# Copyright (C) 2009-2021 by the Free Software Foundation, Inc.
#
# This file is part of GNU Mailman.
#
# GNU Mailman 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.
#
# GNU Mailman 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
# GNU Mailman.  If not, see <https://www.gnu.org/licenses/>.

"""String utilities."""

import logging

from email.errors import HeaderParseError
from email.header import decode_header, make_header
from mailman.config import config
from public import public
from string import Template, whitespace
from textwrap import TextWrapper, dedent


EMPTYSTRING = ''
NL = '\n'

log = logging.getLogger('mailman.error')


@public
def expand(template, mlist=None, extras=None, template_class=Template):
    """Expand string template with substitutions.

    :param template: A PEP 292 $-string template.
    :type template: string
    :param mlist: Optional mailing list.  If given, the standard set of
        list-specific substitution variables are used automatically.
    :type mlist: `IMailingList`
    :param extras: An additional substitutions dictionary.  These are used to
        augment any standard, list-specific substitutions.
    :type extras: dict
    :param template_class: The template class to use.
    :type template_class: class
    :return: The substituted string.
    :rtype: string
    """
    substitutions = dict(
        site_email=config.mailman.site_owner,
        )
    if mlist is not None:
        substitutions.update(dict(
            listname=mlist.fqdn_listname,
            list_id=mlist.list_id,
            display_name=mlist.display_name,
            short_listname=mlist.list_name,
            domain=mlist.mail_host,
            description=mlist.description,
            info=mlist.info,
            request_email=mlist.request_address,
            owner_email=mlist.owner_address,
            language=mlist.preferred_language.code,
            ))
    if extras is not None:
        substitutions.update(extras)
    return template_class(template).safe_substitute(substitutions)


@public
def oneline(s, cset='us-ascii', in_unicode=False):
    """Decode a header string in one line and convert into specified charset.

    :param s: The header string
    :type s: string
    :param cset: The character set (encoding) to use.
    :type cset: string
    :param in_unicode: Flag specifying whether to return the converted string
        as a unicode (True) or an 8-bit string (False, the default).
    :type in_unicode: bool
    :return: The decoded header string.  If an error occurs while converting
        the input string, return the string undecoded, as an 8-bit string.
    :rtype: string
    """
    try:
        h = str(make_header(decode_header(s)))
        line = EMPTYSTRING.join(h.splitlines())
        if in_unicode:
            return line
        else:
            return line.encode(cset, 'replace')
    except (LookupError, UnicodeError, ValueError, HeaderParseError):
        # possibly charset problem. return with undecoded string in one line.
        return EMPTYSTRING.join(s.splitlines())


@public
def wrap(text, column=70, honor_leading_ws=True):
    """Wrap and fill the text to the specified column.

    The input text is wrapped and filled as done by the standard library
    textwrap module.  The differences here being that this function is capable
    of filling multiple paragraphs (as defined by text separated by blank
    lines).  Also, when `honor_leading_ws` is True (the default), paragraphs
    that being with whitespace are not wrapped.  This is the algorithm that
    the Python FAQ wizard used.
    """
    # First, split the original text into paragraph, keeping all blank lines
    # between them.
    paragraphs = []
    paragraph = []
    last_indented = False
    for line in text.splitlines(True):
        is_indented = (len(line) > 0 and line[0] in whitespace)
        if line == NL:
            if len(paragraph) > 0:
                paragraphs.append(EMPTYSTRING.join(paragraph))
            paragraphs.append(line)
            last_indented = False
            paragraph = []
        elif last_indented != is_indented:
            # The indentation level changed.  We treat this as a paragraph
            # break but no blank line will be issued between paragraphs.
            if len(paragraph) > 0:
                paragraphs.append(EMPTYSTRING.join(paragraph))
            # The next paragraph starts with this line.
            paragraph = [line]
            last_indented = is_indented
        else:
            # This line does not constitute a paragraph break.
            paragraph.append(line)
    # We've consumed all the lines in the original text.  Transfer the last
    # paragraph we were collecting to the full set of paragraphs, but only if
    # it's not empty.
    if len(paragraph) > 0:
        paragraphs.append(EMPTYSTRING.join(paragraph))
    # Now iterate through all paragraphs, wrapping as necessary.
    wrapped_paragraphs = []
    # The dedented wrapper.
    wrapper = TextWrapper(width=column,
                          break_on_hyphens=False,
                          fix_sentence_endings=True)
    # The indented wrapper.  For this one, we'll clobber initial_indent and
    # subsequent_indent as needed per indented chunk of text.
    iwrapper = TextWrapper(width=column,
                           break_on_hyphens=False,
                           fix_sentence_endings=True,
                           )
    add_paragraph_break = False
    for paragraph in paragraphs:
        if add_paragraph_break:
            wrapped_paragraphs.append(NL)
            add_paragraph_break = False
        paragraph_text = EMPTYSTRING.join(paragraph)
        # Just copy the blank lines to the final set of paragraphs.
        if len(paragraph) == 0 or paragraph == NL:
            wrapped_paragraphs.append(NL)
        # Choose the wrapper based on whether the paragraph is indented or
        # not.  Also, do not wrap indented paragraphs if honor_leading_ws is
        # set.
        elif paragraph[0] in whitespace:
            if honor_leading_ws:
                # Leave the indented paragraph verbatim.
                wrapped_paragraphs.append(paragraph_text)
            else:
                # The paragraph should be wrapped, but it must first be
                # dedented.  The leading whitespace on the first line of the
                # original text will be used as the indentation for all lines
                # in the wrapped text.
                for i, ch in enumerate(paragraph_text):   # pragma: no branch
                    if ch not in whitespace:
                        break
                leading_ws = paragraph[:i]
                iwrapper.initial_indent = leading_ws
                iwrapper.subsequent_indent = leading_ws
                paragraph_text = dedent(paragraph_text)
                wrapped_paragraphs.append(iwrapper.fill(paragraph_text))
                add_paragraph_break = True
        else:
            # Fill this paragraph.  fill() consumes the trailing newline.
            wrapped_paragraphs.append(wrapper.fill(paragraph_text))
            add_paragraph_break = True
    return EMPTYSTRING.join(wrapped_paragraphs)
