import json
from collections import UserList

from django.conf import settings
from django.core.exceptions import ValidationError  # backwards compatibility
from django.utils import timezone
from django.utils.html import escape, format_html, format_html_join, html_safe
from django.utils.translation import gettext_lazy as _


def pretty_name(name):
    """Convert 'first_name' to 'First name'."""
    if not name:
        return ''
    return name.replace('_', ' ').capitalize()


def flatatt(attrs):
    """
    Convert a dictionary of attributes to a single string.
    The returned string will contain a leading space followed by key="value",
    XML-style pairs. In the case of a boolean value, the key will appear
    without a value. It is assumed that the keys do not need to be
    XML-escaped. If the passed dictionary is empty, then return an empty
    string.

    The result is passed through 'mark_safe' (by way of 'format_html_join').
    """
    key_value_attrs = []
    boolean_attrs = []
    for attr, value in attrs.items():
        if isinstance(value, bool):
            if value:
                boolean_attrs.append((attr,))
        elif value is not None:
            key_value_attrs.append((attr, value))

    return (
        format_html_join('', ' {}="{}"', sorted(key_value_attrs)) +
        format_html_join('', ' {}', sorted(boolean_attrs))
    )


@html_safe
class ErrorDict(dict):
    """
    A collection of errors that knows how to display itself in various formats.

    The dictionary keys are the field names, and the values are the errors.
    """
    def as_data(self):
        return {f: e.as_data() for f, e in self.items()}

    def get_json_data(self, escape_html=False):
        return {f: e.get_json_data(escape_html) for f, e in self.items()}

    def as_json(self, escape_html=False):
        return json.dumps(self.get_json_data(escape_html))

    def as_ul(self):
        if not self:
            return ''
        return format_html(
            '<ul class="errorlist">{}</ul>',
            format_html_join('', '<li>{}{}</li>', self.items())
        )

    def as_text(self):
        output = []
        for field, errors in self.items():
            output.append('* %s' % field)
            output.append('\n'.join('  * %s' % e for e in errors))
        return '\n'.join(output)

    def __str__(self):
        return self.as_ul()


@html_safe
class ErrorList(UserList, list):
    """
    A collection of errors that knows how to display itself in various formats.
    """
    def __init__(self, initlist=None, error_class=None):
        super().__init__(initlist)

        if error_class is None:
            self.error_class = 'errorlist'
        else:
            self.error_class = 'errorlist {}'.format(error_class)

    def as_data(self):
        return ValidationError(self.data).error_list

    def get_json_data(self, escape_html=False):
        errors = []
        for error in self.as_data():
            message = next(iter(error))
            errors.append({
                'message': escape(message) if escape_html else message,
                'code': error.code or '',
            })
        return errors

    def as_json(self, escape_html=False):
        return json.dumps(self.get_json_data(escape_html))

    def as_ul(self):
        if not self.data:
            return ''

        return format_html(
            '<ul class="{}">{}</ul>',
            self.error_class,
            format_html_join('', '<li>{}</li>', ((e,) for e in self))
        )

    def as_text(self):
        return '\n'.join('* %s' % e for e in self)

    def __str__(self):
        return self.as_ul()

    def __repr__(self):
        return repr(list(self))

    def __contains__(self, item):
        return item in list(self)

    def __eq__(self, other):
        return list(self) == other

    def __getitem__(self, i):
        error = self.data[i]
        if isinstance(error, ValidationError):
            return next(iter(error))
        return error

    def __reduce_ex__(self, *args, **kwargs):
        # The `list` reduce function returns an iterator as the fourth element
        # that is normally used for repopulating. Since we only inherit from
        # `list` for `isinstance` backward compatibility (Refs #17413) we
        # nullify this iterator as it would otherwise result in duplicate
        # entries. (Refs #23594)
        info = super(UserList, self).__reduce_ex__(*args, **kwargs)
        return info[:3] + (None, None)


# Utilities for time zone support in DateTimeField et al.

def from_current_timezone(value):
    """
    When time zone support is enabled, convert naive datetimes
    entered in the current time zone to aware datetimes.
    """
    if settings.USE_TZ and value is not None and timezone.is_naive(value):
        current_timezone = timezone.get_current_timezone()
        try:
            return timezone.make_aware(value, current_timezone)
        except Exception as exc:
            raise ValidationError(
                _('%(datetime)s couldn\'t be interpreted '
                  'in time zone %(current_timezone)s; it '
                  'may be ambiguous or it may not exist.'),
                code='ambiguous_timezone',
                params={'datetime': value, 'current_timezone': current_timezone}
            ) from exc
    return value


def to_current_timezone(value):
    """
    When time zone support is enabled, convert aware datetimes
    to naive datetimes in the current time zone for display.
    """
    if settings.USE_TZ and value is not None and timezone.is_aware(value):
        return timezone.make_naive(value)
    return value
