: m_rows(0), m_columns(0), m_start_row_index(0)

{

maybe_grab_cout();

{

// Blocks until input received.

std::string str;

char ch;

std::cin.get(ch);

str += ch;

if (ansi_code::is_escape_char(ch)) // Start of ANSI escape sequence.

{

do

{

std::cin.get(ch);

str += ch;

} while (!std::isalpha(ch)); // ANSI escape sequence ends with a letter.

}

return str;

{

// Unfortunately need to access _internal namespace of termcolor to check if a tty.

if (termcolor::_internal::is_atty(std::cout))

{

// Should we do anything with cerr?

m_cout_rdbuf = std::cout.rdbuf(&m_stringbuf);

}

else

{

m_cout_rdbuf = std::cout.rdbuf();

}

{

if (input.size() == 0)

{

return true;

}

switch (input[0])

{

case 'q':

case 'Q':

return true; // Exit pager.

case 'u':

case 'U':

scroll(true, true); // Up a page.

return false;

case 'd':

case 'D':

case ' ':

scroll(false, true); // Down a page.

return false;

case '\n':

scroll(false, false); // Down a line.

return false;

case '\e': // ANSI escape sequence.

// Cannot switch on a std::string.

if (ansi_code::is_up_arrow(input))

{

scroll(true, false); // Up a line.

return false;

}

else if (ansi_code::is_down_arrow(input))

{

scroll(false, false); // Down a line.

return false;

}

}

std::cout << ansi_code::bel;

return false;

{

auto end_row_index = m_start_row_index + m_rows - 1;

std::cout << ansi_code::erase_screen;

std::cout << ansi_code::cursor_to_top;

for (size_t i = m_start_row_index; i < end_row_index; i++)

{

if (i >= m_lines.size())

{

break;

}

std::cout << m_lines[i] << std::endl;

}

std::cout << ansi_code::cursor_to_row(m_rows); // Move cursor to bottom row of terminal.

std::cout << ":";

{

update_terminal_size();

const auto old_start_row_index = m_start_row_index;

size_t offset = page ? m_rows - 1 : 1;

if (up)

{

// Care needed to avoid underflow of unsigned size_t.

if (m_start_row_index >= offset)

{

m_start_row_index -= offset;

}

else

{

m_start_row_index = 0;

}

}

else

{

m_start_row_index += offset;

auto end_row_index = m_start_row_index + m_rows - 1;

if (end_row_index > m_lines.size())

{

m_start_row_index = m_lines.size() - (m_rows - 1);

}

}

if (m_start_row_index == old_start_row_index)

{

std::cout << ansi_code::bel;

}

else

{

render_terminal();

}

{

release_cout();

split_input_at_newlines(m_stringbuf.view());

update_terminal_size();

if (m_rows == 0 || m_lines.size() <= m_rows - 1)

{

// Don't need to use pager, can display directly.

for (auto line : m_lines)

{

std::cout << line << std::endl;

}

m_lines.clear();

return;

}

alternative_buffer alt_buffer;

m_start_row_index = 0;

render_terminal();

bool stop = false;

do

{

stop = process_input(get_input());

} while (!stop);

m_lines.clear();

m_start_row_index = 0;

{

auto split = str | std::ranges::views::split('\n')

| std::ranges::views::transform([](auto&& range) {

return std::string(range.begin(), range.end());

});

m_lines = std::vector<std::string>{split.begin(), split.end()};

{

struct winsize size;

int err = ioctl(fileno(stdout), TIOCGWINSZ, &size);

if (err == 0)

{

m_rows = size.ws_row;

m_columns = size.ws_col;

}

else

{

m_rows = m_columns = 0;

}