refactor: abstract out more terminal operations

include/dwarfs/terminal.h

@@ -73,6 +73,9 @@ class terminal {
   virtual std::string
   colored(std::string text, termcolor color, bool enable = true,
           termstyle style = termstyle::NORMAL) const = 0;
+  virtual std::string_view carriage_return() const = 0;
+  virtual std::string_view rewind_line() const = 0;
+  virtual std::string_view clear_line() const = 0;
 };
 
 std::string_view

src/dwarfs/console_writer.cpp

@@ -155,15 +155,18 @@ console_writer::console_writer(std::shared_ptr<terminal const> term,
 void console_writer::rewind(int next_rewind_lines) {
   if (!statebuf_.empty()) {
     auto& os = log_stream();
+    auto& term = this->term();
+    auto clear_line = term.clear_line();
+    auto rewind_line = term.rewind_line();
 
-    os << '\r';
+    os << term.carriage_return();
 
     int num_erase = rewind_lines_ - next_rewind_lines;
 
     for (int i = 0; i < rewind_lines_; ++i) {
-      os << "\x1b[A";
+      os << rewind_line;
       if (num_erase > 0) {
-        os << "\x1b[2K";
+        os << clear_line;
         --num_erase;
       }
     }

src/dwarfs/terminal.cpp

@@ -115,6 +115,25 @@ std::string terminal_ansi_colored(std::string_view text, termcolor color,
 
 namespace {
 
+class terminal_ansi : public terminal {
+ public:
+  std::string_view
+  color(termcolor color, termstyle style = termstyle::NORMAL) const override {
+    return terminal_ansi_color(color, style);
+  }
+
+  std::string colored(std::string text, termcolor color, bool enable = true,
+                      termstyle style = termstyle::NORMAL) const override {
+    return terminal_ansi_colored(std::move(text), color, enable, style);
+  }
+
+  std::string_view carriage_return() const override { return "\r"; }
+
+  std::string_view rewind_line() const override { return "\x1b[A"; }
+
+  std::string_view clear_line() const override { return "\x1b[2K"; }
+};
+
 #if defined(_WIN32)
 
 void WindowsEmulateVT100Terminal(DWORD std_handle) {
@@ -140,7 +159,7 @@ void WindowsEmulateVT100Terminal(DWORD std_handle) {
   ::SetConsoleMode(hdl, out_mode);
 }
 
-class terminal_windows : public terminal {
+class terminal_windows : public terminal_ansi {
  public:
   size_t width() const override {
     CONSOLE_SCREEN_BUFFER_INFO csbi;
@@ -157,21 +176,11 @@ class terminal_windows : public terminal {
     }
     return false;
   }
-
-  std::string_view
-  color(termcolor color, termstyle style = termstyle::NORMAL) const override {
-    return terminal_ansi_color(color, style);
-  }
-
-  std::string colored(std::string text, termcolor color, bool enable = true,
-                      termstyle style = termstyle::NORMAL) const override {
-    return terminal_ansi_colored(std::move(text), color, enable, style);
-  }
 };
 
 #else
 
-class terminal_posix : public terminal {
+class terminal_posix : public terminal_ansi {
  public:
   size_t width() const override {
     struct ::winsize w;
@@ -189,16 +198,6 @@ class terminal_posix : public terminal {
     auto term = ::getenv("TERM");
     return term && term[0] != '\0' && ::strcmp(term, "dumb") != 0;
   }
-
-  std::string_view
-  color(termcolor color, termstyle style = termstyle::NORMAL) const override {
-    return terminal_ansi_color(color, style);
-  }
-
-  std::string colored(std::string text, termcolor color, bool enable = true,
-                      termstyle style = termstyle::NORMAL) const override {
-    return terminal_ansi_colored(std::move(text), color, enable, style);
-  }
 };
 
 #endif

test/test_helpers.h

@@ -160,6 +160,9 @@ class test_terminal : public terminal {
   std::string_view color(termcolor color, termstyle style) const override;
   std::string colored(std::string text, termcolor color, bool enable,
                       termstyle style) const override;
+  std::string_view carriage_return() const override;
+  std::string_view rewind_line() const override;
+  std::string_view clear_line() const override;
 
  private:
   std::ostream* out_;

test/test_iolayer.cpp

@@ -219,6 +219,12 @@ bool test_terminal::is_fancy(std::ostream& os) const {
   return fancy_ && (&os == out_ || &os == err_);
 }
 
+std::string_view test_terminal::carriage_return() const { return "<cr>"; }
+
+std::string_view test_terminal::rewind_line() const { return "<rewind>"; }
+
+std::string_view test_terminal::clear_line() const { return "<clear>"; }
+
 std::string_view test_terminal::color(termcolor color, termstyle style) const {
   static constexpr std::array<std::string_view,
                               static_cast<size_t>(termcolor::NUM_COLORS)>