package session

import (
	"context"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"fmt"
	"time"

	"github.com/jackc/pgx/v5/pgxpool"
	"github.com/redis/go-redis/v9"
)

// Session represents a Virtual Banker session
type Session struct {
	ID             string
	TenantID       string
	UserID         string
	EphemeralToken string
	Config         *TenantConfig
	CreatedAt      time.Time
	ExpiresAt      time.Time
	LastActivityAt time.Time
}

// TenantConfig holds tenant-specific configuration
type TenantConfig struct {
	Theme         map[string]interface{} `json:"theme"`
	AvatarEnabled bool                   `json:"avatar_enabled"`
	Greeting      string                 `json:"greeting"`
	AllowedTools  []string               `json:"allowed_tools"`
	Policy        *PolicyConfig          `json:"policy"`
}

// PolicyConfig holds policy settings
type PolicyConfig struct {
	MaxSessionDuration time.Duration `json:"max_session_duration"`
	RateLimitPerMinute int           `json:"rate_limit_per_minute"`
	RequireConsent     bool          `json:"require_consent"`
}

// Manager manages sessions
type Manager struct {
	db    *pgxpool.Pool
	redis *redis.Client
}

// NewManager creates a new session manager
func NewManager(db *pgxpool.Pool, redisClient *redis.Client) *Manager {
	return &Manager{
		db:    db,
		redis: redisClient,
	}
}

// CreateSession creates a new session
func (m *Manager) CreateSession(ctx context.Context, tenantID, userID string, authAssertion string) (*Session, error) {
	// Validate JWT/auth assertion (simplified - should validate with tenant JWKs)
	if authAssertion == "" {
		return nil, errors.New("auth assertion required")
	}

	// Load tenant config
	config, err := m.loadTenantConfig(ctx, tenantID)
	if err != nil {
		return nil, fmt.Errorf("failed to load tenant config: %w", err)
	}

	// Generate session ID
	sessionID, err := generateSessionID()
	if err != nil {
		return nil, fmt.Errorf("failed to generate session ID: %w", err)
	}

	// Generate ephemeral token
	ephemeralToken, err := generateEphemeralToken()
	if err != nil {
		return nil, fmt.Errorf("failed to generate ephemeral token: %w", err)
	}

	now := time.Now()
	sessionDuration := config.Policy.MaxSessionDuration
	if sessionDuration == 0 {
		sessionDuration = 30 * time.Minute // default
	}

	session := &Session{
		ID:             sessionID,
		TenantID:       tenantID,
		UserID:         userID,
		EphemeralToken: ephemeralToken,
		Config:         config,
		CreatedAt:      now,
		ExpiresAt:      now.Add(sessionDuration),
		LastActivityAt: now,
	}

	// Save to database
	if err := m.saveSessionToDB(ctx, session); err != nil {
		return nil, fmt.Errorf("failed to save session: %w", err)
	}

	// Cache in Redis
	if err := m.cacheSession(ctx, session); err != nil {
		return nil, fmt.Errorf("failed to cache session: %w", err)
	}

	return session, nil
}

// GetSession retrieves a session by ID
func (m *Manager) GetSession(ctx context.Context, sessionID string) (*Session, error) {
	// Try Redis first
	session, err := m.getSessionFromCache(ctx, sessionID)
	if err == nil && session != nil {
		return session, nil
	}

	// Fallback to database
	session, err = m.getSessionFromDB(ctx, sessionID)
	if err != nil {
		return nil, fmt.Errorf("session not found: %w", err)
	}

	// Cache it
	_ = m.cacheSession(ctx, session)

	return session, nil
}

// RefreshToken refreshes the ephemeral token for a session
func (m *Manager) RefreshToken(ctx context.Context, sessionID string) (string, error) {
	session, err := m.GetSession(ctx, sessionID)
	if err != nil {
		return "", err
	}

	// Check if session is expired
	if time.Now().After(session.ExpiresAt) {
		return "", errors.New("session expired")
	}

	// Generate new token
	newToken, err := generateEphemeralToken()
	if err != nil {
		return "", fmt.Errorf("failed to generate token: %w", err)
	}

	session.EphemeralToken = newToken
	session.LastActivityAt = time.Now()

	// Update in database and cache
	if err := m.saveSessionToDB(ctx, session); err != nil {
		return "", fmt.Errorf("failed to update session: %w", err)
	}
	_ = m.cacheSession(ctx, session)

	return newToken, nil
}

// EndSession ends a session
func (m *Manager) EndSession(ctx context.Context, sessionID string) error {
	// Remove from Redis
	_ = m.redis.Del(ctx, fmt.Sprintf("session:%s", sessionID))

	// Mark as ended in database
	query := `UPDATE sessions SET ended_at = $1 WHERE id = $2`
	_, err := m.db.Exec(ctx, query, time.Now(), sessionID)
	return err
}

// loadTenantConfig loads tenant configuration
func (m *Manager) loadTenantConfig(ctx context.Context, tenantID string) (*TenantConfig, error) {
	query := `
		SELECT theme, avatar_enabled, greeting, allowed_tools, policy
		FROM tenants
		WHERE id = $1
	`

	var config TenantConfig
	var themeJSON, policyJSON []byte
	var allowedToolsJSON []byte

	err := m.db.QueryRow(ctx, query, tenantID).Scan(
		&themeJSON,
		&config.AvatarEnabled,
		&config.Greeting,
		&allowedToolsJSON,
		&policyJSON,
	)
	if err != nil {
		// Return default config if tenant not found
		return &TenantConfig{
			Theme:         map[string]interface{}{"primaryColor": "#0066cc"},
			AvatarEnabled: true,
			Greeting:      "Hello! How can I help you today?",
			AllowedTools:  []string{},
			Policy: &PolicyConfig{
				MaxSessionDuration: 30 * time.Minute,
				RateLimitPerMinute: 10,
				RequireConsent:     true,
			},
		}, nil
	}

	// Parse JSON fields (simplified - should use json.Unmarshal)
	// For now, return default with basic parsing
	config.Policy = &PolicyConfig{
		MaxSessionDuration: 30 * time.Minute,
		RateLimitPerMinute: 10,
		RequireConsent:     true,
	}

	return &config, nil
}

// saveSessionToDB saves session to database
func (m *Manager) saveSessionToDB(ctx context.Context, session *Session) error {
	query := `
		INSERT INTO sessions (id, tenant_id, user_id, ephemeral_token, created_at, expires_at, last_activity_at)
		VALUES ($1, $2, $3, $4, $5, $6, $7)
		ON CONFLICT (id) DO UPDATE SET
			ephemeral_token = $4,
			last_activity_at = $7
	`

	_, err := m.db.Exec(ctx, query,
		session.ID,
		session.TenantID,
		session.UserID,
		session.EphemeralToken,
		session.CreatedAt,
		session.ExpiresAt,
		session.LastActivityAt,
	)
	return err
}

// getSessionFromDB retrieves session from database
func (m *Manager) getSessionFromDB(ctx context.Context, sessionID string) (*Session, error) {
	query := `
		SELECT id, tenant_id, user_id, ephemeral_token, created_at, expires_at, last_activity_at
		FROM sessions
		WHERE id = $1 AND ended_at IS NULL
	`

	var session Session
	err := m.db.QueryRow(ctx, query, sessionID).Scan(
		&session.ID,
		&session.TenantID,
		&session.UserID,
		&session.EphemeralToken,
		&session.CreatedAt,
		&session.ExpiresAt,
		&session.LastActivityAt,
	)
	if err != nil {
		return nil, err
	}

	// Load config
	config, err := m.loadTenantConfig(ctx, session.TenantID)
	if err != nil {
		return nil, err
	}
	session.Config = config

	return &session, nil
}

// cacheSession caches session in Redis
func (m *Manager) cacheSession(ctx context.Context, session *Session) error {
	key := fmt.Sprintf("session:%s", session.ID)
	ttl := time.Until(session.ExpiresAt)
	if ttl <= 0 {
		return nil
	}

	// Store as JSON (simplified - should serialize properly)
	return m.redis.Set(ctx, key, session.ID, ttl).Err()
}

// getSessionFromCache retrieves session from Redis cache
func (m *Manager) getSessionFromCache(ctx context.Context, sessionID string) (*Session, error) {
	key := fmt.Sprintf("session:%s", sessionID)
	val, err := m.redis.Get(ctx, key).Result()
	if err != nil {
		return nil, err
	}

	if val != sessionID {
		return nil, errors.New("cache mismatch")
	}

	// If cached, fetch full session from DB
	return m.getSessionFromDB(ctx, sessionID)
}

// generateSessionID generates a unique session ID
func generateSessionID() (string, error) {
	b := make([]byte, 16)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return base64.URLEncoding.EncodeToString(b), nil
}

// generateEphemeralToken generates an ephemeral token
func generateEphemeralToken() (string, error) {
	b := make([]byte, 32)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return base64.URLEncoding.EncodeToString(b), nil
}