from pg8000.native import Connection, InterfaceError, identifier
import boto3
import csv
from botocore.exceptions import ClientError
import logging
import json
from datetime import datetime
import re


logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)

# DB Exception class


class DBConnectionException(Exception):
    """Wraps pg8000.native Error or DatabaseError."""

    def __init__(self, e):
        """Initialise with provided error message."""
        self.message = str(e)
        super().__init__(self.message)


def lambda_handler(event, context):
    """This lambda function connects to the Totesys database, lists the contents of the ingestion bucket,
    and converts all tables to CSV and if any of those tables do not exist in, or are different to the ones in s3, it uploads them
    it uses 3 helper functions to achieve these 3 functionalities
    """
    try:
        db = connect_to_database()
        existing_files = list_existing_s3_files()
        any_changes = process_and_upload_tables(db, existing_files)

        if not any_changes["updated"]:
            logger.info("No changes detected in the database.")
            return {
                "statusCode": 200,
                "body": json.dumps("No changes detected, no CSV files were uploaded."),
            }
        return {
            "statusCode": 200,
            "body": json.dumps(
                f"""CSV files processed for {', '.join(any_changes['updated'])} and uploaded successfully.{
                'The following tables were not updated: '+', '.join(any_changes['no change']) if any_changes['no change'] else ''}"""
            ),
        }
    except Exception as e:
        logger.error(f"Error: {e}")
        return {"statusCode": 500, "body": json.dumps("Internal server error.")}
    finally:
        if db:
            db.close()


def retrieve_secrets():
    secret_name = "bentley-secrets"
    region_name = "eu-west-2"

    # Create a Secrets Manager client
    session = boto3.session.Session()
    client = session.client(service_name="secretsmanager", region_name=region_name)

    try:
        get_secret_value_response = client.get_secret_value(SecretId=secret_name)
    except ClientError as e:
        raise e

    return get_secret_value_response["SecretString"]


def connect_to_database() -> Connection:
    try:
        secrets = retrieve_secrets()
        host = secrets["host"]
        port = secrets["port"]
        user = secrets["user"]
        password = secrets["password"]
        database = secrets["database"]

        return Connection(
            database=database, user=user, password=password, host=host, port=port
        )
    except InterfaceError as i:
        logger.error(f"Interface error: {i}")
        raise DBConnectionException("Failed to connect to database")


def extract_bucket(client=boto3.client("s3")):
    response = client.list_buckets()
    extract_bucket_filter = [
        bucket["Name"] for bucket in response["Buckets"] if "extract" in bucket["Name"]
    ]

    return extract_bucket_filter[0]


def list_existing_s3_files(bucket_name=extract_bucket(), client=boto3.client("s3")):
    """Creates a dictionary and populates it with the
    results of listing the contents of the s3 bucket, then
    returns the populated dictionary
    """

    existing_files = {}

    try:
        response = client.list_objects_v2(Bucket=bucket_name)

        if "Contents" in response:
            for obj in response["Contents"]:
                s3_key = obj["Key"]
                try:
                    file_obj = client.get_object(Bucket=bucket_name, Key=s3_key)
                    file_content = file_obj["Body"].read().decode("utf-8")
                    existing_files[s3_key] = file_content
                except ClientError as e:
                    logger.error(f"Error retrieving S3 object {s3_key}: {e}")
        else:
            logger.error("The bucket is empty")

    except ClientError as e:
        logger.error(f"Error listing S3 objects: {e}")

    return existing_files


def process_and_upload_tables(db, existing_files, client=boto3.client("s3")):
    """Creates a list of the tables from a database query and
    then selects everything from each table in individual queries
    it then writes each table to CSV files and compares with the item
    in the existing_files dictionary with the same name. If it finds any changes
    to files, or new tables/files it uploads them to the s3 bucket
    """
    load_status = {"updated": [], "no change": []}
    # Retrieving the latest file timestamp from S3 extract bucket
    all_datetimes = []
    for file_names in existing_files.keys():
        datetime_str_on_s3 = "".join(
            re.search(r"\/(.+/).+_(.+)\.csv", file_names).group(1, 2)
        )
        all_datetimes.append(datetime.strptime(datetime_str_on_s3, "%Y/%m/%d/%H:%M:%S"))
    latest_timestamp = max(all_datetimes)

    # Iterating through tables on the database and retrieving only latest changes vs previous file load
    tables = db.run(
        """
                    SELECT table_name 
                    FROM information_schema.tables 
                    WHERE table_schema='public' AND table_type='BASE TABLE';"""
    )
    for table in tables:
        print(tables)
        table_name = table[0]
        rows = db.run(
            f"SELECT * FROM {identifier(table_name)} WHERE last_updated >= :latest;",
            latest={datetime.strftime(latest_timestamp, "%Y-%m-%d %H:%M:%S")},
        )
        print("rows", rows)
        # Creating a temporary file path and writing the column name to it followed by each row of data
        if rows:
            csv_file_path = f"/tmp/{table_name}.csv"
            with open(csv_file_path, "w", newline="") as file:
                writer = csv.writer(file)
                # column_names = [desc["name"] for desc in db.columns(f"SELECT * FROM {table_name};")]
                column_names = [
                    col_name[0]
                    for col_name in db.run(
                        """SELECT column_name FROM INFORMATION_SCHEMA.COLUMNS 
                                       WHERE table_name = :table ;""",
                        table=table_name,
                    )
                ]
                writer.writerow(column_names)
                writer.writerows(rows)
            s3_key = datetime.strftime(
                datetime.today(), f"{table_name}/%Y/%m/%d/{table_name}_%H:%M:%S.csv"
            )

            # Writing the new file to S3 extract bucket:
            try:
                client.upload_file(csv_file_path, extract_bucket(), s3_key)
                load_status["updated"].append(table_name)
                logger.info(f"Uploaded {s3_key} to S3.")
            except ClientError as e:
                logger.error(f"Error uploading to S3: {e}")
        else:
            load_status["no change"].append(table_name)
            logger.info(f"No new data")
    return load_status