Refactor Colorize#surround

This is one of the separations of crystal-lang#3925.

Remove `surround` and rename `push` to `surround`, now `push` is
derecated.
(This reason is dscribed in crystal-lang#3925 (comment))

spec/std/colorize_spec.cr

@@ -1,6 +1,14 @@
 require "spec"
 require "colorize"
 
+private class ColorizeToS
+  def to_s(io)
+    io << "hello"
+    io << "world".colorize.blue
+    io << "bye"
+  end
+end
+
 describe "colorize" do
   it "colorizes without change" do
     "hello".colorize.to_s.should eq("hello")
@@ -97,44 +105,56 @@ describe "colorize" do
     "hello".colorize(:red).inspect.should eq("\e[31m\"hello\"\e[0m")
   end
 
-  it "colorizes io with method" do
+  it "colorizes with surround" do
     io = IO::Memory.new
     with_color.red.surround(io) do
       io << "hello"
+      with_color.green.surround(io) do
+        io << "world"
+      end
+      io << "bye"
     end
-    io.to_s.should eq("\e[31mhello\e[0m")
+    io.to_s.should eq("\e[31mhello\e[0;32mworld\e[0;31mbye\e[0m")
   end
 
-  it "colorizes io with symbol" do
+  it "colorizes with surround and reset" do
     io = IO::Memory.new
-    with_color(:red).surround(io) do
+    with_color.red.surround(io) do
       io << "hello"
+      with_color.green.bold.surround(io) do
+        io << "world"
+      end
+      io << "bye"
     end
-    io.to_s.should eq("\e[31mhello\e[0m")
+    io.to_s.should eq("\e[31mhello\e[0;32;1mworld\e[0;31mbye\e[0m")
   end
 
-  it "colorizes with push and pop" do
+  it "colorizes with surround and no reset" do
     io = IO::Memory.new
-    with_color.red.push(io) do
+    with_color.red.surround(io) do
       io << "hello"
-      with_color.green.push(io) do
+      with_color.red.surround(io) do
         io << "world"
       end
       io << "bye"
     end
-    io.to_s.should eq("\e[31mhello\e[0;32mworld\e[0;31mbye\e[0m")
+    io.to_s.should eq("\e[31mhelloworldbye\e[0m")
   end
 
-  it "colorizes with push and pop resets" do
+  it "colorizes with surround and default" do
     io = IO::Memory.new
-    with_color.red.push(io) do
+    with_color.red.surround(io) do
       io << "hello"
-      with_color.green.bold.push(io) do
+      with_color.surround(io) do
         io << "world"
       end
       io << "bye"
     end
-    io.to_s.should eq("\e[31mhello\e[0;32;1mworld\e[0;31mbye\e[0m")
+    io.to_s.should eq("\e[31mhello\e[0mworld\e[31mbye\e[0m")
+  end
+
+  it "colorizes with to_s" do
+    ColorizeToS.new.colorize.red.to_s.should eq("\e[31mhello\e[0;34mworld\e[0;31mbye\e[0m")
   end
 
   it "toggles off" do

src/colorize.cr

@@ -239,64 +239,88 @@ struct Colorize::Object(T)
   end
 
   def surround(io = STDOUT)
-    must_append_end = append_start(io)
-    yield io
-    append_end(io) if must_append_end
-  end
+    return yield io unless @on
 
-  STACK = [] of Colorize::Object(String)
+    Object.surround(io, to_named_tuple) do |io|
+      yield io
+    end
+  end
 
+  # DEPRECATED: Use `#surround`.
   def push(io = STDOUT)
-    last_color = STACK.last?
-
-    append_start(io, !!last_color)
+    {{ puts "Warning: `Colorize::Object#push` is deprecated and will be removed, use `Colorize::Object#surround` instead".id }}
+    surround(io) { |io| yield io }
+  end
 
-    STACK.push self
-    yield io
-    STACK.pop
+  private def to_named_tuple
+    {
+      fore: @fore,
+      back: @back,
+      mode: @mode,
+    }
+  end
 
-    if last_color
-      last_color.append_start(io, true)
-    else
-      append_end(io)
+  @@last_color = {
+    fore: FORE_DEFAULT,
+    back: BACK_DEFAULT,
+    mode: 0,
+  }
+
+  protected def self.surround(io, color)
+    last_color = @@last_color
+    must_append_end = append_start(io, color)
+    @@last_color = color
+
+    begin
+      yield io
+    ensure
+      append_start(io, last_color) if must_append_end
+      @@last_color = last_color
     end
   end
 
-  protected def append_start(io, reset = false)
-    return false unless @on
+  private def self.append_start(io, color)
+    last_color_is_default =
+      @@last_color[:fore] == FORE_DEFAULT &&
+        @@last_color[:back] == BACK_DEFAULT &&
+        @@last_color[:mode] == 0
+
+    fore = color[:fore]
+    back = color[:back]
+    mode = color[:mode]
 
-    fore_is_default = @fore == FORE_DEFAULT
-    back_is_default = @back == BACK_DEFAULT
-    mode_is_default = @mode == 0
+    fore_is_default = fore == FORE_DEFAULT
+    back_is_default = back == BACK_DEFAULT
+    mode_is_default = mode == 0
 
-    if fore_is_default && back_is_default && mode_is_default && !reset
+    if fore_is_default && back_is_default && mode_is_default && last_color_is_default || @@last_color == color
       false
     else
       io << "\e["
 
       printed = false
 
-      if reset
+      unless last_color_is_default
         io << MODE_DEFAULT
         printed = true
       end
 
       unless fore_is_default
         io << ";" if printed
-        io << @fore
+        io << fore
         printed = true
       end
 
       unless back_is_default
         io << ";" if printed
-        io << @back
+        io << back
         printed = true
       end
 
       unless mode_is_default
         # Can't reuse MODES constant because it has bold/bright duplicated
         {% for name in %w(bold dim underline blink reverse hidden) %}
-          if (@mode & MODE_{{name.upcase.id}}_FLAG) != 0
+          if (mode & MODE_{{name.upcase.id}}_FLAG) != 0
             io << ";" if printed
             io << MODE_{{name.upcase.id}}
             printed = true
@@ -309,8 +333,4 @@ struct Colorize::Object(T)
       true
     end
   end
-
-  protected def append_end(io)
-    io << "\e[0m"
-  end
 end