1 files changed, 72 insertions, 0 deletions
diff --git a/lib/gitlab/ci/interpolation/context.rb b/lib/gitlab/ci/interpolation/context.rb
new file mode 100644
index 00000000000..ce7a86a3c9b
--- /dev/null
+++ b/lib/gitlab/ci/interpolation/context.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    module Interpolation
+      ##
+      # Interpolation::Context is a class that represents the data that can be used when performing string interpolation
+      # on a CI configuration.
+      #
+      class Context
+        ContextTooComplexError = Class.new(StandardError)
+        NotSymbolizedContextError = Class.new(StandardError)
+
+        MAX_DEPTH = 3
+
+        def initialize(hash)
+          @context = hash
+
+          raise ContextTooComplexError if depth > MAX_DEPTH
+        end
+
+        def valid?
+          errors.none?
+        end
+
+        ##
+        # This method is here because `Context` will be responsible for validating specs, inputs and defaults.
+        #
+        def errors
+          []
+        end
+
+        def depth
+          deep_depth(@context)
+        end
+
+        def fetch(field)
+          @context.fetch(field)
+        end
+
+        def to_h
+          @context.to_h
+        end
+
+        private
+
+        def deep_depth(context, depth = 0)
+          values = context.values.map do |value|
+            if value.is_a?(Hash)
+              deep_depth(value, depth + 1)
+            else
+              depth + 1
+            end
+          end
+
+          values.max
+        end
+
+        def self.fabricate(context)
+          case context
+          when Hash
+            new(context)
+          when Interpolation::Context
+            context
+          else
+            raise ArgumentError, 'unknown interpolation context'
+          end
+        end
+      end
+    end
+  end
+end