"""Utility for calling pandoc"""
#-----------------------------------------------------------------------------
# Copyright (c) 2013 the IPython Development Team.
#
# Distributed under the terms of the Modified BSD License.
#
# The full license is in the file COPYING.txt, distributed with this software.
#-----------------------------------------------------------------------------

#-----------------------------------------------------------------------------
# Imports
#-----------------------------------------------------------------------------

from __future__ import print_function

# Stdlib imports
import sys
import subprocess

# IPython imports
from IPython.utils.py3compat import cast_bytes

#-----------------------------------------------------------------------------
# Classes and functions
#-----------------------------------------------------------------------------

def pandoc(source, fmt, to, extra_args=None, encoding='utf-8'):
    """Convert an input string in format `from` to format `to` via pandoc.

    This function will raise an error if pandoc is not installed.
    Any error messages generated by pandoc are printed to stderr.

    Parameters
    ----------
    source : string
      Input string, assumed to be valid format `from`.
    fmt : string
      The name of the input format (markdown, etc.)
    to : string
      The name of the output format (html, etc.)

    Returns
    -------
    out : unicode
      Output as returned by pandoc.
    """
    command = ['pandoc', '-f', fmt, '-t', to]
    if extra_args:
        command.extend(extra_args)
    try:
        p = subprocess.Popen(command,
                            stdin=subprocess.PIPE, stdout=subprocess.PIPE
        )
    except OSError:
        sys.exit("ERROR: Unable to launch pandoc. Please install pandoc:\n"
                 "(http://johnmacfarlane.net/pandoc/installing.html)")
    out, _ = p.communicate(cast_bytes(source, encoding))
    out = out.decode(encoding, 'replace')
    return out[:-1]