[Feature] Import posts from CSV in Admin section (#706)

app/admin/post.rb

@@ -1,4 +1,19 @@
 ActiveAdmin.register Post do
+  action_item :upload_csv, only: :index do
+    link_to I18n.t("active_admin.users.upload_from_csv"), action: "upload_csv"
+  end
+
+  collection_action :upload_csv do
+    render "admin/csv/upload_csv"
+  end
+
+  collection_action :import_csv, method: :post do
+    errors = PostImporter.call(params[:dump][:organization_id], params[:dump][:file])
+    flash[:error] = errors.join("<br/>").html_safe if errors.present?
+
+    redirect_to action: :index
+  end
+
   index do
     id_column
     column :class

app/services/post_importer.rb

@@ -0,0 +1,60 @@
+# Used in the Admin section to import posts
+# to a specific organization, from a CSV file.
+
+require "csv"
+
+class PostImporter
+  Row = Struct.new(
+    :user_id,
+    :type,
+    :title,
+    :description,
+    :category_id,
+    :created_at,
+    :start_on,
+    :end_on
+  ) do
+    def post_from_row
+      Object.const_get(type).new(
+        user_id: user_id,
+        title: title,
+        description: description,
+        category_id: category_id,
+        created_at: created_at,
+        start_on: start_on,
+        end_on: end_on
+      )
+    end
+  end
+
+  class << self
+    def call(organization_id, csv_data)
+      data = csv_data.read
+      errors = []
+
+      CSV.parse(data, headers: false) do |data_row|
+        row = Row.new(
+          data_row[0],
+          data_row[1],
+          data_row[2],
+          data_row[3],
+          data_row[4],
+          data_row[5],
+          data_row[6],
+          data_row[7]
+        )
+        process_row(row, organization_id, errors)
+      end
+
+      errors
+    end
+
+    def process_row(row, organization_id, errors)
+      post = row.post_from_row
+      post.organization_id = organization_id
+      return if post.save
+
+      errors.push(user_id: row.user_id, title: row.title, errors: post.errors.full_messages)
+    end
+  end
+end