truncate status on small terminals

When the TTY is too narrow to contain the output, the assumption
that a carriage return and whitespace while erase the line no
longer holds. Prior to printing, check the number of columns
available in the TTY.

See alire-project/alire#1329 for a demonstration of the issue.

simple_logging.gpr

@@ -7,6 +7,8 @@ project Simple_Logging is
    for Object_Dir use "obj";
    for Library_Dir use "lib";
 
+   for Languages use ("C", "Ada");
+
    package Builder is
       for Switches ("ada") use ("-j0", "-g");
    end Builder;

src/simple_logging.adb

@@ -5,13 +5,18 @@ with GNAT.IO;
 with Simple_Logging.Decorators;
 with Simple_Logging.Filtering;
 
+with Interfaces.C;
+
 pragma Warnings (Off);
 --  This is compiler-internal unit. We only use the Clock, which is highly
 --  unlikely to change its specification.
 with System.OS_Primitives;
 pragma Warnings (On);
 
 package body Simple_Logging is
+   function Get_Term_Width return Interfaces.C.Int;
+   pragma Import
+      (Convention => C, Entity => Get_Term_Width, External_Name => "simple_logging_term_width");
 
    ---------
    -- Log --
@@ -172,6 +177,8 @@ package body Simple_Logging is
       Line : Unbounded_String;
       Pred : Unbounded_String;
       --  Status of the precedent scope, to eliminate duplicates
+
+      Effective_Length : Integer;
    begin
       for Status of Statuses loop
          if Status.Level <= Simple_Logging.Level
@@ -187,7 +194,12 @@ package body Simple_Logging is
          Line := Indicator & " " & Line;
       end if;
 
-      return To_String (Line);
+      Effective_Length := Integer (Get_Term_Width);
+      if Effective_Length = -1 or else Effective_Length > Length (Line) then
+         Effective_Length := Length (Line);
+      end if;
+
+      return To_String (Head (Line, Effective_Length));
    end Build_Status_Line;
 
    -----------------------
@@ -255,5 +267,4 @@ package body Simple_Logging is
          end if;
       end;
    end Step;
-
 end Simple_Logging;

src/term.c

@@ -0,0 +1,21 @@
+#include <stdbool.h>
+#include <sys/ioctl.h>
+#include <termios.h>
+
+bool ioctl_failure = false;
+
+int simple_logging_term_width(void)
+{
+	struct winsize x;
+	int r;
+
+	if (ioctl_failure) return -1;
+	r = ioctl(2, TIOCGWINSZ, &x);
+
+	if (r != 0) {
+		ioctl_failure = true;
+		return -1;
+	} else {
+		return x.ws_col;
+	}
+}