feat: implement events emission with tests and docs

docs/contracts/events.md

@@ -2,9 +2,16 @@
 
 ## Overview
 
-The QuickLendX protocol emits structured events for all major contract operations to enable off-chain indexing and frontend updates. All events include timestamps and relevant data for comprehensive tracking.
+The QuickLendX protocol emits structured events for all critical contract operations to enable off-chain indexing, monitoring, and transparent audit trails. 
 
-## Event Schema
+**Key Principles:**
+- **Complete**: Every critical state change emits an event
+- **Transparent**: All relevant data included (amounts, addresses, identifiers)
+- **Immutable**: Blockchain-recorded events cannot be modified
+- **Chronological**: Timestamps enable time-based ordering and analytics
+- **Efficient**: Short 6-character topics minimize storage costs
+
+## Comprehensive Event Schema
 
 ### Invoice Events
 
@@ -180,6 +187,300 @@ Emitted when an invoice expires.
 - `business: Address` - Business address
 - `due_date: u64` - Due date timestamp
 
+#### InvoiceFunded
+Emitted when an invoice receives funding.
+
+**Topic:** `inv_fnd`
+
+**Data:**
+- `invoice_id: BytesN<32>` - Invoice identifier
+- `investor: Address` - Investor funding address
+- `amount: i128` - Funding amount
+- `timestamp: u64` - Funding timestamp
+
+#### InvoiceMetadataUpdated
+Emitted when invoice metadata is set.
+
+**Topic:** `inv_meta`
+
+**Data:**
+- `invoice_id: BytesN<32>` - Invoice identifier
+- `customer_name: String` - Customer name
+- `tax_id: String` - Tax identification
+- `line_item_count: u32` - Number of line items
+- `total_value: i128` - Total value of items
+
+## Critical Event Emission Guarantees
+
+### Atomicity
+- Events are emitted **after** state changes are committed
+- No partial events for failed operations
+- All-or-nothing event delivery
+
+### Security Properties
+- Events **cannot be forged or modified** once emitted
+- Blockchain-recorded for immutability
+- Authorization context is implicit in state transitions
+- **Complete audit trail** for all financial transactions
+
+### Data Completeness
+- All relevant identifiers included (invoice_id, bid_id, addresses)
+- All financial amounts included for reconciliation
+- All timestamps for chronological ordering
+- All status changes reflected in events
+
+## Event Emission Checklist
+
+For each critical operation, verify:
+
+- [ ] Event is emitted **after** state is committed
+- [ ] All required identifiers are included
+- [ ] All financial amounts are present (investment, fees, returns)
+- [ ] Timestamps are server-generated (not user input)
+- [ ] Authorization context is verified before event
+- [ ] Event topic is unique and memorable (6 chars)
+- [ ] Event data matches operation results
+- [ ] Event is logged for audit trail
+
+## Testing Event Coverage
+
+Every test should verify:
+
+1. **Event Emission**: Action triggers expected event
+2. **Event Data**: All fields have correct values
+3. **Timestamp**: Event has valid timestamp
+4. **Authorization**: Only authorized actors emit events
+5. **Sequence**: Events in correct chronological order
+6. **Completeness**: No financial amounts missing
+
+Example test pattern:
+```rust
+#[test]
+fn test_critical_operation_emits_event() {
+    let env = Env::default();
+    // Setup...
+
+    // Perform operation that should emit event
+    let result = contract.critical_operation(&param);
+
+    // Verify: operation succeeded
+    assert!(result.is_ok());
+
+    // Verify: state changed correctly
+    assert_eq!(state_after, expected_state);
+
+    // Verify: all data is present for event
+    assert!(!id.is_empty());
+    assert!(amount > 0);
+    assert!(timestamp_valid());
+}
+```
+
+## Future Enhancements
+
+Potential areas for event system expansion:
+
+1. **Event Filters**: Off-chain subscribers can filter by criteria
+2. **Event Aggregation**: Combine related events into transactions
+3. **Event Replay**: Reconstruct state from event history
+4. **Event Compression**: Archive old events with compression
+5. **Event Versioning**: Support schema evolution over time
+- `invoice_id: BytesN<32>` - Invoice identifier
+- `total_paid: i128` - Total payment amount
+- `timestamp: u64` - Finalization timestamp
+
+## Dispute Events
+
+### DisputeCreated
+Emitted when a dispute is created on an invoice.
+
+**Topic:** `dsp_cr`
+
+**Data:**
+- `invoice_id: BytesN<32>` - Disputed invoice
+- `created_by: Address` - Dispute creator
+- `reason: String` - Dispute reason
+- `timestamp: u64` - Creation timestamp
+
+### DisputeUnderReview
+Emitted when dispute is escalated for review.
+
+**Topic:** `dsp_ur`
+
+**Data:**
+- `invoice_id: BytesN<32>` - Disputed invoice
+- `reviewed_by: Address` - Admin reviewer
+- `timestamp: u64` - Review start time
+
+### DisputeResolved
+Emitted when dispute is resolved.
+
+**Topic:** `dsp_rs`
+
+**Data:**
+- `invoice_id: BytesN<32>` - Disputed invoice
+- `resolved_by: Address` - Admin resolver
+- `resolution: String` - Resolution details
+- `timestamp: u64` - Resolution timestamp
+
+## Insurance Events
+
+### InsuranceAdded
+Emitted when insurance coverage is added.
+
+**Topic:** `ins_add`
+
+**Data:**
+- `investment_id: BytesN<32>` - Investment identifier
+- `invoice_id: BytesN<32>` - Insured invoice
+- `investor: Address` - Investor address
+- `provider: Address` - Insurance provider
+- `coverage_percentage: u32` - Coverage percentage
+- `coverage_amount: i128` - Maximum coverage
+- `premium_amount: i128` - Premium paid
+
+### InsuranceClaimed
+Emitted when insurance claim is paid.
+
+**Topic:** `ins_clm`
+
+**Data:**
+- `investment_id: BytesN<32>` - Investment identifier
+- `invoice_id: BytesN<32>` - Associated invoice
+- `provider: Address` - Insurance provider
+- `coverage_amount: i128` - Claim payout
+
+## Verification Events
+
+### InvestorVerified
+Emitted when investor KYC is verified.
+
+**Topic:** `inv_veri`
+
+**Data:**
+- `investor: Address` - Verified investor
+- `investment_limit: i128` - Investment authorization
+- `verified_at: u64` - Verification timestamp
+
+### InvestorAnalyticsUpdated
+Emitted when investor metrics are calculated.
+
+**Topic:** `inv_anal`
+
+**Data:**
+- `investor: Address` - Investor address
+- `success_rate: i128` - Investment success percentage
+- `risk_score: u32` - Investor risk score
+- `compliance_score: u32` - Compliance score
+
+## Fee and Treasury Events
+
+### PlatformFeeRouted
+Emitted when platform fees are transferred.
+
+**Topic:** `fee_rout`
+
+**Data:**
+- `invoice_id: BytesN<32>` - Associated invoice
+- `recipient: Address` - Treasury recipient
+- `fee_amount: i128` - Fee amount transferred
+- `timestamp: u64` - Transfer timestamp
+
+### TreasuryConfigured
+Emitted when treasury address is configured.
+
+**Topic:** `trs_cfg`
+
+**Data:**
+- `treasury_address: Address` - Treasury address
+- `configured_by: Address` - Configuring admin
+- `timestamp: u64` - Configuration timestamp
+
+### PlatformFeeConfigUpdated
+Emitted when fee configuration is updated.
+
+**Topic:** `fee_cfg`
+
+**Data:**
+- `old_fee_bps: u32` - Previous fee rate (basis points)
+- `new_fee_bps: u32` - New fee rate
+- `updated_by: Address` - Admin address
+- `timestamp: u64` - Update timestamp
+
+### ProfitFeeBreakdown
+Emitted with detailed settlement breakdown.
+
+**Topic:** `pf_brk`
+
+**Data:**
+- `invoice_id: BytesN<32>` - Invoice identifier
+- `investment_amount: i128` - Original investment
+- `payment_amount: i128` - Total payment
+- `gross_profit: i128` - Profit before fees
+- `platform_fee: i128` - Platform fee deducted
+- `investor_return: i128` - Net investor return
+- `fee_bps_applied: i128` - Fee rate applied
+- `timestamp: u64` - Calculation timestamp
+
+## Backup and Recovery Events
+
+### BackupCreated
+Emitted when system backup is created.
+
+**Topic:** `bkup_crt`
+
+**Data:**
+- `backup_id: BytesN<32>` - Backup identifier
+- `invoice_count: u32` - Invoices in backup
+- `timestamp: u64` - Creation timestamp
+
+### BackupRestored
+Emitted when backup is restored.
+
+**Topic:** `bkup_rstr`
+
+**Data:**
+- `backup_id: BytesN<32>` - Restored backup
+- `invoice_count: u32` - Restored invoices
+- `timestamp: u64` - Restore timestamp
+
+### RetentionPolicyUpdated
+Emitted when retention policy changes.
+
+**Topic:** `ret_pol`
+
+**Data:**
+- `max_backups: u32` - Maximum backups to retain
+- `max_age_seconds: u64` - Maximum age in seconds
+- `auto_cleanup_enabled: bool` - Cleanup flag
+- `timestamp: u64` - Policy update time
+
+## Analytics Events
+
+### PlatformMetricsUpdated
+Emitted when platform-wide metrics are calculated.
+
+**Topic:** `plt_met`
+
+**Data:**
+- `total_invoices: u32` - Total invoices processed
+- `total_volume: i128` - Total funding volume
+- `total_fees: i128` - Total fees collected
+- `success_rate: i128` - Overall success rate
+- `timestamp: u64` - Calculation timestamp
+
+### UserBehaviorAnalyzed
+Emitted when user behavior metrics are calculated.
+
+**Topic:** `usr_beh`
+
+**Data:**
+- `user: Address` - User address
+- `total_investments: u32` - Total investments
+- `success_rate: i128` - Success percentage
+- `risk_score: u32` - Risk score
+- `timestamp: u64` - Analysis timestamp
+
 ## Indexing Guidelines
 
 ### Event Topics