Operational Workflows & State Machines

The POS domain executes retail operations through clearly defined workflows and state transitions. Cashier shifts and individual receipts each follow controlled lifecycles that enforce business invariants and preserve cash accountability.

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1. Cashier Shift Lifecycle

The following diagram illustrates the complete operational cycle of a cashier shift, from clock-in through reconciliation and close.

flowchart TD
    A[Cashier Clock-in] --> B[Select Terminal]
    B --> C[Count Opening Float]
    C --> D{Float Matches Expected?}
    D -->|Yes| E[Open Session]
    D -->|No| F[Record Variance with Supervisor]
    F --> E
    E --> G[High-Velocity Sales / Returns]
    G --> H[Mid-Shift Cash Drop]
    H --> I[More Transactions]
    I --> J[Count Closing Cash]
    J --> K{Reconcile Expected vs. Actual}
    K -->|Balanced| L[Close Session]
    K -->|Overage / Shortage| M[Record Discrepancy]
    M --> L
    L --> N[End-of-Day Settlement]

Shift Stage Descriptions

Stage	Description	Key Domain Event
Clock-in	Cashier authenticates at the terminal or store system.	CashierAuthenticated
Opening Float Count	Cashier counts and declares cash in drawer at shift start.	OpeningFloatDeclared
Session Opened	Terminal session activated; drawer unlocked for transactions.	PosSessionOpened
Transaction Activity	Sales, refunds, voids, drops, and petty expenses occur.	PosSaleCompleted, PosSaleRefunded, PosCashDropRecorded
Cash Drop	Excess cash removed to safe during shift.	PosCashDropRecorded
Closing Count	Cashier counts cash at shift end.	ClosingCashDeclared
Reconciliation	Expected vs. actual cash compared; discrepancy recorded.	PosSessionClosed
Settlement	Aggregated totals sent to FMS for deposit and ledger posting.	PosSessionClosed

Opening Float Exception

If the physical opening float does not match the expected float from the prior session:

Scenario	Action
Shortage from prior close	Record variance with supervisor approval; prior session discrepancy adjusted via compensating journal.
Overage from prior close	Record variance; excess may be deposited or counted as current session float.
Unexplained difference	Session may still open with documented variance; investigation initiated.

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2. High-Speed Checkout Flow

The following diagram illustrates the typical checkout transaction from scan to receipt.

flowchart TD
    A[Item Barcode Scan] --> B[Retrieve Product Snapshot]
    B --> C[Add Line Item]
    C --> D{Discount / Modifier?}
    D -->|Yes| E[Apply Discount / Modifier]
    D -->|No| F[Subtotal Calculation]
    E --> F
    F --> G[Tax Calculation]
    G --> H[Display Total]
    H --> I[Select Tender Type]
    I --> J{Split Tender?}
    J -->|Yes| K[Capture Multiple Tenders]
    J -->|No| L[Capture Single Tender]
    K --> M[Validate Total Coverage]
    L --> M
    M --> N[Calculate Change]
    N --> O{Payment Authorized?}
    O -->|Yes| P[Print Receipt / Open Drawer]
    O -->|No| Q[Prompt for Alternative Tender]
    Q --> I
    P --> R[Emit Completion Event]

Checkout Stage Descriptions

Stage	Description	Business Rule
Barcode Scan	Product identified by barcode or manual lookup.	Product must exist in local cache; price snapshot loaded.
Line Item Added	Quantity and unit price added to receipt.	Quantity must be positive.
Discount / Modifier	Price adjustment or option applied to line.	Discount authorization may be required.
Tax Calculation	Taxes computed by product category and jurisdiction.	Tax rules active at sale time applied.
Tender Selection	Customer chooses payment method(s).	Tender type must be allowed at terminal.
Total Coverage	System validates that tenders cover total.	Transaction cannot complete if underpaid.
Change Calculation	Cash change computed if applicable.	Change must be non-negative.
Payment Authorization	Card/wallet payments authorized by acquirer.	Offline mode may queue authorization.
Receipt Issuance	Receipt printed or emailed.	Receipt snapshot frozen.

Void and Cancel Handling

Action	Timing	Effect
Void Line Item	Before payment	Removes line from receipt; no inventory or financial impact yet.
Cancel Receipt	Before payment	Abandons entire transaction; no receipt issued.
Refund / Return	After payment	Creates separate return receipt; reverses sale and restores inventory.

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3. POS Session State Transition Table

Current State	Trigger / Event	Next State	Business Validation Rule
Locked	Cashier authenticates and selects terminal.	Pre-Session	Identity verified; terminal available.
Pre-Session	Opening float counted and declared.	Float Declared	Float amount is non-negative and recorded.
Float Declared	Supervisor approves variance (if any).	Open	Drawer assigned; session activated.
Open	First transaction initiated.	Active	Session is ready for sales.
Active	Transaction completed.	Active	Transaction added to session ledger.
Active	Cash drop performed.	Active	Drop reason and amount recorded.
Active	Petty expense recorded.	Active	Expense reason and amount recorded.
Active	Closing count initiated.	Closing	No new transactions allowed.
Closing	Closing cash count entered.	Reconciling	Expected vs. actual cash compared.
Reconciling	Discrepancy accepted or zero.	Closed	Session sealed; totals finalized.
Active	Supervisor initiates forced close.	Forced Closed	Forced close reason recorded; discrepancy accepted.
Any active state	Terminal or application crash.	Recovery Pending	Session restored from local state; transactions replayed.
Recovery Pending	Local state validated.	Previous active state	Session continues or closes under supervision.

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4. POS Receipt State Transition Table

Current State	Trigger / Event	Next State	Business Validation Rule
Draft	Items scanned or added.	In Progress	Line items present; total calculated.
In Progress	Line item voided.	In Progress	Void recorded; total recalculated.
In Progress	Entire receipt cancelled.	Cancelled	No payment processed; cancellation audited.
In Progress	Tender selected and validated.	Awaiting Payment	Total coverage confirmed.
Awaiting Payment	Payment authorized or cash accepted.	Paid	Non-negative change calculated.
Awaiting Payment	Payment declined.	In Progress	Alternative tender required.
Paid	Receipt printed or emailed.	Completed	Receipt snapshot frozen; completion event emitted.
Completed	Customer requests return.	Return Initiated	Original receipt referenced; return eligibility verified.
Return Initiated	Items accepted and refund tendered.	Refunded	Separate return receipt created; inventory restored.
Completed	Manager voids receipt after close.	Voided by Return	Return receipt created; original remains visible.

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5. Offline Transaction Workflow

When a terminal loses connectivity, it continues operating using local state and queues transactions for replay.

flowchart TD
    A[Network Disconnection Detected] --> B[Switch to Offline Mode]
    B --> C[Use Local Product / Price Cache]
    C --> D[Assign Monotonic Sequence]
    D --> E[Store Transaction Locally]
    E --> F[Issue Local Receipt]
    F --> G{Network Restored?}
    G -->|No| H[Continue Offline Operation]
    H --> D
    G -->|Yes| I[Replay Queued Transactions]
    I --> J{Sequence Valid?}
    J -->|Yes| K[Central Acceptance]
    J -->|Gap / Duplicate| L[Conflict Resolution]
    L --> M[Manual Review or Auto-Reconciliation]
    M --> K
    K --> N[Sync Completed]

Offline Operational Rules

Rule	Invariant
Cache Freshness	Local cache is refreshed when online; stale cache must be flagged after a configured age.
Sequence Continuity	Offline transactions continue the same monotonic sequence as online transactions.
Local Receipt Issuance	Customers receive a local receipt; central receipt number may be assigned on sync.
Stock Indicator	Local stock indicators may be decremented optimistically; central WMS reconciles on sync.
High-Risk Tenders	Some tender types (e.g., gift cards, store credit) may be blocked offline if balance cannot be verified.

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6. Cash Drop Workflow

Cash drops reduce drawer exposure by moving excess cash to a safe during the shift.

flowchart TD
    A[Drawer Cash Exceeds Threshold] --> B[Cashier Initiates Drop]
    B --> C[Supervisor Authorization]
    C --> D[Count Drop Amount]
    D --> E[Place Cash in Safe]
    E --> F[Record Drop Slip]
    F --> G[Update Drawer Expected Balance]
    G --> H[Emit PosCashDropRecorded]

Cash Drop Rules

Rule	Invariant
Threshold Policy	Drops may be triggered automatically when drawer cash exceeds a configured threshold.
Dual Control	Drops typically require cashier and supervisor verification.
Immediate Log	Drop amount and timestamp are recorded immediately, before cash leaves the drawer.
Safe Receipt	Physical safe receipt or slip number is captured for audit.

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7. End-of-Day Settlement Workflow

After all sessions in a store are closed, totals are aggregated for financial settlement.

Settlement Element	Source
Gross Sales	Sum of all completed sale receipts across sessions.
Refunds	Sum of all return/refund receipts.
Net Sales	Gross Sales minus Refunds.
Cash Collected	Cash tenders minus cash refunds and change.
Card Collected	Card/digital wallet tenders minus refunds.
Other Tenders	Gift cards, store credit, checks, etc.
Tax Collected	Sum of tax lines by category.
Cash Discrepancies	Sum of overages and shortages across sessions.
Depositable Cash	Cash collected minus drops and petty expenses, adjusted for discrepancies.

Settlement Reconciliation

$$ \text{Depositable Cash} = \text{Opening Floats} + \text{Cash Sales} - \text{Cash Refunds} - \text{Cash Drops} - \text{Petty Expenses} \pm \text{Net Discrepancy} $$

The settlement payload is emitted to FMS via the PosSessionClosed event for ledger posting and bank deposit reconciliation.

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8. Exception Handling

Exception	Handling Rule
Cashier unable to reconcile drawer	Supervisor reviews discrepancy; session may be forced closed with documented reason.
Terminal crash during active session	Session state recovered from local cache; transactions replayed; session continues or closes under supervision.
Product not found in local cache	Cashier may use fallback lookup or escalate; transaction may be queued offline if central lookup fails.
Payment terminal offline	Cash tender encouraged; card transactions may be queued for offline authorization where acquirer supports it.
Customer disputes change	Audit trail of tender and change calculation reviewed; receipt is authoritative.
Duplicate receipt printed	Reprint audited; no financial duplicate created.

These workflows and state machines ensure that every retail transaction is executed, recorded, and reconciled through a consistent, auditable, and invariant-preserving process.