import os
import re
import pandas as pd
from typing import Optional
from utils.config import AppConfig
from utils.tracing import Tracer


class SQLTool:
    def __init__(self, cfg: AppConfig, tracer: Tracer):
        self.cfg = cfg
        self.tracer = tracer
        self.backend = cfg.sql_backend  # "bigquery" or "motherduck"

        if self.backend == "bigquery":
            from google.cloud import bigquery
            from google.oauth2 import service_account

            key_json = os.getenv("GCP_SERVICE_ACCOUNT_JSON")
            if not key_json:
                raise RuntimeError("Missing GCP_SERVICE_ACCOUNT_JSON secret")

            # Accept full JSON string from Space Secret
            if key_json.strip().startswith("{"):
                import json
                info = json.loads(key_json)
            else:
                info = {}

            creds = service_account.Credentials.from_service_account_info(info)
            self.client = bigquery.Client(credentials=creds, project=cfg.gcp_project)

        elif self.backend == "motherduck":
            import duckdb

            token = self.cfg.motherduck_token or os.getenv("MOTHERDUCK_TOKEN")
            db_name = self.cfg.motherduck_db or "default"
            if not token:
                raise RuntimeError("Missing MOTHERDUCK_TOKEN")

            # Plain DuckDB connection
            self.client = duckdb.connect()

            # Ensure MotherDuck extension is available and loaded
            self.client.execute("INSTALL motherduck;")
            self.client.execute("LOAD motherduck;")

            # Attach the remote MotherDuck database and use it
            self.client.execute(f"SET motherduck_token='{token}';")
            self.client.execute(f"ATTACH 'md:/{db_name}' AS md;")
            self.client.execute("USE md;")  # subsequent queries run against 'md' by default
        else:
            raise RuntimeError("Unknown SQL backend")

    def _nl_to_sql(self, message: str) -> str:
        """
        Minimal NL2SQL heuristic; replace with your own mapping or LLM prompt.
        Expect users to include table names. Example:
        "avg metric by month from analytics.events"
        """
        m = message.lower()

        # Very basic template example (edit to your tables/columns)
        if "avg" in m and " by " in m:
            return (
                "-- Example template; edit me\n"
                "SELECT DATE_TRUNC('month', date_col) AS month, "
                "AVG(metric) AS avg_metric "
                "FROM analytics.table "
                "GROUP BY 1 ORDER BY 1;"
            )

        # Pass-through if the user typed SQL explicitly
        if re.match(r"^\s*select ", m):
            return message

        # Fallback
        return "SELECT * FROM analytics.table LIMIT 100;"

    def run(self, message: str) -> pd.DataFrame:
        sql = self._nl_to_sql(message)
        self.tracer.trace_event("sql_query", {"sql": sql, "backend": self.backend})

        if self.backend == "bigquery":
            df = self.client.query(sql).to_dataframe()
        else:
            # DuckDB (MotherDuck): fetch_df returns a pandas DataFrame
            df = self.client.execute(sql).fetch_df()

        return df