# -*- coding: utf-8 -*-
"""A Pelican plugin to use Pandoc software.

Pandoc is a powerful tool to transform text from different formats (e.g. ReST,
Markdown) to others. It is really helpful to generate PDF or EPUB.

This plugin provides a powerful interface to handle document generation through
Pandoc.

Here is the list of configuration variables.

PANDOC_OUTPUTS          a dict where the keys are the output formats and the
                        values are the destination directories. Note if
                        to_format is set at "pdf", the "to"-argument is set at
                        latex" for Pandoc which does not support "-t pdf"
                        argument.
PANDOC_EXPORT_ARTICLES  True (default) if you want to export articles, False
                        else.
PANDOC_EXPORT_PAGES     True (default) if you want to export pages, False else.

PANDOC_MARKDOWN_EXTENSIONS  a list with Pandoc's markdown extensions
PANDOC_EXECUTABLE       path to pandoc executable
PANDOC_EXTRA_OPTIONS    extra options to pandoc executable

Important note: this plugin requires Pandoc to be installed on your system to work!

"""

from __future__ import unicode_literals

import os
import logging

from pelican import signals
from pelican.generators import Generator

from subprocess import check_call


logger = logging.getLogger(__name__)


class PandocGenerator(Generator):
    """The Pandoc generator.

    It takes the list of articles / pages and generates files according to
    PANDOC_OUTPUTS configuration variable.

    """

    def guess_format(self, content):
        """Return the format used by a given content.

        Since Pelican only supports reStructuredText and MarkDown files, this
        method returns just "md" or "rst".

        It is based on the file extension.

        TODO: it could be great if Pelican could support this method itself.

        :param content: the content (article or page)
        :type content: pelican.contents.Content
        :return: the article type (rst or md)
        :rtype: str
        :raises: KeyError if the file extension is not supported

        """
        formats = {
            '.rst': 'rst',
            '.md': 'md',
            '.markdown': 'md',
            '.mkd': 'md',
            '.mdown': 'md',
        }

        file_name, file_extension = os.path.splitext(content.source_path)

        return formats[file_extension]

    def check_output_dir(self, dir_):
        """Check and create if needed the given directory."""
        if not os.path.isdir(dir_):
            try:
                os.mkdir(dir_)
            except OSError:
                return False

        return True

    def generate_files(self, content):
        """Generates the list of files for a given content.

        :param content: the content to generate.
        :type content: pelican.contents.Content

        """

        if self.settings.get('PDF_PROCESSOR', False) == False:
            return

        try:
            from_format = self.guess_format(content)
        except KeyError:
            logger.error("Unsupported format for {filename}".format(
                filename=content.source_path
            ))
            return

        list_outputs = self.settings.get('PANDOC_OUTPUTS', {})
        for to_format, output_dir in list_outputs.items():
            output_dir = os.path.join(self.output_path, output_dir)

            if not self.check_output_dir(output_dir):
                logger.error("Couldn't create the {format} output "
                             "folder in {dir}".format(format=to_format,
                                                      dir=output_dir))
                continue

            filename = "{id_file}.{extension}".format(
                id_file=content.slug,
                extension=to_format
            )
            filepath = os.path.join(output_dir, filename)

            # Pandoc don't take "pdf" as an output value. Use latex instead.
            to_format = 'latex' if to_format == 'pdf' else to_format
            # Use the same format as Pelican (paticularly for metadata!)
            if from_format == 'md':
                from_format = 'markdown' + \
                        ''.join(self.settings.get('PANDOC_MARKDOWN_EXTENSIONS', []))

            # Here is the magic!
            # TODO: support extra_args extending (it could be useful to use
            # specific Pandoc template).
            check_call([self.settings.get('PANDOC_EXECUTABLE', 'pandoc')] +
                       self.settings.get('PANDOC_EXTRA_OPTIONS', []) +
                       ['-f', from_format, '-t', to_format ] +
                       ['--standalone', '-o', filepath, content.source_path])

            logger.info("[ok] writing {filepath}".format(
                filepath=filepath
            ))

    def generate_output(self, writer=None):
        """Generate files for each articles and pages.

        If PANDOC_EXPORT_ARTICLES is False, articles are not generated.
        If PANDOC_EXPORT_PAGES is False, pages are not generated.

        We don't use the writer passed as argument since we write our own
        files ((c) PDF plugin :)).

        """
        contents_to_export = []
        if self.settings.get('PANDOC_EXPORT_ARTICLES', True):
            contents_to_export += self.context['articles']

        if self.settings.get('PANDOC_EXPORT_PAGES', True):
            contents_to_export += self.context['pages']

        for content_to_export in contents_to_export:
            self.generate_files(content_to_export)


def get_generators(generators):
    return PandocGenerator


def register():
    """Register our Pandoc class to the Pelican generators."""
    signals.get_generators.connect(get_generators)