import re
from . import err


#: Regular expression for :meth:`Cursor.executemany`.
#: executemany only supports simple bulk insert.
#: You can use it to load large dataset.
RE_INSERT_VALUES = re.compile(
    r"\s*((?:INSERT|REPLACE)\b.+\bVALUES?\s*)"
    + r"(\(\s*(?:%s|%\([^)]+\)s)\s*(?:,\s*(?:%s|%\([^)]+\)s)\s*)*\))"
    + r'(\s*(?:AS\s+(?:`[^`]+`|"[^"]+"|[0-9A-Za-z_$]+)\s*'
    + r'(?:\(\s*(?:`[^`]+`|"[^"]+"|[0-9A-Za-z_$]+)\s*'
    + r'(?:,\s*(?:`[^`]+`|"[^"]+"|[0-9A-Za-z_$]+)\s*)*\))?\s*)?'
    + r"(?:ON DUPLICATE.*)?);?\s*\Z",
    re.IGNORECASE | re.DOTALL,
)


def _backquote_escape(s):
    return s.replace("`", "``")


class Cursor:
    """
    This is the object used to interact with the database.

    Do not create an instance of a Cursor yourself. Call
    connections.Connection.cursor().

    See `Cursor <https://www.python.org/dev/peps/pep-0249/#cursor-objects>`_ in
    the specification.
    """

    #: Max statement size which :meth:`executemany` generates.
    #:
    #: Max size of allowed statement is max_allowed_packet - packet_header_size.
    #: Default value of max_allowed_packet is 1048576.
    max_stmt_length = 1024000

    def __init__(self, connection):
        self.connection = connection
        self.warning_count = 0
        self.description = None
        self.rownumber = 0
        self.rowcount = -1
        self.arraysize = 1
        self._executed = None
        self._result = None
        self._rows = None

    def close(self):
        """
        Closing a cursor just exhausts all remaining data.
        """
        conn = self.connection
        if conn is None:
            return
        try:
            while self.nextset():
                pass
        finally:
            self.connection = None

    def __enter__(self):
        return self

    def __exit__(self, *exc_info):
        del exc_info
        self.close()

    def _get_db(self):
        if not self.connection:
            raise err.ProgrammingError("Cursor closed")
        return self.connection

    def _check_executed(self):
        if not self._executed:
            raise err.ProgrammingError("execute() first")

    def _conv_row(self, row):
        return row

    def setinputsizes(self, *args):
        """Does nothing, required by DB API."""

    def setoutputsizes(self, *args):
        """Does nothing, required by DB API."""

    def _nextset(self, unbuffered=False):
        """Get the next query set."""
        conn = self._get_db()
        current_result = self._result
        if current_result is None or current_result is not conn._result:
            return None
        if not current_result.has_next:
            return None
        self._result = None
        self._clear_result()
        conn.next_result(unbuffered=unbuffered)
        self._do_get_result()
        return True

    def nextset(self):
        return self._nextset(False)

    def _escape_args(self, args, conn):
        if isinstance(args, (tuple, list)):
            return tuple(conn.literal(arg) for arg in args)
        elif isinstance(args, dict):
            return {key: conn.literal(val) for (key, val) in args.items()}
        else:
            # If it's not a dictionary let's try escaping it anyways.
            # Worst case it will throw a Value error
            return conn.escape(args)

    def mogrify(self, query, args=None):
        """
        Returns the exact string that would be sent to the database by calling the
        execute() method.

        :param query: Query to mogrify.
        :type query: str

        :param args: Parameters used with query. (optional)
        :type args: tuple, list or dict

        :return: The query with argument binding applied.
        :rtype: str

        This method follows the extension to the DB API 2.0 followed by Psycopg.
        """
        conn = self._get_db()

        if args is not None:
            query = query % self._escape_args(args, conn)

        return query

    def execute(self, query, args=None):
        """Execute a query.

        :param query: Query to execute.
        :type query: str

        :param args: Parameters used with query. (optional)
        :type args: tuple, list or dict

        :return: Number of affected rows.
        :rtype: int

        If args is a list or tuple, %s can be used as a placeholder in the query.
        If args is a dict, %(name)s can be used as a placeholder in the query.
        """
        while self.nextset():
            pass

        query = self.mogrify(query, args)

        result = self._query(query)
        self._executed = query
        return result

    def executemany(self, query, args):
        """Run several data against one query.

        :param query: Query to execute.
        :type query: str

        :param args: Sequence of sequences or mappings. It is used as parameter.
        :type args: tuple or list

        :return: Number of rows affected, if any.
        :rtype: int or None

        This method improves performance on multiple-row INSERT and
        REPLACE. Otherwise it is equivalent to looping over args with
        execute().
        """
        if not args:
            return

        m = RE_INSERT_VALUES.match(query)
        if m:
            q_prefix = m.group(1) % ()
            q_values = m.group(2).rstrip()
            q_postfix = m.group(3) or ""
            assert q_values[0] == "(" and q_values[-1] == ")"
            return self._do_execute_many(
                q_prefix,
                q_values,
                q_postfix,
                args,
                self.max_stmt_length,
                self._get_db().encoding,
            )

        self.rowcount = sum(self.execute(query, arg) for arg in args)
        return self.rowcount

    def _do_execute_many(
        self, prefix, values, postfix, args, max_stmt_length, encoding
    ):
        conn = self._get_db()
        escape = self._escape_args
        if isinstance(prefix, str):
            prefix = prefix.encode(encoding)
        if isinstance(postfix, str):
            postfix = postfix.encode(encoding)
        sql = bytearray(prefix)
        args = iter(args)
        v = values % escape(next(args), conn)
        if isinstance(v, str):
            v = v.encode(encoding, "surrogateescape")
        sql += v
        rows = 0
        for arg in args:
            v = values % escape(arg, conn)
            if isinstance(v, str):
                v = v.encode(encoding, "surrogateescape")
            if len(sql) + len(v) + len(postfix) + 1 > max_stmt_length:
                rows += self.execute(sql + postfix)
                sql = bytearray(prefix)
            else:
                sql += b","
            sql += v
        rows += self.execute(sql + postfix)
        self.rowcount = rows
        return rows

    def callproc(self, procname, args=()):
        """Execute stored procedure procname with args.

        :param procname: Name of procedure to execute on server.
        :type procname: str

        :param args: Sequence of parameters to use with procedure.
        :type args: tuple or list

        Returns the original args.

        Compatibility warning: PEP-249 specifies that any modified
        parameters must be returned. This is currently impossible
        as they are only available by storing them in a server
        variable and then retrieved by a query. Since stored
        procedures return zero or more result sets, there is no
        reliable way to get at OUT or INOUT parameters via callproc.
        The server variables are named @_procname_n, where procname
        is the parameter above and n is the position of the parameter
        (from zero). Once all result sets generated by the procedure
        have been fetched, you can issue a SELECT @_procname_0, ...
        query using .execute() to get any OUT or INOUT values.

        Compatibility warning: The act of calling a stored procedure
        itself creates an empty result set. This appears after any
        result sets generated by the procedure. This is non-standard
        behavior with respect to the DB-API. Be sure to use nextset()
        to advance through all result sets; otherwise you may get
        disconnected.
        """
        procname_escaped = _backquote_escape(procname)
        conn = self._get_db()

        if args:
            fmt = f"@`_{procname_escaped}_%d`=%s"
            self._query(
                "SET %s"
                % ",".join(
                    fmt % (index, conn.escape(arg)) for index, arg in enumerate(args)
                )
            )
            self.nextset()

        q = "CALL `{}`({})".format(
            procname_escaped,
            ",".join([f"@`_{procname_escaped}_{i}`" for i in range(len(args))]),
        )
        self._query(q)
        self._executed = q
        return args

    def fetchone(self):
        """Fetch the next row."""
        self._check_executed()
        if self._rows is None or self.rownumber >= len(self._rows):
            return None
        result = self._rows[self.rownumber]
        self.rownumber += 1
        return result

    def fetchmany(self, size=None):
        """Fetch several rows."""
        self._check_executed()
        if self._rows is None:
            # Django expects () for EOF.
            # https://github.com/django/django/blob/0c1518ee429b01c145cf5b34eab01b0b92f8c246/django/db/backends/mysql/features.py#L8
            return ()
        end = self.rownumber + (size or self.arraysize)
        result = self._rows[self.rownumber : end]
        self.rownumber = min(end, len(self._rows))
        return result

    def fetchall(self):
        """Fetch all the rows."""
        self._check_executed()
        if self._rows is None:
            return []
        if self.rownumber:
            result = self._rows[self.rownumber :]
        else:
            result = self._rows
        self.rownumber = len(self._rows)
        return result

    def scroll(self, value, mode="relative"):
        self._check_executed()
        if mode == "relative":
            r = self.rownumber + value
        elif mode == "absolute":
            r = value
        else:
            raise err.ProgrammingError("unknown scroll mode %s" % mode)

        if not (0 <= r < len(self._rows)):
            raise IndexError("out of range")
        self.rownumber = r

    def _query(self, q):
        conn = self._get_db()
        self._clear_result()
        conn.query(q)
        self._do_get_result()
        return self.rowcount

    def _clear_result(self):
        self.rownumber = 0
        self._result = None

        self.rowcount = 0
        self.warning_count = 0
        self.description = None
        self.lastrowid = None
        self._rows = None

    def _do_get_result(self):
        conn = self._get_db()

        self._result = result = conn._result

        self.rowcount = result.affected_rows
        self.warning_count = result.warning_count
        self.description = result.description
        self.lastrowid = result.insert_id
        self._rows = result.rows

    def __iter__(self):
        return self

    def __next__(self):
        row = self.fetchone()
        if row is None:
            raise StopIteration
        return row


class DictCursorMixin:
    # You can override this to use OrderedDict or other dict-like types.
    dict_type = dict

    def _do_get_result(self):
        super()._do_get_result()
        fields = []
        if self.description:
            for f in self._result.fields:
                name = f.name
                if name in fields:
                    name = f.table_name + "." + name
                fields.append(name)
            self._fields = fields

        if fields and self._rows:
            self._rows = [self._conv_row(r) for r in self._rows]

    def _conv_row(self, row):
        if row is None:
            return None
        return self.dict_type(zip(self._fields, row))


class DictCursor(DictCursorMixin, Cursor):
    """A cursor which returns results as a dictionary"""


class SSCursor(Cursor):
    """
    Unbuffered Cursor, mainly useful for queries that return a lot of data,
    or for connections to remote servers over a slow network.

    Instead of copying every row of data into a buffer, this will fetch
    rows as needed. The upside of this is the client uses much less memory,
    and rows are returned much faster when traveling over a slow network
    or if the result set is very big.

    There are limitations, though. The MySQL protocol doesn't support
    returning the total number of rows, so the only way to tell how many rows
    there are is to iterate over every row returned. Also, it currently isn't
    possible to scroll backwards, as only the current row is held in memory.
    """

    def _conv_row(self, row):
        return row

    def close(self):
        conn = self.connection
        if conn is None:
            return

        if self._result is not None and self._result is conn._result:
            self._result._finish_unbuffered_query()

        try:
            while self.nextset():
                pass
        finally:
            self.connection = None

    __del__ = close

    def _query(self, q):
        conn = self._get_db()
        self._clear_result()
        conn.query(q, unbuffered=True)
        self._do_get_result()
        return self.rowcount

    def nextset(self):
        return self._nextset(unbuffered=True)

    def read_next(self):
        """Read next row."""
        return self._conv_row(self._result._read_rowdata_packet_unbuffered())

    def fetchone(self):
        """Fetch next row."""
        self._check_executed()
        row = self.read_next()
        if row is None:
            self.warning_count = self._result.warning_count
            return None
        self.rownumber += 1
        return row

    def fetchall(self):
        """
        Fetch all, as per MySQLdb. Pretty useless for large queries, as
        it is buffered. See fetchall_unbuffered(), if you want an unbuffered
        generator version of this method.
        """
        return list(self.fetchall_unbuffered())

    def fetchall_unbuffered(self):
        """
        Fetch all, implemented as a generator, which isn't to standard,
        however, it doesn't make sense to return everything in a list, as that
        would use ridiculous memory for large result sets.
        """
        return iter(self.fetchone, None)

    def fetchmany(self, size=None):
        """Fetch many."""
        self._check_executed()
        if size is None:
            size = self.arraysize

        rows = []
        for i in range(size):
            row = self.read_next()
            if row is None:
                self.warning_count = self._result.warning_count
                break
            rows.append(row)
            self.rownumber += 1
        if not rows:
            # Django expects () for EOF.
            # https://github.com/django/django/blob/0c1518ee429b01c145cf5b34eab01b0b92f8c246/django/db/backends/mysql/features.py#L8
            return ()
        return rows

    def scroll(self, value, mode="relative"):
        self._check_executed()

        if mode == "relative":
            if value < 0:
                raise err.NotSupportedError(
                    "Backwards scrolling not supported by this cursor"
                )

            for _ in range(value):
                self.read_next()
            self.rownumber += value
        elif mode == "absolute":
            if value < self.rownumber:
                raise err.NotSupportedError(
                    "Backwards scrolling not supported by this cursor"
                )

            end = value - self.rownumber
            for _ in range(end):
                self.read_next()
            self.rownumber = value
        else:
            raise err.ProgrammingError("unknown scroll mode %s" % mode)


class SSDictCursor(DictCursorMixin, SSCursor):
    """An unbuffered cursor, which returns results as a dictionary"""
