#!/usr/bin/python
#
# Extract field from YAML format morphologies, using a very simple
# query language. This is useful for black box testing.
#
# Usage: yaml-extract FILE PARAM...
#
# Where FILE is the name of the YAML morphology, and PARAM are a sequence
# of query parameters.
#
# The program reads in the YAML file, and then selects successively deeper
# parts of the object hieararchy in the file. If the object currently
# being looked at is a dictionary, PARAM is a field in the dictionary,
# and the next PARAM will look at the value stored with that key.
# If the current object is a list, PARAM can either be an integer list
# index, or a search key of the form KEY=VALUE, in which case the list
# is searched for the first member, which must be a dict, which has
# a key KEY that stores a value VALUE.
#
# Example:
#
#   yaml-extract system.morph strata morph=core ref
#
# This would report the ref of the core stratum in a system.
#
# Note that this does not try to parse morphologies as morphologies,
# and so doesn't do special processing such as providing computed
# values for missing fields (e.g., the morph field if name is given).
# Construct your tests accordingly.

# Copyright (C) 2013-2014  Codethink Limited
# 
# This program 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; version 2 of the License.
# 
# This program 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 this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.


import sys
import yaml


with open(sys.argv[1]) as f:
    obj = yaml.safe_load(f)
for thing in sys.argv[2:]:
    if type(obj) == dict:
        if thing not in obj:
            raise Exception("Object does not contain %s" % thing)
        obj = obj[thing]
    elif type(obj) == list:
        if '=' in thing:
            # We need to search a list member dict with a given field.
            key, value = thing.split('=', 1)
            for item in obj:
                if item.get(key) == value:
                    obj = item
                    break
            else:
                raise Exception(
                    "Couldn't find list item containing %s" % thing)
        else:
            # We can just index.
            obj = obj[int(thing)]
    else:
        raise Exception("Can't handle %s with %s" % (repr(obj), repr(thing)))

print obj