Draft API to get all collections by an account (#37139)

app/controllers/api/v1_alpha/collections_controller.rb

@@ -3,20 +3,34 @@
 class Api::V1Alpha::CollectionsController < Api::BaseController
   include Authorization
 
+  DEFAULT_COLLECTIONS_LIMIT = 40
+
   rescue_from ActiveRecord::RecordInvalid, Mastodon::ValidationError do |e|
     render json: { error: ValidationErrorFormatter.new(e).as_json }, status: 422
   end
 
   before_action :check_feature_enabled
 
+  before_action -> { authorize_if_got_token! :read, :'read:collections' }, only: [:index, :show]
   before_action -> { doorkeeper_authorize! :write, :'write:collections' }, only: [:create, :update, :destroy]
 
   before_action :require_user!, only: [:create, :update, :destroy]
 
+  before_action :set_account, only: [:index]
+  before_action :set_collections, only: [:index]
   before_action :set_collection, only: [:show, :update, :destroy]
 
+  after_action :insert_pagination_headers, only: [:index]
+
   after_action :verify_authorized
 
+  def index
+    cache_if_unauthenticated!
+    authorize Collection, :index?
+
+    render json: @collections, each_serializer: REST::BaseCollectionSerializer
+  end
+
   def show
     cache_if_unauthenticated!
     authorize @collection, :show?
@@ -50,6 +64,18 @@ class Api::V1Alpha::CollectionsController < Api::BaseController
 
   private
 
+  def set_account
+    @account = Account.find(params[:account_id])
+  end
+
+  def set_collections
+    @collections = @account.collections
+                           .with_item_count
+                           .order(created_at: :desc)
+                           .offset(offset_param)
+                           .limit(limit_param(DEFAULT_COLLECTIONS_LIMIT))
+  end
+
   def set_collection
     @collection = Collection.find(params[:id])
   end
@@ -65,4 +91,24 @@ class Api::V1Alpha::CollectionsController < Api::BaseController
   def check_feature_enabled
     raise ActionController::RoutingError unless Mastodon::Feature.collections_enabled?
   end
+
+  def next_path
+    return unless records_continue?
+
+    api_v1_alpha_account_collections_url(@account, pagination_params(offset: offset_param + limit_param(DEFAULT_COLLECTIONS_LIMIT)))
+  end
+
+  def prev_path
+    return if offset_param.zero?
+
+    api_v1_alpha_account_collections_url(@account, pagination_params(offset: offset_param - limit_param(DEFAULT_COLLECTIONS_LIMIT)))
+  end
+
+  def records_continue?
+    ((offset_param * limit_param(DEFAULT_COLLECTIONS_LIMIT)) + @collections.size) < @account.collections.size
+  end
+
+  def offset_param
+    params[:offset].to_i
+  end
 end