nzbToMedia/libs/beetsplug/inline.py

# -*- coding: utf-8 -*-
# This file is part of beets.
# Copyright 2016, Adrian Sampson.
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.

"""Allows inline path template customization code in the config file.
"""
from __future__ import division, absolute_import, print_function

import traceback
import itertools

from beets.plugins import BeetsPlugin
from beets import config

FUNC_NAME = u'__INLINE_FUNC__'


class InlineError(Exception):
    """Raised when a runtime error occurs in an inline expression.
    """
    def __init__(self, code, exc):
        super(InlineError, self).__init__(
            (u"error in inline path field code:\n"
             u"%s\n%s: %s") % (code, type(exc).__name__, unicode(exc))
        )


def _compile_func(body):
    """Given Python code for a function body, return a compiled
    callable that invokes that code.
    """
    body = u'def {0}():\n    {1}'.format(
        FUNC_NAME,
        body.replace('\n', '\n    ')
    )
    code = compile(body, 'inline', 'exec')
    env = {}
    eval(code, env)
    return env[FUNC_NAME]


class InlinePlugin(BeetsPlugin):
    def __init__(self):
        super(InlinePlugin, self).__init__()

        config.add({
            'pathfields': {},  # Legacy name.
            'item_fields': {},
            'album_fields': {},
        })

        # Item fields.
        for key, view in itertools.chain(config['item_fields'].items(),
                                         config['pathfields'].items()):
            self._log.debug(u'adding item field {0}', key)
            func = self.compile_inline(view.get(unicode), False)
            if func is not None:
                self.template_fields[key] = func

        # Album fields.
        for key, view in config['album_fields'].items():
            self._log.debug(u'adding album field {0}', key)
            func = self.compile_inline(view.get(unicode), True)
            if func is not None:
                self.album_template_fields[key] = func

    def compile_inline(self, python_code, album):
        """Given a Python expression or function body, compile it as a path
        field function. The returned function takes a single argument, an
        Item, and returns a Unicode string. If the expression cannot be
        compiled, then an error is logged and this function returns None.
        """
        # First, try compiling as a single function.
        try:
            code = compile(u'({0})'.format(python_code), 'inline', 'eval')
        except SyntaxError:
            # Fall back to a function body.
            try:
                func = _compile_func(python_code)
            except SyntaxError:
                self._log.error(u'syntax error in inline field definition:\n'
                                u'{0}', traceback.format_exc())
                return
            else:
                is_expr = False
        else:
            is_expr = True

        def _dict_for(obj):
            out = dict(obj)
            if album:
                out['items'] = list(obj.items())
            return out

        if is_expr:
            # For expressions, just evaluate and return the result.
            def _expr_func(obj):
                values = _dict_for(obj)
                try:
                    return eval(code, values)
                except Exception as exc:
                    raise InlineError(python_code, exc)
            return _expr_func
        else:
            # For function bodies, invoke the function with values as global
            # variables.
            def _func_func(obj):
                func.__globals__.update(_dict_for(obj))
                try:
                    return func()
                except Exception as exc:
                    raise InlineError(python_code, exc)
            return _func_func