gochat/backend/internal/autoassignment/service.go

package autoassignment

// AssignmentService provides the core auto-assignment logic.
//
// Reference: Chatwoot AutoAssignment pattern
//   - AssignmentService: bulk assigns conversations in an inbox.
//     Finds unassigned open conversations, filters by team and rate limit,
//     then uses RoundRobinSelector.
//   - AgentAssignmentService: assigns a specific conversation.
//     Intersects online agents with allowed agents, then round-robin.
//
// In gochat, we combine both into a single AssignmentService that handles:
//   - Bulk assignment of unassigned conversations in an inbox
//   - Single conversation assignment for a specific conversation
//   - Rate limiting per agent via RateLimiter

import (
	"context"
	"errors"
	"fmt"

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

// AssignmentService handles auto-assignment of conversations to agents.
type AssignmentService struct {
	db          *gorm.DB
	redis       *redis.Client
	roundRobin  *RoundRobinSelector
	lowestLoad  *LowestLoadSelector
	rateLimiter *RateLimiter
}

// NewAssignmentService creates a new AssignmentService.
func NewAssignmentService(db *gorm.DB, rdb *redis.Client) *AssignmentService {
	rr := NewRoundRobinSelector(rdb)
	ll := NewLowestLoadSelector(db)
	rl := NewRateLimiter(rdb)
	return &AssignmentService{
		db:          db,
		redis:       rdb,
		roundRobin:  rr,
		lowestLoad:  ll,
		rateLimiter: rl,
	}
}

// AssignUnassignedConversations bulk assigns all unassigned open conversations
// in the given inbox.
// Reference: Chatwoot AssignmentService.assign_unassigned_conversations
//
// Steps:
//  1. Find all unassigned open conversations for the inbox
//  2. Get the inbox's assignment policy and rate limits
//  3. Get the list of eligible agents (online + members of the inbox)
//  4. For each conversation, select an agent via round-robin + rate limit
//  5. Assign the conversation to the selected agent
func (s *AssignmentService) AssignUnassignedConversations(ctx context.Context, inboxID uint, accountID uint) ([]uint, error) {
	// Step 1: Check if auto-assignment is enabled for this inbox
	inbox, err := s.getInbox(ctx, inboxID)
	if err != nil {
		return nil, fmt.Errorf("get inbox: %w", err)
	}
	if !inbox.EnableAutoAssignment {
		applogger.L().Infof("auto-assignment disabled for inbox %d", inboxID)
		return nil, nil
	}

	// Step 2: Find unassigned open conversations
	conversations, err := s.findUnassignedConversations(ctx, inboxID, accountID)
	if err != nil {
		return nil, fmt.Errorf("find unassigned: %w", err)
	}
	if len(conversations) == 0 {
		return nil, nil
	}

	// Step 3: Get eligible agents
	agents, err := s.getEligibleAgents(ctx, inboxID, accountID)
	if err != nil {
		return nil, fmt.Errorf("get eligible agents: %w", err)
	}
	if len(agents) == 0 {
		applogger.L().Infof("no eligible agents for inbox %d", inboxID)
		return nil, nil
	}

	// Step 4: Get assignment policy and limits
	accountPolicy := s.getAccountPolicy(ctx, accountID)
	inboxPolicy := s.getInboxPolicy(ctx, inboxID)
	policy := EffectivePolicy(accountPolicy, inboxPolicy)
	limit := EffectiveLimit(accountPolicy, inboxPolicy)
	window := EffectiveWindow(accountPolicy, inboxPolicy)

	// Step 5: Reset round-robin queue if members changed
	s.roundRobin.SyncQueue(ctx, inboxID, agents)

	// Step 6: Assign each conversation
	assignedIDs := make([]uint, 0)
	for _, conv := range conversations {
		agentID, err := s.selectAgent(ctx, inboxID, agents, policy, limit, window)
		if err != nil {
			applogger.L().Warnf("failed to select agent for conversation %d: %v", conv.ID, err)
			continue
		}
		if agentID == 0 {
			// All agents hit rate limit, skip
			continue
		}

		if err := s.assignConversation(ctx, conv.ID, agentID); err != nil {
			applogger.L().Warnf("failed to assign conversation %d to agent %d: %v", conv.ID, agentID, err)
			continue
		}

		// Track rate limit
		s.rateLimiter.Increment(ctx, inboxID, agentID, window)

		assignedIDs = append(assignedIDs, conv.ID)
	}

	applogger.L().Infof("auto-assigned %d conversations in inbox %d", len(assignedIDs), inboxID)
	return assignedIDs, nil
}

// AssignConversation assigns a specific conversation to an agent.
// Reference: Chatwoot AgentAssignmentService.assign_conversation
//
// Steps:
//  1. Get eligible agents for the conversation's inbox
//  2. Select an agent via round-robin + rate limit
//  3. Assign the conversation
func (s *AssignmentService) AssignConversation(ctx context.Context, conversationID uint, inboxID uint, accountID uint) (uint, error) {
	// Check if auto-assignment is enabled
	inbox, err := s.getInbox(ctx, inboxID)
	if err != nil {
		return 0, fmt.Errorf("get inbox: %w", err)
	}
	if !inbox.EnableAutoAssignment {
		return 0, nil
	}

	// Get eligible agents
	agents, err := s.getEligibleAgents(ctx, inboxID, accountID)
	if err != nil {
		return 0, fmt.Errorf("get eligible agents: %w", err)
	}
	if len(agents) == 0 {
		return 0, nil
	}

	// Get policy and limits
	accountPolicy := s.getAccountPolicy(ctx, accountID)
	inboxPolicy := s.getInboxPolicy(ctx, inboxID)
	policy := EffectivePolicy(accountPolicy, inboxPolicy)
	limit := EffectiveLimit(accountPolicy, inboxPolicy)
	window := EffectiveWindow(accountPolicy, inboxPolicy)

	// Sync round-robin queue
	s.roundRobin.SyncQueue(ctx, inboxID, agents)

	// Select agent
	agentID, err := s.selectAgent(ctx, inboxID, agents, policy, limit, window)
	if err != nil {
		return 0, fmt.Errorf("select agent: %w", err)
	}
	if agentID == 0 {
		return 0, nil // all agents at rate limit
	}

	// Assign conversation
	if err := s.assignConversation(ctx, conversationID, agentID); err != nil {
		return 0, fmt.Errorf("assign conversation: %w", err)
	}

	// Track rate limit
	s.rateLimiter.Increment(ctx, inboxID, agentID, window)

	return agentID, nil
}

// selectAgent picks an agent for assignment using the selected policy
// and rate limiting.
func (s *AssignmentService) selectAgent(ctx context.Context, inboxID uint, agents []uint, policy AssignmentPolicyType, limit int, window int) (uint, error) {
	switch policy {
	case PolicyRoundRobin:
		return s.selectRoundRobin(ctx, inboxID, agents, limit, window)
	case PolicyLowestLoad:
		return s.selectLowestLoad(ctx, inboxID, agents, limit, window)
	case PolicyLongestWaiting:
		return s.selectLongestWaiting(ctx, inboxID, agents, limit, window)
	default:
		return s.selectRoundRobin(ctx, inboxID, agents, limit, window)
	}
}

// selectRoundRobin selects an agent via round-robin, respecting rate limits.
func (s *AssignmentService) selectRoundRobin(ctx context.Context, inboxID uint, agents []uint, limit int, window int) (uint, error) {
	// Try each agent in round-robin order
	for i := 0; i < len(agents); i++ {
		agentID, err := s.roundRobin.Next(ctx, inboxID)
		if err != nil || agentID == 0 {
			continue
		}

		// Check rate limit
		if s.rateLimiter.IsAllowed(ctx, inboxID, agentID, limit, window) {
			return agentID, nil
		}
		// Agent is at rate limit, skip and try next
	}

	// All agents at rate limit
	return 0, nil
}

// selectLongestWaiting selects the agent with the longest idle time.
// This is a simplified implementation — a full version would track
// idle time in Redis. For now, we fall back to round-robin.
func (s *AssignmentService) selectLongestWaiting(ctx context.Context, inboxID uint, agents []uint, limit int, window int) (uint, error) {
	// TODO: Implement longest-waiting tracking in Redis
	// For now, delegate to round-robin with rate limit checking
	return s.selectRoundRobin(ctx, inboxID, agents, limit, window)
}

// selectLowestLoad selects the agent with the fewest open conversations,
// respecting rate limits.
func (s *AssignmentService) selectLowestLoad(ctx context.Context, inboxID uint, agents []uint, limit int, window int) (uint, error) {
	agentID, err := s.lowestLoad.Select(ctx, inboxID, agents)
	if err != nil {
		return 0, fmt.Errorf("lowest load select: %w", err)
	}

	// Check rate limit for the selected agent
	if s.rateLimiter.IsAllowed(ctx, inboxID, agentID, limit, window) {
		return agentID, nil
	}

	// Selected agent is at rate limit — fall back to round-robin
	applogger.L().Debugf("lowest_load: agent %d at rate limit, falling back to round-robin", agentID)
	return s.selectRoundRobin(ctx, inboxID, agents, limit, window)
}

// findUnassignedConversations returns all open conversations in the inbox
// that have no assignee.
func (s *AssignmentService) findUnassignedConversations(ctx context.Context, inboxID uint, accountID uint) ([]model.Conversation, error) {
	var conversations []model.Conversation
	err := s.db.WithContext(ctx).
		Where("inbox_id = ? AND account_id = ? AND status = ? AND assignee_id IS NULL",
			inboxID, accountID, model.ConversationStatusOpen).
		Find(&conversations).Error
	return conversations, err
}

// getEligibleAgents returns agents that are:
//   - Members of the inbox (via inbox_members table)
//   - Online/available (via user available field)
func (s *AssignmentService) getEligibleAgents(ctx context.Context, inboxID uint, accountID uint) ([]uint, error) {
	var agentIDs []uint
	err := s.db.WithContext(ctx).
		Table("inbox_members").
		Select("inbox_members.user_id").
		Joins("JOIN users ON users.id = inbox_members.user_id").
		Where("inbox_members.inbox_id = ? AND users.available = ? AND users.active = ?",
			inboxID, true, true).
		Pluck("inbox_members.user_id", &agentIDs).Error
	if err != nil {
		return nil, err
	}

	availableIDs := make([]uint, 0, len(agentIDs))
	for _, agentID := range agentIDs {
		hasCapacity, err := s.agentHasInboxCapacity(ctx, accountID, inboxID, agentID, 0)
		if err != nil {
			return nil, err
		}
		if hasCapacity {
			availableIDs = append(availableIDs, agentID)
		}
	}
	return availableIDs, nil
}

func (s *AssignmentService) agentHasInboxCapacity(ctx context.Context, accountID, inboxID, agentID, excludeConversationID uint) (bool, error) {
	var accountUser model.AccountUser
	if err := s.db.WithContext(ctx).
		Where("account_id = ? AND user_id = ?", accountID, agentID).
		First(&accountUser).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return false, nil
		}
		return false, fmt.Errorf("load account user capacity policy: %w", err)
	}
	if accountUser.AgentCapacityPolicyID == nil {
		return true, nil
	}

	var limit model.InboxCapacityLimit
	if err := s.db.WithContext(ctx).
		Where("agent_capacity_policy_id = ? AND inbox_id = ?", *accountUser.AgentCapacityPolicyID, inboxID).
		First(&limit).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return true, nil
		}
		return false, fmt.Errorf("load inbox capacity limit: %w", err)
	}

	q := s.db.WithContext(ctx).Model(&model.Conversation{}).
		Where("account_id = ? AND inbox_id = ? AND assignee_id = ? AND status = ?", accountID, inboxID, agentID, model.ConversationStatusOpen)
	if excludeConversationID != 0 {
		q = q.Where("id <> ?", excludeConversationID)
	}
	var assignedOpenCount int64
	if err := q.Count(&assignedOpenCount).Error; err != nil {
		return false, fmt.Errorf("count assigned open conversations: %w", err)
	}
	return assignedOpenCount < int64(limit.ConversationLimit), nil
}

// getInbox fetches the inbox by ID.
func (s *AssignmentService) getInbox(ctx context.Context, inboxID uint) (*model.Inbox, error) {
	var inbox model.Inbox
	if err := s.db.WithContext(ctx).First(&inbox, inboxID).Error; err != nil {
		return nil, err
	}
	return &inbox, nil
}

// getAccountPolicy returns the assignment policy for an account.
// Returns nil if no policy is configured.
func (s *AssignmentService) getAccountPolicy(ctx context.Context, accountID uint) *AssignmentPolicy {
	var policy AssignmentPolicy
	if err := s.db.WithContext(ctx).
		Where("account_id = ? AND active = ?", accountID, true).
		First(&policy).Error; err != nil {
		return nil // no policy configured
	}
	return &policy
}

// getInboxPolicy returns the assignment policy override for an inbox.
// Returns nil if no inbox-specific policy is configured.
func (s *AssignmentService) getInboxPolicy(ctx context.Context, inboxID uint) *InboxAssignmentPolicy {
	var policy InboxAssignmentPolicy
	if err := s.db.WithContext(ctx).
		Where("inbox_id = ? AND active = ?", inboxID, true).
		First(&policy).Error; err != nil {
		return nil // no inbox-specific policy
	}
	return &policy
}

// assignConversation sets the assignee_id on a conversation.
func (s *AssignmentService) assignConversation(ctx context.Context, conversationID uint, agentID uint) error {
	return s.db.WithContext(ctx).
		Model(&model.Conversation{}).
		Where("id = ?", conversationID).
		Update("assignee_id", agentID).Error
}