"""Shared constants for StatementSetu.

Single source of truth for the closed ledger-category list (spec section 1.4)
and a couple of derived helpers used across the pipeline.
"""

# Fixed, closed set of ledger heads. Keeping this closed-set means the small
# model can never invent a head -- anything off-list is mapped to Suspense.
CATEGORIES = [
    "Sales / Receipts from Debtors",
    "Purchases / Payments to Creditors",
    "Salary & Wages",
    "Office Rent",
    "Electricity & Utilities",
    "Telephone & Internet",
    "Bank Charges",
    "Interest Received",
    "Interest Paid",
    "GST Payment",
    "TDS Payment",
    "Income Tax Payment",
    "Loan EMI",
    "Cash Deposit",
    "Cash Withdrawal",
    "Transfer between Own Accounts (Contra)",
    "Insurance",
    "Professional Fees",
    "Travel & Conveyance",
    "Repairs & Maintenance",
    "Drawings",
    "Capital Introduced",
    "Suspense / Unclassified",
]

SUSPENSE = "Suspense / Unclassified"
CONTRA = "Transfer between Own Accounts (Contra)"

# Confidence below this is forced to Suspense -- a CA trusts "I don't know"
# over a confident wrong answer.
CONFIDENCE_FLOOR = 0.5

CATEGORY_SET = set(CATEGORIES)


def voucher_type_for(debit, credit, category=None):
    """Derive the Tally voucher type from amounts and category.

    debit -> Payment, credit -> Receipt; own-account transfers -> Contra.
    """
    if category == CONTRA:
        return "Contra"
    if debit is not None and debit > 0:
        return "Payment"
    if credit is not None and credit > 0:
        return "Receipt"
    return "Payment"