feat: Add agent capacity controllers (#12200)

## Linear reference:
https://linear.app/chatwoot/issue/CW-4649/re-imagine-assignments

## Description
This PR introduces the foundation for Assignment V2 system by
implementing agent_capacity and their association with inboxes and
users.

## Type of change

- [ ] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

Test Coverage:
-  Controller specs for assignment policies CRUD operations
-  Enterprise-specific specs for balanced assignment order
-  Model specs for community/enterprise separation

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Pranav <pranav@chatwoot.com>

spec/enterprise/controllers/api/v1/accounts/agent_capacity_policies/inbox_limits_controller_spec.rb

@@ -0,0 +1,80 @@
+require 'rails_helper'
+
+RSpec.describe 'Agent Capacity Policy Inbox Limits API', type: :request do
+  let(:account) { create(:account) }
+  let!(:agent_capacity_policy) { create(:agent_capacity_policy, account: account) }
+  let!(:inbox) { create(:inbox, account: account) }
+  let(:administrator) { create(:user, account: account, role: :administrator) }
+  let(:agent) { create(:user, account: account, role: :agent) }
+
+  describe 'POST /api/v1/accounts/{account.id}/agent_capacity_policies/{policy_id}/inbox_limits' do
+    context 'when not admin' do
+      it 'requires admin role' do
+        post "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}/inbox_limits",
+             params: { inbox_id: inbox.id, conversation_limit: 10 },
+             headers: agent.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when admin' do
+      it 'creates an inbox limit' do
+        post "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}/inbox_limits",
+             params: { inbox_id: inbox.id, conversation_limit: 10 },
+             headers: administrator.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:success)
+        json_response = response.parsed_body
+        expect(json_response['conversation_limit']).to eq(10)
+        expect(json_response['inbox_id']).to eq(inbox.id)
+      end
+
+      it 'prevents duplicate inbox assignments' do
+        create(:inbox_capacity_limit, agent_capacity_policy: agent_capacity_policy, inbox: inbox)
+
+        post "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}/inbox_limits",
+             params: { inbox_id: inbox.id, conversation_limit: 10 },
+             headers: administrator.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response.parsed_body['error']).to eq(I18n.t('agent_capacity_policy.inbox_already_assigned'))
+      end
+    end
+  end
+
+  describe 'PUT /api/v1/accounts/{account.id}/agent_capacity_policies/{policy_id}/inbox_limits/{id}' do
+    let!(:inbox_limit) { create(:inbox_capacity_limit, agent_capacity_policy: agent_capacity_policy, inbox: inbox, conversation_limit: 5) }
+
+    context 'when admin' do
+      it 'updates the inbox limit' do
+        put "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}/inbox_limits/#{inbox_limit.id}",
+            params: { conversation_limit: 15 },
+            headers: administrator.create_new_auth_token,
+            as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(response.parsed_body['conversation_limit']).to eq(15)
+        expect(inbox_limit.reload.conversation_limit).to eq(15)
+      end
+    end
+  end
+
+  describe 'DELETE /api/v1/accounts/{account.id}/agent_capacity_policies/{policy_id}/inbox_limits/{id}' do
+    let!(:inbox_limit) { create(:inbox_capacity_limit, agent_capacity_policy: agent_capacity_policy, inbox: inbox) }
+
+    context 'when admin' do
+      it 'removes the inbox limit' do
+        delete "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}/inbox_limits/#{inbox_limit.id}",
+               headers: administrator.create_new_auth_token,
+               as: :json
+
+        expect(response).to have_http_status(:no_content)
+        expect(agent_capacity_policy.inbox_capacity_limits.find_by(id: inbox_limit.id)).to be_nil
+      end
+    end
+  end
+end

spec/enterprise/controllers/api/v1/accounts/agent_capacity_policies/users_controller_spec.rb

@@ -0,0 +1,66 @@
+require 'rails_helper'
+
+RSpec.describe 'Agent Capacity Policy Users API', type: :request do
+  let(:account) { create(:account) }
+  let!(:agent_capacity_policy) { create(:agent_capacity_policy, account: account) }
+  let!(:user) { create(:user, account: account, role: :agent) }
+  let(:administrator) { create(:user, account: account, role: :administrator) }
+  let(:agent) { create(:user, account: account, role: :agent) }
+
+  describe 'GET /api/v1/accounts/{account.id}/agent_capacity_policies/{policy_id}/users' do
+    context 'when admin' do
+      it 'returns assigned users' do
+        user.account_users.first.update!(agent_capacity_policy: agent_capacity_policy)
+
+        get "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}/users",
+            headers: administrator.create_new_auth_token,
+            as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(response.parsed_body.first['id']).to eq(user.id)
+      end
+    end
+  end
+
+  describe 'POST /api/v1/accounts/{account.id}/agent_capacity_policies/{policy_id}/users' do
+    context 'when not admin' do
+      it 'requires admin role' do
+        post "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}/users",
+             params: { user_id: user.id },
+             headers: agent.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when admin' do
+      it 'assigns user to the policy' do
+        post "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}/users",
+             params: { user_id: user.id },
+             headers: administrator.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(user.account_users.first.reload.agent_capacity_policy).to eq(agent_capacity_policy)
+      end
+    end
+  end
+
+  describe 'DELETE /api/v1/accounts/{account.id}/agent_capacity_policies/{policy_id}/users/{id}' do
+    context 'when admin' do
+      before do
+        user.account_users.first.update!(agent_capacity_policy: agent_capacity_policy)
+      end
+
+      it 'removes user from the policy' do
+        delete "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}/users/#{user.id}",
+               headers: administrator.create_new_auth_token,
+               as: :json
+
+        expect(response).to have_http_status(:ok)
+        expect(user.account_users.first.reload.agent_capacity_policy).to be_nil
+      end
+    end
+  end
+end

spec/enterprise/controllers/api/v1/accounts/agent_capacity_policies_controller_spec.rb

@@ -0,0 +1,202 @@
+require 'rails_helper'
+
+RSpec.describe 'Agent Capacity Policies API', type: :request do
+  let(:account) { create(:account) }
+  let!(:agent_capacity_policy) { create(:agent_capacity_policy, account: account) }
+
+  describe 'GET /api/v1/accounts/{account.id}/agent_capacity_policies' do
+    context 'when it is an unauthenticated user' do
+      it 'returns unauthorized' do
+        get "/api/v1/accounts/#{account.id}/agent_capacity_policies"
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when it is an authenticated agent' do
+      let(:agent) { create(:user, account: account, role: :agent) }
+
+      it 'returns unauthorized for agent' do
+        get "/api/v1/accounts/#{account.id}/agent_capacity_policies",
+            headers: agent.create_new_auth_token,
+            as: :json
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when it is an administrator' do
+      let(:administrator) { create(:user, account: account, role: :administrator) }
+
+      it 'returns all agent capacity policies' do
+        get "/api/v1/accounts/#{account.id}/agent_capacity_policies",
+            headers: administrator.create_new_auth_token,
+            as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(response.parsed_body.first['id']).to eq(agent_capacity_policy.id)
+      end
+    end
+  end
+
+  describe 'GET /api/v1/accounts/{account.id}/agent_capacity_policies/{id}' do
+    context 'when it is an unauthenticated user' do
+      it 'returns unauthorized' do
+        get "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}"
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when it is an authenticated agent' do
+      let(:agent) { create(:user, account: account, role: :agent) }
+
+      it 'returns unauthorized for agent' do
+        get "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}",
+            headers: agent.create_new_auth_token,
+            as: :json
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when it is an administrator' do
+      let(:administrator) { create(:user, account: account, role: :administrator) }
+
+      it 'returns the agent capacity policy' do
+        get "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}",
+            headers: administrator.create_new_auth_token,
+            as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(response.parsed_body['id']).to eq(agent_capacity_policy.id)
+      end
+    end
+  end
+
+  describe 'POST /api/v1/accounts/{account.id}/agent_capacity_policies' do
+    context 'when it is an unauthenticated user' do
+      it 'returns unauthorized' do
+        post "/api/v1/accounts/#{account.id}/agent_capacity_policies"
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when it is an authenticated user' do
+      let(:agent) { create(:user, account: account, role: :agent) }
+      let(:administrator) { create(:user, account: account, role: :administrator) }
+
+      it 'returns unauthorized for agent' do
+        params = { agent_capacity_policy: { name: 'Test Policy' } }
+
+        post "/api/v1/accounts/#{account.id}/agent_capacity_policies",
+             params: params,
+             headers: agent.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+
+      it 'creates a new agent capacity policy when administrator' do
+        params = {
+          agent_capacity_policy: {
+            name: 'Test Policy',
+            description: 'Test Description',
+            exclusion_rules: { overall_capacity: 10 }
+          }
+        }
+
+        post "/api/v1/accounts/#{account.id}/agent_capacity_policies",
+             params: params,
+             headers: administrator.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(response.parsed_body['name']).to eq('Test Policy')
+        expect(response.parsed_body['description']).to eq('Test Description')
+      end
+
+      it 'returns validation errors for invalid data' do
+        params = { agent_capacity_policy: { name: '' } }
+
+        post "/api/v1/accounts/#{account.id}/agent_capacity_policies",
+             params: params,
+             headers: administrator.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+    end
+  end
+
+  describe 'PUT /api/v1/accounts/{account.id}/agent_capacity_policies/{id}' do
+    context 'when it is an unauthenticated user' do
+      it 'returns unauthorized' do
+        put "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}"
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when it is an authenticated user' do
+      let(:agent) { create(:user, account: account, role: :agent) }
+      let(:administrator) { create(:user, account: account, role: :administrator) }
+
+      it 'returns unauthorized for agent' do
+        params = { agent_capacity_policy: { name: 'Updated Policy' } }
+
+        put "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}",
+            params: params,
+            headers: agent.create_new_auth_token,
+            as: :json
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+
+      it 'updates the agent capacity policy when administrator' do
+        params = { agent_capacity_policy: { name: 'Updated Policy' } }
+
+        put "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}",
+            params: params,
+            headers: administrator.create_new_auth_token,
+            as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(response.parsed_body['name']).to eq('Updated Policy')
+      end
+    end
+  end
+
+  describe 'DELETE /api/v1/accounts/{account.id}/agent_capacity_policies/{id}' do
+    context 'when it is an unauthenticated user' do
+      it 'returns unauthorized' do
+        delete "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}"
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when it is an authenticated user' do
+      let(:agent) { create(:user, account: account, role: :agent) }
+      let(:administrator) { create(:user, account: account, role: :administrator) }
+
+      it 'returns unauthorized for agent' do
+        delete "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}",
+               headers: agent.create_new_auth_token,
+               as: :json
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+
+      it 'deletes the agent capacity policy when administrator' do
+        delete "/api/v1/accounts/#{account.id}/agent_capacity_policies/#{agent_capacity_policy.id}",
+               headers: administrator.create_new_auth_token,
+               as: :json
+
+        expect(response).to have_http_status(:ok)
+        expect { agent_capacity_policy.reload }.to raise_error(ActiveRecord::RecordNotFound)
+      end
+    end
+  end
+end

spec/enterprise/models/agent_capacity_policy_spec.rb

@@ -0,0 +1,29 @@
+require 'rails_helper'
+
+RSpec.describe AgentCapacityPolicy, type: :model do
+  let(:account) { create(:account) }
+
+  describe 'validations' do
+    it { is_expected.to validate_presence_of(:name) }
+    it { is_expected.to validate_length_of(:name).is_at_most(255) }
+  end
+
+  describe 'destruction' do
+    let(:policy) { create(:agent_capacity_policy, account: account) }
+    let(:user) { create(:user, account: account) }
+    let(:inbox) { create(:inbox, account: account) }
+
+    it 'destroys associated inbox capacity limits' do
+      create(:inbox_capacity_limit, agent_capacity_policy: policy, inbox: inbox)
+      expect { policy.destroy }.to change(InboxCapacityLimit, :count).by(-1)
+    end
+
+    it 'nullifies associated account users' do
+      account_user = user.account_users.first
+      account_user.update!(agent_capacity_policy: policy)
+
+      policy.destroy
+      expect(account_user.reload.agent_capacity_policy).to be_nil
+    end
+  end
+end

spec/enterprise/models/inbox_capacity_limit_spec.rb

@@ -0,0 +1,33 @@
+require 'rails_helper'
+
+RSpec.describe InboxCapacityLimit, type: :model do
+  let(:account) { create(:account) }
+  let(:policy) { create(:agent_capacity_policy, account: account) }
+  let(:inbox) { create(:inbox, account: account) }
+
+  describe 'validations' do
+    subject { create(:inbox_capacity_limit, agent_capacity_policy: policy, inbox: inbox) }
+
+    it { is_expected.to validate_presence_of(:conversation_limit) }
+    it { is_expected.to validate_numericality_of(:conversation_limit).is_greater_than(0).only_integer }
+    it { is_expected.to validate_uniqueness_of(:inbox_id).scoped_to(:agent_capacity_policy_id) }
+  end
+
+  describe 'uniqueness constraint' do
+    it 'prevents duplicate inbox limits for the same policy' do
+      create(:inbox_capacity_limit, agent_capacity_policy: policy, inbox: inbox)
+      duplicate = build(:inbox_capacity_limit, agent_capacity_policy: policy, inbox: inbox)
+
+      expect(duplicate).not_to be_valid
+      expect(duplicate.errors[:inbox_id]).to include('has already been taken')
+    end
+
+    it 'allows the same inbox in different policies' do
+      other_policy = create(:agent_capacity_policy, account: account)
+      create(:inbox_capacity_limit, agent_capacity_policy: policy, inbox: inbox)
+
+      different_policy_limit = build(:inbox_capacity_limit, agent_capacity_policy: other_policy, inbox: inbox)
+      expect(different_policy_limit).to be_valid
+    end
+  end
+end

spec/factories/agent_capacity_policies.rb

@@ -0,0 +1,21 @@
+FactoryBot.define do
+  factory :agent_capacity_policy do
+    account
+    sequence(:name) { |n| "Agent Capacity Policy #{n}" }
+    description { 'Test agent capacity policy' }
+    exclusion_rules { {} }
+
+    trait :with_overall_capacity do
+      exclusion_rules { { 'overall_capacity' => 10 } }
+    end
+
+    trait :with_time_exclusions do
+      exclusion_rules do
+        {
+          'hours' => [0, 1, 2, 3, 4, 5],
+          'days' => %w[saturday sunday]
+        }
+      end
+    end
+  end
+end

spec/factories/inbox_capacity_limits.rb

@@ -0,0 +1,7 @@
+FactoryBot.define do
+  factory :inbox_capacity_limit do
+    association :agent_capacity_policy, factory: :agent_capacity_policy
+    inbox
+    conversation_limit { 5 }
+  end
+end