import datetime
import decimal
import functools
import hashlib
import logging
from contextlib import contextmanager
from time import time

from django.conf import settings
from django.db.utils import NotSupportedError
from django.utils.timezone import utc

logger = logging.getLogger('django.db.backends')


class CursorWrapper:
    def __init__(self, cursor, db):
        self.cursor = cursor
        self.db = db

    WRAP_ERROR_ATTRS = frozenset(['fetchone', 'fetchmany', 'fetchall', 'nextset'])

    def __getattr__(self, attr):
        cursor_attr = getattr(self.cursor, attr)
        if attr in CursorWrapper.WRAP_ERROR_ATTRS:
            return self.db.wrap_database_errors(cursor_attr)
        else:
            return cursor_attr

    def __iter__(self):
        with self.db.wrap_database_errors:
            yield from self.cursor

    def __enter__(self):
        return self

    def __exit__(self, type, value, traceback):
        # Close instead of passing through to avoid backend-specific behavior
        # (#17671). Catch errors liberally because errors in cleanup code
        # aren't useful.
        try:
            self.close()
        except self.db.Database.Error:
            pass

    # The following methods cannot be implemented in __getattr__, because the
    # code must run when the method is invoked, not just when it is accessed.

    def callproc(self, procname, params=None, kparams=None):
        # Keyword parameters for callproc aren't supported in PEP 249, but the
        # database driver may support them (e.g. cx_Oracle).
        if kparams is not None and not self.db.features.supports_callproc_kwargs:
            raise NotSupportedError(
                'Keyword parameters for callproc are not supported on this '
                'database backend.'
            )
        self.db.validate_no_broken_transaction()
        with self.db.wrap_database_errors:
            if params is None and kparams is None:
                return self.cursor.callproc(procname)
            elif kparams is None:
                return self.cursor.callproc(procname, params)
            else:
                params = params or ()
                return self.cursor.callproc(procname, params, kparams)

    def execute(self, sql, params=None):
        return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)

    def executemany(self, sql, param_list):
        return self._execute_with_wrappers(sql, param_list, many=True, executor=self._executemany)

    def _execute_with_wrappers(self, sql, params, many, executor):
        context = {'connection': self.db, 'cursor': self}
        for wrapper in reversed(self.db.execute_wrappers):
            executor = functools.partial(wrapper, executor)
        return executor(sql, params, many, context)

    def _execute(self, sql, params, *ignored_wrapper_args):
        self.db.validate_no_broken_transaction()
        with self.db.wrap_database_errors:
            if params is None:
                return self.cursor.execute(sql)
            else:
                return self.cursor.execute(sql, params)

    def _executemany(self, sql, param_list, *ignored_wrapper_args):
        self.db.validate_no_broken_transaction()
        with self.db.wrap_database_errors:
            return self.cursor.executemany(sql, param_list)


class CursorDebugWrapper(CursorWrapper):

    # XXX callproc isn't instrumented at this time.

    def execute(self, sql, params=None):
        with self.debug_sql(sql, params, use_last_executed_query=True):
            return super().execute(sql, params)

    def executemany(self, sql, param_list):
        with self.debug_sql(sql, param_list, many=True):
            return super().executemany(sql, param_list)

    @contextmanager
    def debug_sql(self, sql=None, params=None, use_last_executed_query=False, many=False):
        start = time()
        try:
            yield
        finally:
            stop = time()
            duration = stop - start
            if use_last_executed_query:
                sql = self.db.ops.last_executed_query(self.cursor, sql, params)
            try:
                times = len(params) if many else ''
            except TypeError:
                # params could be an iterator.
                times = '?'
            self.db.queries_log.append({
                'sql': '%s times: %s' % (times, sql) if many else sql,
                'time': '%.3f' % duration,
            })
            logger.debug(
                '(%.3f) %s; args=%s',
                duration,
                sql,
                params,
                extra={'duration': duration, 'sql': sql, 'params': params},
            )


###############################################
# Converters from database (string) to Python #
###############################################

def typecast_date(s):
    return datetime.date(*map(int, s.split('-'))) if s else None  # return None if s is null


def typecast_time(s):  # does NOT store time zone information
    if not s:
        return None
    hour, minutes, seconds = s.split(':')
    if '.' in seconds:  # check whether seconds have a fractional part
        seconds, microseconds = seconds.split('.')
    else:
        microseconds = '0'
    return datetime.time(int(hour), int(minutes), int(seconds), int((microseconds + '000000')[:6]))


def typecast_timestamp(s):  # does NOT store time zone information
    # "2005-07-29 15:48:00.590358-05"
    # "2005-07-29 09:56:00-05"
    if not s:
        return None
    if ' ' not in s:
        return typecast_date(s)
    d, t = s.split()
    # Remove timezone information.
    if '-' in t:
        t, _ = t.split('-', 1)
    elif '+' in t:
        t, _ = t.split('+', 1)
    dates = d.split('-')
    times = t.split(':')
    seconds = times[2]
    if '.' in seconds:  # check whether seconds have a fractional part
        seconds, microseconds = seconds.split('.')
    else:
        microseconds = '0'
    tzinfo = utc if settings.USE_TZ else None
    return datetime.datetime(
        int(dates[0]), int(dates[1]), int(dates[2]),
        int(times[0]), int(times[1]), int(seconds),
        int((microseconds + '000000')[:6]), tzinfo
    )


###############################################
# Converters from Python to database (string) #
###############################################

def split_identifier(identifier):
    """
    Split a SQL identifier into a two element tuple of (namespace, name).

    The identifier could be a table, column, or sequence name might be prefixed
    by a namespace.
    """
    try:
        namespace, name = identifier.split('"."')
    except ValueError:
        namespace, name = '', identifier
    return namespace.strip('"'), name.strip('"')


def truncate_name(identifier, length=None, hash_len=4):
    """
    Shorten a SQL identifier to a repeatable mangled version with the given
    length.

    If a quote stripped name contains a namespace, e.g. USERNAME"."TABLE,
    truncate the table portion only.
    """
    namespace, name = split_identifier(identifier)

    if length is None or len(name) <= length:
        return identifier

    digest = names_digest(name, length=hash_len)
    return '%s%s%s' % ('%s"."' % namespace if namespace else '', name[:length - hash_len], digest)


def names_digest(*args, length):
    """
    Generate a 32-bit digest of a set of arguments that can be used to shorten
    identifying names.
    """
    h = hashlib.md5()
    for arg in args:
        h.update(arg.encode())
    return h.hexdigest()[:length]


def format_number(value, max_digits, decimal_places):
    """
    Format a number into a string with the requisite number of digits and
    decimal places.
    """
    if value is None:
        return None
    context = decimal.getcontext().copy()
    if max_digits is not None:
        context.prec = max_digits
    if decimal_places is not None:
        value = value.quantize(decimal.Decimal(1).scaleb(-decimal_places), context=context)
    else:
        context.traps[decimal.Rounded] = 1
        value = context.create_decimal(value)
    return "{:f}".format(value)


def strip_quotes(table_name):
    """
    Strip quotes off of quoted table names to make them safe for use in index
    names, sequence names, etc. For example '"USER"."TABLE"' (an Oracle naming
    scheme) becomes 'USER"."TABLE'.
    """
    has_quotes = table_name.startswith('"') and table_name.endswith('"')
    return table_name[1:-1] if has_quotes else table_name
