#!/usr/bin/python
# -*- coding: utf-8 -*-

# Copyright: Ansible Project
# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)

from __future__ import absolute_import, division, print_function
__metaclass__ = type

DOCUMENTATION = r'''
---
module: postgresql_user
short_description: Create, alter, or remove a user (role) from a PostgreSQL server instance
description:
- Creates, alters, or removes a user (role) from a PostgreSQL server instance
  ("cluster" in PostgreSQL terminology) and, optionally,
  grants the user access to an existing database or tables.
- A user is a role with login privilege.
- You can also use it to grant or revoke user's privileges in a particular database.
- You cannot remove a user while it still has any privileges granted to it in any database.
- Set I(fail_on_user) to C(no) to make the module ignore failures when trying to remove a user.
  In this case, the module reports if changes happened as usual and separately reports
  whether the user has been removed or not.
options:
  name:
    description:
    - Name of the user (role) to add or remove.
    type: str
    required: true
    aliases:
    - user
  password:
    description:
    - Set the user's password, before 1.4 this was required.
    - Password can be passed unhashed or hashed (MD5-hashed).
    - An unhashed password is automatically hashed when saved into the
      database if I(encrypted) is set, otherwise it is saved in
      plain text format.
    - When passing an MD5-hashed password, you must generate it with the format
      C('str["md5"] + md5[ password + username ]'), resulting in a total of
      35 characters. An easy way to do this is C(echo "md5$(echo -n
      'verysecretpasswordJOE' | md5sum | awk '{print $1}')").
    - Note that if the provided password string is already in MD5-hashed
      format, then it is used as-is, regardless of I(encrypted) option.
    type: str
  db:
    description:
    - Name of database to connect to and where user's permissions are granted.
    type: str
    aliases:
    - login_db
  fail_on_user:
    description:
    - If C(yes), fails when the user (role) cannot be removed. Otherwise just log and continue.
    default: yes
    type: bool
    aliases:
    - fail_on_role
  priv:
    description:
    - "Slash-separated PostgreSQL privileges string: C(priv1/priv2), where
      you can define the user's privileges for the database ( allowed options - 'CREATE',
      'CONNECT', 'TEMPORARY', 'TEMP', 'ALL'. For example C(CONNECT) ) or
      for table ( allowed options - 'SELECT', 'INSERT', 'UPDATE', 'DELETE',
      'TRUNCATE', 'REFERENCES', 'TRIGGER', 'ALL'. For example
      C(table:SELECT) ). Mixed example of this string:
      C(CONNECT/CREATE/table1:SELECT/table2:INSERT)."
    type: str
  role_attr_flags:
    description:
    - "PostgreSQL user attributes string in the format: CREATEDB,CREATEROLE,SUPERUSER."
    - Note that '[NO]CREATEUSER' is deprecated.
    - To create a simple role for using it like a group, use C(NOLOGIN) flag.
    type: str
    choices: [ '[NO]SUPERUSER', '[NO]CREATEROLE', '[NO]CREATEDB',
               '[NO]INHERIT', '[NO]LOGIN', '[NO]REPLICATION', '[NO]BYPASSRLS' ]
  session_role:
    description:
    - Switch to session role after connecting.
    - The specified session role must be a role that the current login_user is a member of.
    - Permissions checking for SQL commands is carried out as though the session role
      were the one that had logged in originally.
    type: str
  state:
    description:
    - The user (role) state.
    type: str
    default: present
    choices: [ absent, present ]
  encrypted:
    description:
    - Whether the password is stored hashed in the database.
    - You can specify an unhashed password, and PostgreSQL ensures
      the stored password is hashed when I(encrypted=yes) is set.
      If you specify a hashed password, the module uses it as-is,
      regardless of the setting of I(encrypted).
    - "Note: Postgresql 10 and newer does not support unhashed passwords."
    - Previous to Ansible 2.6, this was C(no) by default.
    default: yes
    type: bool
  expires:
    description:
    - The date at which the user's password is to expire.
    - If set to C('infinity'), user's password never expires.
    - Note that this value must be a valid SQL date and time type.
    type: str
  no_password_changes:
    description:
    - If C(yes), does not inspect the database for password changes.
      Useful when C(pg_authid) is not accessible (such as in AWS RDS).
      Otherwise, makes password changes as necessary.
    default: no
    type: bool
  conn_limit:
    description:
    - Specifies the user (role) connection limit.
    type: int
  ssl_mode:
    description:
      - Determines how an SSL session is negotiated with the server.
      - See U(https://www.postgresql.org/docs/current/static/libpq-ssl.html) for more information on the modes.
      - Default of C(prefer) matches libpq default.
    type: str
    default: prefer
    choices: [ allow, disable, prefer, require, verify-ca, verify-full ]
  ca_cert:
    description:
      - Specifies the name of a file containing SSL certificate authority (CA) certificate(s).
      - If the file exists, verifies that the server's certificate is signed by one of these authorities.
    type: str
    aliases: [ ssl_rootcert ]
  groups:
    description:
    - The list of groups (roles) that you want to grant to the user.
    type: list
    elements: str
  comment:
    description:
    - Adds a comment on the user (equivalent to the C(COMMENT ON ROLE) statement).
    type: str
    version_added: '0.2.0'
  trust_input:
    description:
    - If C(no), checks whether values of options I(name), I(password), I(privs), I(expires),
      I(role_attr_flags), I(groups), I(comment), I(session_role) are potentially dangerous.
    - It makes sense to use C(no) only when SQL injections through the options are possible.
    type: bool
    default: yes
    version_added: '0.2.0'
notes:
- The module creates a user (role) with login privilege by default.
  Use C(NOLOGIN) I(role_attr_flags) to change this behaviour.
- If you specify C(PUBLIC) as the user (role), then the privilege changes apply to all users (roles).
  You may not specify password or role_attr_flags when the C(PUBLIC) user is specified.
- SCRAM-SHA-256-hashed passwords (SASL Authentication) require PostgreSQL version 10 or newer.
  On the previous versions the whole hashed string is used as a password.
- 'Working with SCRAM-SHA-256-hashed passwords, be sure you use the I(environment:) variable
  C(PGOPTIONS: "-c password_encryption=scram-sha-256") (see the provided example).'
- Supports ``check_mode``.
seealso:
- module: community.general.postgresql_privs
- module: community.general.postgresql_membership
- module: community.general.postgresql_owner
- name: PostgreSQL database roles
  description: Complete reference of the PostgreSQL database roles documentation.
  link: https://www.postgresql.org/docs/current/user-manag.html
- name: PostgreSQL SASL Authentication
  description: Complete reference of the PostgreSQL SASL Authentication.
  link: https://www.postgresql.org/docs/current/sasl-authentication.html
author:
- Ansible Core Team
extends_documentation_fragment:
- community.general.postgres

'''

EXAMPLES = r'''
- name: Connect to acme database, create django user, and grant access to database and products table
  community.general.postgresql_user:
    db: acme
    name: django
    password: ceec4eif7ya
    priv: "CONNECT/products:ALL"
    expires: "Jan 31 2020"

- name: Add a comment on django user
  community.general.postgresql_user:
    db: acme
    name: django
    comment: This is a test user

# Connect to default database, create rails user, set its password (MD5-hashed),
# and grant privilege to create other databases and demote rails from super user status if user exists
- name: Create rails user, set MD5-hashed password, grant privs
  community.general.postgresql_user:
    name: rails
    password: md59543f1d82624df2b31672ec0f7050460
    role_attr_flags: CREATEDB,NOSUPERUSER

- name: Connect to acme database and remove test user privileges from there
  community.general.postgresql_user:
    db: acme
    name: test
    priv: "ALL/products:ALL"
    state: absent
    fail_on_user: no

- name: Connect to test database, remove test user from cluster
  community.general.postgresql_user:
    db: test
    name: test
    priv: ALL
    state: absent

- name: Connect to acme database and set user's password with no expire date
  community.general.postgresql_user:
    db: acme
    name: django
    password: mysupersecretword
    priv: "CONNECT/products:ALL"
    expires: infinity

# Example privileges string format
# INSERT,UPDATE/table:SELECT/anothertable:ALL

- name: Connect to test database and remove an existing user's password
  community.general.postgresql_user:
    db: test
    user: test
    password: ""

- name: Create user test and grant group user_ro and user_rw to it
  community.general.postgresql_user:
    name: test
    groups:
    - user_ro
    - user_rw

# Create user with a cleartext password if it does not exist or update its password.
# The password will be encrypted with SCRAM algorithm (available since PostgreSQL 10)
- name: Create appclient user with SCRAM-hashed password
  community.general.postgresql_user:
    name: appclient
    password: "secret123"
  environment:
    PGOPTIONS: "-c password_encryption=scram-sha-256"
'''

RETURN = r'''
queries:
  description: List of executed queries.
  returned: always
  type: list
  sample: ['CREATE USER "alice"', 'GRANT CONNECT ON DATABASE "acme" TO "alice"']
'''

import itertools
import re
import traceback
from hashlib import md5, sha256
import hmac
from base64 import b64decode

try:
    import psycopg2
    from psycopg2.extras import DictCursor
except ImportError:
    # psycopg2 is checked by connect_to_db()
    # from ansible.module_utils.postgres
    pass

from ansible.module_utils.basic import AnsibleModule
from ansible_collections.community.general.plugins.module_utils.database import (
    pg_quote_identifier,
    SQLParseError,
    check_input,
)
from ansible_collections.community.general.plugins.module_utils.postgres import (
    connect_to_db,
    get_conn_params,
    PgMembership,
    postgres_common_argument_spec,
)
from ansible.module_utils._text import to_bytes, to_native, to_text
from ansible.module_utils.six import iteritems
import ansible_collections.community.general.plugins.module_utils.saslprep as saslprep

try:
    # pbkdf2_hmac is missing on python 2.6, we can safely assume,
    # that postresql 10 capable instance have at least python 2.7 installed
    from hashlib import pbkdf2_hmac
    pbkdf2_found = True
except ImportError:
    pbkdf2_found = False


FLAGS = ('SUPERUSER', 'CREATEROLE', 'CREATEDB', 'INHERIT', 'LOGIN', 'REPLICATION')
FLAGS_BY_VERSION = {'BYPASSRLS': 90500}

SCRAM_SHA256_REGEX = r'^SCRAM-SHA-256\$(\d+):([A-Za-z0-9+\/=]+)\$([A-Za-z0-9+\/=]+):([A-Za-z0-9+\/=]+)$'

VALID_PRIVS = dict(table=frozenset(('SELECT', 'INSERT', 'UPDATE', 'DELETE', 'TRUNCATE', 'REFERENCES', 'TRIGGER', 'ALL')),
                   database=frozenset(
                       ('CREATE', 'CONNECT', 'TEMPORARY', 'TEMP', 'ALL')),
                   )

# map to cope with idiosyncracies of SUPERUSER and LOGIN
PRIV_TO_AUTHID_COLUMN = dict(SUPERUSER='rolsuper', CREATEROLE='rolcreaterole',
                             CREATEDB='rolcreatedb', INHERIT='rolinherit', LOGIN='rolcanlogin',
                             REPLICATION='rolreplication', BYPASSRLS='rolbypassrls')

executed_queries = []


class InvalidFlagsError(Exception):
    pass


class InvalidPrivsError(Exception):
    pass

# ===========================================
# PostgreSQL module specific support methods.
#


def user_exists(cursor, user):
    # The PUBLIC user is a special case that is always there
    if user == 'PUBLIC':
        return True
    query = "SELECT rolname FROM pg_roles WHERE rolname=%(user)s"
    cursor.execute(query, {'user': user})
    return cursor.rowcount > 0


def user_add(cursor, user, password, role_attr_flags, encrypted, expires, conn_limit):
    """Create a new database user (role)."""
    # Note: role_attr_flags escaped by parse_role_attrs and encrypted is a
    # literal
    query_password_data = dict(password=password, expires=expires)
    query = ['CREATE USER "%(user)s"' %
             {"user": user}]
    if password is not None and password != '':
        query.append("WITH %(crypt)s" % {"crypt": encrypted})
        query.append("PASSWORD %(password)s")
    if expires is not None:
        query.append("VALID UNTIL %(expires)s")
    if conn_limit is not None:
        query.append("CONNECTION LIMIT %(conn_limit)s" % {"conn_limit": conn_limit})
    query.append(role_attr_flags)
    query = ' '.join(query)
    executed_queries.append(query)
    cursor.execute(query, query_password_data)
    return True


def user_should_we_change_password(current_role_attrs, user, password, encrypted):
    """Check if we should change the user's password.

    Compare the proposed password with the existing one, comparing
    hashes if encrypted. If we can't access it assume yes.
    """

    if current_role_attrs is None:
        # on some databases, E.g. AWS RDS instances, there is no access to
        # the pg_authid relation to check the pre-existing password, so we
        # just assume password is different
        return True

    # Do we actually need to do anything?
    pwchanging = False
    if password is not None:
        # Empty password means that the role shouldn't have a password, which
        # means we need to check if the current password is None.
        if password == '':
            if current_role_attrs['rolpassword'] is not None:
                pwchanging = True

        # SCRAM hashes are represented as a special object, containing hash data:
        # `SCRAM-SHA-256$<iteration count>:<salt>$<StoredKey>:<ServerKey>`
        # for reference, see https://www.postgresql.org/docs/current/catalog-pg-authid.html
        elif current_role_attrs['rolpassword'] is not None \
                and pbkdf2_found \
                and re.match(SCRAM_SHA256_REGEX, current_role_attrs['rolpassword']):

            r = re.match(SCRAM_SHA256_REGEX, current_role_attrs['rolpassword'])
            try:
                # extract SCRAM params from rolpassword
                it = int(r.group(1))
                salt = b64decode(r.group(2))
                server_key = b64decode(r.group(4))
                # we'll never need `storedKey` as it is only used for server auth in SCRAM
                # storedKey = b64decode(r.group(3))

                # from RFC5802 https://tools.ietf.org/html/rfc5802#section-3
                # SaltedPassword  := Hi(Normalize(password), salt, i)
                # ServerKey       := HMAC(SaltedPassword, "Server Key")
                normalized_password = saslprep.saslprep(to_text(password))
                salted_password = pbkdf2_hmac('sha256', to_bytes(normalized_password), salt, it)

                server_key_verifier = hmac.new(salted_password, digestmod=sha256)
                server_key_verifier.update(b'Server Key')

                if server_key_verifier.digest() != server_key:
                    pwchanging = True
            except Exception:
                # We assume the password is not scram encrypted
                # or we cannot check it properly, e.g. due to missing dependencies
                pwchanging = True

        # 32: MD5 hashes are represented as a sequence of 32 hexadecimal digits
        #  3: The size of the 'md5' prefix
        # When the provided password looks like a MD5-hash, value of
        # 'encrypted' is ignored.
        elif (password.startswith('md5') and len(password) == 32 + 3) or encrypted == 'UNENCRYPTED':
            if password != current_role_attrs['rolpassword']:
                pwchanging = True
        elif encrypted == 'ENCRYPTED':
            hashed_password = 'md5{0}'.format(md5(to_bytes(password) + to_bytes(user)).hexdigest())
            if hashed_password != current_role_attrs['rolpassword']:
                pwchanging = True

    return pwchanging


def user_alter(db_connection, module, user, password, role_attr_flags, encrypted, expires, no_password_changes, conn_limit):
    """Change user password and/or attributes. Return True if changed, False otherwise."""
    changed = False

    cursor = db_connection.cursor(cursor_factory=DictCursor)
    # Note: role_attr_flags escaped by parse_role_attrs and encrypted is a
    # literal
    if user == 'PUBLIC':
        if password is not None:
            module.fail_json(msg="cannot change the password for PUBLIC user")
        elif role_attr_flags != '':
            module.fail_json(msg="cannot change the role_attr_flags for PUBLIC user")
        else:
            return False

    # Handle passwords.
    if not no_password_changes and (password is not None or role_attr_flags != '' or expires is not None or conn_limit is not None):
        # Select password and all flag-like columns in order to verify changes.
        try:
            select = "SELECT * FROM pg_authid where rolname=%(user)s"
            cursor.execute(select, {"user": user})
            # Grab current role attributes.
            current_role_attrs = cursor.fetchone()
        except psycopg2.ProgrammingError:
            current_role_attrs = None
            db_connection.rollback()

        pwchanging = user_should_we_change_password(current_role_attrs, user, password, encrypted)

        if current_role_attrs is None:
            try:
                # AWS RDS instances does not allow user to access pg_authid
                # so try to get current_role_attrs from pg_roles tables
                select = "SELECT * FROM pg_roles where rolname=%(user)s"
                cursor.execute(select, {"user": user})
                # Grab current role attributes from pg_roles
                current_role_attrs = cursor.fetchone()
            except psycopg2.ProgrammingError as e:
                db_connection.rollback()
                module.fail_json(msg="Failed to get role details for current user %s: %s" % (user, e))

        role_attr_flags_changing = False
        if role_attr_flags:
            role_attr_flags_dict = {}
            for r in role_attr_flags.split(' '):
                if r.startswith('NO'):
                    role_attr_flags_dict[r.replace('NO', '', 1)] = False
                else:
                    role_attr_flags_dict[r] = True

            for role_attr_name, role_attr_value in role_attr_flags_dict.items():
                if current_role_attrs[PRIV_TO_AUTHID_COLUMN[role_attr_name]] != role_attr_value:
                    role_attr_flags_changing = True

        if expires is not None:
            cursor.execute("SELECT %s::timestamptz;", (expires,))
            expires_with_tz = cursor.fetchone()[0]
            expires_changing = expires_with_tz != current_role_attrs.get('rolvaliduntil')
        else:
            expires_changing = False

        conn_limit_changing = (conn_limit is not None and conn_limit != current_role_attrs['rolconnlimit'])

        if not pwchanging and not role_attr_flags_changing and not expires_changing and not conn_limit_changing:
            return False

        alter = ['ALTER USER "%(user)s"' % {"user": user}]
        if pwchanging:
            if password != '':
                alter.append("WITH %(crypt)s" % {"crypt": encrypted})
                alter.append("PASSWORD %(password)s")
            else:
                alter.append("WITH PASSWORD NULL")
            alter.append(role_attr_flags)
        elif role_attr_flags:
            alter.append('WITH %s' % role_attr_flags)
        if expires is not None:
            alter.append("VALID UNTIL %(expires)s")
        if conn_limit is not None:
            alter.append("CONNECTION LIMIT %(conn_limit)s" % {"conn_limit": conn_limit})

        query_password_data = dict(password=password, expires=expires)
        try:
            cursor.execute(' '.join(alter), query_password_data)
            changed = True
        except psycopg2.InternalError as e:
            if e.pgcode == '25006':
                # Handle errors due to read-only transactions indicated by pgcode 25006
                # ERROR:  cannot execute ALTER ROLE in a read-only transaction
                changed = False
                module.fail_json(msg=e.pgerror, exception=traceback.format_exc())
                return changed
            else:
                raise psycopg2.InternalError(e)
        except psycopg2.NotSupportedError as e:
            module.fail_json(msg=e.pgerror, exception=traceback.format_exc())

    elif no_password_changes and role_attr_flags != '':
        # Grab role information from pg_roles instead of pg_authid
        select = "SELECT * FROM pg_roles where rolname=%(user)s"
        cursor.execute(select, {"user": user})
        # Grab current role attributes.
        current_role_attrs = cursor.fetchone()

        role_attr_flags_changing = False

        if role_attr_flags:
            role_attr_flags_dict = {}
            for r in role_attr_flags.split(' '):
                if r.startswith('NO'):
                    role_attr_flags_dict[r.replace('NO', '', 1)] = False
                else:
                    role_attr_flags_dict[r] = True

            for role_attr_name, role_attr_value in role_attr_flags_dict.items():
                if current_role_attrs[PRIV_TO_AUTHID_COLUMN[role_attr_name]] != role_attr_value:
                    role_attr_flags_changing = True

        if not role_attr_flags_changing:
            return False

        alter = ['ALTER USER "%(user)s"' %
                 {"user": user}]
        if role_attr_flags:
            alter.append('WITH %s' % role_attr_flags)

        try:
            cursor.execute(' '.join(alter))
        except psycopg2.InternalError as e:
            if e.pgcode == '25006':
                # Handle errors due to read-only transactions indicated by pgcode 25006
                # ERROR:  cannot execute ALTER ROLE in a read-only transaction
                changed = False
                module.fail_json(msg=e.pgerror, exception=traceback.format_exc())
                return changed
            else:
                raise psycopg2.InternalError(e)

        # Grab new role attributes.
        cursor.execute(select, {"user": user})
        new_role_attrs = cursor.fetchone()

        # Detect any differences between current_ and new_role_attrs.
        changed = current_role_attrs != new_role_attrs

    return changed


def user_delete(cursor, user):
    """Try to remove a user. Returns True if successful otherwise False"""
    cursor.execute("SAVEPOINT ansible_pgsql_user_delete")
    try:
        query = 'DROP USER "%s"' % user
        executed_queries.append(query)
        cursor.execute(query)
    except Exception:
        cursor.execute("ROLLBACK TO SAVEPOINT ansible_pgsql_user_delete")
        cursor.execute("RELEASE SAVEPOINT ansible_pgsql_user_delete")
        return False

    cursor.execute("RELEASE SAVEPOINT ansible_pgsql_user_delete")
    return True


def has_table_privileges(cursor, user, table, privs):
    """
    Return the difference between the privileges that a user already has and
    the privileges that they desire to have.

    :returns: tuple of:
        * privileges that they have and were requested
        * privileges they currently hold but were not requested
        * privileges requested that they do not hold
    """
    cur_privs = get_table_privileges(cursor, user, table)
    have_currently = cur_privs.intersection(privs)
    other_current = cur_privs.difference(privs)
    desired = privs.difference(cur_privs)
    return (have_currently, other_current, desired)


def get_table_privileges(cursor, user, table):
    if '.' in table:
        schema, table = table.split('.', 1)
    else:
        schema = 'public'
    query = ("SELECT privilege_type FROM information_schema.role_table_grants "
             "WHERE grantee=%(user)s AND table_name=%(table)s AND table_schema=%(schema)s")
    cursor.execute(query, {'user': user, 'table': table, 'schema': schema})
    return frozenset([x[0] for x in cursor.fetchall()])


def grant_table_privileges(cursor, user, table, privs):
    # Note: priv escaped by parse_privs
    privs = ', '.join(privs)
    query = 'GRANT %s ON TABLE %s TO "%s"' % (
        privs, pg_quote_identifier(table, 'table'), user)
    executed_queries.append(query)
    cursor.execute(query)


def revoke_table_privileges(cursor, user, table, privs):
    # Note: priv escaped by parse_privs
    privs = ', '.join(privs)
    query = 'REVOKE %s ON TABLE %s FROM "%s"' % (
        privs, pg_quote_identifier(table, 'table'), user)
    executed_queries.append(query)
    cursor.execute(query)


def get_database_privileges(cursor, user, db):
    priv_map = {
        'C': 'CREATE',
        'T': 'TEMPORARY',
        'c': 'CONNECT',
    }
    query = 'SELECT datacl FROM pg_database WHERE datname = %s'
    cursor.execute(query, (db,))
    datacl = cursor.fetchone()[0]
    if datacl is None:
        return set()
    r = re.search(r'%s\\?"?=(C?T?c?)/[^,]+,?' % user, datacl)
    if r is None:
        return set()
    o = set()
    for v in r.group(1):
        o.add(priv_map[v])
    return normalize_privileges(o, 'database')


def has_database_privileges(cursor, user, db, privs):
    """
    Return the difference between the privileges that a user already has and
    the privileges that they desire to have.

    :returns: tuple of:
        * privileges that they have and were requested
        * privileges they currently hold but were not requested
        * privileges requested that they do not hold
    """
    cur_privs = get_database_privileges(cursor, user, db)
    have_currently = cur_privs.intersection(privs)
    other_current = cur_privs.difference(privs)
    desired = privs.difference(cur_privs)
    return (have_currently, other_current, desired)


def grant_database_privileges(cursor, user, db, privs):
    # Note: priv escaped by parse_privs
    privs = ', '.join(privs)
    if user == "PUBLIC":
        query = 'GRANT %s ON DATABASE %s TO PUBLIC' % (
                privs, pg_quote_identifier(db, 'database'))
    else:
        query = 'GRANT %s ON DATABASE %s TO "%s"' % (
                privs, pg_quote_identifier(db, 'database'), user)

    executed_queries.append(query)
    cursor.execute(query)


def revoke_database_privileges(cursor, user, db, privs):
    # Note: priv escaped by parse_privs
    privs = ', '.join(privs)
    if user == "PUBLIC":
        query = 'REVOKE %s ON DATABASE %s FROM PUBLIC' % (
                privs, pg_quote_identifier(db, 'database'))
    else:
        query = 'REVOKE %s ON DATABASE %s FROM "%s"' % (
                privs, pg_quote_identifier(db, 'database'), user)

    executed_queries.append(query)
    cursor.execute(query)


def revoke_privileges(cursor, user, privs):
    if privs is None:
        return False

    revoke_funcs = dict(table=revoke_table_privileges,
                        database=revoke_database_privileges)
    check_funcs = dict(table=has_table_privileges,
                       database=has_database_privileges)

    changed = False
    for type_ in privs:
        for name, privileges in iteritems(privs[type_]):
            # Check that any of the privileges requested to be removed are
            # currently granted to the user
            differences = check_funcs[type_](cursor, user, name, privileges)
            if differences[0]:
                revoke_funcs[type_](cursor, user, name, privileges)
                changed = True
    return changed


def grant_privileges(cursor, user, privs):
    if privs is None:
        return False

    grant_funcs = dict(table=grant_table_privileges,
                       database=grant_database_privileges)
    check_funcs = dict(table=has_table_privileges,
                       database=has_database_privileges)

    changed = False
    for type_ in privs:
        for name, privileges in iteritems(privs[type_]):
            # Check that any of the privileges requested for the user are
            # currently missing
            differences = check_funcs[type_](cursor, user, name, privileges)
            if differences[2]:
                grant_funcs[type_](cursor, user, name, privileges)
                changed = True
    return changed


def parse_role_attrs(cursor, role_attr_flags):
    """
    Parse role attributes string for user creation.
    Format:

        attributes[,attributes,...]

    Where:

        attributes := CREATEDB,CREATEROLE,NOSUPERUSER,...
        [ "[NO]SUPERUSER","[NO]CREATEROLE", "[NO]CREATEDB",
                            "[NO]INHERIT", "[NO]LOGIN", "[NO]REPLICATION",
                            "[NO]BYPASSRLS" ]

    Note: "[NO]BYPASSRLS" role attribute introduced in 9.5
    Note: "[NO]CREATEUSER" role attribute is deprecated.

    """
    flags = frozenset(role.upper() for role in role_attr_flags.split(',') if role)

    valid_flags = frozenset(itertools.chain(FLAGS, get_valid_flags_by_version(cursor)))
    valid_flags = frozenset(itertools.chain(valid_flags, ('NO%s' % flag for flag in valid_flags)))

    if not flags.issubset(valid_flags):
        raise InvalidFlagsError('Invalid role_attr_flags specified: %s' %
                                ' '.join(flags.difference(valid_flags)))

    return ' '.join(flags)


def normalize_privileges(privs, type_):
    new_privs = set(privs)
    if 'ALL' in new_privs:
        new_privs.update(VALID_PRIVS[type_])
        new_privs.remove('ALL')
    if 'TEMP' in new_privs:
        new_privs.add('TEMPORARY')
        new_privs.remove('TEMP')

    return new_privs


def parse_privs(privs, db):
    """
    Parse privilege string to determine permissions for database db.
    Format:

        privileges[/privileges/...]

    Where:

        privileges := DATABASE_PRIVILEGES[,DATABASE_PRIVILEGES,...] |
            TABLE_NAME:TABLE_PRIVILEGES[,TABLE_PRIVILEGES,...]
    """
    if privs is None:
        return privs

    o_privs = {
        'database': {},
        'table': {}
    }
    for token in privs.split('/'):
        if ':' not in token:
            type_ = 'database'
            name = db
            priv_set = frozenset(x.strip().upper()
                                 for x in token.split(',') if x.strip())
        else:
            type_ = 'table'
            name, privileges = token.split(':', 1)
            priv_set = frozenset(x.strip().upper()
                                 for x in privileges.split(',') if x.strip())

        if not priv_set.issubset(VALID_PRIVS[type_]):
            raise InvalidPrivsError('Invalid privs specified for %s: %s' %
                                    (type_, ' '.join(priv_set.difference(VALID_PRIVS[type_]))))

        priv_set = normalize_privileges(priv_set, type_)
        o_privs[type_][name] = priv_set

    return o_privs


def get_valid_flags_by_version(cursor):
    """
    Some role attributes were introduced after certain versions. We want to
    compile a list of valid flags against the current Postgres version.
    """
    current_version = cursor.connection.server_version

    return [
        flag
        for flag, version_introduced in FLAGS_BY_VERSION.items()
        if current_version >= version_introduced
    ]


def get_comment(cursor, user):
    """Get user's comment."""
    query = ("SELECT pg_catalog.shobj_description(r.oid, 'pg_authid') "
             "FROM pg_catalog.pg_roles r "
             "WHERE r.rolname = %(user)s")
    cursor.execute(query, {'user': user})
    return cursor.fetchone()[0]


def add_comment(cursor, user, comment):
    """Add comment on user."""
    if comment != get_comment(cursor, user):
        query = 'COMMENT ON ROLE "%s" IS ' % user
        cursor.execute(query + '%(comment)s', {'comment': comment})
        executed_queries.append(cursor.mogrify(query + '%(comment)s', {'comment': comment}))
        return True
    else:
        return False


# ===========================================
# Module execution.
#

def main():
    argument_spec = postgres_common_argument_spec()
    argument_spec.update(
        user=dict(type='str', required=True, aliases=['name']),
        password=dict(type='str', default=None, no_log=True),
        state=dict(type='str', default='present', choices=['absent', 'present']),
        priv=dict(type='str', default=None),
        db=dict(type='str', default='', aliases=['login_db']),
        fail_on_user=dict(type='bool', default=True, aliases=['fail_on_role']),
        role_attr_flags=dict(type='str', default=''),
        encrypted=dict(type='bool', default=True),
        no_password_changes=dict(type='bool', default=False, no_log=False),
        expires=dict(type='str', default=None),
        conn_limit=dict(type='int', default=None),
        session_role=dict(type='str'),
        groups=dict(type='list', elements='str'),
        comment=dict(type='str', default=None),
        trust_input=dict(type='bool', default=True),
    )
    module = AnsibleModule(
        argument_spec=argument_spec,
        supports_check_mode=True
    )

    user = module.params["user"]
    password = module.params["password"]
    state = module.params["state"]
    fail_on_user = module.params["fail_on_user"]
    if module.params['db'] == '' and module.params["priv"] is not None:
        module.fail_json(msg="privileges require a database to be specified")
    privs = parse_privs(module.params["priv"], module.params["db"])
    no_password_changes = module.params["no_password_changes"]
    if module.params["encrypted"]:
        encrypted = "ENCRYPTED"
    else:
        encrypted = "UNENCRYPTED"
    expires = module.params["expires"]
    conn_limit = module.params["conn_limit"]
    role_attr_flags = module.params["role_attr_flags"]
    groups = module.params["groups"]
    if groups:
        groups = [e.strip() for e in groups]
    comment = module.params["comment"]
    session_role = module.params['session_role']

    trust_input = module.params['trust_input']
    if not trust_input:
        # Check input for potentially dangerous elements:
        check_input(module, user, password, privs, expires,
                    role_attr_flags, groups, comment, session_role)

    conn_params = get_conn_params(module, module.params, warn_db_default=False)
    db_connection = connect_to_db(module, conn_params)
    cursor = db_connection.cursor(cursor_factory=DictCursor)

    try:
        role_attr_flags = parse_role_attrs(cursor, role_attr_flags)
    except InvalidFlagsError as e:
        module.fail_json(msg=to_native(e), exception=traceback.format_exc())

    kw = dict(user=user)
    changed = False
    user_removed = False

    if state == "present":
        if user_exists(cursor, user):
            try:
                changed = user_alter(db_connection, module, user, password,
                                     role_attr_flags, encrypted, expires, no_password_changes, conn_limit)
            except SQLParseError as e:
                module.fail_json(msg=to_native(e), exception=traceback.format_exc())
        else:
            try:
                changed = user_add(cursor, user, password,
                                   role_attr_flags, encrypted, expires, conn_limit)
            except psycopg2.ProgrammingError as e:
                module.fail_json(msg="Unable to add user with given requirement "
                                     "due to : %s" % to_native(e),
                                 exception=traceback.format_exc())
            except SQLParseError as e:
                module.fail_json(msg=to_native(e), exception=traceback.format_exc())
        try:
            changed = grant_privileges(cursor, user, privs) or changed
        except SQLParseError as e:
            module.fail_json(msg=to_native(e), exception=traceback.format_exc())

        if groups:
            target_roles = []
            target_roles.append(user)
            pg_membership = PgMembership(module, cursor, groups, target_roles)
            changed = pg_membership.grant() or changed
            executed_queries.extend(pg_membership.executed_queries)

        if comment is not None:
            try:
                changed = add_comment(cursor, user, comment) or changed
            except Exception as e:
                module.fail_json(msg='Unable to add comment on role: %s' % to_native(e),
                                 exception=traceback.format_exc())

    else:
        if user_exists(cursor, user):
            if module.check_mode:
                changed = True
                kw['user_removed'] = True
            else:
                try:
                    changed = revoke_privileges(cursor, user, privs)
                    user_removed = user_delete(cursor, user)
                except SQLParseError as e:
                    module.fail_json(msg=to_native(e), exception=traceback.format_exc())
                changed = changed or user_removed
                if fail_on_user and not user_removed:
                    msg = "Unable to remove user"
                    module.fail_json(msg=msg)
                kw['user_removed'] = user_removed

    if changed:
        if module.check_mode:
            db_connection.rollback()
        else:
            db_connection.commit()

    kw['changed'] = changed
    kw['queries'] = executed_queries
    module.exit_json(**kw)


if __name__ == '__main__':
    main()