1 files changed, 55 insertions, 0 deletions
diff --git a/lib/mastodon/migration_warning.rb b/lib/mastodon/migration_warning.rb
new file mode 100644
index 000000000..227f6705d
--- /dev/null
+++ b/lib/mastodon/migration_warning.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+module Mastodon
+  module MigrationWarning
+    WARNING_SECONDS = 10
+
+    DEFAULT_WARNING = <<~WARNING_MESSAGE
+      WARNING: This migration may take a *long* time for large instances.
+      It will *not* lock tables for any significant time, but it may run
+      for a very long time. We will pause for #{WARNING_SECONDS} seconds to allow you to
+      interrupt this migration if you are not ready.
+    WARNING_MESSAGE
+
+    def migration_duration_warning(explanation = nil)
+      return unless valid_environment?
+
+      announce_warning(explanation)
+
+      announce_countdown
+    end
+
+    private
+
+    def announce_countdown
+      WARNING_SECONDS.downto(1) do |i|
+        say "Continuing in #{i} second#{i == 1 ? '' : 's'}...", true
+        sleep 1
+      end
+    end
+
+    def valid_environment?
+      $stdout.isatty && Rails.env.production?
+    end
+
+    def announce_warning(explanation)
+      announce_message prepare_message(explanation)
+    end
+
+    def announce_message(text)
+      say ''
+      text.each_line do |line|
+        say(line)
+      end
+      say ''
+    end
+
+    def prepare_message(explanation)
+      if explanation.blank?
+        DEFAULT_WARNING
+      else
+        DEFAULT_WARNING + "\n#{explanation}"
+      end
+    end
+  end
+end