package main

import (
	"context"
	"database/sql"
	"embed"
	_ "embed"
	"encoding/json"
	"errors"
	"fmt"
	"github.com/SherClockHolmes/webpush-go"
	"github.com/go-co-op/gocron/v2"
	"github.com/google/uuid"
	"github.com/joho/godotenv"
	"google.golang.org/genai"
	"html/template"
	"io"
	"log"
	"mime"
	_ "modernc.org/sqlite"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"
)

type apiKey struct {
	openWeatherMap string
}

type location struct {
	lat      float32
	lon      float32
	ianaName string
}

// pageTemplate stores all pre-compiled HTML templates for the application
type pageTemplate struct {
	summary *template.Template
}

// summaryTemplateData stores template data for summary.html
type summaryTemplateData struct {
	Summary  string
	Location string
}

// updateSubscription is the request body for creating/updating registration
type updateSubscription struct {
	Subscription webpush.Subscription `json:"subscription"`
	Locations    []string             `json:"locations"`
}

// registeredSubscription represents a registered webpush subscription.
type registeredSubscription struct {
	ID           uuid.UUID             `json:"id"`
	Subscription *webpush.Subscription `json:"-"`
	Locations    []string              `json:"locations"`
}

type state struct {
	ctx      context.Context
	db       *sql.DB
	genai    *genai.Client
	apiKey   apiKey
	template pageTemplate

	// summaries maps location keys to their latest weather summary
	summaries sync.Map
	// summaryChans stores a map of location key to the corresponding summary channel
	// which is used to track summary updates
	summaryChans map[string]chan string

	// subscriptions maps location keys to the list of registered subscriptions
	// that are subscribed to updates for the location
	subscriptions map[string][]registeredSubscription
	// subscriptionsMutex syncs writes to subscriptions
	subscriptionsMutex sync.Mutex

	// vapidPublicKey is the base64 url encoded VAPID public key
	vapidPublicKey string
	// vapidPrivateKey is the base64 url encoded VAPID private key
	vapidPrivateKey string
}

//go:embed web
var webDir embed.FS

var prompt = "Provide a summaries of the weather below, mentioning the location. Provide suggestions on how to cope with the weather. Use celsius and fahrenheit for temperature. Do not add anything else. Respond in one line."

var supportedLocations = map[string]location{
	"london": {51.507351, -0.127758, "Europe/London"},
	"sf":     {37.774929, -122.419418, "America/Los_Angeles"},
	"sj":     {37.338207, -121.886330, "America/Los_Angeles"},
	"la":     {34.052235, -118.243683, "America/Los_Angeles"},
	"nyc":    {40.712776, -74.005974, "America/New_York"},
	"tokyo":  {35.689487, 139.691711, "Asia/Tokyo"},
}

func main() {
	err := godotenv.Load()
	if err != nil {
		log.Fatalln("please create a .env file using the provided template!")
	}

	db, err := initDB()
	if err != nil {
		log.Fatalf("failed to initialize db: %e\n", err)
	}

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	genaiClient, err := genai.NewClient(ctx, &genai.ClientConfig{
		APIKey:  os.Getenv("GEMINI_API_KEY"),
		Backend: genai.BackendGeminiAPI,
	})
	if err != nil {
		log.Fatalf("failed to initialize gemini client: %e\n", err)
	}

	summaryHTML, _ := webDir.ReadFile("web/summary.html")
	summaryPageTemplate, _ := template.New("summary.html").Parse(string(summaryHTML))

	state := state{
		ctx: ctx,
		db:  db,
		apiKey: apiKey{
			openWeatherMap: os.Getenv("OPEN_WEATHER_MAP_API_KEY"),
		},
		template: pageTemplate{
			summary: summaryPageTemplate,
		},
		summaries:    sync.Map{},
		summaryChans: map[string]chan string{},
		genai:        genaiClient,

		subscriptions: map[string][]registeredSubscription{},

		vapidPublicKey:  os.Getenv("VAPID_PUBLIC_KEY_BASE64"),
		vapidPrivateKey: os.Getenv("VAPID_PRIVATE_KEY_BASE64"),
	}

	var schedulers []gocron.Scheduler

	// schedule periodic updates of weather summary for each supported location
	for locKey, loc := range supportedLocations {
		l, err := time.LoadLocation(loc.ianaName)
		if err != nil {
			log.Fatal(err)
		}

		s, err := gocron.NewScheduler(gocron.WithLocation(l))
		if err != nil {
			log.Fatal(err)
		}

		_, err = s.NewJob(
			gocron.DurationJob(time.Minute),
			gocron.NewTask(updateSummaries, &state, locKey, &loc),
			gocron.WithStartAt(gocron.WithStartImmediately()),
		)
		if err != nil {
			log.Fatal(err)
		}

		schedulers = append(schedulers, s)
		c := make(chan string)

		state.subscriptions[locKey] = []registeredSubscription{}
		state.summaryChans[locKey] = c

		// listen for summary updates, and publish updates to all update subscribers via web push
		go listenForSummaryUpdates(&state, locKey)

		s.Start()
	}

	err = loadSubscriptions(&state)
	if err != nil {
		log.Fatalf("failed to load existing subscriptions: %e\n", err)
	}

	http.HandleFunc("/", handleHTTPRequest(&state))
	err = http.ListenAndServe(":8080", nil)

	if err != nil {
		log.Printf("failed to start http server: %e\n", err)
	}

	for _, s := range schedulers {
		s.Shutdown()
	}
}

func handleHTTPRequest(state *state) http.HandlerFunc {
	return func(writer http.ResponseWriter, request *http.Request) {
		path := strings.TrimPrefix(request.URL.Path, "/")

		if path == "" {
			if request.Method == "" || request.Method == "GET" {
				index, _ := webDir.ReadFile("web/index.html")
				writer.Write(index)
			} else {
				writer.WriteHeader(http.StatusMethodNotAllowed)
			}
		} else if path == "vapid" {
			if request.Method == "" || request.Method == "GET" {
				writer.Write([]byte(state.vapidPublicKey))
			} else {
				writer.WriteHeader(http.StatusMethodNotAllowed)
			}
		} else if strings.HasPrefix(path, "registrations") {
			if path == "registrations" && request.Method == "POST" {
				defer request.Body.Close()

				update := updateSubscription{}
				err := json.NewDecoder(request.Body).Decode(&update)
				if err != nil {
					writer.WriteHeader(http.StatusBadRequest)
					return
				}

				reg, err := registerSubscription(state, &update)
				if err != nil {
					writer.WriteHeader(http.StatusBadRequest)
					return
				}

				err = json.NewEncoder(writer).Encode(reg)
				if err != nil {
					writer.WriteHeader(http.StatusBadRequest)
				}
			} else if request.Method == "PATCH" || request.Method == "DELETE" {
				parts := strings.Split(path, "/")
				if len(parts) < 2 {
					writer.WriteHeader(http.StatusMethodNotAllowed)
					return
				}

				regID, err := uuid.Parse(parts[1])
				if err != nil {
					writer.WriteHeader(http.StatusNotFound)
					return
				}

				switch request.Method {
				case "PATCH":
					defer request.Body.Close()

					update := updateSubscription{}
					err = json.NewDecoder(request.Body).Decode(&update)
					if err != nil {
						writer.WriteHeader(http.StatusBadRequest)
						return
					}

					reg, err := updateRegisteredSubscription(state, regID, &update)
					if err != nil {
						if errors.Is(err, sql.ErrNoRows) {
							writer.WriteHeader(http.StatusNotFound)
						} else {
							writer.WriteHeader(http.StatusInternalServerError)
						}
					} else {
						json.NewEncoder(writer).Encode(reg)
					}

				case "DELETE":
					err = deleteSubscription(state, regID)
					if err != nil {
						if errors.Is(err, sql.ErrNoRows) {
							writer.WriteHeader(http.StatusNotFound)
						} else {
							writer.WriteHeader(http.StatusInternalServerError)
						}
					} else {
						writer.WriteHeader(http.StatusNoContent)
					}
				}

			} else {
				writer.WriteHeader(http.StatusMethodNotAllowed)
			}

		} else {
			if request.Method != "" && request.Method != "GET" {
				writer.WriteHeader(http.StatusMethodNotAllowed)
				return
			}

			summary, ok := state.summaries.Load(path)
			if ok {
				state.template.summary.Execute(writer, summaryTemplateData{summary.(string), path})
			} else {
				f, err := webDir.ReadFile("web/" + path)
				if err != nil {
					writer.WriteHeader(http.StatusNotFound)
				} else {
					m := mime.TypeByExtension(filepath.Ext(path))
					if m != "" {
						writer.Header().Set("Content-Type", m)
					}
					writer.Write(f)
				}
			}
		}
	}
}

func initDB() (*sql.DB, error) {
	db, err := sql.Open("sqlite", "file:data.sqlite")
	if err != nil {
		log.Fatalln("failed to initialize database")
	}

	_, err = db.Exec(`
		CREATE TABLE IF NOT EXISTS subscriptions(
			id TEXT PRIMARY KEY,
			locations TEXT NOT NULL,
			subscription_json TEXT NOT NULL
		);
	`)
	if err != nil {
		return nil, err
	}

	return db, nil
}

func loadSubscriptions(state *state) error {
	rows, err := state.db.Query(`SELECT id, locations, subscription_json FROM subscriptions;`)
	if err != nil {
		return err
	}

	for rows.Next() {
		var id string
		var locations string
		var j string

		err := rows.Scan(&id, &locations, &j)
		if err != nil {
			continue
		}

		s := webpush.Subscription{}
		err = json.Unmarshal([]byte(j), &s)
		if err != nil {
			continue
		}

		reg := registeredSubscription{
			ID:           uuid.MustParse(id),
			Locations:    strings.Split(locations, ","),
			Subscription: &s,
		}

		for _, l := range reg.Locations {
			state.subscriptions[l] = append(state.subscriptions[l], reg)
		}
	}

	return nil
}

func updateRegisteredSubscription(state *state, id uuid.UUID, update *updateSubscription) (*registeredSubscription, error) {
	j, err := json.Marshal(update.Subscription)
	if err != nil {
		return nil, err
	}

	_, err = state.db.Exec(
		"UPDATE subscriptions SET subscription_json = ?, locations = ? WHERE id = ?",
		string(j), strings.Join(update.Locations, ","), id,
	)
	if err != nil {
		return nil, err
	}

	return &registeredSubscription{
		ID:           id,
		Subscription: &update.Subscription,
		Locations:    update.Locations,
	}, nil
}

func registerSubscription(state *state, sub *updateSubscription) (*registeredSubscription, error) {
	j, err := json.Marshal(sub.Subscription)
	if err != nil {
		return nil, err
	}

	id, err := uuid.NewV7()
	if err != nil {
		return nil, err
	}

	_, err = state.db.Exec(
		"INSERT INTO subscriptions (id, locations, subscription_json) VALUES (?, ?, ?);",
		id, strings.Join(sub.Locations, ","), string(j),
	)
	if err != nil {
		return nil, err
	}

	reg := registeredSubscription{
		ID:           id,
		Subscription: &sub.Subscription,
		Locations:    sub.Locations,
	}

	for _, l := range sub.Locations {
		state.subscriptionsMutex.Lock()
		state.subscriptions[l] = append(state.subscriptions[l], reg)
		state.subscriptionsMutex.Unlock()
	}

	return &reg, nil
}

func deleteSubscription(state *state, regID uuid.UUID) error {
	_, err := state.db.Exec("DELETE FROM subscriptions WHERE id = ?", regID)
	return err
}

func updateSummaries(state *state, locKey string, loc *location) {
	log.Printf("updating summary for %v...\n", locKey)

	resp, err := http.Get(fmt.Sprintf("https://api.openweathermap.org/data/2.5/weather?lat=%f&lon=%f&appid=%v", loc.lat, loc.lon, state.apiKey.openWeatherMap))
	if err != nil {
		log.Printf("error updating summaries for %s: %e\n", locKey, err)
		return
	}

	b, err := io.ReadAll(resp.Body)
	defer resp.Body.Close()
	if err != nil {
		log.Printf("error updating summaries for %s: %e\n", locKey, err)
		return
	}

	result, err := state.genai.Models.GenerateContent(state.ctx, "gemini-2.0-flash", []*genai.Content{{
		Parts: []*genai.Part{
			{Text: prompt},
			{Text: string(b)},
		},
	}}, nil)
	if err != nil {
		log.Printf("error updating summaries for %s: %e\n", locKey, err)
		return
	}

	summary := result.Text()
	c := state.summaryChans[locKey]

	state.summaries.Store(locKey, summary)
	if len(state.subscriptions[locKey]) > 0 {
		c <- summary
	}

	log.Printf("updated summary for %v successfully\n", locKey)
}

func listenForSummaryUpdates(state *state, locKey string) {
	c := state.summaryChans[locKey]

	opts := webpush.Options{
		VAPIDPublicKey:  state.vapidPublicKey,
		VAPIDPrivateKey: state.vapidPrivateKey,
		TTL:             30,
	}

	for {
		select {
		case summary := <-c:
			log.Printf("sending summary for %v to subscribers...\n", locKey)

			var wg sync.WaitGroup
			for _, sub := range state.subscriptions[locKey] {
				wg.Add(1)
				go func() {
					defer wg.Done()
					_, err := webpush.SendNotificationWithContext(state.ctx, []byte(summary), sub.Subscription, &opts)
					if err != nil {
						log.Printf("failed to send summary for %v to sub id %v: %e\n", locKey, sub.ID, err)
					}
				}()
			}

			wg.Wait()

		case <-state.ctx.Done():
			return
		}
	}
}