package main

import (
	"bufio"
	"context"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"runtime"
	"strings"
	"syscall"
	"time"

	"github.com/chromedp/cdproto/page"
	"github.com/chromedp/chromedp"
	"golang.org/x/crypto/ssh/terminal"
)

const (
	loginButton   = "#app-navbar-collapse > ul.nav.navbar-nav.navbar-right > li:nth-child(1) > a"
	usernameInput = "body > div > div > div > div.modal-body > form > div:nth-child(2) > input"
	passwordInput = "body > div > div > div > div.modal-body > form > div:nth-child(3) > input"
	rememberMe    = `body > div > div > div > div.modal-body > form > div.checkbox > label > input[type="checkbox"]`
	submitButton  = "body > div > div > div > div.modal-body > form > button"
	errorDiv      = "body > div > div > div > div.modal-body > form > div.alert.alert-danger"

	menuPresencas     = "#app-navbar-collapse > ul:nth-child(1) > li:nth-child(4) > a"
	btnMarcarPresenca = ".btn.btn-primary"

	maxRetries = 5

	credFile    = ".credentials"
	encryptSalt = "IPLeiriaAutoAttendance" // Salt for encryption, ideally should be unique per installation
)

type Credentials struct {
	Username string
	Password string
}

func deriveKey(passphrase string) []byte {
	hash := sha256.Sum256([]byte(passphrase))
	return hash[:]
}

func encrypt(plaintext, passphrase string) (string, error) {
	key := deriveKey(passphrase)

	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}

	aesGCM, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	nonce := make([]byte, aesGCM.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", err
	}

	ciphertext := aesGCM.Seal(nonce, nonce, []byte(plaintext), nil)
	return hex.EncodeToString(ciphertext), nil
}

func decrypt(encryptedHex, passphrase string) (string, error) {
	key := deriveKey(passphrase)

	ciphertext, err := hex.DecodeString(encryptedHex)
	if err != nil {
		return "", err
	}

	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}

	aesGCM, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	nonceSize := aesGCM.NonceSize()
	if len(ciphertext) < nonceSize {
		return "", fmt.Errorf("ciphertext too short")
	}

	nonce, ciphertext := ciphertext[:nonceSize], ciphertext[nonceSize:]
	plaintext, err := aesGCM.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return "", err
	}

	return string(plaintext), nil
}

func parseFlags() (int, bool, bool, string, int, bool, error) {
	//* Set the flags
	wait := flag.Int("w", 10, "\tTime to wait in between refreshes")
	flag.IntVar(wait, "wait", 10, "\tTime to wait in between refreshes")

	// Verbose mode
	isVerbose := flag.Bool("v", false, "\tEnable verbose mode")
	flag.BoolVar(isVerbose, "verbose", false, "\tEnable verbose mode")

	// By default, run in headless mode
	headless := flag.Bool("h", true, "\tRun in headless mode")
	flag.BoolVar(headless, "headless", true, "\tRun in headless mode")

	// Log to file
	logFile := flag.String("l", "", "\tLog output to file")
	flag.StringVar(logFile, "log", "", "\tLog output to file")

	// Maximum time to run the program (minutes)
	maxTime := flag.Int("m", -1, "\tMaximum time to run the program (minutes)")
	flag.IntVar(maxTime, "maxtime", -1, "\tMaximum time to run the program (minutes)")

	replacePass := flag.Bool("r", false, "\tReplace saved credentials")
	flag.BoolVar(replacePass, "replace", false, "\tReplace saved credentials")

	flag.Parse()

	if *wait < 0 {
		return 0, false, false, "", -1, false, fmt.Errorf("invalid wait time: %d", *wait)
	}

	return *wait, *isVerbose, *headless, *logFile, *maxTime, *replacePass, nil
}

func welcomeMessage() {
	fmt.Println("******************************************************************************************")
	fmt.Println("*                        Welcome to IPLeiria AutoAttendance!                             *")
	fmt.Println("* This program will automatically mark your attendance in the IPLeiria's GISEM platform. *")
	fmt.Println("*                  Please make sure you have your credentials ready.                     *")
	fmt.Println("*                                      Enjoy!                                            *")
	fmt.Println("******************************************************************************************")
}

func getCredsFilePath() (string, error) {
	var configDir string
	var err error

	switch runtime.GOOS {
	case "windows":
		configDir = os.Getenv("APPDATA")
		if configDir == "" {
			configDir, err = os.UserHomeDir()
			if err != nil {
				return "", err
			}
		}
	default:
		home, err := os.UserHomeDir()
		if err != nil {
			return "", err
		}
		configDir = filepath.Join(home, ".config")
	}

	appConfigDir := filepath.Join(configDir, "gisem-presencas")

	// Create directory if it doesn't exist
	if err := os.MkdirAll(appConfigDir, 0700); err != nil {
		return "", fmt.Errorf("failed to create config directory: %v", err)
	}

	return filepath.Join(appConfigDir, credFile), nil
}

func getCreds() (Credentials, error) {
	credPath, err := getCredsFilePath()
	if err != nil {
		return Credentials{}, fmt.Errorf("could not determine credentials path: %v", err)
	}

	// Check if credentials file exists
	if _, err := os.Stat(credPath); os.IsNotExist(err) {
		// File doesn't exist, prompt user for credentials
		return promptAndSaveCreds(credPath)
	}

	file, err := os.Open(credPath)
	if err != nil {
		return Credentials{}, fmt.Errorf("failed to open credentials file: %v", err)
	}
	defer file.Close()

	var creds Credentials
	if err := json.NewDecoder(file).Decode(&creds); err != nil {
		return Credentials{}, fmt.Errorf("failed to read credentials: %v", err)
	}

	if creds.Username == "" || creds.Password == "" {
		return promptAndSaveCreds(credPath)
	}

	return creds, nil

}

func promptAndSaveCreds(credPath string) (Credentials, error) {
	reader := bufio.NewReader(os.Stdin)

	fmt.Print("Enter your GISEM username: ")
	username, err := reader.ReadString('\n')
	if err != nil {
		return Credentials{}, fmt.Errorf("failed to read username: %v", err)
	}

	username = strings.TrimSpace(username)

	fmt.Print("Enter your GISEM password: ")
	passwordBytes, err := terminal.ReadPassword(int(syscall.Stdin))
	if err != nil {
		// Fallback to regular input if terminal.ReadPassword fails
		fmt.Println("\nSecure password input not available, using regular input:")
		fmt.Print("Enter your GISEM password: ")
		passwordStr, err := reader.ReadString('\n')
		if err != nil {
			return Credentials{}, fmt.Errorf("could not read password: %v", err)
		}
		password := strings.TrimSpace(passwordStr)

		return saveCreds(credPath, username, password)
	}

	fmt.Println()
	password := strings.TrimSpace(string(passwordBytes))

	return saveCreds(credPath, username, password)
}

func saveCreds(filePath, username, password string) (Credentials, error) {
	creds := Credentials{
		Username: username,
		Password: password,
	}

	pwd, err := encrypt(creds.Password, encryptSalt+username)
	if err != nil {
		return Credentials{}, fmt.Errorf("failed to encrypt password: %v", err)
	}

	creds.Password = pwd

	file, err := os.OpenFile(filePath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		return Credentials{}, fmt.Errorf("could not open file: %v", err)
	}
	defer file.Close()

	encoder := json.NewEncoder(file)
	if err := encoder.Encode(creds); err != nil {
		return Credentials{}, fmt.Errorf("could not write credentials to file: %v", err)
	}

	log.Println("Credentials saved successfully!")
	return creds, nil
}

func login(ctx context.Context, creds Credentials) error {
	//* Fill the login form and save the cookies

	pwd, err := decrypt(creds.Password, encryptSalt+creds.Username)
	if err != nil {
		return fmt.Errorf("failed to decrypt password: %v", err)
	}

	if err := chromedp.Run(ctx,
		chromedp.WaitVisible(".modal-content"),
		chromedp.SendKeys(usernameInput, creds.Username),
		chromedp.SendKeys(passwordInput, pwd),
		chromedp.Click(submitButton),
	); err != nil {
		log.Fatalf("Failed to fill the login form: %v", err)
	}
	return nil
}

func marcarPresenca(ctx context.Context) error {
	var attempt int

	startTime := time.Now()

	if isVerbose || maxTime != -1 {
		log.Printf("Starting attendance registration at %s\n", startTime.Format(time.RFC1123))
	}

	for attempt = 1; attempt <= maxRetries; attempt++ {
		if err := chromedp.Run(ctx,
			chromedp.ActionFunc(func(ctx context.Context) error {
				for {
					waitCtx, cancel := context.WithTimeout(ctx, time.Duration(waitTime)*time.Second)
					defer cancel()

					err := chromedp.Run(waitCtx,
						chromedp.WaitVisible(menuPresencas))

					if err == nil {
						if isVerbose && logFile != "" {
							log.Println("Navigation menu is visible!")
						}
					}

					chromedp.Run(waitCtx, chromedp.Click(menuPresencas))
					var currentURL string
					if err := chromedp.Location(&currentURL).Do(ctx); err != nil {
						return err
					}
					if strings.Contains(currentURL, "obterAulasMarcarPresenca") {
						log.Println("Attendance page loaded :", time.Now().Format(time.RFC1123))
						log.Println("Registering attendance... : ", time.Now().Format(time.RFC1123))
						break
					}

					if err := chromedp.Reload().Do(ctx); err != nil {
						return err
					}
					time.Sleep(time.Duration(waitTime) * time.Second)

					if maxTime != -1 {
						elapsedMinutes := time.Since(startTime).Minutes()
						if int(elapsedMinutes) >= maxTime {
							log.Println("Maximum time reached, attendance not registered", time.Now().Format(time.RFC1123))
							return errors.New("maximum time reached")
						}
					}
				}
				return nil
			}),
			chromedp.WaitVisible(btnMarcarPresenca),
			chromedp.Click(btnMarcarPresenca),

			// Wait and check alert message
			chromedp.ActionFunc(func(ctx context.Context) error {
				ch := make(chan string, 1)
				chromedp.ListenTarget(ctx, func(ev any) {
					if ev, ok := ev.(*page.EventJavascriptDialogOpening); ok {
						ch <- ev.Message
					}
				})
				select {
				case alertMessage := <-ch:
					if strings.Contains(alertMessage, "sucesso") {
						log.Println("Attendance registered successfully! : ", time.Now().Format(time.RFC1123))
					} else if strings.Contains(alertMessage, "anteriormente") {
						log.Println("Attendance previously registered! : ", time.Now().Format(time.RFC1123))
					} else {
						log.Println("Error registering attendance: ", alertMessage)
					}
				case <-time.After(time.Duration(waitTime) * time.Second):
					return fmt.Errorf("timeout waiting for alert")
				}
				return nil
			}),
		); err != nil {
			// Check if the error was due to maximum time reached
			if err.Error() == "maximum time reached" {
				return err
			}
			log.Printf("Attempt %d: Failed to register attendance: %v", attempt, err)
			time.Sleep(5 * time.Second)
			continue
		}
		return nil
	}
	return fmt.Errorf("failed to register attendance after %d attempts", maxRetries)
}