package service

import (
	"crypto/rand"
	"crypto/subtle"
	"database/sql"
	"encoding/base64"
	"log/slog"
	"net/http"
	"net/mail"
	"strings"
	"time"

	"me-fit/template"
	"me-fit/template/auth"
	tempMail "me-fit/template/mail"
	"me-fit/types"
	"me-fit/utils"

	"github.com/a-h/templ"
	"github.com/google/uuid"
	"golang.org/x/crypto/argon2"
)

func HandleSignInPage(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		user := utils.GetUserFromSession(db, r)
		if user == nil || !user.SessionValid {
			userComp := UserInfoComp(nil)
			signIn := auth.SignInOrUpComp(true)
			template.Layout(signIn, userComp).Render(r.Context(), w)
			return
		} else if !user.EmailVerified {
			utils.DoRedirect(w, r, "/auth/verify")
			return
		} else {
			utils.DoRedirect(w, r, "/")
			return
		}
	}
}

func HandleSignUpPage(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		user := utils.GetUserFromSession(db, r)
		if user == nil || !user.SessionValid {
			userComp := UserInfoComp(nil)
			signUpComp := auth.SignInOrUpComp(false)
			template.Layout(signUpComp, userComp).Render(r.Context(), w)
			return
		} else if !user.EmailVerified {
			utils.DoRedirect(w, r, "/auth/verify")
			return
		} else {
			utils.DoRedirect(w, r, "/")
			return
		}
	}
}

func HandleSignUpVerifyPage(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		user := utils.GetUserFromSession(db, r)
		if user == nil || !user.SessionValid {
			utils.DoRedirect(w, r, "/auth/signin")
			return
		}
		if user.EmailVerified {
			utils.DoRedirect(w, r, "/")
			return
		} else {
			userComp := UserInfoComp(user)
			signIn := auth.VerifyComp()
			template.Layout(signIn, userComp).Render(r.Context(), w)
		}
	}
}

func HandleSignUpVerifyResponsePage(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		code := r.URL.Query().Get("code")
		if code == "" {
			utils.DoRedirect(w, r, "/auth/verify")
			return
		}

		userId, err := uuid.Parse(code)
		if err != nil {
			utils.DoRedirect(w, r, "/auth/verify")
			return
		}

		_, err = db.Exec("UPDATE user SET email_verified = true, email_verified_at = datetime() WHERE user_uuid = ?", userId)
		utils.DoRedirect(w, r, "/")
	}
}

func UserInfoComp(user *types.User) templ.Component {

	if user != nil {
		return auth.UserComp(user.Email)
	} else {
		return auth.UserComp("")
	}
}

func HandleSignUpComp(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		var email = r.FormValue("email")
		var password = r.FormValue("password")

		_, err := mail.ParseAddress(email)
		if err != nil {
			http.Error(w, "Invalid email", http.StatusBadRequest)
			return
		}

		if len(password) < 8 ||
			!strings.ContainsAny(password, "0123456789") ||
			!strings.ContainsAny(password, "ABCDEFGHIJKLMNOPQRSTUVWXYZ") ||
			!strings.ContainsAny(password, "abcdefghijklmnopqrstuvwxyz") ||
			!strings.ContainsAny(password, "!@#$%^&*()_+-=[]{}\\|;:'\",.<>/?") {
			http.Error(w, "Password needs to be 8 characters long, contain at least one number, one special, one uppercase and one lowercase character", http.StatusBadRequest)
			return
		}

		userId, err := uuid.NewRandom()
		if err != nil {
			slog.Error("Could not generate UUID: %v", err)
			auth.Error("Internal Server Error").Render(r.Context(), w)
			return
		}

		salt := make([]byte, 16)
		_, err = rand.Read(salt)
		if err != nil {
			slog.Error("Could not generate salt: %v", err)
			auth.Error("Internal Server Error").Render(r.Context(), w)
			return
		}

		hash := getHashPassword(password, salt)

		_, err = db.Exec("INSERT INTO user (user_uuid, email, email_verified, is_admin, password, salt, created_at) VALUES (?, ?, FALSE, FALSE, ?, ?, datetime())", userId, email, hash, salt)
		if err != nil {
			// This does leak information about the email being in use, though not specifically stated
			// It needs to be refacoteres to "If the email is not already in use, an email has been send to your address", or something
			// The happy path, currently a redirect, needs to send the same message!
			// Then it is also important to have the same compute time in both paths
			// Otherwise an attacker could guess emails when comparing the response time
			if strings.Contains(err.Error(), "email") {
				auth.Error("Bad Request").Render(r.Context(), w)
				return
			}

			auth.Error("Internal Server Error").Render(r.Context(), w)
			slog.Error("Could not insert user: %v", err)
			return
		}

		result := tryCreateSessionAndSetCookie(r, w, db, userId)
		if !result {
			return
		}

		// Send verification email as a goroutine
		go sendVerificationEmail(db, r, userId.String(), email)

		utils.DoRedirect(w, r, "/auth/verify")
	}
}

func HandleSignInComp(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		var email = r.FormValue("email")
		var password = r.FormValue("password")

		var result bool = true
		start := time.Now()

		var (
			userId        uuid.UUID
			savedHash     []byte
			salt          []byte
			emailVerified bool
		)
		err := db.QueryRow("SELECT user_uuid, password, salt, email_verified FROM user WHERE email = ?", email).Scan(&userId, &savedHash, &salt, &emailVerified)
		if err != nil {
			result = false
		}

		if result {
			new_hash := getHashPassword(password, salt)

			if subtle.ConstantTimeCompare(new_hash, savedHash) == 0 {
				result = false
			}
		}

		if result {
			result := tryCreateSessionAndSetCookie(r, w, db, userId)
			if !result {
				return
			}
		}

		duration := time.Since(start)
		timeToWait := 100 - duration.Milliseconds()
		// It is important to sleep for a while to prevent timing attacks
		// If the email is correct, the server will calculate the hash, which will take some time
		// This way an attacker could guess emails when comparing the response time
		// Because of that, we cant use WriteHeader in the middle of the function. We have to wait until the end
		// Unfortunatly this makes the code harder to read
		time.Sleep(time.Duration(timeToWait) * time.Millisecond)

		if result {
			if !emailVerified {
				utils.DoRedirect(w, r, "/auth/verify")
			} else {
				utils.DoRedirect(w, r, "/")
			}
		} else {
			auth.Error("Invalid email or password").Render(r.Context(), w)
		}
	}
}

func HandleSignOutComp(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		user := utils.GetUserFromSession(db, r)

		if user != nil {
			_, err := db.Exec("DELETE FROM session WHERE session_id = ?", user.SessionId)
			if err != nil {
				slog.Error("Could not delete session: %v", err)
				http.Error(w, err.Error(), http.StatusInternalServerError)
				return
			}
		}

		c := http.Cookie{
			Name:     "id",
			Value:    "",
			MaxAge:   -1,
			Secure:   true,
			HttpOnly: true,
			SameSite: http.SameSiteStrictMode,
			Path:     "/",
		}

		http.SetCookie(w, &c)
		w.Header().Add("HX-Redirect", "/")
	}
}

func HandleVerifyResendComp(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		user := utils.GetUserFromSession(db, r)
		if user == nil || !user.SessionValid || user.EmailVerified {
			utils.DoRedirect(w, r, "/auth/signin")
			return
		}

		sendVerificationEmail(db, r, user.Id.String(), user.Email)

		w.Write([]byte("<p class=\"mt-8\">Verification email sent</p>"))
	}
}

func sendVerificationEmail(db *sql.DB, r *http.Request, userId string, email string) {
	registerComp := tempMail.Register(userId)

	var writer strings.Builder

	registerComp.Render(r.Context(), &writer)
	utils.SendMail(email, "Welcome to ME-FIT", writer.String())
}

func tryCreateSessionAndSetCookie(r *http.Request, w http.ResponseWriter, db *sql.DB, user_uuid uuid.UUID) bool {
	var session_id_bytes []byte = make([]byte, 32)
	_, err := rand.Reader.Read(session_id_bytes)
	if err != nil {
		slog.Error("Could not generate session ID: %v", err)
		auth.Error("Internal Server Error").Render(r.Context(), w)
		return false
	}
	session_id := base64.StdEncoding.EncodeToString(session_id_bytes)

	// Delete old inactive sessions
	_, err = db.Exec("DELETE FROM session WHERE created_at < datetime('now','-8 hours') AND user_uuid = ?", user_uuid)
	if err != nil {
		slog.Error("Could not delete old sessions: " + err.Error())
	}

	_, err = db.Exec("INSERT INTO session (session_id, user_uuid, created_at) VALUES (?, ?, datetime())", session_id, user_uuid)
	if err != nil {
		slog.Error("Could not insert session: " + err.Error())
		auth.Error("Internal Server Error").Render(r.Context(), w)
		return false
	}

	cookie := http.Cookie{
		Name:     "id",
		Value:    session_id,
		MaxAge:   60 * 60 * 8, // 8 hours
		Secure:   true,
		HttpOnly: true,
		SameSite: http.SameSiteStrictMode,
		Path:     "/",
	}
	http.SetCookie(w, &cookie)

	return true
}

func getHashPassword(password string, salt []byte) []byte {
	return argon2.IDKey([]byte(password), salt, 1, 64*1024, 1, 16)
}