Extract code from `Namespace#clean_path` for ghost user generation.

1. Create a `Uniquify` class, which generalizes the process of generating unique
   strings, by accepting a function that defines what "uniqueness" means in a
   given context.

2. WIP: Make sure tests for `Namespace` pass, add more if necessary.

3. WIP: Add tests for `Uniquify`

1 files changed, 25 insertions, 0 deletions

diff --git a/app/models/concerns/uniquify.rb b/app/models/concerns/uniquify.rb
new file mode 100644
index 00000000000..1485ab6ae99
--- /dev/null
+++ b/app/models/concerns/uniquify.rb
@@ -0,0 +1,25 @@
+class Uniquify
+  # Return a version of the given 'base' string that is unique
+  # by appending a counter to it. Uniqueness is determined by
+  # repeated calls to `exists_fn`.
+  #
+  # If `base` is a function/proc, we expect that calling it with a
+  # candidate counter returns a string to test/return.
+  def string(base, exists_fn)
+    @counter = nil
+
+    if base.respond_to?(:call)
+      increment_counter! while exists_fn[base.call(@counter)]
+      base.call(@counter)
+    else
+      increment_counter! while exists_fn["#{base}#{@counter}"]
+      "#{base}#{@counter}"
+    end
+  end
+
+  private
+
+  def increment_counter!
+    @counter = @counter ? @counter.next : 1
+  end
+end