-sdk-go/backend"
	data "github.com/grafana/grafana-plugin-sdk-go/experimental/apis/data/v0alpha1"
	semconv "go.opentelemetry.io/otel/semconv/v1.21.0"
	"k8s.io/component-base/tracing"
	"k8s.io/klog/v2"

	aggregationv0alpha1 "github.com/grafana/grafana/pkg/aggregator/apis/aggregation/v0alpha1"
	grafanasemconv "github.com/grafana/grafana/pkg/semconv"
)

type pluginHandler struct {
	mux      *http.ServeMux
	delegate http.Handler

	client                PluginClient
	pluginContextProvider PluginContextProvider

	dataplaneService aggregationv0alpha1.DataPlaneService
}

func newPluginHandler(
	client PluginClient,
	dataplaneService aggregationv0alpha1.DataPlaneService,
	pluginContextProvider PluginContextProvider,
	delegate http.Handler,
) *pluginHandler {
	mux := http.NewServeMux()
	h := &pluginHandler{
		mux:                   mux,
		delegate:              delegate,
		client:                client,
		pluginContextProvider: pluginContextProvider,
		dataplaneService:      dataplaneService,
	}

	for _, service := range dataplaneService.Spec.Services {
		switch service.Type {
		case aggregationv0alpha1.QueryServiceType:
			proxyPath := fmt.Sprintf("/apis/%s/%s/namespaces/{namespace}/connections/{uid}/query", dataplaneService.Spec.Group, dataplaneService.Spec.Version)
			mux.Handle(proxyPath, h.QueryDataHandler())
		case aggregationv0alpha1.StreamServiceType:
			// TODO: implement in future PR
		case aggregationv0alpha1.AdmissionControlServiceType:
			// TODO: implement in future PR
		case aggregationv0alpha1.RouteServiceType:
			// TODO: implement in future PR
		case aggregationv0alpha1.ConversionServiceType:
			// TODO: implement in future PR
		case aggregationv0alpha1.DataSourceProxyServiceType:
			// TODO: implement in future PR
		}
	}

	// fallback to the delegate
	mux.Handle("/", delegate)

	return h
}

func (h *pluginHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	h.mux.ServeHTTP(w, req)
}

func (h *pluginHandler) QueryDataHandler() http.HandlerFunc {
	return func(w http.ResponseWriter, req *http.Request) {
		ctx := req.Context()
		span := tracing.SpanFromContext(ctx)
		span.AddEvent("QueryDataHandler")
		responder := &responder{w: w}
		dqr := data.QueryDataRequest{}
		if err := json.NewDecoder(req.Body).Decode(&dqr); err != nil {
			responder.Error(w, req, err)
			return
		}

		dsUID := req.PathValue("uid")
		dsType := h.dataplaneService.Spec.PluginID

		queries, dsRef, err := data.ToDataSourceQueries(dqr)
		if err != nil {
			responder.Error(w, req, err)
			return
		}

		// this shouldn't happen, but just in case
		if dsRef == nil {
			responder.Error(w, req, fmt.Errorf("missing datasource reference"))
			return
		}

		// the datasource type in the query body should match the plugin ID
		if dsRef.Type != dsType {
			err := errors.New("invalid datasource type")
			klog.ErrorS(err, "type", dsType, "ref.Type", dsRef.Type)
			responder.Error(w, req, err)
			return
		}

		// the UID in the query body should match the UID in the URL
		if dsRef.UID != dsUID {
			err := errors.New("invalid datasource UID")
			klog.ErrorS(err, "path", dsUID, "ref.UID", dsRef.UID)
			responder.Error(w, req, err)
			return
		}

		span.AddEvent("GetPluginContext",
			grafanasemconv.GrafanaDatasourceUid(dsRef.UID),
			grafanasemconv.GrafanaDatasourceType(dsRef.Type),
		)
		pluginContext, err := h.pluginContextProvider.GetPluginContext(ctx, dsRef.Type, dsRef.UID)
		if err != nil {
			responder.Error(w, req, fmt.Errorf("unable to get plugin context: %w", err))
			return
		}

		ctx = backend.WithGrafanaConfig(ctx, pluginContext.GrafanaConfig)
		span.AddEvent("QueryData start", grafanasemconv.GrafanaDatasourceRequestQueryCount(len(queries)))
		rsp, err := h.client.QueryData(ctx, &backend.QueryDataRequest{
			Queries:       queries,
			PluginContext: pluginContext,
		})
		if err != nil {
			responder.Error(w, req, err)
			return
		}
		statusCode := 200
		span.AddEvent("QueryData end", semconv.HTTPResponseStatusCode(statusCode))
		responder.Object(statusCode,
			&aggregationv0alpha1.QueryDataResponse{QueryDataResponse: *rsp},
		)
	}
}