Add support for showing code context lines (#181)

* Add support for showing code context lines

* Show context lines only in ExplainFormatter

* Add spec coverage for context_lines option

spec/ameba/formatter/util_spec.cr

@@ -22,7 +22,38 @@ module Ameba::Formatter
           a = 1
         )
         location = Crystal::Location.new("filename", 1, 1)
-        subject.affected_code(source, location).should eq "> a = 1\n  \e[33m^\e[0m"
+        subject.deansify(subject.affected_code(source, location))
+          .should eq "> a = 1\n  ^"
+      end
+
+      it "returns correct line if it is found" do
+        source = Source.new <<-EOF
+          # pre:1
+            # pre:2
+              # pre:3
+                # pre:4
+                  # pre:5
+          a = 1
+                  # post:1
+                # post:2
+              # post:3
+            # post:4
+          # post:5
+          EOF
+
+        location = Crystal::Location.new("filename", 6, 1)
+        subject.deansify(subject.affected_code(source, location, context_lines: 3))
+          .should eq <<-STR
+            >     # pre:3
+            >       # pre:4
+            >         # pre:5
+            > a = 1
+              ^
+            >         # post:1
+            >       # post:2
+            >     # post:3
+
+            STR
       end
     end
   end

src/ameba/formatter/explain_formatter.cr

@@ -49,7 +49,7 @@ module Ameba::Formatter
         @location.to_s.colorize(:cyan).to_s,
       ]
 
-      if affected_code = affected_code(source, @location)
+      if affected_code = affected_code(source, @location, context_lines: 3)
         output_title "AFFECTED CODE"
         output_paragraph affected_code
       end

src/ameba/formatter/util.cr

@@ -1,23 +1,75 @@
 module Ameba::Formatter
   module Util
-    def affected_code(source, location, max_length = 100, placeholder = " ...", prompt = "> ")
+    def deansify(message : String?) : String?
-      line, column = location.line_number, location.column_number
+      message.try &.gsub(/\x1b[^m]*m/, "").presence
-      affected_line = source.lines[line - 1]?.presence
-
-      return unless affected_line
-
-      if affected_line.size > max_length && column < max_length
-        affected_line = affected_line[0, max_length - placeholder.size - 1] + placeholder
     end
 
+    def affected_code(source, location, context_lines = 0, max_length = 100, placeholder = " ...", prompt = "> ")
+      lines = source.lines
+      lineno, column =
+        location.line_number, location.column_number
+
+      return unless affected_line = lines[lineno - 1]?.presence
+
+      trim_line = Proc(String, String).new do |line|
+        if line.size > max_length
+          line = line[0, max_length - placeholder.size - 1] + placeholder
+        end
+        line
+      end
+
+      if column < max_length
+        affected_line = trim_line.call(affected_line)
+      end
+
+      show_context = context_lines > 0
+      if show_context
+        pre_context, post_context = %w[], %w[]
+
+        lines.each_with_index do |line, i|
+          case i + 1
+          when lineno - context_lines...lineno
+            pre_context << trim_line.call(line)
+          when lineno
+            #
+          when lineno + 1..lineno + context_lines
+            post_context << trim_line.call(line)
+          end
+        end
+
+        # remove empty lines at the beginning/end
+        pre_context.shift? unless pre_context.first?.presence
+        post_context.pop? unless post_context.last?.presence
+      end
+
+      String.build do |str|
+        if show_context
+          pre_context.try &.each do |line|
+            str << prompt
+            str.puts(line.colorize(:dark_gray))
+          end
+
+          str << prompt
+          str.puts(affected_line.colorize(:white))
+
+          str << " " * (prompt.size + column - 1)
+          str.puts("^".colorize(:yellow))
+
+          post_context.try &.each do |line|
+            str << prompt
+            str.puts(line.colorize(:dark_gray))
+          end
+        else
           stripped = affected_line.lstrip
           position = column - (affected_line.size - stripped.size) + prompt.size
 
-      String.build do |str|
+          str << prompt
-        str << prompt << stripped << '\n'
+          str.puts(stripped)
+
           str << " " * (position - 1)
           str << "^".colorize(:yellow)
         end
       end
     end
   end
+end