import datetime
import decimal
import unicodedata
from importlib import import_module

from django.conf import settings
from django.utils import dateformat, datetime_safe, numberformat
from django.utils.functional import lazy
from django.utils.translation import (
    check_for_language, get_language, to_locale,
)

# format_cache is a mapping from (format_type, lang) to the format string.
# By using the cache, it is possible to avoid running get_format_modules
# repeatedly.
_format_cache = {}
_format_modules_cache = {}

ISO_INPUT_FORMATS = {
    'DATE_INPUT_FORMATS': ['%Y-%m-%d'],
    'TIME_INPUT_FORMATS': ['%H:%M:%S', '%H:%M:%S.%f', '%H:%M'],
    'DATETIME_INPUT_FORMATS': [
        '%Y-%m-%d %H:%M:%S',
        '%Y-%m-%d %H:%M:%S.%f',
        '%Y-%m-%d %H:%M',
        '%Y-%m-%d'
    ],
}


FORMAT_SETTINGS = frozenset([
    'DECIMAL_SEPARATOR',
    'THOUSAND_SEPARATOR',
    'NUMBER_GROUPING',
    'FIRST_DAY_OF_WEEK',
    'MONTH_DAY_FORMAT',
    'TIME_FORMAT',
    'DATE_FORMAT',
    'DATETIME_FORMAT',
    'SHORT_DATE_FORMAT',
    'SHORT_DATETIME_FORMAT',
    'YEAR_MONTH_FORMAT',
    'DATE_INPUT_FORMATS',
    'TIME_INPUT_FORMATS',
    'DATETIME_INPUT_FORMATS',
])


def reset_format_cache():
    """Clear any cached formats.

    This method is provided primarily for testing purposes,
    so that the effects of cached formats can be removed.
    """
    global _format_cache, _format_modules_cache
    _format_cache = {}
    _format_modules_cache = {}


def iter_format_modules(lang, format_module_path=None):
    """Find format modules."""
    if not check_for_language(lang):
        return

    if format_module_path is None:
        format_module_path = settings.FORMAT_MODULE_PATH

    format_locations = []
    if format_module_path:
        if isinstance(format_module_path, str):
            format_module_path = [format_module_path]
        for path in format_module_path:
            format_locations.append(path + '.%s')
    format_locations.append('django.conf.locale.%s')
    locale = to_locale(lang)
    locales = [locale]
    if '_' in locale:
        locales.append(locale.split('_')[0])
    for location in format_locations:
        for loc in locales:
            try:
                yield import_module('%s.formats' % (location % loc))
            except ImportError:
                pass


def get_format_modules(lang=None, reverse=False):
    """Return a list of the format modules found."""
    if lang is None:
        lang = get_language()
    if lang not in _format_modules_cache:
        _format_modules_cache[lang] = list(iter_format_modules(lang, settings.FORMAT_MODULE_PATH))
    modules = _format_modules_cache[lang]
    if reverse:
        return list(reversed(modules))
    return modules


def get_format(format_type, lang=None, use_l10n=None):
    """
    For a specific format type, return the format for the current
    language (locale). Default to the format in the settings.
    format_type is the name of the format, e.g. 'DATE_FORMAT'.

    If use_l10n is provided and is not None, it forces the value to
    be localized (or not), overriding the value of settings.USE_L10N.
    """
    use_l10n = use_l10n or (use_l10n is None and settings.USE_L10N)
    if use_l10n and lang is None:
        lang = get_language()
    cache_key = (format_type, lang)
    try:
        return _format_cache[cache_key]
    except KeyError:
        pass

    # The requested format_type has not been cached yet. Try to find it in any
    # of the format_modules for the given lang if l10n is enabled. If it's not
    # there or if l10n is disabled, fall back to the project settings.
    val = None
    if use_l10n:
        for module in get_format_modules(lang):
            val = getattr(module, format_type, None)
            if val is not None:
                break
    if val is None:
        if format_type not in FORMAT_SETTINGS:
            return format_type
        val = getattr(settings, format_type)
    elif format_type in ISO_INPUT_FORMATS:
        # If a list of input formats from one of the format_modules was
        # retrieved, make sure the ISO_INPUT_FORMATS are in this list.
        val = list(val)
        for iso_input in ISO_INPUT_FORMATS.get(format_type, ()):
            if iso_input not in val:
                val.append(iso_input)
    _format_cache[cache_key] = val
    return val


get_format_lazy = lazy(get_format, str, list, tuple)


def date_format(value, format=None, use_l10n=None):
    """
    Format a datetime.date or datetime.datetime object using a
    localizable format.

    If use_l10n is provided and is not None, that will force the value to
    be localized (or not), overriding the value of settings.USE_L10N.
    """
    return dateformat.format(value, get_format(format or 'DATE_FORMAT', use_l10n=use_l10n))


def time_format(value, format=None, use_l10n=None):
    """
    Format a datetime.time object using a localizable format.

    If use_l10n is provided and is not None, it forces the value to
    be localized (or not), overriding the value of settings.USE_L10N.
    """
    return dateformat.time_format(value, get_format(format or 'TIME_FORMAT', use_l10n=use_l10n))


def number_format(value, decimal_pos=None, use_l10n=None, force_grouping=False):
    """
    Format a numeric value using localization settings.

    If use_l10n is provided and is not None, it forces the value to
    be localized (or not), overriding the value of settings.USE_L10N.
    """
    if use_l10n or (use_l10n is None and settings.USE_L10N):
        lang = get_language()
    else:
        lang = None
    return numberformat.format(
        value,
        get_format('DECIMAL_SEPARATOR', lang, use_l10n=use_l10n),
        decimal_pos,
        get_format('NUMBER_GROUPING', lang, use_l10n=use_l10n),
        get_format('THOUSAND_SEPARATOR', lang, use_l10n=use_l10n),
        force_grouping=force_grouping
    )


def localize(value, use_l10n=None):
    """
    Check if value is a localizable type (date, number...) and return it
    formatted as a string using current locale format.

    If use_l10n is provided and is not None, it forces the value to
    be localized (or not), overriding the value of settings.USE_L10N.
    """
    if isinstance(value, str):  # Handle strings first for performance reasons.
        return value
    elif isinstance(value, bool):  # Make sure booleans don't get treated as numbers
        return str(value)
    elif isinstance(value, (decimal.Decimal, float, int)):
        return number_format(value, use_l10n=use_l10n)
    elif isinstance(value, datetime.datetime):
        return date_format(value, 'DATETIME_FORMAT', use_l10n=use_l10n)
    elif isinstance(value, datetime.date):
        return date_format(value, use_l10n=use_l10n)
    elif isinstance(value, datetime.time):
        return time_format(value, 'TIME_FORMAT', use_l10n=use_l10n)
    return value


def localize_input(value, default=None):
    """
    Check if an input value is a localizable type and return it
    formatted with the appropriate formatting string of the current locale.
    """
    if isinstance(value, str):  # Handle strings first for performance reasons.
        return value
    elif isinstance(value, bool):  # Don't treat booleans as numbers.
        return str(value)
    elif isinstance(value, (decimal.Decimal, float, int)):
        return number_format(value)
    elif isinstance(value, datetime.datetime):
        value = datetime_safe.new_datetime(value)
        format = default or get_format('DATETIME_INPUT_FORMATS')[0]
        return value.strftime(format)
    elif isinstance(value, datetime.date):
        value = datetime_safe.new_date(value)
        format = default or get_format('DATE_INPUT_FORMATS')[0]
        return value.strftime(format)
    elif isinstance(value, datetime.time):
        format = default or get_format('TIME_INPUT_FORMATS')[0]
        return value.strftime(format)
    return value


def sanitize_separators(value):
    """
    Sanitize a value according to the current decimal and
    thousand separator setting. Used with form field input.
    """
    if isinstance(value, str):
        parts = []
        decimal_separator = get_format('DECIMAL_SEPARATOR')
        if decimal_separator in value:
            value, decimals = value.split(decimal_separator, 1)
            parts.append(decimals)
        if settings.USE_THOUSAND_SEPARATOR:
            thousand_sep = get_format('THOUSAND_SEPARATOR')
            if thousand_sep == '.' and value.count('.') == 1 and len(value.split('.')[-1]) != 3:
                # Special case where we suspect a dot meant decimal separator (see #22171)
                pass
            else:
                for replacement in {
                        thousand_sep, unicodedata.normalize('NFKD', thousand_sep)}:
                    value = value.replace(replacement, '')
        parts.append(value)
        value = '.'.join(reversed(parts))
    return value
