1 files changed, 42 insertions, 0 deletions
diff --git a/lib/gitlab/ci/pipeline/expression/statement.rb b/lib/gitlab/ci/pipeline/expression/statement.rb
new file mode 100644
index 00000000000..4f0e101b730
--- /dev/null
+++ b/lib/gitlab/ci/pipeline/expression/statement.rb
@@ -0,0 +1,42 @@
+module Gitlab
+  module Ci
+    module Pipeline
+      module Expression
+        class Statement
+          StatementError = Class.new(StandardError)
+
+          GRAMMAR = [
+            %w[variable equals string],
+            %w[variable equals variable],
+            %w[variable equals null],
+            %w[string equals variable],
+            %w[null equals variable],
+            %w[variable]
+          ].freeze
+
+          def initialize(statement, pipeline)
+            @lexer = Expression::Lexer.new(statement)
+
+            @variables = pipeline.variables.map do |variable|
+              [variable.key, variable.value]
+            end
+          end
+
+          def parse_tree
+            raise StatementError if @lexer.lexemes.empty?
+
+            unless GRAMMAR.find { |syntax| syntax == @lexer.lexemes }
+              raise StatementError, 'Unknown pipeline expression!'
+            end
+
+            Expression::Parser.new(@lexer.tokens).tree
+          end
+
+          def evaluate
+            parse_tree.evaluate(@variables.to_h)
+          end
+        end
+      end
+    end
+  end
+end