#!/usr/bin/env python

"""
convert JSON list of hashes to CSV
"""
# Note: we could use https://docs.python.org/2/library/csv.html#csv.DictWriter
# but we're being careful here since we actually want this data structure in code,
# not just for de/serialization


import argparse
import csv
import json
import sys
from .cast import unify
from .cli import ConfigurationParser


def flatten_list_of_dicts(list_of_dicts, header=None):
    """
    flattens a list of dicts into a list of lists.

    Returns (header, list_of_lists)
    """

    if not list_of_dicts:
        return []

    # sanity
    keys = list_of_dicts[0].keys()
    if header:
        if not set(header).issubset(keys):
            raise AssertionError("header contains elements not seen in the set: {}".format(', '.format(set(header).difference(keys))))
    for item in list_of_dicts:
        # ensure each item has the same keys
        if set(keys) != set(item.keys()):
            raise AssertionError("Keys not consistent! {} != {}".format(sorted(keys),
                                                                        sorted(item.keys())))

    if not header:
        header = keys  # to sort?

    # flatten it!
    retval = []
    for item in list_of_dicts:
        retval.append([item[key] for key in header])

    return (header, retval)


def main(args=sys.argv[1:]):
    """CLI"""

    # parse command line
    parser = ConfigurationParser(description=__doc__)
    parser.add_argument('json', type=argparse.FileType('r'),
                        help="JSON file of list of hashes")
    parser.add_argument('-H', '--header', dest='header', nargs='+',
                        help="use these fields for header")
    parser.add_argument('-o', '--output', dest='output',
                        type=argparse.FileType('w'), default=sys.stdout,
                        help="path to output, or stdout by default")
    options = parser.parse_args(args)

    # read
    data = json.load(options.json)

    # flatten
    header, flattened = flatten_list_of_dicts(data, header=options.header)

    # write
    writer = csv.writer(options.output)
    writer.writerow(header)
    for row in flattened:
        writer.writerow([unify(v) for v in row])

if __name__ == '__main__':
    main()