package auth

// Reference: M13 §4 — Unified SSO Middleware + Provider Router
// Provides a single entry point for enterprise SSO authentication that routes
// requests to the correct provider (SAML, LDAP, OIDC) based on the account's
// configuration. This is the "glue" that ties all enterprise auth providers together.
//
// Enterprise feature: GoChat's unified SSO middleware is a multi-tenant routing layer
// that Chatwoot does not offer. While Chatwoot only supports SAML (and basic OAuth),
// GoChat provides LDAP, OIDC, and SAML with per-account isolation, enabling enterprise
// customers to choose the identity provider that fits their infrastructure.
//
// Flow:
// 1. Client sends auth request to /api/v1/sso/authenticate or /api/v1/sso/callback
// 2. SSO middleware resolves the account's configured provider (SAML, LDAP, OIDC)
// 3. Middleware delegates to the appropriate service (SAMLService, LDAPService, OIDCService)
// 4. After successful authentication, middleware:
//    a. Auto-provisions GoChat user if configured
//    b. Maps external groups/roles to GoChat roles
//    c. Creates SSO session in Redis
//    d. Issues JWT token for API access
//
// Provider resolution priority (per-account):
// - If account has active SAML settings → SAML
// - If account has active OIDC settings → OIDC
// - If account has active LDAP settings → LDAP
// - If multiple providers are active, the first configured wins (SAML > OIDC > LDAP)
// - Override via query param: ?provider=ldap or ?provider=oidc

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/golang-jwt/jwt/v5"

	"github.com/gochat/gochat/internal/config"
	"github.com/gochat/gochat/internal/model"
	applogger "github.com/gochat/gochat/pkg/logger"
	"github.com/redis/go-redis/v9"
	"gorm.io/gorm"
)

// SSOProviderType identifies the enterprise SSO provider.
type SSOProviderType string

const (
	SSOProviderSAML SSOProviderType = "saml"
	SSOProviderLDAP SSOProviderType = "ldap"
	SSOProviderOIDC SSOProviderType = "oidc"
)

// SSOAuthResult holds the result of a unified SSO authentication attempt.
type SSOAuthResult struct {
	Provider      SSOProviderType // which provider authenticated the user
	UserID        uint            // GoChat user ID (0 if auto-provision needed)
	AccountID     uint            // account context
	Email         string          // user email from IdP
	Name          string          // user display name from IdP
	FirstName     string          // first name (if available)
	LastName      string          // last name (if available)
	Subject       string          // unique identifier from IdP (NameID, DN, sub)
	Role          string          // mapped GoChat role
	Groups        []string        // groups from IdP (for audit/logging)
	AutoProvision bool            // whether the user needs auto-provisioning
}

// SSOMiddleware provides unified SSO routing and post-authentication processing.
type SSOMiddleware struct {
	db          *gorm.DB
	rdb         redis.Cmdable
	cfg         *config.Config
	samlService *SAMLService
	ldapService *LDAPService
	oidcService *OIDCService
	jwtSecret   string
	jwtExpiry   time.Duration
}

// NewSSOMiddleware creates the unified SSO middleware.
func NewSSOMiddleware(
	db *gorm.DB,
	rdb redis.Cmdable,
	cfg *config.Config,
	samlSvc *SAMLService,
	ldapSvc *LDAPService,
	oidcSvc *OIDCService,
) *SSOMiddleware {
	jwtExpiry := 24 * time.Hour // default 24h JWT expiry
	if cfg.Session.ExpirySeconds > 0 {
		jwtExpiry = time.Duration(cfg.Session.ExpirySeconds) * time.Second
	}

	return &SSOMiddleware{
		db:          db,
		rdb:         rdb,
		cfg:         cfg,
		samlService: samlSvc,
		ldapService: ldapSvc,
		oidcService: oidcSvc,
		jwtSecret:   cfg.JWT.Secret,
		jwtExpiry:   jwtExpiry,
	}
}

// ResolveProvider determines which SSO provider is active for a given account.
// Returns the provider type, or empty string if no provider is configured.
// Optional override via providerHint query parameter.
func (m *SSOMiddleware) ResolveProvider(ctx context.Context, accountID uint, providerHint string) (SSOProviderType, error) {
	// If an explicit provider hint is given, validate it's active for this account
	if providerHint != "" {
		pt := SSOProviderType(strings.ToLower(providerHint))
		active, err := m.isProviderActive(ctx, accountID, pt)
		if err != nil {
			return "", fmt.Errorf("provider %s check failed: %w", pt, err)
		}
		if !active {
			return "", fmt.Errorf("provider %s is not active for account %d", pt, accountID)
		}
		return pt, nil
	}

	// Priority: SAML > OIDC > LDAP (SAML is the most mature enterprise SSO protocol)
	providers := []SSOProviderType{SSOProviderSAML, SSOProviderOIDC, SSOProviderLDAP}
	for _, pt := range providers {
		active, err := m.isProviderActive(ctx, accountID, pt)
		if err != nil {
			applogger.L().Warnf("SSO provider check failed (account=%d, provider=%s): %v", accountID, pt, err)
			continue
		}
		if active {
			return pt, nil
		}
	}

	return "", fmt.Errorf("no SSO provider configured for account %d", accountID)
}

// isProviderActive checks whether a given SSO provider is active for an account.
func (m *SSOMiddleware) isProviderActive(ctx context.Context, accountID uint, provider SSOProviderType) (bool, error) {
	switch provider {
	case SSOProviderSAML:
		if m.cfg.SAML.Enabled {
			var settings model.AccountSamlSettings
			err := m.db.WithContext(ctx).Where("account_id = ? AND active = ?", accountID, true).First(&settings).Error
			if err == nil {
				return true, nil // per-account SAML is active
			}
			if err == gorm.ErrRecordNotFound {
				return m.cfg.SAML.Enabled, nil // fall back to global
			}
			return false, err
		}
		return false, nil

	case SSOProviderLDAP:
		if m.cfg.LDAP.Enabled {
			var settings model.AccountLDAPSettings
			err := m.db.WithContext(ctx).Where("account_id = ? AND active = ?", accountID, true).First(&settings).Error
			if err == nil {
				return true, nil
			}
			if err == gorm.ErrRecordNotFound {
				return m.cfg.LDAP.Enabled, nil
			}
			return false, err
		}
		return false, nil

	case SSOProviderOIDC:
		if m.cfg.OIDC.Enabled {
			var settings model.AccountOIDCSettings
			err := m.db.WithContext(ctx).Where("account_id = ? AND active = ?", accountID, true).First(&settings).Error
			if err == nil {
				return true, nil
			}
			if err == gorm.ErrRecordNotFound {
				return m.cfg.OIDC.Enabled, nil
			}
			return false, err
		}
		return false, nil

	default:
		return false, fmt.Errorf("unknown SSO provider: %s", provider)
	}
}

// AuthenticateLDAP performs LDAP authentication via the unified SSO middleware.
// Returns SSOAuthResult with user info and provisioning status.
func (m *SSOMiddleware) AuthenticateLDAP(ctx context.Context, accountID uint, username, password string) (*SSOAuthResult, error) {
	if m.ldapService == nil {
		return nil, fmt.Errorf("LDAP service not initialized")
	}

	userInfo, err := m.ldapService.Authenticate(ctx, accountID, username, password)
	if err != nil {
		return nil, fmt.Errorf("LDAP authentication failed: %w", err)
	}

	// Resolve the GoChat user from LDAP attributes
	result := &SSOAuthResult{
		Provider:      SSOProviderLDAP,
		AccountID:     accountID,
		Email:         userInfo.Email,
		Name:          userInfo.DisplayName,
		FirstName:     userInfo.FirstName,
		LastName:      userInfo.LastName,
		Subject:       userInfo.DN, // LDAP DN is the unique identifier
		Groups:        userInfo.Groups,
	}

	// Map LDAP groups to GoChat role
	ldapSettings := m.getLDAPSettings(accountID)
	if ldapSettings != nil {
		result.Role = m.ldapService.MapLDAPGroupsToRoles(ldapSettings, userInfo.Groups)
	} else {
		result.Role = "agent" // default role
	}

	// Look up existing GoChat user by email
	user, err := m.findOrCreateUser(ctx, accountID, userInfo.Email, userInfo.DisplayName, userInfo.DN, "ldap", result.Role)
	if err != nil {
		return nil, fmt.Errorf("failed to resolve GoChat user: %w", err)
	}

	result.UserID = user.ID
	result.AutoProvision = user.ID == 0

	return result, nil
}

// AuthenticateOIDC performs OIDC callback processing via the unified SSO middleware.
// Returns SSOAuthResult with user info and provisioning status.
func (m *SSOMiddleware) AuthenticateOIDC(ctx context.Context, state, code string) (*SSOAuthResult, error) {
	if m.oidcService == nil {
		return nil, fmt.Errorf("OIDC service not initialized")
	}

	oidcUserInfo, oidcState, err := m.oidcService.HandleCallback(ctx, state, code)
	if err != nil {
		return nil, fmt.Errorf("OIDC authentication failed: %w", err)
	}

	result := &SSOAuthResult{
		Provider:      SSOProviderOIDC,
		AccountID:     oidcState.AccountID,
		Email:         oidcUserInfo.Email,
		Name:          oidcUserInfo.Name,
		FirstName:     oidcUserInfo.FirstName,
		LastName:      oidcUserInfo.LastName,
		Subject:       oidcUserInfo.Subject, // OIDC sub claim
		Groups:        oidcUserInfo.Groups,
	}

	// Map OIDC groups to GoChat role
	oidcSettings, _ := m.oidcService.getAccountSettings(oidcState.AccountID)
	if oidcSettings != nil {
		result.Role = m.oidcService.MapOIDCGroupsToRoles(oidcSettings, oidcUserInfo.Groups)
	} else {
		result.Role = "agent"
	}

	// Look up existing GoChat user by email
	user, err := m.findOrCreateUser(ctx, oidcState.AccountID, oidcUserInfo.Email, oidcUserInfo.Name, oidcUserInfo.Subject, "oidc", result.Role)
	if err != nil {
		return nil, fmt.Errorf("failed to resolve GoChat user: %w", err)
	}

	result.UserID = user.ID
	result.AutoProvision = user.ID == 0

	return result, nil
}

// IssueJWT creates a JWT token for the authenticated SSO user.
func (m *SSOMiddleware) IssueJWT(result *SSOAuthResult) (string, error) {
	if result.UserID == 0 {
		return "", fmt.Errorf("cannot issue JWT for unprovisioned user")
	}

	claims := jwt.MapClaims{
		"user_id":    result.UserID,
		"account_id": result.AccountID,
		"role":       result.Role,
		"provider":   string(result.Provider),
		"subject":    result.Subject,
		"email":      result.Email,
		"iat":        time.Now().Unix(),
		"exp":        time.Now().Add(m.jwtExpiry).Unix(),
	}

	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString([]byte(m.jwtSecret))
}

// CreateSSOSession creates an SSO session in Redis for the authenticated user.
func (m *SSOMiddleware) CreateSSOSession(ctx context.Context, result *SSOAuthResult) (string, error) {
	sessionID, err := generateSSOSessionID()
	if err != nil {
		return "", fmt.Errorf("failed to generate SSO session ID: %w", err)
	}

	sessionData := SSOSessionData{
		SessionID: sessionID,
		UserID:    result.UserID,
		Provider:  string(result.Provider),
		AccountID: result.AccountID,
		Role:      result.Role,
		NameID:    result.Subject,
		CreatedAt: time.Now().Unix(),
		ExpiresAt: time.Now().Add(m.jwtExpiry).Unix(),
	}

	// Store session data in Redis
	sessionJSON, _ := json.Marshal(sessionData)
	key := fmt.Sprintf("sso:session:%s", sessionID)
	if err := m.rdb.Set(ctx, key, sessionJSON, m.jwtExpiry).Err(); err != nil {
		return "", fmt.Errorf("failed to store SSO session: %w", err)
	}

	// Also track user→sessions mapping for SLO (single logout)
	userSessionsKey := fmt.Sprintf("sso:user_sessions:%d", result.UserID)
	m.rdb.SAdd(ctx, userSessionsKey, sessionID)

	applogger.L().Infof("SSO session created (user=%d, account=%d, provider=%s, session=%s)",
		result.UserID, result.AccountID, result.Provider, sessionID)

	return sessionID, nil
}

// --- Gin middleware handler for SSO session validation ---

// SSOSessionValidator returns a gin.HandlerFunc that validates SSO sessions
// from the Authorization header or query parameter.
// This middleware is optional — it supplements the regular JWT AuthMiddleware
// by also checking SSO session validity in Redis.
func (m *SSOMiddleware) SSOSessionValidator() gin.HandlerFunc {
	return func(c *gin.Context) {
		// Get session ID from header or query
		sessionID := c.GetHeader("X-SSO-Session")
		if sessionID == "" {
			sessionID = c.Query("sso_session")
		}

		if sessionID == "" {
			// No SSO session provided — skip SSO validation (regular JWT auth continues)
			c.Next()
			return
		}

		// Validate session in Redis
		key := fmt.Sprintf("sso:session:%s", sessionID)
		val, err := m.rdb.Get(c.Request.Context(), key).Bytes()
		if err != nil {
			if err == redis.Nil {
				c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{
					"error": "SSO session expired or invalid",
				})
				return
			}
			applogger.L().Warnf("SSO session lookup failed: %v", err)
			c.AbortWithStatusJSON(http.StatusInternalServerError, gin.H{
				"error": "SSO session validation failed",
			})
			return
		}

		var sessionData SSOSessionData
		if err := json.Unmarshal(val, &sessionData); err != nil {
			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{
				"error": "SSO session data corrupt",
			})
			return
		}

		// Set SSO session data in gin context for downstream handlers
		c.Set("sso_session", sessionData)
		c.Set("sso_provider", sessionData.Provider)
		c.Set("user_id", sessionData.UserID)
		c.Set("account_id", sessionData.AccountID)
		c.Set("role", sessionData.Role)

		c.Next()
	}
}

// --- Internal helpers ---

// getLDAPSettings loads per-account LDAP settings for the middleware.
func (m *SSOMiddleware) getLDAPSettings(accountID uint) *model.AccountLDAPSettings {
	if m.db == nil {
		return nil
	}
	var settings model.AccountLDAPSettings
	err := m.db.Where("account_id = ? AND active = ?", accountID, true).First(&settings).Error
	if err != nil {
		if err == gorm.ErrRecordNotFound {
			// Return nil — LDAPService.Authenticate will use global defaults
			return nil
		}
		applogger.L().Warnf("LDAP settings lookup failed (account=%d): %v", accountID, err)
		return nil
	}
	return &settings
}

// findOrCreateUser looks up an existing GoChat user by email/provider/uid,
// or creates a new user if auto-provision is enabled.
func (m *SSOMiddleware) findOrCreateUser(ctx context.Context, accountID uint, email, name, uid, provider, role string) (*model.User, error) {
	if m.db == nil {
		return nil, fmt.Errorf("database not available")
	}

	// 1. Try to find existing user by email
	var user model.User
	err := m.db.WithContext(ctx).Where("email = ?", email).First(&user).Error
	if err == nil {
		// User found — ensure they belong to this account
		m.ensureAccountMembership(ctx, user.ID, accountID, role)
		return &user, nil
	}

	if err != gorm.ErrRecordNotFound {
		return nil, fmt.Errorf("user lookup failed: %w", err)
	}

	// 2. No user found — auto-provision if enabled
	autoProvision := true // default
	switch provider {
	case "ldap":
		settings := m.getLDAPSettings(accountID)
		if settings != nil {
			autoProvision = settings.AutoProvision
		}
	case "oidc":
		if m.oidcService != nil {
			oidcSettings, _ := m.oidcService.getAccountSettings(accountID)
			if oidcSettings != nil {
				autoProvision = oidcSettings.AutoProvision
			}
		}
	case "saml":
		// SAML model has no AutoProvision field — default to true.
		// Role mapping is handled by the SAML service itself.
		autoProvision = true
	}

	if !autoProvision {
		return &model.User{}, fmt.Errorf("user %s not found and auto-provision is disabled", email)
	}

	// 3. Create new user
	newUser := model.User{
		Email:    email,
		Name:     name,
		Provider: provider,
		UID:      uid,
	}

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

	applogger.L().Infof("Auto-provisioned user (id=%d, email=%s, provider=%s)", newUser.ID, email, provider)

	// 4. Add user to account with mapped role
	m.ensureAccountMembership(ctx, newUser.ID, accountID, role)

	return &newUser, nil
}

// ensureAccountMembership ensures a user belongs to the given account with the specified role.
func (m *SSOMiddleware) ensureAccountMembership(ctx context.Context, userID, accountID uint, role string) {
	var accountUser model.AccountUser
	err := m.db.WithContext(ctx).Where("account_id = ? AND user_id = ?", accountID, userID).First(&accountUser).Error
	if err == nil {
		// Already a member — update role if needed
		if accountUser.Role != role {
			m.db.WithContext(ctx).Model(&accountUser).Update("role", role)
		}
		return
	}

	// Not a member yet — add them
	accountUser = model.AccountUser{
		AccountID: accountID,
		UserID:    userID,
		Role:      role,
	}
	if err := m.db.WithContext(ctx).Create(&accountUser).Error; err != nil {
		applogger.L().Warnf("Failed to add user %d to account %d: %v", userID, accountID, err)
	} else {
		applogger.L().Infof("Added user %d to account %d with role %s", userID, accountID, role)
	}
}