#!/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

ANSIBLE_METADATA = {
    'metadata_version': '1.1',
    'status': ['stableinterface'],
    'supported_by': 'community'
}

DOCUMENTATION = r'''
---
module: postgresql_user
short_description: Add or remove a user (role) from a PostgreSQL server instance
description:
- Adds 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
  (see U(https://www.postgresql.org/docs/11/role-attributes.html) for more information).
- The fundamental function of the module is to create, or delete, users from
  a PostgreSQL instances. Privilege assignment, or removal, is an optional
  step, which works on one database at a time. This allows for the module to
  be called several times in the same module to modify the permissions on
  different databases, or to grant permissions to already existing users.
- A user cannot be removed until all the privileges have been stripped from
  the user. In such situation, if the module tries to remove the user it
  will fail. To avoid this from happening the fail_on_user option signals
  the module to try to remove the user, but if not possible keep going; the
  module will report if changes happened and separately if the user was
  removed or not.
version_added: '0.6'
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).
    - Unhashed password will automatically be hashed when saved into the
      database if C(encrypted) parameter is set, otherwise it will be save in
      plain text format.
    - When passing a hashed password it must be generated 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 C(encrypted) parameter.
    type: str
  db:
    description:
    - Name of database to connect to and where user's permissions will be granted.
    type: str
    aliases:
    - login_db
  fail_on_user:
    description:
    - If C(yes), fail when user (role) can't 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
      privileges can be defined for 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:
    version_added: '2.8'
    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.
    - Passwords can be passed already hashed or unhashed, and postgresql
      ensures the stored password is hashed when C(encrypted) is set.
    - "Note: Postgresql 10 and newer doesn't support unhashed passwords."
    - Previous to Ansible 2.6, this was C(no) by default.
    default: 'yes'
    type: bool
    version_added: '1.4'
  expires:
    description:
    - The date at which the user's password is to expire.
    - If set to C('infinity'), user's password never expire.
    - Note that this value should be a valid SQL date and time type.
    type: str
    version_added: '1.4'
  no_password_changes:
    description:
    - If C(yes), don't inspect database for password changes. Effective when
      C(pg_authid) is not accessible (such as AWS RDS). Otherwise, make
      password changes as necessary.
    default: 'no'
    type: bool
    version_added: '2.0'
  conn_limit:
    description:
    - Specifies the user (role) connection limit.
    type: int
    version_added: '2.4'
  ssl_mode:
    description:
      - Determines whether or with what priority a secure SSL TCP/IP connection will be negotiated with the server.
      - See 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 ]
    version_added: '2.3'
  ca_cert:
    description:
      - Specifies the name of a file containing SSL certificate authority (CA) certificate(s).
      - If the file exists, the server's certificate will be verified to be signed by one of these authorities.
    type: str
    aliases: [ ssl_rootcert ]
    version_added: '2.3'
notes:
- The module creates a user (role) with login privilege by default.
  Use NOLOGIN role_attr_flags to change this behaviour.
- The default authentication assumes that you are either logging in as or
  sudo'ing to the postgres account on the host.
- This module uses psycopg2, a Python PostgreSQL database adapter. You must
  ensure that psycopg2 is installed on the host before using this module. If
  the remote host is the PostgreSQL server (which is the default case), then
  PostgreSQL must also be installed on the remote host. For Ubuntu-based
  systems, install the postgresql, libpq-dev, and python-psycopg2 packages
  on the remote host before using this module.
- If you specify PUBLIC as the user (role), then the privilege changes will apply to all users (roles).
  You may not specify password or role_attr_flags when the PUBLIC user is specified.
- The ca_cert parameter requires at least Postgres version 8.4 and I(psycopg2) version 2.4.3.

requirements:
- psycopg2

author:
- Ansible Core Team
extends_documentation_fragment: postgres
'''

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

# 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
  postgresql_user:
    name: rails
    password: md59543f1d82624df2b31672ec0f7050460
    role_attr_flags: CREATEDB,NOSUPERUSER

- name: Connect to acme database and remove test user privileges from there
  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
  postgresql_user:
    db: test
    name: test
    priv: ALL
    state: absent

- name: Connect to acme database and set user's password with no expire date
  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
  postgresql_user:
    db: test
    user: test
    password: ""
'''

RETURN = r'''
queries:
  description: List of executed queries.
  returned: always
  type: list
  sample: ['CREATE USER "alice"', 'GRANT CONNECT ON DATABASE "acme" TO "alice"']
  version_added: '2.8'
'''

import itertools
import re
import traceback
from hashlib import md5

PSYCOPG2_IMP_ERR = None
try:
    import psycopg2
    import psycopg2.extras
    HAS_PSYCOPG2 = True
except ImportError:
    PSYCOPG2_IMP_ERR = traceback.format_exc()
    HAS_PSYCOPG2 = False

from ansible.module_utils.basic import AnsibleModule, missing_required_lib
from ansible.module_utils.database import pg_quote_identifier, SQLParseError
from ansible.module_utils.postgres import postgres_common_argument_spec
from ansible.module_utils._text import to_bytes, to_native
from ansible.module_utils.six import iteritems


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

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": pg_quote_identifier(user, 'role')}]
    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
        # 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=psycopg2.extras.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": pg_quote_identifier(user, 'role')}]
        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": pg_quote_identifier(user, 'role')}]
        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" % pg_quote_identifier(user, 'role')
        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='%s' AND table_name='%s' AND table_schema='%s'" % (user, table, schema))
    cursor.execute(query)
    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'), pg_quote_identifier(user, 'role'))
    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'), pg_quote_identifier(user, 'role'))
    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'),
                pg_quote_identifier(user, 'role'))

    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'),
                pg_quote_identifier(user, 'role'))

    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
    ]


# ===========================================
# 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='yes', aliases=['fail_on_role']),
        role_attr_flags=dict(type='str', default=''),
        encrypted=dict(type='bool', default='yes'),
        no_password_changes=dict(type='bool', default='no'),
        expires=dict(type='str', default=None),
        conn_limit=dict(type='int', default=None),
        session_role=dict(type='str'),
    )
    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"]
    db = module.params["db"]
    session_role = module.params["session_role"]
    if 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"], db)
    no_password_changes = module.params["no_password_changes"]
    if module.params["encrypted"]:
        encrypted = "ENCRYPTED"
    else:
        encrypted = "UNENCRYPTED"
    expires = module.params["expires"]
    sslrootcert = module.params["ca_cert"]
    conn_limit = module.params["conn_limit"]
    role_attr_flags = module.params["role_attr_flags"]

    if not HAS_PSYCOPG2:
        module.fail_json(msg=missing_required_lib('psycopg2'), exception=PSYCOPG2_IMP_ERR)

    # To use defaults values, keyword arguments must be absent, so
    # check which values are empty and don't include in the **kw
    # dictionary
    params_map = {
        "login_host": "host",
        "login_user": "user",
        "login_password": "password",
        "port": "port",
        "db": "database",
        "ssl_mode": "sslmode",
        "ca_cert": "sslrootcert"
    }
    kw = dict((params_map[k], v) for (k, v) in iteritems(module.params)
              if k in params_map and v != "" and v is not None)

    # If a login_unix_socket is specified, incorporate it here.
    is_localhost = "host" not in kw or kw["host"] == "" or kw["host"] == "localhost"
    if is_localhost and module.params["login_unix_socket"] != "":
        kw["host"] = module.params["login_unix_socket"]

    if psycopg2.__version__ < '2.4.3' and sslrootcert is not None:
        module.fail_json(
            msg='psycopg2 must be at least 2.4.3 in order to user the ca_cert parameter')

    try:
        db_connection = psycopg2.connect(**kw)
        cursor = db_connection.cursor(
            cursor_factory=psycopg2.extras.DictCursor)

    except TypeError as e:
        if 'sslrootcert' in e.args[0]:
            module.fail_json(
                msg='Postgresql server must be at least version 8.4 to support sslrootcert')
        module.fail_json(msg="Unable to connect to database: %s" % to_native(e), exception=traceback.format_exc())

    except Exception as e:
        module.fail_json(msg="Unable to connect to database: %s" % to_native(e), exception=traceback.format_exc())

    if session_role:
        try:
            cursor.execute('SET ROLE %s' % pg_quote_identifier(session_role, 'role'))
        except Exception as e:
            module.fail_json(msg="Could not switch role: %s" % to_native(e), exception=traceback.format_exc())

    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())
    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()
