import datetime
import decimal
import functools
import re
import unicodedata
from importlib import import_module

from django.conf import settings
from django.utils import dateformat, 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):
    """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))
    return _format_modules_cache[lang]


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_INTERNAL
        if hasattr(settings, '_USE_L10N_INTERNAL')
        else 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.
    """
    use_l10n = use_l10n or (use_l10n is None and (
        settings._USE_L10N_INTERNAL
        if hasattr(settings, '_USE_L10N_INTERNAL')
        else settings.USE_L10N
    ))
    lang = get_language() if use_l10n else 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,
        use_l10n=use_l10n,
    )


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)):
        if use_l10n is False:
            return str(value)
        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):
        format = default or get_format('DATETIME_INPUT_FORMATS')[0]
        format = sanitize_strftime_format(format)
        return value.strftime(format)
    elif isinstance(value, datetime.date):
        format = default or get_format('DATE_INPUT_FORMATS')[0]
        format = sanitize_strftime_format(format)
        return value.strftime(format)
    elif isinstance(value, datetime.time):
        format = default or get_format('TIME_INPUT_FORMATS')[0]
        return value.strftime(format)
    return value


@functools.lru_cache()
def sanitize_strftime_format(fmt):
    """
    Ensure that certain specifiers are correctly padded with leading zeros.

    For years < 1000 specifiers %C, %F, %G, and %Y don't work as expected for
    strftime provided by glibc on Linux as they don't pad the year or century
    with leading zeros. Support for specifying the padding explicitly is
    available, however, which can be used to fix this issue.

    FreeBSD, macOS, and Windows do not support explicitly specifying the
    padding, but return four digit years (with leading zeros) as expected.

    This function checks whether the %Y produces a correctly padded string and,
    if not, makes the following substitutions:

    - %C → %02C
    - %F → %010F
    - %G → %04G
    - %Y → %04Y

    See https://bugs.python.org/issue13305 for more details.
    """
    if datetime.date(1, 1, 1).strftime('%Y') == '0001':
        return fmt
    mapping = {'C': 2, 'F': 10, 'G': 4, 'Y': 4}
    return re.sub(
        r'((?:^|[^%])(?:%%)*)%([CFGY])',
        lambda m: r'%s%%0%s%s' % (m[1], mapping[m[2]], m[2]),
        fmt,
    )


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