package handlers

import (
	"context"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"

	"github.com/containerd/containerd"
	"github.com/containerd/containerd/namespaces"
	gocni "github.com/containerd/go-cni"

	"github.com/openfaas/faas-provider/types"
	faasd "github.com/openfaas/faasd/pkg"
)

func MakeReplicaUpdateHandler(client *containerd.Client, cni gocni.CNI) func(w http.ResponseWriter, r *http.Request) {

	return func(w http.ResponseWriter, r *http.Request) {

		if r.Body == nil {
			http.Error(w, "expected a body", http.StatusBadRequest)
			return
		}

		defer r.Body.Close()

		body, _ := ioutil.ReadAll(r.Body)
		log.Printf("[Scale] request: %s\n", string(body))

		req := types.ScaleServiceRequest{}
		err := json.Unmarshal(body, &req)

		if err != nil {
			log.Printf("[Scale] error parsing input: %s\n", err)
			http.Error(w, err.Error(), http.StatusBadRequest)

			return
		}

		name := req.ServiceName

		if _, err := GetFunction(client, name); err != nil {
			msg := fmt.Sprintf("service %s not found", name)
			log.Printf("[Scale] %s\n", msg)
			http.Error(w, msg, http.StatusNotFound)
			return
		}

		ctx := namespaces.WithNamespace(context.Background(), faasd.FunctionNamespace)

		ctr, ctrErr := client.LoadContainer(ctx, name)
		if ctrErr != nil {
			msg := fmt.Sprintf("cannot load service %s, error: %s", name, ctrErr)
			log.Printf("[Scale] %s\n", msg)
			http.Error(w, msg, http.StatusNotFound)
			return
		}

		var taskExists bool
		var taskStatus *containerd.Status

		task, taskErr := ctr.Task(ctx, nil)
		if taskErr != nil {
			msg := fmt.Sprintf("cannot load task for service %s, error: %s", name, taskErr)
			log.Printf("[Scale] %s\n", msg)
			taskExists = false
		} else {
			taskExists = true
			status, statusErr := task.Status(ctx)
			if statusErr != nil {
				msg := fmt.Sprintf("cannot load task status for %s, error: %s", name, statusErr)
				log.Printf("[Scale] %s\n", msg)
				http.Error(w, msg, http.StatusInternalServerError)
				return
			} else {
				taskStatus = &status
			}
		}

		createNewTask := false

		// Scale to zero
		if req.Replicas == 0 {
			// If a task is running, pause it
			if taskExists && taskStatus.Status == containerd.Running {
				if pauseErr := task.Pause(ctx); pauseErr != nil {
					wrappedPauseErr := fmt.Errorf("error pausing task %s, error: %s", name, pauseErr)
					log.Printf("[Scale] %s\n", wrappedPauseErr.Error())
					http.Error(w, wrappedPauseErr.Error(), http.StatusNotFound)
					return
				}
			}
		}

		if taskExists {
			if taskStatus != nil {
				if taskStatus.Status == containerd.Paused {
					if resumeErr := task.Resume(ctx); resumeErr != nil {
						log.Printf("[Scale] error resuming task %s, error: %s\n", name, resumeErr)
						http.Error(w, resumeErr.Error(), http.StatusBadRequest)
						return
					}
				} else if taskStatus.Status == containerd.Stopped {
					// Stopped tasks cannot be restarted, must be removed, and created again
					if _, delErr := task.Delete(ctx); delErr != nil {
						log.Printf("[Scale] error deleting stopped task %s, error: %s\n", name, delErr)
						http.Error(w, delErr.Error(), http.StatusBadRequest)
						return
					}
					createNewTask = true
				}
			}
		} else {
			createNewTask = true
		}

		if createNewTask {
			deployErr := createTask(ctx, client, ctr, cni)
			if deployErr != nil {
				log.Printf("[Scale] error deploying %s, error: %s\n", name, deployErr)
				http.Error(w, deployErr.Error(), http.StatusBadRequest)
				return
			}
		}
	}
}
