package queue

import (
	"context"
	"fmt"
	"html/template"
	"math/rand"
	"net/http"
	"path/filepath"
	"strconv"
	"sync"
	"sync/atomic"
	"time"

	"forge.cadoles.com/Cadoles/go-proxy"
	"forge.cadoles.com/Cadoles/go-proxy/wildcard"
	"forge.cadoles.com/cadoles/bouncer/internal/proxy/director"
	"forge.cadoles.com/cadoles/bouncer/internal/store"
	"github.com/Masterminds/sprig/v3"
	"github.com/google/uuid"
	"github.com/pkg/errors"
	"github.com/prometheus/client_golang/prometheus"
	"gitlab.com/wpetit/goweb/logger"
)

const LayerType store.LayerType = "queue"

type Queue struct {
	adapter Adapter

	defaultKeepAlive time.Duration

	templateDir string
	loadOnce    sync.Once
	tmpl        *template.Template

	refreshJobRunning       uint32
	updateMetricsJobRunning uint32
	postKeepAliveDebouncer  *DebouncerMap
}

// LayerType implements director.MiddlewareLayer
func (q *Queue) LayerType() store.LayerType {
	return LayerType
}

// Middleware implements director.MiddlewareLayer
func (q *Queue) Middleware(layer *store.Layer) proxy.Middleware {
	return func(h http.Handler) http.Handler {
		fn := func(w http.ResponseWriter, r *http.Request) {
			ctx := r.Context()

			options, err := fromStoreOptions(layer.Options, q.defaultKeepAlive)
			if err != nil {
				logger.Error(ctx, "could not parse layer options", logger.E(errors.WithStack(err)))
				http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

				return
			}

			matches := wildcard.MatchAny(r.URL.String(), options.MatchURLs...)
			if !matches {
				h.ServeHTTP(w, r)

				return
			}

			defer q.updateMetrics(layer.Proxy, layer.Name, options)

			cookieName := q.getCookieName(layer.Name)

			cookie, err := r.Cookie(cookieName)
			if err != nil && !errors.Is(err, http.ErrNoCookie) {
				logger.Error(ctx, "could not retrieve cookie", logger.E(errors.WithStack(err)))
			}

			if cookie == nil {
				cookie = &http.Cookie{
					Name:  cookieName,
					Value: uuid.NewString(),
					Path:  "/",
				}

				w.Header().Add("Set-Cookie", cookie.String())
			}

			sessionID := cookie.Value
			queueName := string(layer.Name)

			rank, err := q.adapter.Touch(ctx, queueName, sessionID)
			if err != nil {
				logger.Error(ctx, "could not retrieve session rank", logger.E(errors.WithStack(err)))
				http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

				return
			}

			if rank >= options.Capacity {
				q.renderQueuePage(w, r, queueName, options, rank)

				return
			}

			ctx = logger.With(ctx,
				logger.F("queueSessionId", sessionID),
				logger.F("queueName", queueName),
				logger.F("queueSessionRank", rank),
			)
			r = r.WithContext(ctx)

			h.ServeHTTP(w, r)
		}

		return http.HandlerFunc(fn)
	}
}

func (q *Queue) updateSessionsMetric(ctx context.Context, proxyName store.ProxyName, layerName store.LayerName) {
	if !atomic.CompareAndSwapUint32(&q.updateMetricsJobRunning, 0, 1) {
		return
	}

	defer atomic.StoreUint32(&q.updateMetricsJobRunning, 0)

	queueName := string(layerName)

	status, err := q.adapter.Status(ctx, queueName)
	if err != nil {
		logger.Error(ctx, "could not retrieve queue status", logger.E(errors.WithStack(err)))

		return
	}

	metricQueueSessions.With(
		prometheus.Labels{
			metricLabelLayer: string(layerName),
			metricLabelProxy: string(proxyName),
		},
	).Set(float64(status.Sessions))
}

func (q *Queue) renderQueuePage(w http.ResponseWriter, r *http.Request, queueName string, options *LayerOptions, rank int64) {
	ctx := r.Context()

	status, err := q.adapter.Status(ctx, queueName)
	if err != nil {
		logger.Error(ctx, "could not retrieve queue status", logger.E(errors.WithStack(err)))
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	q.loadOnce.Do(func() {
		pattern := filepath.Join(q.templateDir, "*.gohtml")

		logger.Info(ctx, "loading queue page templates", logger.F("pattern", pattern))

		tmpl, err := template.New("").Funcs(sprig.FuncMap()).ParseGlob(pattern)
		if err != nil {
			logger.Error(ctx, "could not load queue templates", logger.E(errors.WithStack(err)))

			return
		}

		q.tmpl = tmpl
	})

	if q.tmpl == nil {
		logger.Error(ctx, "queue page templates not loaded", logger.E(errors.WithStack(err)))
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	refreshRate := time.Duration(int64(options.KeepAlive.Seconds()/2)) * time.Second

	templateData := struct {
		QueueName       string
		LayerOptions    *LayerOptions
		Rank            int64
		CurrentSessions int64
		MaxSessions     int64
		RefreshRate     time.Duration
	}{
		QueueName:       queueName,
		LayerOptions:    options,
		Rank:            rank + 1,
		CurrentSessions: status.Sessions,
		MaxSessions:     options.Capacity,
		RefreshRate:     refreshRate,
	}

	w.Header().Add("Cache-Control", "no-cache")
	w.Header().Add("Retry-After", strconv.FormatInt(int64(refreshRate.Seconds()), 10))
	w.WriteHeader(http.StatusServiceUnavailable)

	if err := q.tmpl.ExecuteTemplate(w, "queue", templateData); err != nil {
		logger.Error(ctx, "could not render queue page", logger.E(errors.WithStack(err)))
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}
}

func (q *Queue) refreshQueue(ctx context.Context, layerName store.LayerName, keepAlive time.Duration) {
	if !atomic.CompareAndSwapUint32(&q.refreshJobRunning, 0, 1) {
		return
	}

	defer atomic.StoreUint32(&q.refreshJobRunning, 0)

	if err := q.adapter.Refresh(ctx, string(layerName), keepAlive); err != nil {
		logger.Error(ctx, "could not refresh queue",
			logger.E(errors.WithStack(err)),
			logger.F("queue", layerName),
		)
	}
}

func (q *Queue) updateMetrics(proxyName store.ProxyName, layerName store.LayerName, options *LayerOptions) {
	ctx := context.Background()

	// Update queue capacity metric
	metricQueueCapacity.With(
		prometheus.Labels{
			metricLabelLayer: string(layerName),
			metricLabelProxy: string(proxyName),
		},
	).Set(float64(options.Capacity))

	// Refresh queue data and metrics
	q.refreshQueue(ctx, layerName, options.KeepAlive)
	q.updateSessionsMetric(ctx, proxyName, layerName)

	// (Re)schedule an update job after session ttl + semi-random time padding
	// to update metrics after last session expiration
	randDuration := rand.Int63n(int64(options.KeepAlive))
	timePadding := options.KeepAlive/2 + time.Duration(randDuration)
	after := options.KeepAlive + timePadding

	debouncingKey := fmt.Sprintf("%s/%s", proxyName, layerName)

	q.postKeepAliveDebouncer.Do(debouncingKey, after, func() {
		ctx := logger.With(
			context.Background(),
			logger.F("proxy", proxyName),
			logger.F("layer", layerName),
			logger.F("after", after),
		)

		logger.Info(ctx, "running post keep alive refresh job")

		q.refreshQueue(ctx, layerName, options.KeepAlive)
		q.updateSessionsMetric(ctx, proxyName, layerName)
	})
}

func (q *Queue) getCookieName(layerName store.LayerName) string {
	return fmt.Sprintf("_bouncer_%s_%s", LayerType, layerName)
}

func New(adapter Adapter, funcs ...OptionFunc) *Queue {
	opts := defaultOptions()
	for _, fn := range funcs {
		fn(opts)
	}

	return &Queue{
		adapter:                adapter,
		templateDir:            opts.TemplateDir,
		defaultKeepAlive:       opts.DefaultKeepAlive,
		postKeepAliveDebouncer: NewDebouncerMap(),
	}
}

var _ director.MiddlewareLayer = &Queue{}