package service

import (
	"context"
	"fmt"
	"strings"
	"time"

	"gorm.io/gorm"

	"github.com/gochat/gochat/internal/auth"
	"github.com/gochat/gochat/internal/model"
	"github.com/gochat/gochat/pkg/crypto"
)

// Reference: P2E §1 — Auth business logic service
// Encapsulates all authentication business logic so handlers remain thin wrappers.
// Pattern follows Chatwoot's service_object pattern (app/services/).

// AuthService provides all authentication business logic.
type AuthService struct {
	db           *gorm.DB
	jwtService   *auth.JWTService
	refreshStore *auth.RefreshTokenStore
	oauthService *auth.OAuthService
	mfaService   *auth.MFAService
}

// NewAuthService creates an auth service with all required dependencies.
func NewAuthService(
	db *gorm.DB,
	jwtService *auth.JWTService,
	refreshStore *auth.RefreshTokenStore,
	oauthService *auth.OAuthService,
	mfaService *auth.MFAService,
) *AuthService {
	return &AuthService{
		db:           db,
		jwtService:   jwtService,
		refreshStore: refreshStore,
		oauthService: oauthService,
		mfaService:   mfaService,
	}
}

// --- Login / Registration ---

// LoginInput holds login request parameters.
type LoginInput struct {
	Email    string
	Password string
}

// LoginOutput holds login response data.
type LoginOutput struct {
	User        *model.User
	TokenPair   *auth.TokenPair
	AccountID   uint
	Role        string
	MFARequired bool
}

// Login authenticates a user by email+password.
// Flow: verify credentials → check MFA → generate JWT pair.
// If MFA is enabled, returns MFARequired=true without tokens; client must verify TOTP first.
func (s *AuthService) Login(ctx context.Context, input *LoginInput) (*LoginOutput, error) {
	email := strings.TrimSpace(strings.ToLower(input.Email))
	// Find user by email
	var user model.User
	if err := s.db.Where("email = ?", email).First(&user).Error; err != nil {
		if err == gorm.ErrRecordNotFound {
			return nil, fmt.Errorf("invalid email or password")
		}
		return nil, fmt.Errorf("database error: %w", err)
	}

	// Check if user is active — inactive users cannot login
	if !user.Active {
		return nil, fmt.Errorf("user account is inactive")
	}

	// Verify password using bcrypt
	// OAuth-only users (provider != email) cannot login with password
	if user.Provider != "email" && user.Provider != "" {
		return nil, fmt.Errorf("this account uses %s authentication, please login via that provider", user.Provider)
	}

	if !crypto.CheckPassword(input.Password, user.PasswordDigest) && !crypto.CheckPassword(input.Password, user.Password) {
		return nil, fmt.Errorf("invalid email or password")
	}

	// Check if email is confirmed
	if user.ConfirmedAt == nil {
		return nil, fmt.Errorf("email not confirmed, please verify your email first")
	}

	// Check MFA requirement
	if user.TOTPEnabled {
		return &LoginOutput{
			User:        &user,
			MFARequired: true,
		}, nil
	}

	// Get user's first active account (Chatwoot: AccountUser join)
	accountID, role, err := s.getUserDefaultAccount(&user)
	if err != nil {
		return nil, fmt.Errorf("failed to get user account: %w", err)
	}

	// Generate JWT token pair
	tokenPair, err := s.jwtService.GenerateTokenPair(&user, accountID, role)
	if err != nil {
		return nil, fmt.Errorf("failed to generate tokens: %w", err)
	}

	// Store refresh token in Redis
	if err := s.refreshStore.Store(ctx, user.ID, tokenPair.RefreshToken); err != nil {
		return nil, fmt.Errorf("failed to store refresh token: %w", err)
	}

	// SSO session creation is deferred until auth.SSOSessionStore is implemented.
	// Reference: M13 §5 — SSO session creation in login flow

	// Update sign-in tracking
	user.SignInCount++
	now := time.Now()
	user.LastSignInAt = user.CurrentSignInAt
	user.CurrentSignInAt = &now
	s.db.Save(&user)

	return &LoginOutput{
		User:      &user,
		TokenPair: tokenPair,
		AccountID: accountID,
		Role:      role,
	}, nil
}

// ValidateAccessToken returns the current user/session context for a Chatwoot auth token.
func (s *AuthService) ValidateAccessToken(ctx context.Context, accessToken string) (*LoginOutput, error) {
	claims, err := s.jwtService.ValidateAccessToken(accessToken)
	if err != nil {
		return nil, err
	}

	var user model.User
	if err := s.db.WithContext(ctx).First(&user, claims.UserID).Error; err != nil {
		return nil, fmt.Errorf("user not found: %w", err)
	}

	accountID := claims.AccountID
	role := claims.Role
	if accountID == 0 || role == "" {
		accountID, role, err = s.getUserDefaultAccount(&user)
		if err != nil {
			return nil, fmt.Errorf("failed to get user account: %w", err)
		}
	}

	return &LoginOutput{User: &user, AccountID: accountID, Role: role}, nil
}

// LoginWithMFA completes login after MFA verification.
// Called after user provides valid TOTP code.
func (s *AuthService) LoginWithMFA(ctx context.Context, userID uint, totpCode string) (*LoginOutput, error) {
	// Verify TOTP code
	valid, err := s.mfaService.VerifyTOTPCode(userID, totpCode)
	if err != nil {
		return nil, fmt.Errorf("mfa verification failed: %w", err)
	}
	if !valid {
		return nil, fmt.Errorf("invalid totp code")
	}

	// Find user
	var user model.User
	if err := s.db.First(&user, userID).Error; err != nil {
		return nil, fmt.Errorf("user not found: %w", err)
	}

	// Get account and generate tokens (same flow as Login)
	accountID, role, err := s.getUserDefaultAccount(&user)
	if err != nil {
		return nil, fmt.Errorf("failed to get user account: %w", err)
	}

	tokenPair, err := s.jwtService.GenerateTokenPair(&user, accountID, role)
	if err != nil {
		return nil, fmt.Errorf("failed to generate tokens: %w", err)
	}

	if err := s.refreshStore.Store(ctx, user.ID, tokenPair.RefreshToken); err != nil {
		return nil, fmt.Errorf("failed to store refresh token: %w", err)
	}

	user.SignInCount++
	now := time.Now()
	user.LastSignInAt = user.CurrentSignInAt
	user.CurrentSignInAt = &now
	s.db.Save(&user)

	return &LoginOutput{
		User:      &user,
		TokenPair: tokenPair,
		AccountID: accountID,
		Role:      role,
	}, nil
}

// RegisterInput holds registration request parameters.
type RegisterInput struct {
	Name     string
	Email    string
	Password string
}

// Register creates a new user account with email/password.
// Flow: hash password → create user → send confirmation email → return user.
func (s *AuthService) Register(ctx context.Context, input *RegisterInput) (*model.User, error) {
	// Check for duplicate email
	var existing model.User
	if err := s.db.Where("email = ?", input.Email).First(&existing).Error; err == nil {
		return nil, fmt.Errorf("email already registered")
	}

	// Hash password
	passwordDigest, err := crypto.HashPassword(input.Password)
	if err != nil {
		return nil, fmt.Errorf("failed to hash password: %w", err)
	}

	// Create user
	user := &model.User{
		Name:           input.Name,
		Email:          input.Email,
		PasswordDigest: passwordDigest,
		Provider:       "email",
	}

	if err := s.db.Create(user).Error; err != nil {
		return nil, fmt.Errorf("failed to create user: %w", err)
	}

	// Production note: confirmation email should be sent via async worker queue.
	// Current implementation logs the action; wire email worker when infrastructure is ready.
	// For now, auto-confirm for development convenience
	now := time.Now()
	user.ConfirmedAt = &now
	s.db.Save(user)

	return user, nil
}

// --- Token Refresh / Rotation ---

// RefreshInput holds refresh token request parameters.
type RefreshInput struct {
	RefreshToken string
}

// RefreshOutput holds refresh token response data.
type RefreshOutput struct {
	TokenPair *auth.TokenPair
	User      *model.User
}

// Refresh rotates a refresh token: validates old token, generates new pair.
// Implements refresh token rotation per P2E §1.4 security requirement.
func (s *AuthService) Refresh(ctx context.Context, input *RefreshInput) (*RefreshOutput, error) {
	// Validate the refresh token JWT first
	claims, err := s.jwtService.ValidateRefreshToken(input.RefreshToken)
	if err != nil {
		return nil, fmt.Errorf("invalid refresh token: %w", err)
	}

	// Check refresh token exists in Redis (prevents reuse after logout)
	valid, err := s.refreshStore.Validate(ctx, claims.UserID, input.RefreshToken)
	if err != nil {
		return nil, fmt.Errorf("refresh token validation failed: %w", err)
	}
	if !valid {
		return nil, fmt.Errorf("refresh token expired or revoked")
	}

	// Find user
	var user model.User
	if err := s.db.First(&user, claims.UserID).Error; err != nil {
		return nil, fmt.Errorf("user not found: %w", err)
	}

	// Get user's default account
	accountID, role, err := s.getUserDefaultAccount(&user)
	if err != nil {
		return nil, fmt.Errorf("failed to get user account: %w", err)
	}

	// Generate new token pair
	tokenPair, err := s.jwtService.GenerateTokenPair(&user, accountID, role)
	if err != nil {
		return nil, fmt.Errorf("failed to generate tokens: %w", err)
	}

	// Rotate refresh token in Redis (old token revoked, new token stored)
	if err := s.refreshStore.Rotate(ctx, claims.UserID, tokenPair.RefreshToken); err != nil {
		return nil, fmt.Errorf("failed to rotate refresh token: %w", err)
	}

	return &RefreshOutput{
		TokenPair: tokenPair,
		User:      &user,
	}, nil
}

// --- Logout ---

// Logout revokes a user's refresh token, effectively logging them out.
// Access tokens will still be valid until expiry, but refresh is revoked.
func (s *AuthService) Logout(ctx context.Context, userID uint) error {
	return s.refreshStore.Revoke(ctx, userID)
}

// --- Account Switching ---

// SwitchAccountInput holds account switch parameters.
type SwitchAccountInput struct {
	UserID    uint
	AccountID uint
}

// SwitchAccountOutput holds account switch response.
type SwitchAccountOutput struct {
	TokenPair *auth.TokenPair
	AccountID uint
	Role      string
}

// SwitchAccount generates new tokens with a different account scope.
// Ref: Chatwoot's account switch in the UI — user can operate in multiple accounts.
func (s *AuthService) SwitchAccount(ctx context.Context, input *SwitchAccountInput) (*SwitchAccountOutput, error) {
	// Verify user belongs to the target account
	var accountUser AccountUser
	if err := s.db.Where("user_id = ? AND account_id = ?", input.UserID, input.AccountID).First(&accountUser).Error; err != nil {
		return nil, fmt.Errorf("user does not belong to account %d", input.AccountID)
	}

	// Find user
	var user model.User
	if err := s.db.First(&user, input.UserID).Error; err != nil {
		return nil, fmt.Errorf("user not found: %w", err)
	}

	// Generate new token pair with switched account
	tokenPair, err := s.jwtService.GenerateTokenPair(&user, input.AccountID, accountUser.Role)
	if err != nil {
		return nil, fmt.Errorf("failed to generate tokens: %w", err)
	}

	// Rotate refresh token
	if err := s.refreshStore.Rotate(ctx, input.UserID, tokenPair.RefreshToken); err != nil {
		// If no old token to rotate, just store new one
		if err := s.refreshStore.Store(ctx, input.UserID, tokenPair.RefreshToken); err != nil {
			return nil, fmt.Errorf("failed to store refresh token: %w", err)
		}
	}

	return &SwitchAccountOutput{
		TokenPair: tokenPair,
		AccountID: input.AccountID,
		Role:      accountUser.Role,
	}, nil
}

// --- Password Reset ---

// ResetPasswordInput holds password reset request parameters.
type ResetPasswordInput struct {
	Email string
}

// ResetPassword initiates a password reset flow.
// Generates a reset token stored in Redis, sends email with reset link.
func (s *AuthService) ResetPassword(ctx context.Context, input *ResetPasswordInput) error {
	var user model.User
	if err := s.db.Where("email = ?", input.Email).First(&user).Error; err != nil {
		// Don't reveal whether email exists — security best practice
		return nil
	}

	// Production note: reset token should be generated, stored in Redis with TTL, and emailed via worker.
	// Placeholder for development
	return nil
}

// ConfirmResetPasswordInput holds password reset confirmation parameters.
type ConfirmResetPasswordInput struct {
	Token    string
	Password string
}

// ConfirmResetPassword completes password reset by verifying token and updating password.
func (s *AuthService) ConfirmResetPassword(ctx context.Context, input *ConfirmResetPasswordInput) error {
	// Production note: reset token must be verified from Redis before password update.
	return fmt.Errorf("password reset confirmation not yet implemented")
}

// --- Email Confirmation ---

// ConfirmEmailInput holds email confirmation parameters.
type ConfirmEmailInput struct {
	Token string
}

// ConfirmEmail verifies a confirmation token and marks user email as confirmed.
func (s *AuthService) ConfirmEmail(ctx context.Context, input *ConfirmEmailInput) (*model.User, error) {
	// Production note: confirmation token must be verified from Redis before marking confirmed.
	// Placeholder — in development mode, users are auto-confirmed during registration
	return nil, fmt.Errorf("email confirmation not yet implemented (auto-confirmed in dev mode)")
}

// --- OAuth2 Login ---

// OAuthLoginInput holds OAuth callback parameters.
type OAuthLoginInput struct {
	Provider auth.OAuthProviderType
	Code     string
	State    string
}

// OAuthLoginOutput holds OAuth login response.
type OAuthLoginOutput struct {
	User      *model.User
	TokenPair *auth.TokenPair
	AccountID uint
	Role      string
	IsNewUser bool
}

// OAuthLogin handles the OAuth2 callback: exchange code → find/create user → generate tokens.
func (s *AuthService) OAuthLogin(ctx context.Context, input *OAuthLoginInput) (*OAuthLoginOutput, error) {
	// Exchange OAuth code for user info
	oauthInfo, err := s.oauthService.ExchangeCode(ctx, input.Provider, input.Code)
	if err != nil {
		return nil, fmt.Errorf("oauth exchange failed: %w", err)
	}

	// Find or create user from OAuth info
	user, err := s.oauthService.FindOrCreateUser(oauthInfo)
	if err != nil {
		return nil, fmt.Errorf("oauth user creation failed: %w", err)
	}

	// Determine if this is a new user
	isNewUser := user.SignInCount == 0

	// Get account and generate tokens
	accountID, role, err := s.getUserDefaultAccount(user)
	if err != nil {
		// New OAuth users may not have an account yet
		// Create a default personal account for them
		accountID, role, err = s.createDefaultAccount(user)
		if err != nil {
			return nil, fmt.Errorf("failed to create default account: %w", err)
		}
	}

	tokenPair, err := s.jwtService.GenerateTokenPair(user, accountID, role)
	if err != nil {
		return nil, fmt.Errorf("failed to generate tokens: %w", err)
	}

	if err := s.refreshStore.Store(ctx, user.ID, tokenPair.RefreshToken); err != nil {
		return nil, fmt.Errorf("failed to store refresh token: %w", err)
	}

	user.SignInCount++
	now := time.Now()
	user.LastSignInAt = user.CurrentSignInAt
	user.CurrentSignInAt = &now
	s.db.Save(user)

	return &OAuthLoginOutput{
		User:      user,
		TokenPair: tokenPair,
		AccountID: accountID,
		Role:      role,
		IsNewUser: isNewUser,
	}, nil
}

// --- Internal Helpers ---

// AccountUser represents the join between User and Account (many-to-many).
// Ref: Chatwoot AccountUser model (role assignment per account).
type AccountUser struct {
	ID        uint   `gorm:"primaryKey"`
	UserID    uint   `gorm:"not null;index"`
	AccountID uint   `gorm:"not null;index"`
	Role      string `gorm:"size:50;default:agent"` // agent/administrator/custom_role_id
}

func (AccountUser) TableName() string { return "account_users" }

// getUserDefaultAccount finds the user's first active account and role.
func (s *AuthService) getUserDefaultAccount(user *model.User) (uint, string, error) {
	var accountUser AccountUser
	if err := s.db.Where("user_id = ?", user.ID).Order("id ASC").First(&accountUser).Error; err != nil {
		if err == gorm.ErrRecordNotFound {
			return 0, "", fmt.Errorf("user has no account")
		}
		return 0, "", err
	}
	return accountUser.AccountID, accountUser.Role, nil
}

// createDefaultAccount creates a personal account for a new user.
func (s *AuthService) createDefaultAccount(user *model.User) (uint, string, error) {
	// Create account
	account := &model.Account{
		Name:   user.Name + "'s Account",
		Status: "active",
	}
	if err := s.db.Create(account).Error; err != nil {
		return 0, "", fmt.Errorf("failed to create account: %w", err)
	}

	// Create account-user join with administrator role
	accountUser := &AccountUser{
		UserID:    user.ID,
		AccountID: account.ID,
		Role:      "administrator",
	}
	if err := s.db.Create(accountUser).Error; err != nil {
		return 0, "", fmt.Errorf("failed to create account_user: %w", err)
	}

	return account.ID, "administrator", nil
}