import copy
import re
import warnings

from collections import OrderedDict
from itertools import chain

from django.conf import settings
from django.utils.encoding import force_text


CHILD_SRC_DEPRECATION_WARNING = \
    'child-src is deprecated in CSP v3. Use frame-src and worker-src.'


def from_settings():
    return {
        'default-src': getattr(settings, 'CSP_DEFAULT_SRC', ["'self'"]),
        'script-src': getattr(settings, 'CSP_SCRIPT_SRC', None),
        'object-src': getattr(settings, 'CSP_OBJECT_SRC', None),
        'style-src': getattr(settings, 'CSP_STYLE_SRC', None),
        'img-src': getattr(settings, 'CSP_IMG_SRC', None),
        'media-src': getattr(settings, 'CSP_MEDIA_SRC', None),
        'frame-src': getattr(settings, 'CSP_FRAME_SRC', None),
        'font-src': getattr(settings, 'CSP_FONT_SRC', None),
        'connect-src': getattr(settings, 'CSP_CONNECT_SRC', None),
        'sandbox': getattr(settings, 'CSP_SANDBOX', None),
        'report-uri': getattr(settings, 'CSP_REPORT_URI', None),
        'base-uri': getattr(settings, 'CSP_BASE_URI', None),
        'child-src': getattr(settings, 'CSP_CHILD_SRC', None),
        'form-action': getattr(settings, 'CSP_FORM_ACTION', None),
        'frame-ancestors': getattr(settings, 'CSP_FRAME_ANCESTORS', None),
        'manifest-src': getattr(settings, 'CSP_MANIFEST_SRC', None),
        'worker-src': getattr(settings, 'CSP_WORKER_SRC', None),
        'plugin-types': getattr(settings, 'CSP_PLUGIN_TYPES', None),
        'require-sri-for': getattr(settings, 'CSP_REQUIRE_SRI_FOR', None),
        'upgrade-insecure-requests': getattr(
            settings, 'CSP_UPGRADE_INSECURE_REQUESTS', False),
        'block-all-mixed-content': getattr(
            settings, 'CSP_BLOCK_ALL_MIXED_CONTENT', False),
    }


def build_policy(config=None, update=None, replace=None, nonce=None):
    """Builds the policy as a string from the settings."""

    if config is None:
        config = from_settings()
        # Be careful, don't mutate config as it could be from settings

    update = update if update is not None else {}
    replace = replace if replace is not None else {}
    csp = {}

    for k in set(chain(config, replace)):
        if k in replace:
            v = replace[k]
        else:
            v = config[k]
        if v is not None:
            v = copy.copy(v)
            if not isinstance(v, (list, tuple)):
                v = (v,)
            csp[k] = v

    for k, v in update.items():
        if v is not None:
            if not isinstance(v, (list, tuple)):
                v = (v,)
            if csp.get(k) is None:
                csp[k] = v
            else:
                csp[k] += tuple(v)

    report_uri = csp.pop('report-uri', None)

    policy_parts = {}
    for key, value in csp.items():
        # flag directives with an empty directive value
        if len(value) and value[0] is True:
            policy_parts[key] = ''
        elif len(value) and value[0] is False:
            pass
        else:  # directives with many values like src lists
            policy_parts[key] = ' '.join(value)

        if key == 'child-src':
            warnings.warn(CHILD_SRC_DEPRECATION_WARNING, DeprecationWarning)

    if report_uri:
        report_uri = map(force_text, report_uri)
        policy_parts['report-uri'] = ' '.join(report_uri)

    if nonce:
        include_nonce_in = getattr(settings, 'CSP_INCLUDE_NONCE_IN',
                                   ['default-src'])
        for section in include_nonce_in:
            policy = policy_parts.get(section, '')
            policy_parts[section] = ("%s %s" %
                                     (policy, "'nonce-%s'" % nonce)).strip()

    return '; '.join(['{} {}'.format(k, val).strip()
                      for k, val in policy_parts.items()])


def _default_attr_mapper(attr_name, val):
    if val:
        return ' {}="{}"'.format(attr_name, val)
    else:
        return ''


def _bool_attr_mapper(attr_name, val):
    # Only return the bare word if the value is truthy
    # ie - defer=False should actually return an empty string
    if val:
        return ' {}'.format(attr_name)
    else:
        return ''


def _async_attr_mapper(attr_name, val):
    """The `async` attribute works slightly different than the other bool
    attributes. It can be set explicitly to `false` with no surrounding quotes
    according to the spec."""
    if val in [False, 'False']:
        return ' {}=false'.format(attr_name)
    elif val:
        return ' {}'.format(attr_name)
    else:
        return ''


# Allow per-attribute customization of returned string template
SCRIPT_ATTRS = OrderedDict()
SCRIPT_ATTRS['nonce'] = _default_attr_mapper
SCRIPT_ATTRS['id'] = _default_attr_mapper
SCRIPT_ATTRS['src'] = _default_attr_mapper
SCRIPT_ATTRS['type'] = _default_attr_mapper
SCRIPT_ATTRS['async'] = _async_attr_mapper
SCRIPT_ATTRS['defer'] = _bool_attr_mapper
SCRIPT_ATTRS['integrity'] = _default_attr_mapper
SCRIPT_ATTRS['nomodule'] = _bool_attr_mapper

# Generates an interpolatable string of valid attrs eg - '{nonce}{id}...'
ATTR_FORMAT_STR = ''.join(['{{{}}}'.format(a) for a in SCRIPT_ATTRS])


def _unwrap_script(text):
    """Extract content defined between script tags"""
    matches = re.search(r'<script[\s|\S]*>([\s|\S]+?)</script>', text)
    if matches and len(matches.groups()):
        return matches.group(1).strip()

    return text


def build_script_tag(content=None, **kwargs):
    data = {}
    # Iterate all possible script attrs instead of kwargs to make
    # interpolation as easy as possible below
    for attr_name, mapper in SCRIPT_ATTRS.items():
        data[attr_name] = mapper(attr_name, kwargs.get(attr_name))

    # Don't render block contents if the script has a 'src' attribute
    c = _unwrap_script(content) if content and not kwargs.get('src') else ''
    attrs = ATTR_FORMAT_STR.format(**data).rstrip()
    return ('<script{}>{}</script>'.format(attrs, c).strip())