1 files changed, 67 insertions, 0 deletions
diff --git a/lib/gitlab/ci/interpolation/template.rb b/lib/gitlab/ci/interpolation/template.rb
new file mode 100644
index 00000000000..0211279f266
--- /dev/null
+++ b/lib/gitlab/ci/interpolation/template.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    module Interpolation
+      class Template
+        include Gitlab::Utils::StrongMemoize
+
+        attr_reader :blocks, :ctx
+
+        TooManyBlocksError = Class.new(StandardError)
+        InvalidBlockError = Class.new(StandardError)
+
+        MAX_BLOCKS = 10_000
+
+        def initialize(config, ctx)
+          @config = Interpolation::Config.fabricate(config)
+          @ctx = Interpolation::Context.fabricate(ctx)
+          @errors = []
+          @blocks = {}
+
+          interpolate! if valid?
+        end
+
+        def valid?
+          errors.none?
+        end
+
+        def errors
+          @errors + @config.errors + @ctx.errors + @blocks.values.flat_map(&:errors)
+        end
+
+        def size
+          @blocks.size
+        end
+
+        def interpolated
+          @result if valid?
+        end
+
+        private
+
+        def interpolate!
+          @result = @config.replace! do |data|
+            Interpolation::Block.match(data) do |block, data|
+              evaluate_block(block, data)
+            end
+          end
+        rescue TooManyBlocksError
+          @errors.push('too many interpolation blocks')
+        rescue InvalidBlockError
+          @errors.push('interpolation interrupted by errors')
+        end
+        strong_memoize_attr :interpolate!
+
+        def evaluate_block(block, data)
+          block = (@blocks[block] ||= Interpolation::Block.new(block, data, ctx))
+
+          raise TooManyBlocksError if @blocks.count > MAX_BLOCKS
+          raise InvalidBlockError unless block.valid?
+
+          block.value
+        end
+      end
+    end
+  end
+end