from contextlib import contextmanager
from .termui import get_terminal_size
from .parser import split_opt
from ._compat import term_len


# Can force a width.  This is used by the test system
FORCED_WIDTH = None


def measure_table(rows):
    widths = {}
    for row in rows:
        for idx, col in enumerate(row):
            widths[idx] = max(widths.get(idx, 0), term_len(col))
    return tuple(y for x, y in sorted(widths.items()))


def iter_rows(rows, col_count):
    for row in rows:
        row = tuple(row)
        yield row + ('',) * (col_count - len(row))


def wrap_text(text, width=78, initial_indent='', subsequent_indent='',
              preserve_paragraphs=False):
    """A helper function that intelligently wraps text.  By default, it
    assumes that it operates on a single paragraph of text but if the
    `preserve_paragraphs` parameter is provided it will intelligently
    handle paragraphs (defined by two empty lines).

    If paragraphs are handled, a paragraph can be prefixed with an empty
    line containing the ``\\b`` character (``\\x08``) to indicate that
    no rewrapping should happen in that block.

    :param text: the text that should be rewrapped.
    :param width: the maximum width for the text.
    :param initial_indent: the initial indent that should be placed on the
                           first line as a string.
    :param subsequent_indent: the indent string that should be placed on
                              each consecutive line.
    :param preserve_paragraphs: if this flag is set then the wrapping will
                                intelligently handle paragraphs.
    """
    from ._textwrap import TextWrapper
    text = text.expandtabs()
    wrapper = TextWrapper(width, initial_indent=initial_indent,
                          subsequent_indent=subsequent_indent,
                          replace_whitespace=False)
    if not preserve_paragraphs:
        return wrapper.fill(text)

    p = []
    buf = []
    indent = None

    def _flush_par():
        if not buf:
            return
        if buf[0].strip() == '\b':
            p.append((indent or 0, True, '\n'.join(buf[1:])))
        else:
            p.append((indent or 0, False, ' '.join(buf)))
        del buf[:]

    for line in text.splitlines():
        if not line:
            _flush_par()
            indent = None
        else:
            if indent is None:
                orig_len = term_len(line)
                line = line.lstrip()
                indent = orig_len - term_len(line)
            buf.append(line)
    _flush_par()

    rv = []
    for indent, raw, text in p:
        with wrapper.extra_indent(' ' * indent):
            if raw:
                rv.append(wrapper.indent_only(text))
            else:
                rv.append(wrapper.fill(text))

    return '\n\n'.join(rv)


class HelpFormatter(object):
    """This class helps with formatting text-based help pages.  It's
    usually just needed for very special internal cases, but it's also
    exposed so that developers can write their own fancy outputs.

    At present, it always writes into memory.

    :param indent_increment: the additional increment for each level.
    :param width: the width for the text.  This defaults to the terminal
                  width clamped to a maximum of 78.
    """

    def __init__(self, indent_increment=2, width=None, max_width=None):
        self.indent_increment = indent_increment
        if max_width is None:
            max_width = 80
        if width is None:
            width = FORCED_WIDTH
            if width is None:
                width = max(min(get_terminal_size()[0], max_width) - 2, 50)
        self.width = width
        self.current_indent = 0
        self.buffer = []

    def write(self, string):
        """Writes a unicode string into the internal buffer."""
        self.buffer.append(string)

    def indent(self):
        """Increases the indentation."""
        self.current_indent += self.indent_increment

    def dedent(self):
        """Decreases the indentation."""
        self.current_indent -= self.indent_increment

    def write_usage(self, prog, args='', prefix='Usage: '):
        """Writes a usage line into the buffer.

        :param prog: the program name.
        :param args: whitespace separated list of arguments.
        :param prefix: the prefix for the first line.
        """
        usage_prefix = '%*s%s ' % (self.current_indent, prefix, prog)
        text_width = self.width - self.current_indent

        if text_width >= (term_len(usage_prefix) + 20):
            # The arguments will fit to the right of the prefix.
            indent = ' ' * term_len(usage_prefix)
            self.write(wrap_text(args, text_width,
                                 initial_indent=usage_prefix,
                                 subsequent_indent=indent))
        else:
            # The prefix is too long, put the arguments on the next line.
            self.write(usage_prefix)
            self.write('\n')
            indent = ' ' * (max(self.current_indent, term_len(prefix)) + 4)
            self.write(wrap_text(args, text_width,
                                 initial_indent=indent,
                                 subsequent_indent=indent))

        self.write('\n')

    def write_heading(self, heading):
        """Writes a heading into the buffer."""
        self.write('%*s%s:\n' % (self.current_indent, '', heading))

    def write_paragraph(self):
        """Writes a paragraph into the buffer."""
        if self.buffer:
            self.write('\n')

    def write_text(self, text):
        """Writes re-indented text into the buffer.  This rewraps and
        preserves paragraphs.
        """
        text_width = max(self.width - self.current_indent, 11)
        indent = ' ' * self.current_indent
        self.write(wrap_text(text, text_width,
                             initial_indent=indent,
                             subsequent_indent=indent,
                             preserve_paragraphs=True))
        self.write('\n')

    def write_dl(self, rows, col_max=30, col_spacing=2):
        """Writes a definition list into the buffer.  This is how options
        and commands are usually formatted.

        :param rows: a list of two item tuples for the terms and values.
        :param col_max: the maximum width of the first column.
        :param col_spacing: the number of spaces between the first and
                            second column.
        """
        rows = list(rows)
        widths = measure_table(rows)
        if len(widths) != 2:
            raise TypeError('Expected two columns for definition list')

        first_col = min(widths[0], col_max) + col_spacing

        for first, second in iter_rows(rows, len(widths)):
            self.write('%*s%s' % (self.current_indent, '', first))
            if not second:
                self.write('\n')
                continue
            if term_len(first) <= first_col - col_spacing:
                self.write(' ' * (first_col - term_len(first)))
            else:
                self.write('\n')
                self.write(' ' * (first_col + self.current_indent))

            text_width = max(self.width - first_col - 2, 10)
            lines = iter(wrap_text(second, text_width).splitlines())
            if lines:
                self.write(next(lines) + '\n')
                for line in lines:
                    self.write('%*s%s\n' % (
                        first_col + self.current_indent, '', line))
            else:
                self.write('\n')

    @contextmanager
    def section(self, name):
        """Helpful context manager that writes a paragraph, a heading,
        and the indents.

        :param name: the section name that is written as heading.
        """
        self.write_paragraph()
        self.write_heading(name)
        self.indent()
        try:
            yield
        finally:
            self.dedent()

    @contextmanager
    def indentation(self):
        """A context manager that increases the indentation."""
        self.indent()
        try:
            yield
        finally:
            self.dedent()

    def getvalue(self):
        """Returns the buffer contents."""
        return ''.join(self.buffer)


def join_options(options):
    """Given a list of option strings this joins them in the most appropriate
    way and returns them in the form ``(formatted_string,
    any_prefix_is_slash)`` where the second item in the tuple is a flag that
    indicates if any of the option prefixes was a slash.
    """
    rv = []
    any_prefix_is_slash = False
    for opt in options:
        prefix = split_opt(opt)[0]
        if prefix == '/':
            any_prefix_is_slash = True
        rv.append((len(prefix), opt))

    rv.sort(key=lambda x: x[0])

    rv = ', '.join(x[1] for x in rv)
    return rv, any_prefix_is_slash
