// codeberg.org/mapleopentech/monorepo/cloud/maplefile-backend/internal/service/me/change_email_verify.go
package me

import (
	"context"
	"errors"
	"fmt"
	"html"
	"strings"
	"time"

	"github.com/gocql/gocql"
	"go.uber.org/zap"

	"codeberg.org/mapleopentech/monorepo/cloud/maplefile-backend/config"
	"codeberg.org/mapleopentech/monorepo/cloud/maplefile-backend/config/constants"
	uc_user "codeberg.org/mapleopentech/monorepo/cloud/maplefile-backend/internal/usecase/user"
	"codeberg.org/mapleopentech/monorepo/cloud/maplefile-backend/pkg/auditlog"
	"codeberg.org/mapleopentech/monorepo/cloud/maplefile-backend/pkg/emailer/mailgun"
	"codeberg.org/mapleopentech/monorepo/cloud/maplefile-backend/pkg/httperror"
	"codeberg.org/mapleopentech/monorepo/cloud/maplefile-backend/pkg/validation"
)

type ChangeEmailVerifyRequestDTO struct {
	VerificationCode string `json:"verification_code"`
}

type ChangeEmailVerifyResponseDTO struct {
	Message  string `json:"message"`
	Success  bool   `json:"success"`
	NewEmail string `json:"new_email"`
}

type ChangeEmailVerifyService interface {
	Execute(ctx context.Context, req *ChangeEmailVerifyRequestDTO) (*ChangeEmailVerifyResponseDTO, error)
}

type changeEmailVerifyServiceImpl struct {
	config             *config.Configuration
	logger             *zap.Logger
	auditLogger        auditlog.AuditLogger
	userGetByIDUseCase uc_user.UserGetByIDUseCase
	userUpdateUseCase  uc_user.UserUpdateUseCase
	emailer            mailgun.Emailer
}

func NewChangeEmailVerifyService(
	config *config.Configuration,
	logger *zap.Logger,
	auditLogger auditlog.AuditLogger,
	userGetByIDUseCase uc_user.UserGetByIDUseCase,
	userUpdateUseCase uc_user.UserUpdateUseCase,
	emailer mailgun.Emailer,
) ChangeEmailVerifyService {
	logger = logger.Named("ChangeEmailVerifyService")

	return &changeEmailVerifyServiceImpl{
		config:             config,
		logger:             logger,
		auditLogger:        auditLogger,
		userGetByIDUseCase: userGetByIDUseCase,
		userUpdateUseCase:  userUpdateUseCase,
		emailer:            emailer,
	}
}

func (svc *changeEmailVerifyServiceImpl) Execute(ctx context.Context, req *ChangeEmailVerifyRequestDTO) (*ChangeEmailVerifyResponseDTO, error) {
	//
	// Get user from context
	//

	userID, ok := ctx.Value(constants.SessionUserID).(gocql.UUID)
	if !ok {
		svc.logger.Error("Failed getting user id from context")
		return nil, errors.New("user id not found in context")
	}

	//
	// Validation
	//

	if req == nil {
		svc.logger.Warn("Request is nil")
		return nil, httperror.NewForBadRequestWithSingleField("non_field_error", "Request is required")
	}

	req.VerificationCode = strings.TrimSpace(req.VerificationCode)

	e := make(map[string]string)
	if req.VerificationCode == "" {
		e["verification_code"] = "Verification code is required"
	} else if len(req.VerificationCode) != 8 {
		e["verification_code"] = "Verification code must be 8 digits"
	} else {
		// Validate that code is numeric
		for _, c := range req.VerificationCode {
			if c < '0' || c > '9' {
				e["verification_code"] = "Verification code must contain only numbers"
				break
			}
		}
	}

	if len(e) != 0 {
		svc.logger.Warn("Validation failed", zap.Any("errors", e))
		return nil, httperror.NewForBadRequest(&e)
	}

	//
	// Get current user
	//

	user, err := svc.userGetByIDUseCase.Execute(ctx, userID)
	if err != nil {
		svc.logger.Error("Failed getting user by ID", zap.Error(err))
		return nil, err
	}
	if user == nil {
		err := fmt.Errorf("user is nil after lookup for id: %v", userID.String())
		svc.logger.Error("User not found", zap.Error(err))
		return nil, err
	}

	//
	// Check if there's a pending email change
	//

	if user.SecurityData.PendingEmail == "" {
		svc.logger.Warn("No pending email change found",
			zap.String("user_id", user.ID.String()))
		return nil, httperror.NewBadRequestError("No pending email change request found")
	}

	//
	// Check if verification code matches
	//

	svc.logger.Debug("Comparing verification codes",
		zap.String("user_id", user.ID.String()),
		zap.String("pending_email", validation.MaskEmail(user.SecurityData.PendingEmail)),
		zap.String("expected_code", user.SecurityData.PendingEmailCode),
		zap.String("provided_code", req.VerificationCode),
		zap.Int("expected_length", len(user.SecurityData.PendingEmailCode)),
		zap.Int("provided_length", len(req.VerificationCode)),
		zap.String("expected_bytes", fmt.Sprintf("%v", []byte(user.SecurityData.PendingEmailCode))),
		zap.String("provided_bytes", fmt.Sprintf("%v", []byte(req.VerificationCode))))

	if user.SecurityData.PendingEmailCode != req.VerificationCode {
		svc.logger.Warn("Invalid verification code provided",
			zap.String("user_id", user.ID.String()),
			zap.String("pending_email", validation.MaskEmail(user.SecurityData.PendingEmail)),
			zap.String("expected_code", user.SecurityData.PendingEmailCode),
			zap.String("provided_code", req.VerificationCode),
			zap.Int("expected_length", len(user.SecurityData.PendingEmailCode)),
			zap.Int("provided_length", len(req.VerificationCode)))

		// Audit log failed attempt
		svc.auditLogger.LogAuth(ctx, "email_change_verify_failed", auditlog.OutcomeFailure,
			validation.MaskEmail(user.Email), "", map[string]string{
				"user_id": user.ID.String(),
				"reason":  "invalid_code",
			})

		return nil, httperror.NewBadRequestError("Invalid verification code")
	}

	//
	// Check if verification code has expired
	//

	if time.Now().After(user.SecurityData.PendingEmailExpiry) {
		svc.logger.Warn("Verification code expired",
			zap.String("user_id", user.ID.String()),
			zap.Time("expiry", user.SecurityData.PendingEmailExpiry))

		// Audit log expired attempt
		svc.auditLogger.LogAuth(ctx, "email_change_verify_failed", auditlog.OutcomeFailure,
			validation.MaskEmail(user.Email), "", map[string]string{
				"user_id": user.ID.String(),
				"reason":  "code_expired",
			})

		// Clear expired pending email change
		user.SecurityData.PendingEmail = ""
		user.SecurityData.PendingEmailCode = ""
		user.SecurityData.PendingEmailExpiry = time.Time{}
		svc.userUpdateUseCase.Execute(ctx, user)

		return nil, httperror.NewBadRequestError("Verification code has expired. Please request a new email change.")
	}

	//
	// Perform the email change
	//

	oldEmail := user.Email
	newEmail := user.SecurityData.PendingEmail

	user.Email = newEmail
	user.SecurityData.PendingEmail = ""
	user.SecurityData.PendingEmailCode = ""
	user.SecurityData.PendingEmailExpiry = time.Time{}
	user.ModifiedAt = time.Now()

	// IMPORTANT: Email is still verified - don't reset WasEmailVerified flag
	// The user has proven ownership of the new email by verifying the code

	if err := svc.userUpdateUseCase.Execute(ctx, user); err != nil {
		svc.logger.Error("Failed to update user email",
			zap.String("user_id", user.ID.String()),
			zap.Error(err))
		return nil, httperror.NewInternalServerError("Failed to complete email change. Please try again.")
	}

	//
	// Send confirmation emails
	//

	// Send confirmation to NEW email
	if err := svc.sendConfirmationEmail(ctx, newEmail, user.FirstName, oldEmail); err != nil {
		// Log error but don't fail the request - email change succeeded
		svc.logger.Warn("Failed to send confirmation email to new address",
			zap.String("email", validation.MaskEmail(newEmail)),
			zap.Error(err))
	}

	// Send notification to OLD email
	if err := svc.sendOldEmailNotification(ctx, oldEmail, user.FirstName, newEmail); err != nil {
		// Log error but don't fail the request - email change succeeded
		svc.logger.Warn("Failed to send notification to old email",
			zap.String("email", validation.MaskEmail(oldEmail)),
			zap.Error(err))
	}

	//
	// Audit log
	//

	svc.auditLogger.LogAuth(ctx, "email_changed", auditlog.OutcomeSuccess,
		validation.MaskEmail(newEmail), "", map[string]string{
			"user_id":   user.ID.String(),
			"old_email": validation.MaskEmail(oldEmail),
			"new_email": validation.MaskEmail(newEmail),
		})

	svc.logger.Info("Email changed successfully",
		zap.String("user_id", user.ID.String()),
		zap.String("old_email", validation.MaskEmail(oldEmail)),
		zap.String("new_email", validation.MaskEmail(newEmail)))

	return &ChangeEmailVerifyResponseDTO{
		Message:  "Email address changed successfully. You can now log in with your new email address.",
		Success:  true,
		NewEmail: newEmail,
	}, nil
}

func (svc *changeEmailVerifyServiceImpl) sendConfirmationEmail(ctx context.Context, newEmail, firstName, oldEmail string) error {
	subject := "Email Address Changed Successfully"
	sender := svc.emailer.GetSenderEmail()

	// Escape user input to prevent HTML injection
	safeFirstName := html.EscapeString(firstName)
	maskedOldEmail := validation.MaskEmail(oldEmail)

	htmlContent := fmt.Sprintf(`
		<html>
			<body>
				<h2>Hi %s,</h2>
				<p><strong>Your email address has been changed successfully!</strong></p>
				<p><strong>Previous email:</strong> %s</p>
				<p><strong>New email:</strong> %s</p>
				<p>You can now log in to MapleFile using your new email address.</p>
				<p><strong>If you did NOT make this change:</strong></p>
				<ul>
					<li>Your account may be compromised</li>
					<li>Contact support immediately at support@maplefile.com</li>
				</ul>
			</body>
		</html>
	`, safeFirstName, maskedOldEmail, newEmail)

	return svc.emailer.Send(ctx, sender, subject, newEmail, htmlContent)
}

func (svc *changeEmailVerifyServiceImpl) sendOldEmailNotification(ctx context.Context, oldEmail, firstName, newEmail string) error {
	subject := "Your MapleFile Email Address Was Changed"
	sender := svc.emailer.GetSenderEmail()

	// Escape user input to prevent HTML injection
	safeFirstName := html.EscapeString(firstName)
	safeNewEmail := html.EscapeString(newEmail) // Show full new email so user knows where their account was moved

	htmlContent := fmt.Sprintf(`
		<html>
			<body>
				<h2>Hi %s,</h2>
				<p><strong>This is a notification that your MapleFile account email address has been changed.</strong></p>
				<p><strong>New email address:</strong> %s</p>
				<p>This change was completed at %s.</p>
				<p><strong>If you made this change, you can ignore this email.</strong></p>
				<p><strong>If you did NOT make this change:</strong></p>
				<ul>
					<li>Your account has been compromised</li>
					<li>Contact support immediately at support@maplefile.com</li>
					<li>Provide your user ID and details of the unauthorized change</li>
				</ul>
				<p>This email was sent to your previous email address for security purposes.</p>
			</body>
		</html>
	`, safeFirstName, safeNewEmail, time.Now().Format("January 2, 2006 at 3:04 PM MST"))

	return svc.emailer.Send(ctx, sender, subject, oldEmail, htmlContent)
}