feat: add assignment service

app/services/auto_assignment/assignment_service.rb

@@ -0,0 +1,99 @@
+class AutoAssignment::AssignmentService
+  pattr_initialize [:inbox!]
+
+  def perform_for_conversation(conversation)
+    return false unless assignable?(conversation)
+
+    agent = find_available_agent
+    return false unless agent
+
+    assign_conversation(conversation, agent)
+  end
+
+  def perform_bulk_assignment(limit: 100)
+    return 0 unless inbox.enable_auto_assignment?
+
+    assigned_count = 0
+
+    unassigned_conversations(limit).find_each do |conversation|
+      assigned_count += 1 if perform_for_conversation(conversation)
+    end
+
+    assigned_count
+  end
+
+  private
+
+  def assignable?(conversation)
+    inbox.enable_auto_assignment? &&
+      conversation.status == 'open' &&
+      conversation.assignee_id.nil?
+  end
+
+  def unassigned_conversations(limit)
+    scope = inbox.conversations.unassigned.open
+
+    # Apply conversation priority from config
+    scope = apply_conversation_priority(scope)
+    scope.limit(limit)
+  end
+
+  def apply_conversation_priority(scope)
+    case assignment_config['conversation_priority']
+    when 'longest_waiting'
+      scope.order(last_activity_at: :asc, created_at: :asc)
+    else
+      scope.order(created_at: :asc)
+    end
+  end
+
+  def find_available_agent
+    agents = filter_agents_by_rate_limit(inbox.available_agents)
+    return nil if agents.empty?
+
+    round_robin_selector.select_agent(agents)
+  end
+
+  def filter_agents_by_rate_limit(agents)
+    agents.select do |agent_member|
+      rate_limiter = build_rate_limiter(agent_member.user)
+      rate_limiter.within_limit?
+    end
+  end
+
+  def assign_conversation(conversation, agent)
+    conversation.update!(assignee: agent)
+
+    rate_limiter = build_rate_limiter(agent)
+    rate_limiter.track_assignment(conversation)
+
+    dispatch_assignment_event(conversation, agent)
+    true
+  rescue ActiveRecord::RecordInvalid => e
+    Rails.logger.error "AutoAssignment failed for conversation #{conversation.id}: #{e.message}"
+    false
+  end
+
+  def dispatch_assignment_event(conversation, agent)
+    Rails.configuration.dispatcher.dispatch(
+      Events::Types::ASSIGNEE_CHANGED,
+      Time.zone.now,
+      conversation: conversation,
+      user: agent
+    )
+  end
+
+  def build_rate_limiter(agent)
+    AutoAssignment::RateLimiter.new(inbox: inbox, agent: agent)
+  end
+
+  def round_robin_selector
+    @round_robin_selector ||= AutoAssignment::RoundRobinSelector.new(inbox: inbox)
+  end
+
+  def assignment_config
+    @assignment_config ||= inbox.auto_assignment_config || {}
+  end
+end
+
+AutoAssignment::AssignmentService.prepend_mod_with('AutoAssignment::AssignmentService')

app/services/auto_assignment/rate_limiter.rb

@@ -0,0 +1,49 @@
+class AutoAssignment::RateLimiter
+  pattr_initialize [:inbox!, :agent!]
+
+  def within_limit?
+    return true unless enabled?
+
+    current_count < limit
+  end
+
+  def track_assignment(conversation)
+    return unless enabled?
+
+    assignment_key = build_assignment_key(conversation.id)
+    Redis::Alfred.set(assignment_key, conversation.id.to_s, ex: window)
+  end
+
+  def current_count
+    return 0 unless enabled?
+
+    pattern = assignment_key_pattern
+    Redis::Alfred.keys_count(pattern)
+  end
+
+  private
+
+  def enabled?
+    limit.present? && limit.positive?
+  end
+
+  def limit
+    config['fair_distribution_limit']&.to_i
+  end
+
+  def window
+    config['fair_distribution_window']&.to_i || 3600
+  end
+
+  def config
+    @config ||= inbox.auto_assignment_config || {}
+  end
+
+  def assignment_key_pattern
+    "assignment:#{inbox.id}:agent:#{agent.id}:*"
+  end
+
+  def build_assignment_key(conversation_id)
+    "assignment:#{inbox.id}:agent:#{agent.id}:conversation:#{conversation_id}"
+  end
+end

app/services/auto_assignment/round_robin_selector.rb

@@ -0,0 +1,16 @@
+class AutoAssignment::RoundRobinSelector
+  pattr_initialize [:inbox!]
+
+  def select_agent(available_agents)
+    return nil if available_agents.empty?
+
+    agent_user_ids = available_agents.map(&:user_id).map(&:to_s)
+    round_robin_service.available_agent(allowed_agent_ids: agent_user_ids)
+  end
+
+  private
+
+  def round_robin_service
+    @round_robin_service ||= AutoAssignment::InboxRoundRobinService.new(inbox: inbox)
+  end
+end