package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"time"

	"github.com/golang-jwt/jwt/v5"
	"github.com/jmoiron/sqlx"
	"github.com/joho/godotenv"
	"golang.org/x/crypto/bcrypt"

	_ "github.com/mattn/go-sqlite3"
)

var (
	addr = flag.String("addr", ":5000", "http server address")
)

type User struct {
	ID        int64  `json:"id" db:"id"`
	Email     string `json:"email" db:"email"`
	Password  string `json:"-" db:"password"`
	CreatedAt string `json:"created_at" db:"created_at"`
	UpdatedAt string `json:"updated_at" db:"updated_at"`
}

func readJSON(r *http.Request, s any) error {
	return json.NewDecoder(r.Body).Decode(s)
}

func sendJSON(w http.ResponseWriter, data any, status int) error {
	w.WriteHeader(status)
	return json.NewEncoder(w).Encode(data)
}

func sendApiError(w http.ResponseWriter, msg string, err error, status int) {
	var e struct {
		Message string `json:"message"`
		Error   string `json:"error,omitempty"`
	}
	e.Message = msg
	if err != nil {
		e.Error = err.Error()
	}
	sendJSON(w, e, status)
}

var jwtSecretKey []byte

func init() {
	if err := godotenv.Load(); err != nil {
		panic("couldn't parse env")
	}

	s := os.Getenv("JWT_SECRET")
	if s == "" {
		panic("JWT_SECRET env doesn't exist")
	}
	jwtSecretKey = []byte(s)
}

func generateAccessToken(userId int64) (string, error) {
	exp := time.Now().Add(time.Hour * 24 * 7)
	claims := jwt.MapClaims{
		"id":  userId,
		"exp": exp.Unix(),
	}
	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString(jwtSecretKey)
}

type AuthResponse struct {
	AccessToken string `json:"access_token"`
}

func handler(mux *http.ServeMux) http.HandlerFunc {
	fmt.Printf("starting http server at %s\n", *addr)

	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Access-Control-Allow-Credentials", "true")
		w.Header().Set("Access-Control-Allow-Origin", "http://localhost:3000")
		w.Header().Set("Access-Control-Allow-Headers", "Authorization,Content-Type,Content-Length")
		w.Header().Set("Access-Control-Allow-Methods", "GET,POST,PATCH,DELETE,OPTIONS")

		mux.ServeHTTP(w, r)
	}
}

func main() {
	flag.Parse()

	db, err := sqlx.Connect("sqlite3", "./sqlite.db")
	if err != nil {
		log.Fatalf("failed to connect to db: %v\n", err)
	}
	defer db.Close()

	if err := db.Ping(); err != nil {
		log.Fatalf("failed to ping db: %v\n", err)
	}

	mux := http.NewServeMux()

	mux.HandleFunc("OPTIONS /", func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(200)
		fmt.Fprintf(w, "ok")
	})

	mux.HandleFunc("POST /auth/register", func(w http.ResponseWriter, r *http.Request) {
		var body struct {
			Email    string `json:"email"`
			Password string `json:"password"`
		}
		if err := readJSON(r, &body); err != nil {
			sendApiError(w, "couldn't parse body", err, 500)
			return
		}

		if body.Email == "" || body.Password == "" {
			sendApiError(w, "invalid request", nil, 400)
			return
		}

		p, err := bcrypt.GenerateFromPassword([]byte(body.Password), 10)
		if err != nil {
			sendApiError(w, "couldn't hash password", err, 500)
			return
		}

		res, err := db.Exec("INSERT INTO users (email, password) VALUES (?, ?)", body.Email, string(p))
		if err != nil {
			sendApiError(w, "couldn't create user", err, 500)
			return
		}
		_ = res

		id, err := res.LastInsertId()
		if err != nil {
			sendApiError(w, "couldn't get user id", err, 500)
			return
		}

		token, err := generateAccessToken(id)
		if err != nil {
			sendApiError(w, "couldn't generate token", err, 500)
			return
		}

		sendJSON(w, AuthResponse{token}, 201)
	})

	mux.HandleFunc("POST /auth/login", func(w http.ResponseWriter, r *http.Request) {
		var body struct {
			Email    string `json:"email"`
			Password string `json:"password"`
		}
		if err := readJSON(r, &body); err != nil {
			sendApiError(w, "couldn't parse body", err, 500)
			return
		}

		if body.Email == "" || body.Password == "" {
			sendApiError(w, "invalid request", nil, 400)
			return
		}

		row := db.QueryRowx("SELECT * FROM users WHERE email = ?", body.Email)
		if row.Err() != nil {
			sendApiError(w, "couldn't find user", err, 404)
			return
		}

		var user User
		if err := row.StructScan(&user); err != nil {
			sendApiError(w, "couldn't find user", err, 404)
			return
		}

		if err := bcrypt.CompareHashAndPassword([]byte(user.Password), []byte(body.Password)); err != nil {
			sendApiError(w, "invalid password", nil, 400)
			return
		}

		token, err := generateAccessToken(user.ID)
		if err != nil {
			sendApiError(w, "couldn't generate token", err, 500)
			return
		}

		sendJSON(w, AuthResponse{token}, 200)
	})

	if err := http.ListenAndServe(*addr, handler(mux)); err != nil {
		log.Fatalf("failed to start http server: %v\n", err)
	}
}