/*

Copyright (C) 1993-2019 John W. Eaton

This file is part of Octave.

Octave is free software: you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

Octave is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with Octave; see the file COPYING.  If not, see
<https://www.gnu.org/licenses/>.

*/

#if defined (HAVE_CONFIG_H)
#  include "config.h"
#endif

#include <fstream>
#include <iostream>
#include <string>

#include "child-list.h"
#include "cmd-edit.h"
#include "oct-env.h"
#include "oct-syscalls.h"

#include "defaults.h"
#include "defun.h"
#include "error.h"
#include "errwarn.h"
#include "input.h"
#include "interpreter.h"
#include "interpreter-private.h"
#include "octave.h"
#include "ovl.h"
#include "pager.h"
#include "procstream.h"
#include "sighandlers.h"
#include "unwind-prot.h"
#include "utils.h"
#include "variables.h"

namespace octave
{
  static bool
  pager_event_handler (pid_t pid, int status)
  {
    bool retval = false;

    if (pid > 0)
      {
        if (sys::wifexited (status) || sys::wifsignaled (status))
          {
            // Avoid warning() since that will put us back in the pager,
            // which would be bad news.

            std::cerr << "warning: connection to external pager lost (pid = "
                      << pid << ')' << std::endl;
            std::cerr << "warning: flushing pending output (please wait)"
                      << std::endl;

            // Request removal of this PID from the list of child
            // processes.

            retval = true;
          }
      }

    return retval;
  }

  // Assume our terminal wraps long lines.

  static bool
  more_than_a_screenful (const char *s, int len)
  {
    if (s)
      {
        int available_rows = command_editor::terminal_rows () - 2;

        int cols = command_editor::terminal_cols ();

        int count = 0;

        int chars_this_line = 0;

        for (int i = 0; i < len; i++)
          {
            if (*s++ == '\n')
              {
                count += chars_this_line / cols + 1;
                chars_this_line = 0;
              }
            else
              chars_this_line++;
          }

        if (count > available_rows)
          return true;
      }

    return false;
  }

  static std::string default_pager (void)
  {
    std::string pager_binary = sys::env::getenv ("PAGER");

    if (pager_binary.empty ())
      pager_binary = config::default_pager ();

    return pager_binary;
  }

  int
  pager_buf::sync (void)
  {
    output_system& output_sys = __get_output_system__ ("pager_buf::sync");

    char *buf = eback ();

    int len = pptr () - buf;

    if (output_sys.sync (buf, len))
      {
        flush_current_contents_to_diary ();

        seekoff (0, std::ios::beg);
      }

    return 0;
  }

  void
  pager_buf::flush_current_contents_to_diary (void)
  {
    char *buf = eback () + diary_skip;

    size_t len = pptr () - buf;

    octave_diary.write (buf, len);

    diary_skip = 0;
  }

  void
  pager_buf::set_diary_skip (void)
  {
    diary_skip = pptr () - eback ();
  }

  int
  diary_buf::sync (void)
  {
    output_system& output_sys = __get_output_system__ ("__stdout__");

    std::ofstream& external_diary_file = output_sys.external_diary_file ();

    if (output_sys.write_to_diary_file () && external_diary_file)
      {
        char *buf = eback ();

        int len = pptr () - buf;

        if (len > 0)
          external_diary_file.write (buf, len);
      }

    seekoff (0, std::ios::beg);

    return 0;
  }

  pager_stream::pager_stream (void) : std::ostream (nullptr), pb (nullptr)
  {
    pb = new pager_buf ();
    rdbuf (pb);
    setf (unitbuf);
  }

  pager_stream::~pager_stream (void)
  {
    flush ();
    delete pb;
  }

  std::ostream& pager_stream::stream (void)
  {
    return *this;
  }

  void pager_stream::flush_current_contents_to_diary (void)
  {
    if (pb)
      pb->flush_current_contents_to_diary ();
  }

  void pager_stream::set_diary_skip (void)
  {
    if (pb)
      pb->set_diary_skip ();
  }

  // Reinitialize the pager buffer to avoid hanging on to large internal
  // buffers when they might not be needed.  This function should only be
  // called when the pager is not in use.  For example, just before
  // getting command-line input.

  void pager_stream::reset (void)
  {
    delete pb;
    pb = new pager_buf ();
    rdbuf (pb);
    setf (unitbuf);
  }

  diary_stream::diary_stream (void) : std::ostream (nullptr), db (nullptr)
  {
    db = new diary_buf ();
    rdbuf (db);
    setf (unitbuf);
  }

  diary_stream::~diary_stream (void)
  {
    flush ();
    delete db;
  }

  std::ostream& diary_stream::stream (void)
  {
    return *this;
  }

  // Reinitialize the diary buffer to avoid hanging on to large internal
  // buffers when they might not be needed.  This function should only be
  // called when the pager is not in use.  For example, just before
  // getting command-line input.

  void diary_stream::reset (void)
  {
    delete db;
    db = new diary_buf ();
    rdbuf (db);
    setf (unitbuf);
  }

  void flush_stdout (void)
  {
    output_system& output_sys = __get_output_system__ ("flush_stdout");

    output_sys.flush_stdout ();
  }

  output_system::output_system (interpreter& interp)
    : m_interpreter (interp), m_pager_stream (), m_diary_stream (),
      m_external_pager (nullptr), m_external_diary_file (),
      m_diary_file_name ("diary"), m_PAGER (default_pager ()),
      m_PAGER_FLAGS (), m_page_output_immediately (false),
      m_page_screen_output (false), m_write_to_diary_file (false),
      m_really_flush_to_pager (false), m_flushing_output_to_pager (false)
  { }

  octave_value output_system::PAGER (const octave_value_list& args,
                                     int nargout)
  {
    return set_internal_variable (m_PAGER, args, nargout, "PAGER", false);
  }

  octave_value output_system::PAGER_FLAGS (const octave_value_list& args,
                                           int nargout)
  {
    return set_internal_variable (m_PAGER_FLAGS, args, nargout,
                                  "PAGER_FLAGS", false);
  }

  octave_value
  output_system::page_output_immediately (const octave_value_list& args,
                                          int nargout)
  {
    return set_internal_variable (m_page_output_immediately, args, nargout,
                                  "page_output_immediately");
  }

  octave_value
  output_system::page_screen_output (const octave_value_list& args,
                                     int nargout)
  {
    return set_internal_variable (m_page_screen_output, args, nargout,
                                  "page_screen_output");
  }

  std::string output_system::pager_command (void) const
  {
    std::string cmd = m_PAGER;

    if (! (cmd.empty () || m_PAGER_FLAGS.empty ()))
      cmd += ' ' + m_PAGER_FLAGS;

    return cmd;
  }

  void output_system::reset (void)
  {
    flush_stdout ();

    m_pager_stream.reset ();
    m_diary_stream.reset ();
  }

  void output_system::flush_stdout (void)
  {
    if (! m_flushing_output_to_pager)
      {
        unwind_protect frame;

        frame.protect_var (m_really_flush_to_pager);
        frame.protect_var (m_flushing_output_to_pager);

        m_really_flush_to_pager = true;
        m_flushing_output_to_pager = true;

        std::ostream& pager_ostream = m_pager_stream.stream ();

        pager_ostream.flush ();

        clear_external_pager ();
      }
  }

  void output_system::close_diary (void)
  {
    // Try to flush the current buffer to the diary now, so that things
    // like
    //
    // function foo ()
    //   diary on;
    //   ...
    //   diary off;
    // endfunction
    //
    // will do the right thing.

    m_pager_stream.flush_current_contents_to_diary ();

    if (m_external_diary_file.is_open ())
      {
        octave_diary.flush ();
        m_external_diary_file.close ();
      }
  }

  void output_system::open_diary (void)
  {
    close_diary ();

    // If there is pending output in the pager buf, it should not go
    // into the diary file.

    m_pager_stream.set_diary_skip ();

    m_external_diary_file.open (m_diary_file_name.c_str (), std::ios::app);

    if (! m_external_diary_file)
      error ("diary: can't open diary file '%s'", m_diary_file_name.c_str ());
  }

  bool output_system::sync (const char *buf, int len)
  {
    if (! application::interactive ()
        || application::forced_interactive ()
        || m_really_flush_to_pager
        || (m_page_screen_output && m_page_output_immediately)
        || ! m_page_screen_output)
      {
        bool bypass_pager = (! application::interactive ()
                             || application::forced_interactive ()
                             || ! m_page_screen_output
                             || (m_really_flush_to_pager
                                 && m_page_screen_output
                                 && ! m_page_output_immediately
                                 && ! more_than_a_screenful (buf, len)));

        if (len > 0)
          {
            do_sync (buf, len, bypass_pager);

            return true;
          }
      }

    return false;
  }

  void output_system::clear_external_pager (void)
  {
    if (m_external_pager)
      {
        child_list& kids = m_interpreter.get_child_list ();

        kids.remove (m_external_pager->pid ());

        delete m_external_pager;
        m_external_pager = nullptr;
      }
  }

  void output_system::start_external_pager (void)
  {
    if (m_external_pager)
      return;

    std::string pgr = pager_command ();

    if (! pgr.empty ())
      {
        m_external_pager = new oprocstream (pgr.c_str ());

        child_list& kids = m_interpreter.get_child_list ();

        kids.insert (m_external_pager->pid (),
                     pager_event_handler);
      }
  }

  void output_system::do_sync (const char *msg, int len, bool bypass_pager)
  {
    if (msg && len > 0)
      {
        if (bypass_pager)
          {
            std::cout.write (msg, len);
            std::cout.flush ();
          }
        else
          {
            start_external_pager ();

            if (m_external_pager)
              {
                if (m_external_pager->good ())
                  {
                    m_external_pager->write (msg, len);

                    m_external_pager->flush ();

#if defined (EPIPE)
                    if (errno == EPIPE)
                      m_external_pager->setstate (std::ios::failbit);
#endif
                  }
                else
                  {
                    // FIXME: something is not right with the
                    // pager.  If it died then we should receive a
                    // signal for that.  If there is some other problem,
                    // then what?
                  }
              }
            else
              {
                std::cout.write (msg, len);
                std::cout.flush ();
              }
          }
      }
  }

  std::ostream& __stdout__ (void)
  {
    output_system& output_sys = __get_output_system__ ("__stdout__");

    return output_sys.__stdout__ ();
  }

  std::ostream& __diary__ (void)
  {
    output_system& output_sys = __get_output_system__ ("__diary__");

    return output_sys.__diary__ ();
  }
}

DEFUN (diary, args, nargout,
       doc: /* -*- texinfo -*-
@deftypefn  {} {} diary
@deftypefnx {} {} diary on
@deftypefnx {} {} diary off
@deftypefnx {} {} diary @var{filename}
@deftypefnx {} {[@var{status}, @var{diaryfile}] =} diary
Record a list of all commands @emph{and} the output they produce, mixed
together just as they appear on the terminal.

Valid options are:

@table @asis
@item on
Start recording a session in a file called @file{diary} in the current working
directory.

@item off
Stop recording the session in the diary file.

@item @var{filename}
Record the session in the file named @var{filename}.
@end table

With no input or output arguments, @code{diary} toggles the current diary
state.

If output arguments are requested, @code{diary} ignores inputs and returns
the current status.  The boolean @var{status} indicates whether recording is on
or off, and @var{diaryfile} is the name of the file where the session is
stored.
@seealso{history, evalc}
@end deftypefn */)
{
  int nargin = args.length ();

  if (nargin > 1)
    print_usage ();

  octave::output_system& output_sys = octave::__get_output_system__ ("Fdiary");

  if (nargout > 0)
    {
      // Querying diary variables
      if (nargout == 1)
        return ovl (output_sys.write_to_diary_file ());
      else
        return ovl (output_sys.write_to_diary_file (),
                    output_sys.diary_file_name ());
    }

  if (nargin == 0)
    {
      output_sys.write_to_diary_file (! output_sys.write_to_diary_file ());
      output_sys.open_diary ();
    }
  else
    {
      std::string arg = args(0).xstring_value ("diary: argument must be a string");

      if (arg == "on")
        {
          output_sys.write_to_diary_file (true);
          output_sys.open_diary ();
        }
      else if (arg == "off")
        {
          output_sys.close_diary ();
          output_sys.write_to_diary_file (false);
        }
      else
        {
          output_sys.diary_file_name (arg);
          output_sys.write_to_diary_file (true);
          output_sys.open_diary ();
        }
    }

  return ovl ();
}

DEFMETHOD (more, interp, args, ,
           doc: /* -*- texinfo -*-
@deftypefn  {} {} more
@deftypefnx {} {} more on
@deftypefnx {} {} more off
Turn output pagination on or off.

Without an argument, @code{more} toggles the current state.

The current state can be determined via @code{page_screen_output}.
@seealso{page_screen_output, page_output_immediately, PAGER, PAGER_FLAGS}
@end deftypefn */)
{
  int nargin = args.length ();

  if (nargin > 1)
    print_usage ();

  octave::output_system& output_sys = interp.get_output_system ();

  if (nargin > 0)
    {
      std::string arg = args(0).xstring_value (R"(more: argument must be string "on" or "off")");

      if (arg == "on")
        output_sys.page_screen_output (true);
      else if (arg == "off")
        output_sys.page_screen_output (false);
      else
        error (R"(more: argument must be "on" or "off")");
    }
  else
    output_sys.page_screen_output (! output_sys.page_screen_output ());

  return ovl ();
}

DEFUN (terminal_size, , ,
       doc: /* -*- texinfo -*-
@deftypefn {} {} terminal_size ()
Return a two-element row vector containing the current size of the terminal
window in characters (rows and columns).
@seealso{list_in_columns}
@end deftypefn */)
{
  RowVector size (2, 0.0);

  size(0) = octave::command_editor::terminal_rows ();
  size(1) = octave::command_editor::terminal_cols ();

  return ovl (size);
}

DEFMETHOD (page_output_immediately, interp, args, nargout,
           doc: /* -*- texinfo -*-
@deftypefn  {} {@var{val} =} page_output_immediately ()
@deftypefnx {} {@var{old_val} =} page_output_immediately (@var{new_val})
@deftypefnx {} {} page_output_immediately (@var{new_val}, "local")
Query or set the internal variable that controls whether Octave sends
output to the pager as soon as it is available.

Otherwise, Octave buffers its output and waits until just before the prompt
is printed to flush it to the pager.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@seealso{page_screen_output, more, PAGER, PAGER_FLAGS}
@end deftypefn */)
{
  octave::output_system& output_sys = interp.get_output_system ();

  return output_sys.page_output_immediately (args, nargout);
}

DEFMETHOD (page_screen_output, interp, args, nargout,
           doc: /* -*- texinfo -*-
@deftypefn  {} {@var{val} =} page_screen_output ()
@deftypefnx {} {@var{old_val} =} page_screen_output (@var{new_val})
@deftypefnx {} {} page_screen_output (@var{new_val}, "local")
Query or set the internal variable that controls whether output intended
for the terminal window that is longer than one page is sent through a
pager.

This allows you to view one screenful at a time.  Some pagers
(such as @code{less}---see @ref{Installation}) are also capable of moving
backward on the output.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@seealso{more, page_output_immediately, PAGER, PAGER_FLAGS}
@end deftypefn */)
{
  octave::output_system& output_sys = interp.get_output_system ();

  return output_sys.page_screen_output (args, nargout);
}

DEFMETHOD (PAGER, interp, args, nargout,
           doc: /* -*- texinfo -*-
@deftypefn  {} {@var{val} =} PAGER ()
@deftypefnx {} {@var{old_val} =} PAGER (@var{new_val})
@deftypefnx {} {} PAGER (@var{new_val}, "local")
Query or set the internal variable that specifies the program to use
to display terminal output on your system.

The default value is normally @qcode{"less"}, @qcode{"more"}, or
@qcode{"pg"}, depending on what programs are installed on your system.
@xref{Installation}.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@seealso{PAGER_FLAGS, page_output_immediately, more, page_screen_output}
@end deftypefn */)
{
  octave::output_system& output_sys = interp.get_output_system ();

  return output_sys.PAGER (args, nargout);
}

DEFMETHOD (PAGER_FLAGS, interp, args, nargout,
           doc: /* -*- texinfo -*-
@deftypefn  {} {@var{val} =} PAGER_FLAGS ()
@deftypefnx {} {@var{old_val} =} PAGER_FLAGS (@var{new_val})
@deftypefnx {} {} PAGER_FLAGS (@var{new_val}, "local")
Query or set the internal variable that specifies the options to pass
to the pager.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@seealso{PAGER, more, page_screen_output, page_output_immediately}
@end deftypefn */)
{
  octave::output_system& output_sys = interp.get_output_system ();

  return output_sys.PAGER_FLAGS (args, nargout);
}