#include <iostream>
#include <sstream>
#include <string>

#include <cstdlib>
#include <cstring>

#include <QApplication>
#include <QKeyEvent>
#include <QTextDocument>
#include <QTextEdit>
#include <QTimer>

#include "command-window.h"
#include "interpreter.h"
#include "parser.h"

#include <readline/readline.h>
#include <readline/history.h>

namespace calc
{
  // We could eliminate this global variable and the global
  // command_window::the_command_window variable if readline callbacks
  // could be defined as C++ lambda functions.  Then the lambdas could
  // have direct access to the command_window object and it could
  // contain the next available character.

  static int available_char = 0;

  // vvvvv readline vvvvv

  static int getc (FILE *)
  {
    int tmp = available_char;
    available_char = 0;
    return tmp;
  }

  static void redisplay (void)
  {
    if (command_window::the_command_window)
      emit command_window::the_command_window->redisplay_signal ();
  }

  static void prep_term (int)
  {
    // Anything to do here?
  }

  static void deprep_term (void)
  {
    // Anything to do here?
  }

  static void accept_line (char *line)
  {
    if (command_window::the_command_window)
      {
        if (! line)
          command_window::the_command_window->eof ();
        else
          command_window::the_command_window->accept_line (line);
      }
  }

  static void display_completion_matches (char **matches, int num_matches,
                                          int /* max_length */)
  {
    if (command_window::the_command_window)
      {
        std::ostringstream buf;

        if (num_matches > 1)
          buf << "\n";

        for (int i = 1; i < num_matches; i++)
          buf << matches[i] << "\n";

        command_window::the_command_window->insert_at_end (buf.str ());

        emit command_window::the_command_window->redisplay_signal ();
      }
  }

  static void readline_init (void)
  {
    rl_initialize ();

    rl_getc_function = getc;
    rl_redisplay_function = redisplay;
    rl_prep_term_function = prep_term;
    rl_deprep_term_function = deprep_term;
    rl_completion_display_matches_hook = display_completion_matches;

    rl_callback_handler_install (">> ", accept_line);
  }

  static void readline_fini (void)
  {
    rl_callback_handler_remove ();
  }

  // ^^^^^ readline ^^^^^

  command_window *command_window::the_command_window = nullptr;

  command_window::command_window (QWidget *p)
    : QTextEdit (p), m_buffer (new QTextDocument ()),
      m_interpreter (new calc::qt_interpreter ()),
      beg_mark (), prompt_mark ()
  {
    if (the_command_window)
      {
        std::cerr << "multiple command_windows are not possible!" << std::endl;
        exit (1);
      }

    the_command_window = this;

    setWindowTitle ("Qt::TextEdit example");

    setMinimumSize (QSize (600, 400));

    setDocument (m_buffer);

    connect (m_interpreter, SIGNAL (result_ready (double)),
             this, SLOT (handle_result (double)));

    connect (m_interpreter, SIGNAL (error_signal (const QString&)),
             this, SLOT (handle_error (const QString&)));

    connect (this, SIGNAL (input_char_available (int)),
             this, SLOT (handle_input_char (int)));

    connect (this, SIGNAL (redisplay_signal (void)),
             this, SLOT (redisplay (void)));

    connect (this, SIGNAL (accept_line_signal (const QString&)),
             m_interpreter, SLOT (accept_input_line (const QString&)));

    connect (this, SIGNAL (eof_signal (void)),
             this, SLOT (close (void)));

    insert_at_end
      ("Qt Example Calculator.\n"
       "Available operations: + - * / ^ ()\n"
       "Semicolon terminates statement.\n"
       "Up Arrow key moves to previous line in the command history.\n"
       "Down Arrow key moves to next line in the comand history.\n\n");

    beg_mark = set_mark ();

    readline_init ();

    // Defer initializing and executing the interpreter until after the main
    // window and QApplication are running to prevent race conditions
    QTimer::singleShot (0, m_interpreter, SLOT (execute (void)));
  }

  command_window::~command_window (void)
  {
    readline_fini ();
  }

  // Accept an input line, parse and possibly execute it.

  void command_window::accept_line (const std::string& line)
  {
    insert_at_end ("\n");

    if (! line.empty ())
      {
        add_history (line.c_str ());
        using_history ();

        emit accept_line_signal (QString::fromStdString (line));
      }
  }

  void command_window::eof (void)
  {
    emit eof_signal ();
  }

  void command_window::insert_at_end (const std::string& text)
  {
    scroll_to_bottom ();

    insert_at_cursor (text);
  }

  void command_window::handle_error (const QString& msg)
  {
    insert_at_end ("parse error: " + msg.toStdString () + "\n");

    rl_abort (0, 0);
  }

  // FIXME: do we really need this extra function?
  void command_window::handle_result (double value)
  {
    insert_result (value);
  }

  // Redisplay current command line.

  void command_window::redisplay (void)
  {
    erase_line ();

    interpreter& interp = m_interpreter->get_interpreter ();
    parser& parser = interp.get_parser ();

    std::string line = rl_line_buffer ? rl_line_buffer : "";
    std::string prompt = (rl_prompt && parser.beg_of_stmt ()) ? rl_prompt : "";

    insert_line (prompt, line);

    scroll_to_bottom ();

    QTextCursor cursor = textCursor ();

    cursor.setPosition (prompt_mark + rl_point, QTextCursor::MoveAnchor);

    setTextCursor (cursor);
  }

  void command_window::keyPressEvent (QKeyEvent *event)
  {
    if (! event)
      return;

    if (event->type () == QEvent::KeyPress)
      {
        int key = event->key ();

        switch (key)
          {
          case Qt::Key_Return:
            key = 0x0A;
            break;

          case Qt::Key_Backspace:
            key = 0x08;
            break;

          case Qt::Key_Tab:
            key = 0x09;
            break;

          case Qt::Key_Escape:
            key = 0x1b;
            break;

          case Qt::Key_Up:
          case Qt::Key_Down:
          case Qt::Key_Right:
          case Qt::Key_Left:
            key = do_arrow_key (key);
            break;

          default:
            {
              switch (event->modifiers ())
                {
                case Qt::ControlModifier:
                  if (key > 0x3f && key < 0x7b)
                    key &= 0x1f;
                  else
                    key = -1;
                  break;

                default:
                  {
                    // Don't shoot me, this is just a demo...
                    QString text = event->text ();
                    QByteArray latin_text = text.toLatin1 ();
                    key = latin_text[0];
                  }
                  break;
                }
            }
            break;
          }

        if (key >= 0)
          emit input_char_available (key);
      }
  }

  void command_window::handle_input_char (int key)
  {
    available_char = key;
    rl_callback_read_char ();
  }

  int command_window::do_arrow_key (int arrow_key)
  {
    int retval = 0;

    available_char = 0x1b;
    rl_callback_read_char ();

    available_char = '[';
    rl_callback_read_char ();

    switch (arrow_key)
      {
      case Qt::Key_Up:
        retval = 'A';
        break;

      case Qt::Key_Down:
        retval = 'B';
        break;

      case Qt::Key_Right:
        retval = 'C';
        break;

      case Qt::Key_Left:
        retval = 'D';
        break;
      }

    return retval;
  }

  // Retrieve a command from the history list and insert it on the
  // current command.

  void command_window::history (bool up)
  {
    HIST_ENTRY *entry = up ? previous_history () : next_history ();

    if (entry)
      {
        erase_line ();

        std::string prompt = rl_prompt ? rl_prompt : "";

        insert_line (prompt, entry->line);
      }
    else if (! up)
      erase_line ();

    scroll_to_bottom ();
  }

  void command_window::erase_line (void)
  {
    QTextCursor cursor = textCursor ();

    cursor.movePosition (QTextCursor::End);
    cursor.select (QTextCursor::LineUnderCursor);
    cursor.removeSelectedText ();

    setTextCursor (cursor);
  }

  void command_window::insert_at_cursor (const std::string& text)
  {
    QTextCursor cursor = textCursor ();

    cursor.insertText (QString::fromStdString (text));

    setTextCursor (cursor);
  }

  void command_window::insert_line (const std::string& prompt,
                                    const std::string& line)
  {
    beg_mark = set_mark ();

    insert_at_cursor (prompt);

    prompt_mark = set_mark ();

    insert_at_cursor (line);
  }

  int command_window::set_mark (void)
  {
    return textCursor ().position ();
  }

  void command_window::insert_result (double value)
  {
    std::ostringstream buf;

    buf << "ans = " << value << "\n";

    insert_at_cursor (buf.str ());

    beg_mark = set_mark ();

    scroll_to_bottom ();
  }

  void command_window::scroll_to_bottom (void)
  {
    QTextCursor cursor = textCursor ();

    cursor.movePosition (QTextCursor::End);

    setTextCursor (cursor);
  }
}