"""Integration between SQLAlchemy and Hive.

Some code based on
https://github.com/zzzeek/sqlalchemy/blob/rel_0_5/lib/sqlalchemy/databases/sqlite.py
which is released under the MIT license.
"""

from __future__ import absolute_import
from __future__ import unicode_literals

import datetime
import decimal

import re
from sqlalchemy import exc
from sqlalchemy import processors
from sqlalchemy import types
from sqlalchemy import util
# TODO shouldn't use mysql type
from sqlalchemy.databases import mysql
from sqlalchemy.engine import default
from sqlalchemy.sql import compiler
from sqlalchemy.sql.compiler import SQLCompiler

from pytimbr_sqla import hive
from pytimbr_sqla.common import UniversalSet

from dateutil.parser import parse
from decimal import Decimal


class HiveStringTypeBase(types.TypeDecorator):
    """Translates strings returned by Thrift into something else"""
    impl = types.String

    def process_bind_param(self, value, dialect):
        raise NotImplementedError("Writing to Hive not supported")


class HiveDate(HiveStringTypeBase):
    """Translates date strings to date objects"""
    impl = types.DATE

    def process_result_value(self, value, dialect):
        return processors.str_to_date(value)

    def result_processor(self, dialect, coltype):
        def process(value):
            if isinstance(value, datetime.datetime):
                return value.date()
            elif isinstance(value, datetime.date):
                return value
            elif value is not None:
                return parse(value).date()
            else:
                return None

        return process

    def adapt(self, impltype, **kwargs):
        return self.impl


class HiveTimestamp(HiveStringTypeBase):
    """Translates timestamp strings to datetime objects"""
    impl = types.TIMESTAMP

    def process_result_value(self, value, dialect):
        return processors.str_to_datetime(value)

    def result_processor(self, dialect, coltype):
        def process(value):
            if isinstance(value, datetime.datetime):
                return value
            elif value is not None:
                return parse(value)
            else:
                return None

        return process

    def adapt(self, impltype, **kwargs):
        return self.impl


class HiveDecimal(HiveStringTypeBase):
    """Translates strings to decimals"""
    impl = types.DECIMAL

    def process_result_value(self, value, dialect):
        if value is not None:
            return decimal.Decimal(value)
        else:
            return None

    def result_processor(self, dialect, coltype):
        def process(value):
            if isinstance(value, Decimal):
                return value
            elif value is not None:
                return Decimal(value)
            else:
                return None

        return process

    def adapt(self, impltype, **kwargs):
        return self.impl


class HiveIdentifierPreparer(compiler.IdentifierPreparer):
    # Just quote everything to make things simpler / easier to upgrade
    reserved_words = UniversalSet()

    def __init__(self, dialect):
        super(HiveIdentifierPreparer, self).__init__(
            dialect,
            initial_quote='`',
        )


_type_map = {
    'boolean': types.Boolean,
    'tinyint': mysql.MSTinyInteger,
    'smallint': types.SmallInteger,
    'int': types.Integer,
    'bigint': types.BigInteger,
    'float': types.Float,
    'double': types.Float,
    'string': types.String,
    'varchar': types.String,
    'char': types.String,
    'date': HiveDate,
    'timestamp': HiveTimestamp,
    'binary': types.String,
    'array': types.String,
    'map': types.String,
    'struct': types.String,
    'uniontype': types.String,
    'decimal': HiveDecimal,
}


class HiveCompiler(SQLCompiler):
    def visit_concat_op_binary(self, binary, operator, **kw):
        return "concat(%s, %s)" % (self.process(binary.left), self.process(binary.right))

    def visit_insert(self, *args, **kwargs):
        result = super(HiveCompiler, self).visit_insert(*args, **kwargs)
        # Massage the result into Hive's format
        #   INSERT INTO `pyhive_test_database`.`test_table` (`a`) SELECT ...
        #   =>
        #   INSERT INTO TABLE `pyhive_test_database`.`test_table` SELECT ...
        regex = r'^(INSERT INTO) ([^\s]+) \([^\)]*\)'
        assert re.search(regex, result), "Unexpected visit_insert result: {}".format(result)
        return re.sub(regex, r'\1 TABLE \2', result)

    def visit_column(self, *args, **kwargs):
        result = super(HiveCompiler, self).visit_column(*args, **kwargs)
        dot_count = result.count('.')
        assert dot_count in (0, 1, 2), "Unexpected visit_column result {}".format(result)
        if dot_count == 2:
            # we have something of the form schema.table.column
            # hive doesn't like the schema in front, so chop it out
            result = result[result.index('.') + 1:]
        return result

    def visit_char_length_func(self, fn, **kw):
        return 'length{}'.format(self.function_argspec(fn, **kw))


class HiveTypeCompiler(compiler.GenericTypeCompiler):
    def visit_INTEGER(self, type_):
        return 'INT'

    def visit_NUMERIC(self, type_):
        return 'DECIMAL'

    def visit_CHAR(self, type_):
        return 'STRING'

    def visit_VARCHAR(self, type_):
        return 'STRING'

    def visit_NCHAR(self, type_):
        return 'STRING'

    def visit_TEXT(self, type_):
        return 'STRING'

    def visit_CLOB(self, type_):
        return 'STRING'

    def visit_BLOB(self, type_):
        return 'BINARY'

    def visit_TIME(self, type_):
        return 'TIMESTAMP'

    def visit_DATE(self, type_):
        return 'TIMESTAMP'

    def visit_DATETIME(self, type_):
        return 'TIMESTAMP'


class HiveExecutionContext(default.DefaultExecutionContext):
    """This is pretty much the same as SQLiteExecutionContext to work around the same issue.

    http://docs.sqlalchemy.org/en/latest/dialects/sqlite.html#dotted-column-names

    engine = create_engine('hive://...', execution_options={'hive_raw_colnames': True})
    """

    @util.memoized_property
    def _preserve_raw_colnames(self):
        # Ideally, this would also gate on hive.resultset.use.unique.column.names
        return self.execution_options.get('hive_raw_colnames', False)

    def _translate_colname(self, colname):
        # Adjust for dotted column names.
        # When hive.resultset.use.unique.column.names is true (the default), Hive returns column
        # names as "tablename.colname" in cursor.description.
        if not self._preserve_raw_colnames and '.' in colname:
            return colname.split('.')[-1], colname
        else:
            return colname, None


class TimbrDialect(default.DefaultDialect):
    name = 'timbr'
    driver = 'thrift'
    execution_ctx_cls = HiveExecutionContext
    preparer = HiveIdentifierPreparer
    statement_compiler = HiveCompiler
    supports_views = True
    supports_alter = True
    supports_pk_autoincrement = False
    supports_default_values = False
    supports_empty_insert = False
    supports_native_decimal = True
    supports_native_boolean = True
    supports_unicode_statements = True
    supports_unicode_binds = True
    returns_unicode_strings = True
    description_encoding = None
    supports_multivalues_insert = True
    type_compiler = HiveTypeCompiler
    supports_sane_rowcount = False

    @classmethod
    def dbapi(cls):
        return hive

    def create_connect_args(self, url):
        kwargs = {
            'host': url.host,
            'port': url.port or 11000,
            'username': url.username,
            'password': url.password,
            'database': url.database or 'default',
        }
        kwargs.update(url.query)
        return [], kwargs

    def get_schema_names(self, connection, **kw):
        # Equivalent to SHOW DATABASES
        return [row[0] for row in connection.execute('SHOW SCHEMAS')]

    def get_view_names(self, connection, schema=None, **kw):
        # Hive does not provide functionality to query tableType
        # This allows reflection to not crash at the cost of being inaccurate
        return self.get_table_names(connection, schema, **kw)

    def _get_table_columns(self, connection, table_name, schema):
        full_table = table_name
        if schema:
            full_table = schema + '.' + table_name
        # TODO using TGetColumnsReq hangs after sending TFetchResultsReq.
        # Using DESCRIBE works but is uglier.
        try:
            # This needs the table name to be unescaped (no backticks).
            rows = connection.execute('DESCRIBE {}'.format(full_table)).fetchall()
        except exc.OperationalError as e:
            # Does the table exist?
            regex_fmt = r'TExecuteStatementResp.*SemanticException.*Table not found {}'
            regex = regex_fmt.format(re.escape(full_table))
            if re.search(regex, e.args[0]):
                raise exc.NoSuchTableError(full_table)
            else:
                raise
        else:
            # Hive is stupid: this is what I get from DESCRIBE some_schema.does_not_exist
            regex = r'Table .* does not exist'
            if len(rows) == 1 and re.match(regex, rows[0].col_name):
                raise exc.NoSuchTableError(full_table)
            return rows

    def has_table(self, connection, table_name, schema=None):
        try:
            self._get_table_columns(connection, table_name, schema)
            return True
        except exc.NoSuchTableError:
            return False

    def get_columns(self, connection, table_name, schema=None, **kw):
        rows = self._get_table_columns(connection, table_name, schema)
        # Strip whitespace
        rows = [[col.strip() if col else None for col in row] for row in rows]
        # Filter out empty rows and comment
        rows = [row for row in rows if row[0] and row[0] != '# col_name']
        result = []
        for (col_name, col_type, _comment) in rows:
            if col_name == '# Partition Information':
                break
            # Take out the more detailed type information
            # e.g. 'map<int,int>' -> 'map'
            #      'decimal(10,1)' -> decimal
            col_type = re.search(r'^\w+', col_type).group(0)
            try:
                coltype = _type_map[col_type]
            except KeyError:
                util.warn("Did not recognize type '%s' of column '%s'" % (col_type, col_name))
                coltype = types.NullType

            result.append({
                'name': col_name,
                'type': coltype,
                'nullable': True,
                'default': None,
            })
        return result

    def get_foreign_keys(self, connection, table_name, schema=None, **kw):
        # Hive has no support for foreign keys.
        return []

    def get_pk_constraint(self, connection, table_name, schema=None, **kw):
        # Hive has no support for primary keys.
        return []

    def get_indexes(self, connection, table_name, schema=None, **kw):
        rows = self._get_table_columns(connection, table_name, schema)
        # Strip whitespace
        rows = [[col.strip() if col else None for col in row] for row in rows]
        # Filter out empty rows and comment
        rows = [row for row in rows if row[0] and row[0] != '# col_name']
        for i, (col_name, _col_type, _comment) in enumerate(rows):
            if col_name == '# Partition Information':
                break
        # Handle partition columns
        col_names = []
        for col_name, _col_type, _comment in rows[i + 1:]:
            col_names.append(col_name)
        if col_names:
            return [{'name': 'partition', 'column_names': col_names, 'unique': False}]
        else:
            return []

    def get_table_names(self, connection, schema=None, **kw):
        query = 'SHOW TABLES'
        if schema:
            query += ' IN ' + self.identifier_preparer.quote_identifier(schema)
        return [row[0] for row in connection.execute(query)]

    def do_rollback(self, dbapi_connection):
        # No transactions for Hive
        pass

    def _check_unicode_returns(self, connection, additional_tests=None):
        # We decode everything as UTF-8
        return True

    def _check_unicode_description(self, connection):
        # We decode everything as UTF-8
        return True


class TimbrHTTPDialect(TimbrDialect):

    name = "timbr"
    scheme = "http"
    driver = "rest"

    def create_connect_args(self, url):
        kwargs = {
            "host": url.host,
            "port": url.port or 11000,
            "scheme": self.scheme,
            "username": url.username or None,
            "password": url.password or None,
        }
        if url.query:
            kwargs.update(url.query)
            return [], kwargs
        return ([], kwargs)


class TimbrHTTPSDialect(TimbrHTTPDialect):

    name = "timbr"
    scheme = "https"
