import psycopg2


class DataWrapper:
  def __init__(self, data):
    if isinstance(data, list):
      emptyDict = {dataKey:None for dataKey in data}
      self.__dict__.update(emptyDict)
    elif isinstance(data, dict):
      self.__dict__.update(data)

  def addKey(self, key, val=None):
    self.__dict__.update({key:val})

  def __repr__(self):
    return self.__dict__.__repr__()

class MetaDataLayout:
  def __init__(self, schemaName, allTablesAndCols):
    self.schemaName = schemaName
    self.datalayout = {
        "schema": self.schemaName,
        "selectedTables":{},
        "allTables":allTablesAndCols
    }

  def setSelection(self, tablesAndCols):
    """
    tablesAndCols : {"table1":["col1", "col2"], "table1":["cola","colb"]}
    """
    datalayout = self.datalayout
    for table in tablesAndCols:
      if table in datalayout['allTables'].keys():
        datalayout['selectedTables'][table] = tablesAndCols[table]
      else:
        print(f"Table {table} doesn't exists in the schema")
    self.datalayout = datalayout

  def resetSelection(self):
    datalayout = self.datalayout
    datalayout['selectedTables'] = {}
    self.datalayout = datalayout

  def getSelectedTablesAndCols(self):
    return self.datalayout['selectedTables']
  
  def getAllTablesCols(self):
    return self.datalayout['allTables']

  

  
class DbEngine:
  def __init__(self, dbCreds):
    self.dbCreds = dbCreds
    self.connection = None

  def connect(self):
    dbCreds = self.dbCreds
    if self.connection is None or self.connection.closed != 0:
      self.connection = psycopg2.connect(database=dbCreds.database, user = dbCreds.user,
                  password = dbCreds.password, host = dbCreds.host,
                  port = dbCreds.port)

  def disconnect(self):
    if self.connection is not None and self.connection.closed == 0:
      self.connection.close()

  def execute_query(self, query):
    with self.connection.cursor() as cursor:
      cursor.execute(query)
      result = cursor.fetchall()
    return result

  
def executeQuery(dbEngine, query):
  result = dbEngine.execute_query(query)
  return result

def executeColumnsQuery(dbEngine, columnQuery):
  with dbEngine.connection.cursor() as cursor:
    cursor.execute(columnQuery)
    columns = [desc[0] for desc in cursor.description]
  return columns
  
def closeDbEngine(dbEngine):
  dbEngine.disconnect()

def getAllTablesInfo(dbEngine, schemaName):
  tablesAndCols = {}
  allTablesQuery = f"""SELECT table_name FROM information_schema.tables
    WHERE table_schema = '{schemaName}'"""
  tables = executeQuery(dbEngine, allTablesQuery)
  for table in tables:
    tableName = table[0]
    columnsQuery = f"""Select * FROM {schemaName}.{tableName} LIMIT 0"""
    columns = executeColumnsQuery(dbEngine, columnsQuery)
    tablesAndCols[tableName] = columns
  return tablesAndCols

def getSampleDataForTablesAndCols(dbEngine, schemaName, tablesAndCols, maxRows):

    data = {}
    conn = dbEngine.connection
    for table in tablesAndCols.keys():
      try:
        sqlQuery = f"""select * from {schemaName}.{table} limit {maxRows}"""
        data[table] = pd.read_sql_query(sqlQuery, con=conn)
      except:
        print(f"couldn't read table data. Table: {table}")
    return data