import argparse

import configparser

import datetime

import os.path

import pathlib

from . import loaders

HOME_PATH = pathlib.Path(os.path.expanduser('~'))

CONFFILE_SEED = """

[Historical]

base=USD

"""

def currency_code(s):

    if not (len(s) == 3) and s.isalpha():

        raise ValueError("bad currency code: {!r}".format(s))

    return s.upper()

def date_from(fmt_s):

    def date_from_fmt(s):

        return datetime.datetime.strptime(s, fmt_s).date

    return date_from_fmt

class Configuration:

    DEFAULT_CONFIG_PATH = pathlib.Path(HOME_PATH, '.config', 'oxrlib.ini')

    def __init__(self, arglist):

        argparser = self._build_argparser()

        self.error = argparser.error

        self.args = argparser.parse_args(arglist)

        if self.args.config_file is None:

            self.args.config_file = [self.DEFAULT_CONFIG_PATH]

        self.conffile = self._build_conffile()

        conffile_paths = [path.as_posix() for path in self.args.config_file]

        read_files = self.conffile.read(conffile_paths)

        for expected_path, read_path in zip(conffile_paths, read_files):

            if read_path != expected_path:

                self.error("failed to read configuration file {!r}".format(expected_path))

        try:

            post_hook = getattr(self, '_post_hook_' + self.args.command)

        except AttributeError:

            pass

        else:

            post_hook()

    def _build_argparser(self):

        prog_parser = argparse.ArgumentParser()

        prog_parser.add_argument(

            '--config-file', '-c',

            action='append', type=pathlib.Path,

            help="Path of a configuration file to read",

        )

        subparsers = prog_parser.add_subparsers()

        hist_parser = subparsers.add_parser('historical', aliases=['hist'])

        hist_parser.set_defaults(command='historical')

        hist_parser.add_argument(

            '--base',

            help="Base currency (default USD)",

        )

        hist_parser.add_argument(

            'date',

            type=date_from('%Y-%m-%d'), metavar='YYYY-MM-DD',

        )

        return prog_parser

    def _build_conffile(self):

        conffile = configparser.ConfigParser()

        conffile.read_string(CONFFILE_SEED)

        return conffile

    def _post_hook_historical(self):

        if self.args.base is None:

            self.args.base = self.conffile.get('Historical', 'base')

    def _build_cache_loader(self):

        kwargs = dict(self.conffile.items('Cache'))

        try:

            kwargs['dir_path'] = kwargs.pop('directory')

        except KeyError:

            pass

        return loaders.FileCache(**kwargs)

    def _build_oxrapi_loader(self):

        kwargs = dict(self.conffile.items('OXR'))

        return loaders.OXRAPIRequest(**kwargs)

    def get_loaders(self):

        loader_chain = loaders.LoaderChain()

        for build_func in [

                self._build_cache_loader,

                self._build_oxrapi_loader,

        ]:

            try:

                loader = build_func()

            except (TypeError, ValueError, configparser.NoSectionError):

                pass

            else:

                loader_chain.add_loader(loader)

        return loader_chain