legacy-cobol-explorer

name	legacy-cobol-explorer
description	Domain knowledge for the legacy COBOL accounting system used in Scenario 3 (cloned from github.com/tjsingh85/cobol-accounting-system into examples/scenario-3-legacy-cobol-library/cobol-source). Use when reading, explaining, or modernizing that program.

Legacy COBOL explorer

This skill applies to the COBOL accounting system participants clone in Scenario 3 into examples/scenario-3-legacy-cobol-library/cobol-source/ (source: tjsingh85/cobol-accounting-system). Use it whenever a participant or another agent needs to understand or modernize that program.

The source is not committed to this repo — it is cloned during the scenario. The structure and rules below describe what you'll find once cloned.

What the program does

An interactive, menu-driven single-account accounting app, split across three COBOL programs:

• main.cob (MainProgram) — the menu loop. Reads a choice (1-4) and calls the operations subprogram with a 6-char operation code:
  • 1 → TOTAL (view balance)
  • 2 → CREDIT
  • 3 → DEBIT
  • 4 → exit
• operations.cob (OperationsProgram) — performs the chosen operation: prompts for an amount (credit/debit), reads/writes the balance via the data program, and prints results.
• data.cob (DataProgram) — stores the balance in working storage; supports READ and WRITE operations.

There is no file I/O, database, or network — the balance lives in memory for the session.

Key facts to preserve in any rewrite

• Starting balance is 1000.00 (PIC 9(6)V99, i.e. up to 6 integer digits + 2 decimals, unsigned).
• View balance prints Current balance: <balance>.
• Credit prompts Enter credit amount:, adds it, prints Amount credited. New balance: <balance>.
• Debit prompts Enter debit amount:. If balance >= amount, subtract and print Amount debited. New balance: <balance>. Otherwise print Insufficient funds for this debit. and leave the balance unchanged (no overdraft, ever).
• Amounts are non-negative decimals with 2 implied decimal places.
• The balance is session-scoped — it resets to 1000.00 on each run (no persistence).

Modernization checklist

When rewriting this in a modern language (Scenario 3 targets Node.js):

1. Mirror the three programs as small modules: data (balance store), operations (credit/debit/view with the overdraw guard), main (interactive menu loop).
2. Keep the starting balance and the insufficient-funds rule identical.
3. Reproduce the menu text and result messages so behavior matches the COBOL app.
4. Use the repo's TESTPLAN.md to derive tests: view balance, credit (valid + zero), debit (valid + insufficient funds).
5. Keep the cloned cobol-source/ folder read-only — write the rewrite under modern/.

Things to NOT change

• The starting balance (1000.00).
• The overdraft rejection rule (a debit larger than the balance is refused).
• The set of operations (view balance, credit, debit, exit).