import json, os
from typing import Any, Dict, Iterable, List, Optional, Tuple, Union
from sqlalchemy import create_engine, MetaData, Table, Column, String, Integer, select, text
from sqlalchemy.engine import Engine
from llama_index.core import SQLDatabase
from apps.chat.schemas.utils import read_json, write_json, save_raw_text, examples_to_str
from apps.chat.schemas.m_schema import MSchema


class SchemaEngine(SQLDatabase):
    def __init__(self, engine: Engine, schema: Optional[str] = None, metadata: Optional[MetaData] = None,
                 ignore_tables: Optional[List[str]] = None, include_tables: Optional[List[str]] = None,
                 sample_rows_in_table_info: int = 3, indexes_in_table_info: bool = False,
                 custom_table_info: Optional[dict] = None, view_support: bool = False, max_string_length: int = 300,
                 mschema: Optional[MSchema] = None, db_name: Optional[str] = ''):
        super().__init__(engine, schema, metadata, ignore_tables, include_tables, sample_rows_in_table_info,
                         indexes_in_table_info, custom_table_info, view_support, max_string_length)

        self._db_name = db_name
        # Dictionary to store table names and their corresponding schema
        self._tables_schemas: Dict[str, str] = {}

        # If a schema is specified, filter by that schema and store that value for every table.
        """ if schema:
            self._usable_tables = [
                table_name for table_name in self._usable_tables
                if self._inspector.has_table(table_name, schema)
            ]
            for table_name in self._usable_tables:
                self._tables_schemas[table_name] = schema
        else:
            all_tables = []
            # Iterate through all available schemas
            for s in self.get_schema_names():
                tables = self._inspector.get_table_names(schema=s)
                all_tables.extend(tables)
                for table in tables:
                    self._tables_schemas[table] = s
            self._usable_tables = all_tables """
        d_schema = self.default_schema_name()
        for table_name in self._usable_tables:
            self._tables_schemas[table_name] = d_schema
        
        self._dialect = engine.dialect.name
        if mschema is not None:
            self._mschema = mschema
        else:
            self._mschema = MSchema(db_id=db_name)
            self.init_mschema()

    @property
    def mschema(self) -> MSchema:
        """Return M-Schema"""
        return self._mschema

    def get_pk_constraint(self, table_name: str) -> Dict:
        return self._inspector.get_pk_constraint(table_name, self._tables_schemas[table_name] )['constrained_columns']

    def get_table_comment(self, table_name: str):
        try:
            return self._inspector.get_table_comment(table_name, self._tables_schemas[table_name])['text']
        except:    # sqlite does not support comments
            return ''

    def default_schema_name(self) -> Optional[str]:
        return self._inspector.default_schema_name

    def get_schema_names(self) -> List[str]:
        return self._inspector.get_schema_names()

    def get_foreign_keys(self, table_name: str):
        return self._inspector.get_foreign_keys(table_name, self._tables_schemas[table_name])

    def get_unique_constraints(self, table_name: str):
        return self._inspector.get_unique_constraints(table_name, self._tables_schemas[table_name])

    def fectch_distinct_values(self, table_name: str, column_name: str, max_num: int = 5):
        table = Table(table_name, self.metadata_obj, autoload_with=self._engine, schema=self._tables_schemas[table_name])
        # Construct SELECT DISTINCT query
        query = select(table.c[column_name]).distinct().limit(max_num)
        values = []
        with self._engine.connect() as connection:
            result = connection.execute(query)
            distinct_values = result.fetchall()
            for value in distinct_values:
                if value[0] is not None and value[0] != '':
                    values.append(value[0])
        return values

    def init_mschema(self):
        for table_name in self._usable_tables:
            table_comment = self.get_table_comment(table_name)
            table_comment = '' if table_comment is None else table_comment.strip()
            table_with_schema = self._tables_schemas[table_name] + '.' + table_name
            self._mschema.add_table(table_with_schema, fields={}, comment=table_comment)
            pks = self.get_pk_constraint(table_name)

            fks = self.get_foreign_keys(table_name)
            for fk in fks:
                referred_schema = fk['referred_schema']
                for c, r in zip(fk['constrained_columns'], fk['referred_columns']):
                    self._mschema.add_foreign_key(table_with_schema, c, referred_schema, fk['referred_table'], r)

            fields = self._inspector.get_columns(table_name, schema=self._tables_schemas[table_name])
            for field in fields:
                field_type = f"{field['type']!s}"
                field_name = field['name']
                primary_key = field_name in pks
                field_comment = field.get("comment", None)
                field_comment = "" if field_comment is None else field_comment.strip()
                autoincrement = field.get('autoincrement', False)
                default = field.get('default', None)
                if default is not None:
                    default = f'{default}'

                try:
                    examples = self.fectch_distinct_values(table_name, field_name, 5)
                except:
                    examples = []
                examples = examples_to_str(examples)

                self._mschema.add_field(
                    table_with_schema, field_name, field_type=field_type, primary_key=primary_key,
                    nullable=field['nullable'], default=default, autoincrement=autoincrement,
                    comment=field_comment, examples=examples
                )