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):

Mirror the three programs as small modules: data (balance store), operations (credit/debit/view with the overdraw guard), main (interactive menu loop).
Keep the starting balance and the insufficient-funds rule identical.
Reproduce the menu text and result messages so behavior matches the COBOL app.
Use the repo's TESTPLAN.md to derive tests: view balance, credit (valid + zero), debit (valid + insufficient funds).
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).

Legacy COBOL explorer

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):

Mirror the three programs as small modules: data (balance store), operations (credit/debit/view with the overdraw guard), main (interactive menu loop).

Keep the starting balance and the insufficient-funds rule identical.

Reproduce the menu text and result messages so behavior matches the COBOL app.

Use the repo's TESTPLAN.md to derive tests: view balance, credit (valid + zero), debit (valid + insufficient funds).

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).

legacy-cobol-explorer