corrected handling of rgb colors (foreground and background)

There was an off by one error in the use of the regexp match data

fixes issue #4

.changelog_entries/e17764deb76cf2cd998f0d5d8e14d6f3.json

@@ -0,0 +1 @@
+{"type":"Deprecated","tickets":["4"],"url":"https://github.com/masukomi/oho/issues/4","description":"corrects detection and handling of rgb color escape sequences","tags":["bug"]}

spec/oho/color_escape_code_spec.cr

@@ -137,4 +137,29 @@ describe Oho::ColorEscapeCode do
    ec.background_color.should(eq(""))
   end
 
+  describe "rgb colors" do
+
+    it "should recognize rgb foreground colors" do
+      # breakdown
+      # normal foreground color codes go from 37 to 39 skipping 38
+      # 38 is bug unless followed by 5 or 2
+      # 38;2 -> indicates rgb color is about to follow
+      # thus rgb should be 252, 0, 37
+      escape_code_string = "[38;2;252;0;37m" # the \033 or \e will be stripped before
+      ec = Oho::ColorEscapeCode.new(escape_code_string, default_options)
+      ec.to_span(nil).should(eq(
+       "<span style=\"color: rgb(252,0,37); \">"))
+    end
+    it "should recognize rgb background colors" do
+      # breakdown
+      # normal background color codes go from 47 to 49 skipping 38
+      # 48 is bug unless followed by 5 or 2
+      # 48;2 -> indicates rgb color is about to follow
+      # thus rgb should be 252, 0, 37
+      escape_code_string = "[48;2;252;0;37m" # the \033 or \e will be stripped before
+      ec = Oho::ColorEscapeCode.new(escape_code_string, default_options)
+      ec.to_span(nil).should(eq(
+       "<span style=\"background-color: rgb(252,0,37); \">"))
+    end
+  end
 end

src/oho/color_escape_code.cr

@@ -547,7 +547,7 @@ module Oho
     private def extract_rgb_color(m : Regex::MatchData?) : String
         return "" if m.nil?
         rgb = m.as(Regex::MatchData)
-        "rgb(#{rgb[0]},#{rgb[1]},#{rgb[2]})"
+        "rgb(#{rgb[1]},#{rgb[2]},#{rgb[3]})"
     end
 
     private def extract_foreground_color(string : String) : String
@@ -557,6 +557,9 @@ module Oho
       m = string.match(/38;2;(\d+);(\d+);(\d+)/)
       return extract_rgb_color(m) if ! m.nil?
       ints = extract_ints(string)
+      return "" if ints[0] == 48 
+      # 48;2 and 48;5 are background colors
+      # 48 by itself is a bug
       if ints.size > 0 && ints.last == 0
         return "" # alternately could "initial"
       end
@@ -586,6 +589,9 @@ module Oho
       return extract_rgb_color(m) if ! m.nil?
       # who knows
       ints = extract_ints(string)
+      return "" if ints[0] == 38 
+      # 38;2 and 38;5 are background colors
+      # 38 by itself is a bug
       if ints.size > 0 && ints.last == 0
         return "" # alternately could "initial"
       end