"""
dependency:
    - spark and SPARK_HOME environment variable must be set
"""
from pyspark.sql import SparkSession
from pyspark import SparkContext

import copy

class Iceberg :
    def __init__(self,**_args):
        """
        providing catalog meta information (you must get this from apache iceberg)
        """
        #
        # Turning off logging (it's annoying & un-professional)
        #
        # _spconf = SparkContext()
        # _spconf.setLogLevel("ERROR")
        #
        # @TODO:
        #   Make arrangements for additional configuration elements 
        #
        self._session = SparkSession.builder.getOrCreate()
        # self._session.sparkContext.setLogLevel("ERROR")
        self._catalog = self._session.catalog
        self._table = _args['table'] if 'table' in _args else None
        
        if 'catalog' in _args :
            #
            # Let us set the default catalog
            self._catalog.setCurrentCatalog(_args['catalog'])
            
        else:
            # No current catalog has been set ...
            pass
        if 'database' in _args :
            self._database = _args['database']
            self._catalog.setCurrentDatabase(self._database)
        else:
            #
            # Should we set the default as the first one if available ?
            #
            pass
        self._catalogName = self._catalog.currentCatalog()
        self._databaseName = self._catalog.currentDatabase()
    def meta (self,**_args) :
        """
        This function should return the schema of a table (only)
        """
        _schema = []
        try:
            _tableName = self._getPrefix(**_args) + f".{_args['table']}"
            print (_tableName)
            _tmp = self._session.table(_tableName).schema
            _schema = _tmp.jsonValue()['fields']
            for _item in _schema :
                del _item['nullable'],_item['metadata']
        except Exception as e:
            
            pass
        return _schema
    def _getPrefix (self,**_args):        
        _catName = self._catalogName if 'catalog' not in _args else _args['catalog']
        _datName = self._databaseName if 'database' not in _args else _args['database']
        
        return '.'.join([_catName,_datName])
            
    def has (self,**_args):
        try:
            _prefix = self._getPrefix(**_args)
            if _prefix.endswith('.') :
                return False
            return _args['table'] in [_item.name for _item in self._catalog.listTables(_prefix)]
        except Exception as e:
            print (e)
            return False
    def apply(self,sql):
        pass
class Reader(Iceberg) :
    def __init__(self,**_args):
        super().__init__(**_args)
    def read(self,**_args):
        _table = self._table
        _prefix = self._getPrefix(**_args)        
        if 'table' in _args or _table:
            _table = _args['table'] if 'table' in _args else _table
            _table = _prefix + f'.{_table}'
            return self._session.table(_table).toPandas()
        else:
            sql = _args['sql']
            return self._session.sql(sql).toPandas()
        pass
class Writer (Iceberg):
    """
    Writing data to an Apache Iceberg data warehouse (using pyspark)
    """
    def __init__(self,**_args):
        super().__init__(**_args)
        self._mode = 'append' if 'mode' not in _args else _args['mode']
        self._table = None if 'table' not in _args else _args['table']
    def write(self,_data,**_args):
        _prefix = self._getPrefix(**_args)
        if 'table' not in _args and not self._table :
            raise Exception (f"Table Name should be specified for catalog/database {_prefix}")
        rdd = self._session.createDataFrame(_data)
        _mode = self._mode if 'mode' not in _args else _args['mode']
        _table = self._table if 'table' not in _args else _args['table']
        
        if not self.has(table=_table) :
            _mode = 'overwrite'
            rdd.write.format('iceberg').mode(_mode).saveAsTable(_table)
        else:
            _table = f'{_prefix}.{_table}'
            rdd.write.format('iceberg').mode(_mode).save(_table)