"""
Created on Tue Sep 18 16:20:50 2018

@author: tanya
"""

import os
import sys
import re
import sqlalchemy
import sqlparse
import pandas as pd
import warnings

sys.path.append(os.getcwd())
from cdplib.log import Log
from cdplib.Singleton_Threadsafe import SingletonThreadsafe

class SQLHandlerPool(metaclass=SingletonThreadsafe):
    '''
    '''

    def __init__(self, size: int = 20):
        self._size = size
        self._log = Log(name='SQLHandlerPool')
        self._sql_handlers = [SQLHandler() for _ in range(size)]

    def aquire(self):
        while not self._sql_handlers:
            self._sql_handlers = [SQLHandler() for _ in range(self._size)]
            self._log.warning("Ran out of SQL handlers, 10 more have been added. Are you sure you've returned yours?")
        return self._sql_handlers.pop()

    def release(self, sql_handler):
        sql_handler._engine.dispose()
        if len(self._sql_handlers) < self._size:
            self._sql_handlers.append(sql_handler)

class SQLHandler:
    '''
    Resembles methods for executing sql queries
    with different dabase connectors.
    Remark:in each method we force new opening and
    closing of a database connection,
     this avoids errors when parallelizing with multiprocessing.
    '''
    pass
    def __init__(self, db_uri: str = None,
                 is_case_insensitive: bool = False):
        '''
        :param str db_uri:
            of form
            <sqlalchemy_dialect//user:password@host:port/dbname?charset=utf8&local_infile=1>

         sqlalchemy dialects:
             for mysql : mysql+pymysql
             for db2: ibm_db_sa
        '''
        from sqlalchemy_utils import database_exists, create_database

        self._log = Log(name='SQLHandler')

        if db_uri is None:

            from libraries.configuration import default as cfg

            db_uri = "mysql+pymysql://{0}:{1}@{2}:{3}/{4}?charset=utf8&local_infile=1"\
                     .format(cfg["SQL"]["SQL_USER"],
                             cfg["SQL"]["SQL_PASSWORD"],
                             cfg["SQL"]["SQL_HOST"],
                             cfg["SQL"]["SQL_PORT"],
                             cfg["SQL"]["SQL_DATABASE_NAME"])

        assert(isinstance(db_uri, str)),\
            "Parameter 'db_uri' must be of type str"

        assert(re.match(r'.+://.+:(.+)?@.+:.+/.+', db_uri) is not None),\
            ('database url does not match the pattern: '
             'sqlalchemy_dialect//user:password@host:port/dbname')

        self._db_uri = db_uri

        engine = sqlalchemy.create_engine(self._db_uri)

        if not database_exists(engine.url):
            create_database(engine.url)

        query = "CREATE DATABASE IF NOT EXISTS {}"\
            .format(self._connection_params["db"])

        with warnings.catch_warnings():
            warnings.simplefilter("ignore")
            engine.execute(query)

        assert(isinstance(is_case_insensitive, bool)),\
            "Parameter 'is_case_sensetive' must of type bool"

        if 'ibm' in db_uri and not is_case_insensitive:
            raise Exception('Ibm db2 is case insensitive')

        self._is_case_insensitive = is_case_insensitive

        self._engine = engine


    def __del__(self):
        self.dispose_engine()

    @property
    def _connection_params(self) -> dict:
        '''
        return: connection parameters like user,
        password, host, port, and database name
        rtype: dict
        '''
        try:
            connection_params = {}

            connection_params['user'], connection_params['password'] =\
                self._db_uri.split('//')[1]\
                            .split('@')[0]\
                            .split(':')

            connection_params['host'], connection_params['port'] =\
                self._db_uri.split('//')[1]\
                            .split('@')[1]\
                            .split('/')[0]\
                            .split(':')

            connection_params['db'] = self._db_uri.split('/')[-1]\
                                                  .split('?')[0]

            return connection_params

        except Exception as e:
            err = ("Could not parse connection parameters."
                   "Finished with error {}")\
                   .format(e)

            self._log.error(err)
            raise Exception(err)

    def drop_database(self):
        '''
        '''
        database = self._connection_params["db"]
        self.execute("DROP DATABASE IF EXISTS {}".format(database))
        self._engine.execute("CREATE DATABASE {}".format(database))
        self._engine.execute("USE {}".format(database))

    @property
    def _db_metadata(self) -> dict:
        '''
        Returns a sql-dialect specific information like information schema
        and columnames in information_schema.tables and
        information_schema.columns
        For ibm databases, information_schema is set to syscat,
        else it is set to information_schema
        If these default values do not exist in the given database,
        the output of the method is set to None

        :return: dictionary with information_schema, schema_col,
            table_col, column_col, default_schema
        '''

        db_metadata = {}

        if 'ibm' in self._db_uri:
            db_metadata['information_schema'] = 'syscat'
            db_metadata['schema_col'] = 'tabschema'
            db_metadata['table_col'] = 'tabname'
            db_metadata['column_col'] = 'colname'
            db_metadata['default_schema'] =\
                self._connection_params['user'].upper()
        else:
            db_metadata['information_schema'] = 'information_schema'
            db_metadata['schema_col'] = 'TABLE_SCHEMA'
            db_metadata['table_col'] = 'TABLE_NAME'
            db_metadata['column_col'] = 'COLUMN_NAME'
            db_metadata['default_schema'] =\
                self._connection_params['db']

        # check if it worked to create metadata
        try:
            query = """SELECT *
                       FROM {}.tables
                       LIMIT 1
                    """.format(db_metadata['information_schema'])
            self.execute(query)

        except Exception as e:
            self._log.error(e)
            db_metadata = None

        return db_metadata

    def execute(self, query):
        '''
        Executes an sql-queries.
        Remark: queries like CREATE, DROP, SELECT work
        for majority of sqlalchemy dialects.
         queries like SHOW TABLES, LOAD DATA, and using
         INFORMATION_SCHEMA are mysql specific and might
         not exist in a different dialect.

        :param str query:
        '''
        connection = self._engine.connect()
        transaction = connection.begin()

        errors = []
        results = []

        # in the case of multi-query execute each query
        for sub_query in sqlparse.split(query):
            if len(sub_query) > 0:
                try:
                    result = connection.execute(sub_query)
                    if result.rowcount > 0:
                        data = pd.DataFrame(result.fetchall())
                        data.columns = result.keys()
                        results.append(data)
                except Exception as e:
                    errors.append(str(e))

        if len(errors) > 0:
            err = ('Could not execute some of the queries. '
                   'Obtained exceptions: {}'
                   .format('\n'.join(errors)))

            self._log.error(err)
            raise Exception(err)

        transaction.commit()
        connection.close()
        return results

    def execute_query_from_file(self, filename: str):
        '''
        '''
        with open(filename, 'r') as f:
            query = f.read()

        self.execute(query)

    def get_tablenames(self, schema: str = None, query: str = None):
        '''
        '''
        if (self._db_metadata is None) and (query is None):
            raise Exception('Please specify the query')

        else:
            try:
                if query is None:
                    schema_or_default_schema =\
                        self._db_metadata['default_schema']\
                        if schema is None else schema

                    query = """SELECT DISTINCT {0}
                               FROM {1}.tables
                               WHERE {2} = '{3}'
                            """.format(
                            self._db_metadata['table_col'],
                            self._db_metadata['information_schema'],
                            self._db_metadata['schema_col'],
                            schema_or_default_schema)

                tables = self.read_sql_to_dataframe(query).iloc[:, 0].tolist()
                return tables

            except Exception as e:
                err = ("Could not get tablenames"
                       "Finished with error {}".format(e))

                self._log.error(err)
                raise Exception(err)

    def check_if_table_exists(self, tablename: str,
                              schema: str = None,
                              query: str = None) -> bool:
        '''
        Tries to retrieve table information from database with given query.
        If this does not work, tries to select one row from the given table,
        if this fails, assumes that the table does not exist.

        :param str tablename:
        :param str schema:
        :param str query: if not specified, tries to find
            tablename in information_schema specified in _db_metadata.
        :return: if the table exists or not
        :rtype: bool
        '''
        if self._is_case_insensitive:
            tablename = tablename.upper()

        try:
            tablenames = self.get_tablenames(schema=schema, query=query)

            table_exists = (tablename in tablenames)

        except Exception as e:
            self._log.warning(('Could not execute query to retrieve table '
                               'information. Trying to execute a'
                               'select statement. '
                               'Got exeption {}').format(e))
            try:
                query = """SELECT *
                           FROM {0}{1}
                           LIMIT 1
                        """.format('' if schema is None else schema + '.',
                                   tablename)

                self.execute(query)

                table_exists = True

            except Exception as e:
                self._log.warning(('Failed to select from {0}. '
                                   'Finished with error {1}'
                                   'Conclusion: table does not exist')
                                  .format(tablename, e))

                table_exists = False

        return table_exists

    def create_schema(self, schema: str, query: str = None):
        '''
        Creates a schema if it does not exist, else does nothing

        :param str schema:
        :param str query: if None trying to read schemas from
            information_schema specified in db_metadata
        '''
        if (query is None):

            if self._db_metadata is None:
                raise Exception('Please specify query')
            else:
                query = """SELECT DISTINCT {0}
                           FROM {1}.tables""".format(
                              self._db_metadata['schema_col'],
                              self._db_metadata['information_schema'])

        try:
            schemas = self.read_sql_to_dataframe(query).iloc[:, 0].tolist()
        except Exception as e:
            err = ("Could not retrieve the list of schemas"
                   "from the database. Finished with error {}"
                   .format(e))

            self._log.error(err)
            raise Exception(err)

        if schema not in schemas:
            self.execute("CREATE SCHEMA {}".format(schema))

    def drop_table_if_exists(self, tablename: str,
                             schema: str = None,
                             query: str = None):
        '''
        :param str tablename:
        :param str schema:
        :param str query: if not specified, default value is "DROP TABLE"
        '''
        if self._is_case_insensitive:
            tablename = tablename.upper()

        schema = '' if schema is None else schema + '.'

        if query is None:
            query = "DROP TABLE {0}{1};".format(schema, tablename)

        try:
            if self.check_if_table_exists(tablename):
                self.execute(query)

        except Exception as e:
            err = ("Could not drop the table {0} ."
                   "Finished with error {1}"
                   .format(tablename, e))

            self._log.error(err)
            raise Exception(err)

    def get_column_names(self, tablename: str,
                         schema: str = None,
                         query: str = None) -> list:
        '''
        Tries to retrieve column information from database with given query.
        If this does not work, tries to select one row from the given table.

        :param str tablename:
        :param str schema:
        :param str query: if not specified, tries to select column
            names in the information_schema specified in db_metadata
        '''
        if self._is_case_insensitive:
            tablename = tablename.upper()

        if not self.check_if_table_exists(tablename=tablename,
                                          schema=schema):

            err = "Table {} does not exist".format(tablename)
            self._log.error(err)
            raise Exception(err)

        try:
            if query is None:
                if self._db_metadata is None:
                    raise Exception('Please specify the query')

                else:
                    schema_or_default_schema =\
                        self._db_metadata['default_schema']\
                        if schema is None else schema

                    query = """SELECT DISTINCT {0}
                               FROM {1}.columns
                               WHERE {2} = '{3}'
                               AND {4} = '{5}'
                            """.format(
                            self._db_metadata['column_col'],
                            self._db_metadata['information_schema'],
                            self._db_metadata['schema_col'],
                            schema_or_default_schema,
                            self._db_metadata['table_col'],
                            tablename)

            colnames = [c.lower() for c in
                        self.read_sql_to_dataframe(query).iloc[:, 0].tolist()]

        except Exception as e:
            self._log.warn((
                'Could not select columns from '
                'informational schema. Trying to '
                'load the table into a dataframe and selec column names.'
                'Obtained exception {}').format(e))

            query = """SELECT *
                       FROM {0}{1}
                       LIMIT 1
                    """.format('' if schema is None else schema + '.',
                               tablename)

            data = self.execute(query)
            colnames = data[0].columns.tolist()

        return colnames

    def load_csv_to_db(self, filename: str,
                       tablename: str,
                       schema: str = None,
                       query: str = None,
                       **kwargs):
        '''
        Tries to load data from csv file to database with a given query.
        If this does not work, tries to load data from csv to a
        pandas dataframe first, and then write it to the database.

        :param str filename:
        :param str tablename:
        :param str schema:
        :param str query: if not specified, tries to use
        LOAD DATA LOCAL INFILE query
        '''

        if not self.check_if_table_exists(tablename=tablename,
                                          schema=schema):

            err = ('Table {} test does not exit.'
                   'Please create it first').format(tablename)
            self._log.error(err)
            raise Exception(err)

        else:
            try:
                if query is None:
                    query = """LOAD DATA LOCAL INFILE '{0}'
                               INTO TABLE {1}{2}
                               COLUMNS TERMINATED BY ','
                               OPTIONALLY ENCLOSED BY '"'
                               LINES TERMINATED BY '\r\n'
                               IGNORE 1 LINES
                               ({3})
                               ;""".format(
                                   filename,
                                   '' if schema is None else schema + '.',
                                   tablename,
                                   ','.join(self.get_column_names(tablename)))

                self.execute(query)

            except Exception as e:
                err = ("Could not load the file {0} "
                       "to the table {1} ."
                       "Finished with error {2}")\
                       .format(filename, tablename, e)

                self._log.error(err)
                raise Exception(err)

    def read_sql_to_dataframe(self, query: str, **read_sql_kwargs):
        '''
        :param str query: normally a SELECT sql statement
        :param read_sql_kwargs: additional arguments to pandas read_sql method
        :return: selected data
        :rtype: DataFrame
        '''
        try:
            
            connection = self._engine.connect()

            data = pd.read_sql(sql=query,
                               con=connection,
                               **read_sql_kwargs)

            connection.close()
           
            return data

        except Exception as e:
            err = ("Could not read the query to a dataframe. "
                   "Finished with error {}").format(e)

            self._log.error(err)
            raise Exception(err)

    def read_table(self, tablename: str,
                   schema: str = None,
                   **read_sql_kwargs):
        '''
        :param str tablename:
        :param str schema:
        :param read_sql_kwargs: additional arguments to pands read_sql_method
        :return: selected table
        :rtype: DataFrame
        '''
        schema = '' if schema is None else schema + '.'

        try:
            return self.read_sql_to_dataframe(
                    query="SELECT * FROM {0}{1};".format(schema, tablename),
                    **read_sql_kwargs)
        except Exception as e:
            err = ("Could not read the table {0} to a dataframe. "
                   "Finished with error {1}").format(tablename, e)

            self._log.error(err)
            raise Exception(err)

    def append_to_table(self, data: pd.DataFrame,
                        tablename: str,
                        schema: str = None,
                        to_sql_kwargs={'index': False}):
        '''
        :param DataFrame data: data to append
        :param str tablename: table where data is appended
        :param str schema:
        :param dict to_sql_kwargs: additional arguments to pandas to_sql method
        '''
        if schema is not None:
            self.create_schema(schema)

        try:
            connection = self._engine.connect()

            if self.check_if_table_exists(tablename=tablename, schema=schema):

                data.to_sql(name=tablename,
                            schema=schema,
                            con=connection,
                            if_exists='append',
                            **to_sql_kwargs)
            else:

                self.overwrite_table(data=data,
                                     tablename=tablename,
                                     schema=schema,
                                     to_sql_kwargs=to_sql_kwargs)

            connection.close()

        except Exception as e:
            err = ("Could not append data to the table {0}. "
                   "Finished with error {1}").format(tablename, e)

            self._log.error(err)
            raise Exception(err)

    def overwrite_table(self, data: pd.DataFrame,
                        tablename: str,
                        schema: str = None,
                        to_sql_kwargs={'index': False}):
        '''
        :param DataFrame data: data to write to dabase
        :param str tablename: table where data is written
        :param str schema:
        :param to_sql_kwargs: additional arguments to pandas to_sql method
        '''

        if schema is not None:
            self.create_schema(schema)

        try:

            connection = self._engine.connect()

            data.to_sql(name=tablename,
                        schema=schema,
                        con=connection,
                        if_exists='replace',
                        **to_sql_kwargs)
            connection.close()

        except Exception as e:
            err = ("Could overwrite the table {0}. "
                   "Finished with error {1}").format(tablename, e)

            self._log.error(err)
            raise Exception(err)

    def draw_er_diagram_from_db(self, diagram_path: str = None,
                                schema: str = None,
                                include_tables: list = None):
        '''
        '''
        if diagram_path is None:
            diagram_path = "erd.png"
        else:
            diagram_dir = os.path.dirname(diagram_path)
            if diagram_dir != "":
                os.makedirs(diagram_dir, exist_ok=True)

        import eralchemy
        eralchemy.render_er(self._db_uri,
                            diagram_path,
                            schema=schema,
                            include_tables=include_tables)

    def dispose_engine(self):
        try:
            self._engine.dispose()
        except Exception as e:
            #print(('An error occured when trying to dispose the SQL engine. Error: {}').format(e))
            #raise Exception(e)
            # Exception occures rather frequently, but doesnt seem to affect the execution of the script
            # Exception is thrown when trying to dispose of a engine that no longer exists.
            # The exception has been silenced since no way of seeing if the engine still exists before disposing of it has been found.