# Payment Scenarios with Deductions

This document explains how the module handles different payment scenarios.

## Scenario 1: Payment WITHOUT Expense Account

When you create a vendor payment **without** setting an expense account, the system uses the standard vendor payable account.

### Example:
- Vendor: PT Telkom Indonesia
- Amount: Rp 2,000,000
- Deductions:
  - PPh 21: Rp 100,000
  - PPh 29: Rp 50,000
- Final Payment: Rp 1,850,000

### Journal Entry:
```
Account                              | Debit           | Credit
-------------------------------------|-----------------|------------------
Accounts Payable - PT Telkom         | Rp 2,000,000.00 |
PPh 21 (Tax Payable)                 |                 | Rp 100,000.00
PPh 29 (Tax Payable)                 |                 | Rp 50,000.00
Bank Account                         |                 | Rp 1,850,000.00
-------------------------------------|-----------------|------------------
TOTAL                                | Rp 2,000,000.00 | Rp 2,000,000.00
```

### Explanation:
- The **Accounts Payable** line uses the vendor's payable account (from partner configuration)
- The payable account has the **partner_id** set (PT Telkom Indonesia)
- This is the standard Odoo behavior, just with deductions added

---

## Scenario 2: Payment WITH Expense Account

When you create a vendor payment **with** an expense account set, the system uses that expense account instead of the payable account.

### Example:
- Vendor: PT Telkom Indonesia
- Amount: Rp 2,000,000
- **Expense Account: 611505 Telepon & Internet**
- Deductions:
  - PPh 21: Rp 100,000
  - PPh 29: Rp 50,000
- Final Payment: Rp 1,850,000

### Journal Entry:
```
Account                              | Debit           | Credit
-------------------------------------|-----------------|------------------
611505 Telepon & Internet (Expense)  | Rp 2,000,000.00 |
PPh 21 (Tax Payable)                 |                 | Rp 100,000.00
PPh 29 (Tax Payable)                 |                 | Rp 50,000.00
Bank Account                         |                 | Rp 1,850,000.00
-------------------------------------|-----------------|------------------
TOTAL                                | Rp 2,000,000.00 | Rp 2,000,000.00
```

### Explanation:
- The **Expense Account** replaces the payable account
- This allows direct expense recording without going through payables
- The expense account still has the **partner_id** set for tracking
- This is useful for immediate expense recognition

---

## Key Differences

| Aspect | Without Expense Account | With Expense Account |
|--------|------------------------|---------------------|
| Counterpart Account | Accounts Payable | Expense Account |
| Account Type | liability_payable | expense |
| Partner Required | Yes | Yes |
| Use Case | Standard vendor payment | Direct expense recording |
| Payable Created | Yes | No |

---

## When to Use Each Scenario

### Use WITHOUT Expense Account when:
- You want to track vendor payables
- You need to reconcile with vendor bills
- You're following standard AP workflow
- You need aging reports for vendors

### Use WITH Expense Account when:
- You want immediate expense recognition
- You don't need to track payables
- You're making direct payments (no bill)
- You want simplified accounting

---

## Technical Notes

### Module Integration

This module (`vendor_payment_diff_amount`) works seamlessly with `vendor_batch_payment_merge`:

1. **vendor_batch_payment_merge** provides the `expense_account_id` field
2. **vendor_payment_diff_amount** adds deduction functionality
3. Both modules modify `_prepare_move_line_default_vals()` method
4. The methods are called in sequence (inheritance chain)

### Method Call Order

```
1. Standard Odoo: Creates basic 2-line entry (bank + payable)
2. vendor_batch_payment_merge: Replaces payable with expense (if set)
3. vendor_payment_diff_amount: Adds deduction lines and adjusts bank
```

### Result

Final journal entry has:
- 1 debit line (payable or expense at original amount)
- N credit lines (one per deduction)
- 1 credit line (bank at final_payment_amount)

Total: 2 + N lines (where N = number of deductions)

---

## Validation Rules

The module ensures:

1. ✅ Counterpart line always has `partner_id` set
2. ✅ Counterpart line stays at original amount
3. ✅ Bank line reduced to final_payment_amount
4. ✅ Deduction lines are credits
5. ✅ Deduction lines only have `partner_id` if account type requires it (payable/receivable)
6. ✅ Entry is balanced (total debit = total credit)
7. ✅ All required fields are present

---

## Troubleshooting

### Error: "Missing required account on accountable line"

**Cause**: An accountable line (payable/receivable account) is missing the required `partner_id` field.

**Solution**: The module now automatically handles this:
- Counterpart line (payable/expense) always has `partner_id` set
- Deduction lines only have `partner_id` if the account type requires it
- Tax accounts (liability/expense) don't need `partner_id`

If you still see this error:
1. Check that the partner has a payable account configured
2. Check that the expense account (if used) is valid
3. Verify the payment has a partner selected
4. Ensure deduction accounts are NOT payable/receivable accounts (use tax/expense accounts instead)

### Error: "Entry is not balanced"

**Cause**: The debit and credit totals don't match.

**Solution**: This should not happen with the current implementation. If it does:
1. Check that all deduction amounts are positive
2. Verify currency conversion is working
3. Check for rounding issues

---

## Examples

### Example 1: Simple Payment with One Deduction

```python
# Create payment
payment = env['account.payment'].create({
    'payment_type': 'outbound',
    'partner_type': 'supplier',
    'partner_id': partner.id,
    'amount': 1000.0,
    'journal_id': bank_journal.id,
})

# Add deduction
env['payment.deduction.line'].create({
    'payment_id': payment.id,
    'amount_substract': 100.0,
    'substract_account_id': tax_account.id,
    'name': 'Withholding Tax',
})

# Post payment
payment.action_post()

# Result:
# - Payable: Debit 1000
# - Tax: Credit 100
# - Bank: Credit 900
```

### Example 2: Payment with Expense Account and Multiple Deductions

```python
# Create payment with expense account
payment = env['account.payment'].create({
    'payment_type': 'outbound',
    'partner_type': 'supplier',
    'partner_id': partner.id,
    'amount': 2000.0,
    'expense_account_id': expense_account.id,
    'journal_id': bank_journal.id,
})

# Add multiple deductions
env['payment.deduction.line'].create({
    'payment_id': payment.id,
    'amount_substract': 100.0,
    'substract_account_id': pph21_account.id,
    'name': 'PPh 21',
})

env['payment.deduction.line'].create({
    'payment_id': payment.id,
    'amount_substract': 50.0,
    'substract_account_id': pph29_account.id,
    'name': 'PPh 29',
})

# Post payment
payment.action_post()

# Result:
# - Expense: Debit 2000
# - PPh 21: Credit 100
# - PPh 29: Credit 50
# - Bank: Credit 1850
```