1 files changed, 77 insertions, 0 deletions
diff --git a/activestorage/app/models/active_storage/filename.rb b/activestorage/app/models/active_storage/filename.rb
new file mode 100644
index 0000000000..2a03e0173d
--- /dev/null
+++ b/activestorage/app/models/active_storage/filename.rb
@@ -0,0 +1,77 @@
+# frozen_string_literal: true
+
+# Encapsulates a string representing a filename to provide convenient access to parts of it and sanitization.
+# A Filename instance is returned by ActiveStorage::Blob#filename, and is comparable so it can be used for sorting.
+class ActiveStorage::Filename
+  include Comparable
+
+  class << self
+    # Returns a Filename instance based on the given filename. If the filename is a Filename, it is
+    # returned unmodified. If it is a String, it is passed to ActiveStorage::Filename.new.
+    def wrap(filename)
+      filename.kind_of?(self) ? filename : new(filename)
+    end
+  end
+
+  def initialize(filename)
+    @filename = filename
+  end
+
+  # Returns the part of the filename preceding any extension.
+  #
+  #   ActiveStorage::Filename.new("racecar.jpg").base # => "racecar"
+  #   ActiveStorage::Filename.new("racecar").base     # => "racecar"
+  #   ActiveStorage::Filename.new(".gitignore").base  # => ".gitignore"
+  def base
+    File.basename @filename, extension_with_delimiter
+  end
+
+  # Returns the extension of the filename (i.e. the substring following the last dot, excluding a dot at the
+  # beginning) with the dot that precedes it. If the filename has no extension, an empty string is returned.
+  #
+  #   ActiveStorage::Filename.new("racecar.jpg").extension_with_delimiter # => ".jpg"
+  #   ActiveStorage::Filename.new("racecar").extension_with_delimiter     # => ""
+  #   ActiveStorage::Filename.new(".gitignore").extension_with_delimiter  # => ""
+  def extension_with_delimiter
+    File.extname @filename
+  end
+
+  # Returns the extension of the filename (i.e. the substring following the last dot, excluding a dot at
+  # the beginning). If the filename has no extension, an empty string is returned.
+  #
+  #   ActiveStorage::Filename.new("racecar.jpg").extension_without_delimiter # => "jpg"
+  #   ActiveStorage::Filename.new("racecar").extension_without_delimiter     # => ""
+  #   ActiveStorage::Filename.new(".gitignore").extension_without_delimiter  # => ""
+  def extension_without_delimiter
+    extension_with_delimiter.from(1).to_s
+  end
+
+  alias_method :extension, :extension_without_delimiter
+
+  # Returns the sanitized filename.
+  #
+  #   ActiveStorage::Filename.new("foo:bar.jpg").sanitized # => "foo-bar.jpg"
+  #   ActiveStorage::Filename.new("foo/bar.jpg").sanitized # => "foo-bar.jpg"
+  #
+  # Characters considered unsafe for storage (e.g. \, $, and the RTL override character) are replaced with a dash.
+  def sanitized
+    @filename.encode(Encoding::UTF_8, invalid: :replace, undef: :replace, replace: "�").strip.tr("\u{202E}%$|:;/\t\r\n\\", "-")
+  end
+
+  # Returns the sanitized version of the filename.
+  def to_s
+    sanitized.to_s
+  end
+
+  def as_json(*)
+    to_s
+  end
+
+  def to_json
+    to_s
+  end
+
+  def <=>(other)
+    to_s.downcase <=> other.to_s.downcase
+  end
+end