1 files changed, 100 insertions, 0 deletions
diff --git a/lib/syntax_suggest/code_block.rb b/lib/syntax_suggest/code_block.rb
new file mode 100644
index 0000000000..d842890300
--- /dev/null
+++ b/lib/syntax_suggest/code_block.rb
@@ -0,0 +1,100 @@
+# frozen_string_literal: true
+
+module SyntaxSuggest
+  # Multiple lines form a singular CodeBlock
+  #
+  # Source code is made of multiple CodeBlocks.
+  #
+  # Example:
+  #
+  #   code_block.to_s # =>
+  #     #   def foo
+  #     #     puts "foo"
+  #     #   end
+  #
+  #   code_block.valid? # => true
+  #   code_block.in_valid? # => false
+  #
+  #
+  class CodeBlock
+    UNSET = Object.new.freeze
+    attr_reader :lines, :starts_at, :ends_at
+
+    def initialize(lines: [])
+      @lines = Array(lines)
+      @valid = UNSET
+      @deleted = false
+      @starts_at = @lines.first.number
+      @ends_at = @lines.last.number
+    end
+
+    def delete
+      @deleted = true
+    end
+
+    def deleted?
+      @deleted
+    end
+
+    def visible_lines
+      @lines.select(&:visible?).select(&:not_empty?)
+    end
+
+    def mark_invisible
+      @lines.map(&:mark_invisible)
+    end
+
+    def is_end?
+      to_s.strip == "end"
+    end
+
+    def hidden?
+      @lines.all?(&:hidden?)
+    end
+
+    # This is used for frontier ordering, we are searching from
+    # the largest indentation to the smallest. This allows us to
+    # populate an array with multiple code blocks then call `sort!`
+    # on it without having to specify the sorting criteria
+    def <=>(other)
+      out = current_indent <=> other.current_indent
+      return out if out != 0
+
+      # Stable sort
+      starts_at <=> other.starts_at
+    end
+
+    def current_indent
+      @current_indent ||= lines.select(&:not_empty?).map(&:indent).min || 0
+    end
+
+    def invalid?
+      !valid?
+    end
+
+    def valid?
+      if @valid == UNSET
+        # Performance optimization
+        #
+        # If all the lines were previously hidden
+        # and we expand to capture additional empty
+        # lines then the result cannot be invalid
+        #
+        # That means there's no reason to re-check all
+        # lines with the parser (which is expensive).
+        # Benchmark in commit message
+        @valid = if lines.all? { |l| l.hidden? || l.empty? }
+          true
+        else
+          SyntaxSuggest.valid?(lines.map(&:original).join)
+        end
+      else
+        @valid
+      end
+    end
+
+    def to_s
+      @lines.join
+    end
+  end
+end