Echoes the input message back to the user.

Args:
    message (str): The message to echo.

Sets up the ledger by:
- Creating the SQLAlchemy engine from configuration.
- Running migrations to create tables.
- Creating a default reporting entity, currency, chart of accounts, and taxes if not present.

Records a cash sale transaction.

Args:
    narration: Description of the sale
    amount: Sale amount (excluding tax)
    quantity: Quantity of items sold
    tax_code: Tax code to apply (default: GSTOUT)
    entity_name: Entity name to use

Records a cash purchase (expense) transaction.

Args:
    narration: Description of the purchase
    amount: Purchase amount (excluding tax)
    quantity: Quantity of items purchased
    tax_code: Tax code to apply (default: GSTIN)
    entity_name: Entity name to use

Records a client invoice (credit sale) transaction.

Args:
    narration: Description of the invoice
    amount: Invoice amount (excluding tax)
    quantity: Quantity of items invoiced
    tax_code: Tax code to apply (default: GSTOUT)
    entity_name: Entity name to use

Records a supplier bill (credit purchase) transaction.

Args:
    narration: Description of the bill
    amount: Bill amount (excluding tax)
    quantity: Quantity of items billed
    tax_code: Tax code to apply (default: GSTIN)  
    entity_name: Entity name to use

Generates a Profit & Loss (Income Statement) report in JSON format.

Args:
    entity_name: Entity name to generate report for
    start_date: Start date for the report (YYYY-MM-DD format, optional)
    end_date: End date for the report (YYYY-MM-DD format, optional)

Returns:
    JSON string containing the P&L report