Add basic line length based formatting support

lib/rufo.rb

@@ -14,5 +14,7 @@ def self.format(code, **options)
 require_relative "rufo/command"
 require_relative "rufo/dot_file"
 require_relative "rufo/settings"
+require_relative "rufo/doc_builder"
+require_relative "rufo/doc_printer"
 require_relative "rufo/formatter"
 require_relative "rufo/version"

lib/rufo/doc_builder.rb

@@ -0,0 +1,123 @@
+module Rufo
+  class DocBuilder
+    class InvalidDocError < StandardError; end
+
+    class << self
+
+      # Combine an array of items into a single string.
+      def concat(parts)
+        assert_docs(parts)
+        {
+          type: :concat, parts: parts,
+        }
+      end
+
+      # Increase level of indentation.
+      def indent(contents)
+        assert_doc(contents)
+        {
+          type: :indent, contents: contents,
+        }
+      end
+
+      # Increase indentation by a fixed number.
+      def align(n, contents)
+        assert_doc(contents)
+        {type: :align, contents: contents, n: n}
+      end
+
+      # Groups are items that the printer should try and fit onto a single line.
+      # If the group does not fit then it breaks instead.
+      def group(contents, opts = {})
+        assert_doc(contents)
+        {
+          type: :group,
+          contents: contents,
+          break: !!opts[:should_break],
+          expanded_states: opts[:expanded_states],
+        }
+      end
+
+      # Rather than breaking if the items do not fit this tries a different set
+      # of items.
+      def conditional_group(states, opts = {})
+        group(states.first, opts.merge(expanded_states: states))
+      end
+
+      # Alternative to group. This only breaks the required items rather then
+      # all items if they do not fit.
+      def fill(parts)
+        assert_docs(parts)
+
+        {type: :fill, parts: parts}
+      end
+
+      # Print first arg if the group breaks otherwise print the second.
+      def if_break(break_contents, flat_contents)
+        assert_doc(break_contents) unless break_contents.nil?
+        assert_doc(flat_contents) unless flat_contents.nil?
+
+        {type: :if_break, break_contents: break_contents, flat_contents: flat_contents}
+      end
+
+      # Append content to the end of a line. This gets placed just before a new line.
+      def line_suffix(contents)
+        assert_doc(contents)
+        {type: :line_suffix, contents: contents}
+      end
+
+      # Join list of items with a separator.
+      def join(sep, arr)
+        result = []
+        arr.each_with_index do |element, index|
+          unless index == 0
+            result << sep
+          end
+          result << element
+        end
+        concat(result)
+      end
+
+      def add_alignment_to_doc(doc, size, tab_width)
+        return doc unless size > 0
+        (size/tab_width).times { doc = indent(doc) }
+        doc = align(size % tab_width, doc)
+        align(-Float::INFINITY, doc)
+      end
+
+      private
+
+      def assert_docs(parts)
+        parts.each(&method(:assert_doc))
+      end
+
+      def assert_doc(val)
+        unless val.is_a?(String) || (val.is_a?(Hash) && val[:type].is_a?(Symbol))
+          raise InvalidDocError.new("Value #{val.inspect} is not a valid document")
+        end
+      end
+    end
+
+    # Use this to ensure that line suffixes do not move to the last line in group.
+    LINE_SUFFIX_BOUNDARY = {type: :line_suffix_boundary}
+    # Use this to force the parent to break
+    BREAK_PARENT = {type: :break_parent}
+    # If the content fits on one line the newline will be replaced with a space.
+    # Newlines are what triggers indentation to be added.
+    LINE = {type: :line}
+    # If the content fits on one line the newline will be replaced by nothing.
+    SOFT_LINE = {type: :line, soft: true}
+    # This newline is always included regardless of if the content fits on one
+    # line or not.
+    HARD_LINE = concat([{type: :line, hard: true}, BREAK_PARENT])
+    # This is a newline that is always included and does not cause the
+    # indentation to change subsequently.
+    LITERAL_LINE = concat([
+      {type: :line, hard: true, literal: true},
+      BREAK_PARENT,
+    ])
+
+    # This keeps track of the cursor in the document.
+    CURSOR = {type: :cursor, placeholder: :cursor}
+  end
+end