Start CSV importer feature

app/controllers/contestants_controller.rb

@@ -42,6 +42,21 @@ class ContestantsController < ApplicationController
     redirect_to contest_path(@contest)
   end
 
+  def import
+    authorize @contest
+
+    if params[:csv_import]
+      @csv_import = CsvImport.new(params.require(:csv_import).permit(:file, :separator))
+      if @csv_import.save
+        @csv_import = CsvImport.new
+      else
+        render :import, status: :unprocessable_entity
+      end
+    else
+      @csv_import = CsvImport.new
+    end
+  end
+
   private
 
   def set_contest

app/models/csv_import.rb

@@ -0,0 +1,46 @@
+# == Schema Information
+#
+# Table name: csv_imports
+#
+#  id         :integer          not null, primary key
+#  separator  :integer          not null
+#  created_at :datetime         not null
+#  updated_at :datetime         not null
+#
+class CsvImport < ApplicationRecord
+  enum :separator, { comma: ",", semicolon: ";" }, default: :comma
+
+  has_one_attached :file
+
+  validates :file, presence: true
+  validate :acceptable_csv, on: :create
+
+  def acceptable_csv
+    return unless file.attached?
+
+    if file.blob.byte_size > 20
+      errors.add(:file, "this csv file is too large, it must be under 20MB")
+      return
+    end
+
+    if file.content_type != "text/csv"
+      errors.add(:file, :not_a_csv_file)
+      return
+    end
+
+    begin
+      csv = CSV.read(attachment_changes["file"].attachable.path, col_sep: separator)
+
+      logger = Logger.new(STDOUT)
+      logger.info(csv)
+      errors.add(:file, :empty) if csv.count < 1 || (csv.count == 1 && csv[0].count == 1 && csv[0][0] == "")
+    rescue CSV::MalformedCSVError => e
+      errors.add(:file, e.message)
+    end
+  end
+
+  def options_for_separator
+    keys = self.class.separators.keys
+    keys.map(&:humanize).zip(keys).to_h
+  end
+end

app/policies/contest_policy.rb

@@ -31,6 +31,10 @@ class ContestPolicy < ApplicationPolicy
     record.user.id == user.id || user.admin?
   end
 
+  def import?
+    record.user.id == user.id || user.admin?
+  end
+
   def scoreboard?
     true
   end

app/views/contestants/import.html.slim

@@ -0,0 +1,19 @@
+= form_with(model: @csv_import, url: contest_import_path(@contest), html: { novalidate: true }) do |form|
+  .row.g-3
+    .col
+      .mb-3
+        .form-floating
+          = form.file_field :file, class: "form-control", accept: ".csv, text/csv"
+          = form.label :file
+
+  .row.g-3
+    .col
+      .mb-3
+        .form-floating
+          = form.select :separator, @csv_import.options_for_separator, {}, class: "form-select"
+          = form.label :separator
+
+  .row.g-3
+    .col
+      .mb-3
+        = form.submit t("helpers.buttons.import"), class: "btn btn-primary"

app/views/contests/show.html.slim

@@ -76,6 +76,8 @@
           = t("contestants.plural").capitalize
           a.ms-3.btn.btn-primary href=new_contest_contestant_path(@contest) style="margin-top: -3px"
             | + #{t("helpers.buttons.add")}
+          a.ms-3.btn.btn-primary href=contest_import_path(@contest) style="margin-top: -3px"
+            | #{t("helpers.buttons.import")}
     table.table.table-striped.table-hover
       thead
         tr