#!/usr/bin/env python3
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"""Generate source files from a specification of builtin roles."""

from Cheetah.Template import Template
import argparse
import sys
import yaml

help_epilog="""
The builtin_roles_spec YAML document is a mapping containing one toplevel field:

    `roles` is a mapping for role name to role definitions.

    Each role definition may have 3 possible keys:
        `roles`: (list) A set of references back to other roles
             which this role should inherit from.
             The list item may either be a string to indicate
             a role on the same database,
             or a tuple of {role: 'roleName', db: 'targetDb'}.
    `adminOnly`: (bool) True if this role exist on the
             `admin` database only. False (default) otherwise.
    `privileges`: (list) A set of ResourcePattern and PrivilegeVector tuples.
             Each element mat have the following fields:
                `matchType`: (string, required)
                            One of the MatchType enum values
                            defined in mongo/db/auth/action_types.yml
                `db`: (string) If `matchType` expects a DB (e.g. 'database', 'exact_namespace'),
                            then `db` is the database that the role is defined on by default,
                            but it may be overridden to reference privileges in other DBs.
                            Note that overriding DB is only valid for roles on the admin DB.
                `collection`: (string) If `matchType` expects a collection
                            (e.g. 'collection', 'exact_namespace'), then `collection`
                            is required and provides the obvious meaning.
                `actions`: (list, required) A set of ActionTypes granted for this ResourcePattern.
                            The elements are nominally strings matching those from action_types.yml,
                            however to make compositing lists easier, elements may be lists of strings
                            and will be flattened during the generation process.
"""

def init_parser():
    parser = argparse.ArgumentParser(
            formatter_class=argparse.RawDescriptionHelpFormatter,
            description=__doc__,
            epilog=help_epilog)
    parser.add_argument('--verbose',
            action='store_true',
            help='extra debug logging to stderr')
    parser.add_argument('builtin_roles_spec',
            help='YAML file describing builtin roles')
    parser.add_argument('template_file',
            help='Cheetah template file')
    parser.add_argument('output_file')
    return parser

def render_template(template_path, **kw):
    '''Renders the template file located at template_path, using the variables defined by kw, and
       returns the result as a string'''

    template = Template.compile(
        file=template_path,
        compilerSettings=dict(directiveStartToken="//#", directiveEndToken="//#",
                              commentStartToken="//##"), baseclass=dict, useCache=False)
    return str(template(**kw))

def check_allowed_fields(mapping, allowed):
    for field in mapping:
        if field not in allowed:
            raise Exception("Unknown field '%s' in %r" % (field, mapping))

def check_required_fields(mapping, required):
    for field in required:
        if field not in mapping:
            raise Exception("Missing required field '%s' in %r" % (field, mapping))

def assert_str_field(name, value):
    if type(value) is not str:
        raise Exception("Invalid type for string field '%s', got '%s' ': %r" % (name, type(value), value))

def assert_list_field(name, value):
    if type(value) is not list:
        raise Exception("Invalid type for list field '%s', got '%s' ': %r" % (name, type(value), value))

def get_nonempty_str_field(mapping, fieldName):
    assert_str_field(fieldName, mapping[fieldName])
    if len(mapping[fieldName]) == 0:
        raise Exception("Field '%s' value must be a non-empty string" % (fieldName))
    return mapping[fieldName]

class InheritedRole:
    def __init__(self, spec):
        self.db = None

        if type(spec) is str:
            self.role = spec
        else:
            if type(spec) is not dict:
                raise Exception('Inherited role must be either a simple name, or a role/db tuple, got: %r' % (spec))
            check_allowed_fields(spec, ['role', 'db'])
            check_required_fields(spec, ['role'])
            self.role = get_nonempty_str_field(spec, 'role')
            if 'db' in spec:
                self.db = get_nonempty_str_field(spec, 'db')

class Privilege:
    def __init__(self, spec):

        check_allowed_fields(spec, ['matchType', 'db', 'collection', 'system_buckets', 'actions'])
        check_required_fields(spec, ['matchType', 'actions'])

        self.matchType = get_nonempty_str_field(spec, 'matchType')
        self.db = None
        self.collection = None
        self.system_buckets = None
        self.actions = []

        db_valid_types = ['database', 'exact_namespace', 'system_buckets', 'any_system_buckets_in_db']
        if 'db' in spec:
            if self.matchType in db_valid_types:
                self.db = get_nonempty_str_field(spec, 'db')
            else:
                raise Exception("db field is not valid for matchType: %s" % (self.matchType))

        coll_valid_types = ['collection', 'exact_namespace']
        if self.matchType in coll_valid_types:
            check_required_fields(spec, ['collection'])
            self.collection = get_nonempty_str_field(spec, 'collection')
        elif 'collection' in spec:
            raise Exception("collection field is not valid for matchType: %s" % (self.matchType))

        buckets_valid_types = ['system_buckets', 'system_buckets_in_any_db']
        if self.matchType in buckets_valid_types:
            check_required_fields(spec, ['system_buckets'])
            db.system_buckets = get_nonempty_str_field(spec, 'system_buckets')
        elif 'system_buckets' in spec:
            raise Exception("system_buckets field is not valid for matchType: %s" % (self.matchType))

        assert_list_field('actions', spec['actions'])
        for action in spec['actions']:
            if type(action) is list:
                for subaction in action:
                    assert_str_field('actions', subaction)
                    self.actions.append(subaction)
            else:
                assert_str_field('actions', action)
                self.actions.append(action)

class BuiltinRole:
    def __init__(self, name, spec):
        self.name = name
        self.adminOnly = False
        self.roles = []
        self.privileges = []

        check_allowed_fields(spec, ['adminOnly', 'roles', 'privileges'])

        if 'adminOnly' in spec:
            if type(spec['adminOnly']) is not bool:
                raise Exception('adminOnly must be a bool, got: %r' % (spec['adminOnly']))
            self.adminOnly = spec['adminOnly']

        if 'roles' in spec:
            assert_list_field('roles', spec['roles'])
            for role in spec['roles']:
                self.roles.append(InheritedRole(role))

        if 'privileges' in spec:
            assert_list_field('privileges', spec['privileges'])
            for priv in spec['privileges']:
                self.privileges.append(Privilege(priv))

def parse_builtin_role_definitions_from_file(roles_filename, verbose=False):
    roles = []
    with open(roles_filename, 'r') as roles_file:
        doc = yaml.safe_load(roles_file)

    if verbose:
        yaml.dump(doc, sys.stderr)

    for roleName in doc['roles']:
        roles.append(BuiltinRole(roleName, doc['roles'][roleName]))

    return roles

def main():
    parsed = init_parser().parse_args()
    verbose = parsed.verbose
    template_file = parsed.template_file
    output_file = parsed.output_file

    # Parse and validate builtin_roles.yml
    builtin_roles = parse_builtin_role_definitions_from_file(parsed.builtin_roles_spec, verbose)

    # Render the templates to the output files.
    if verbose:
        print(f'rendering {template_file} => {output_file}')
    text = render_template(template_file, roles=builtin_roles)
    with open(output_file, 'w') as outfile:
        outfile.write(text)

if __name__ == '__main__':
    main()