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PropertySnapshot,
ChangeDetectionResult,
ChangeType,
Severity,
PropertyChange,
DetectionConfig,
Address,
} from './types';
import { matchRecords } from './matcher.service';
const DEFAULT_DETECTION_CONFIG: DetectionConfig = {
ownershipNameThreshold: 0.7,
deedDateSensitivity: 0.9,
taxAmountChangePercent: 15,
};
function classifyFieldChange(field: string, oldValue: unknown, newValue: unknown, config: DetectionConfig): PropertyChange {
let changeType: ChangeType;
switch (field) {
case 'ownerName':
changeType =
typeof oldValue === 'string' && typeof newValue === 'string'
? isSignificantNameChange(oldValue, newValue, config)
? 'ownership_transfer'
: 'metadata_change'
: 'ownership_transfer';
break;
case 'deedDate':
changeType = 'deed_change';
break;
case 'taxAmount':
changeType = 'tax_change';
break;
case 'lienCount':
changeType = (newValue as number) > (oldValue as number) ? 'lien_filing' : 'metadata_change';
break;
case 'taxId':
changeType = 'deed_change';
break;
default:
changeType = 'metadata_change';
}
return { field, oldValue, newValue, changeType };
}
function isSignificantNameChange(oldName: string, newName: string, config: DetectionConfig): boolean {
const dummyAddress: Address = {
streetNumber: '0',
streetName: 'dummy',
city: 'dummy',
state: 'XX',
zip: '00000',
};
const result = matchRecords(oldName, dummyAddress, newName, dummyAddress);
return result.nameScore < config.ownershipNameThreshold;
}
function determineSeverity(changes: PropertyChange[], config: DetectionConfig): Severity {
const severityOverrides = config.severityOverrides || {};
const typeToSeverity: Record<ChangeType, Severity> = {
ownership_transfer: severityOverrides['ownership_transfer'] || 'major',
deed_change: severityOverrides['deed_change'] || 'moderate',
lien_filing: severityOverrides['lien_filing'] || 'moderate',
tax_change: severityOverrides['tax_change'] || 'minor',
metadata_change: severityOverrides['metadata_change'] || 'minor',
};
const severityOrder: Severity[] = ['major', 'moderate', 'minor'];
for (const change of changes) {
const sev = typeToSeverity[change.changeType];
const idx = severityOrder.indexOf(sev);
if (idx === 0) return 'major';
}
for (const change of changes) {
const sev = typeToSeverity[change.changeType];
if (sev === 'moderate') return 'moderate';
}
return 'minor';
}
function computeChangeConfidence(changes: PropertyChange[], config: DetectionConfig): number {
if (changes.length === 0) return 0;
let totalConfidence = 0;
for (const change of changes) {
switch (change.changeType) {
case 'ownership_transfer':
totalConfidence += 0.95;
break;
case 'deed_change':
totalConfidence += config.deedDateSensitivity;
break;
case 'tax_change': {
const oldVal = change.oldValue as number;
const newVal = change.newValue as number;
const pctChange = oldVal ? Math.abs(newVal - oldVal) / oldVal * 100 : 100;
totalConfidence += pctChange >= config.taxAmountChangePercent ? 0.85 : 0.5;
break;
}
case 'lien_filing':
totalConfidence += 0.9;
break;
default:
totalConfidence += 0.4;
}
}
return Math.round((totalConfidence / changes.length) * 1000) / 1000;
}
export function detectChanges(
previous: PropertySnapshot,
current: PropertySnapshot,
config?: Partial<DetectionConfig>,
): ChangeDetectionResult {
const effectiveConfig = { ...DEFAULT_DETECTION_CONFIG, ...config };
const changes: PropertyChange[] = [];
const fieldsToCompare: (keyof Omit<PropertySnapshot, 'id' | 'capturedAt' | 'propertyId'>)[] = [
'ownerName',
'deedDate',
'taxId',
'taxAmount',
'lienCount',
'propertyType',
];
for (const field of fieldsToCompare) {
const oldValue = previous[field];
const newValue = current[field];
if (oldValue !== newValue) {
changes.push(classifyFieldChange(field, oldValue, newValue, effectiveConfig));
}
}
const addressChanges = detectAddressChanges(previous.address, current.address);
changes.push(...addressChanges);
const severity = determineSeverity(changes, effectiveConfig);
const confidence = computeChangeConfidence(changes, effectiveConfig);
let changeType: ChangeType = 'metadata_change';
if (changes.some(c => c.changeType === 'ownership_transfer')) {
changeType = 'ownership_transfer';
} else if (changes.some(c => c.changeType === 'deed_change')) {
changeType = 'deed_change';
} else if (changes.some(c => c.changeType === 'lien_filing')) {
changeType = 'lien_filing';
} else if (changes.some(c => c.changeType === 'tax_change')) {
changeType = 'tax_change';
}
return {
propertyId: previous.propertyId,
changeType,
severity,
confidence,
changes,
previousSnapshot: previous,
currentSnapshot: current,
detectedAt: new Date().toISOString(),
};
}
function detectAddressChanges(oldAddr: Address, newAddr: Address): PropertyChange[] {
const changes: PropertyChange[] = [];
const addressFields: (keyof Address)[] = ['streetNumber', 'streetName', 'streetType', 'unit', 'city', 'state', 'zip'];
for (const field of addressFields) {
const oldVal = oldAddr[field];
const newVal = newAddr[field];
if (oldVal !== newVal) {
changes.push({
field: `address.${field}`,
oldValue: oldVal,
newValue: newVal,
changeType: 'metadata_change',
});
}
}
return changes;
}
export function shouldTriggerAlert(result: ChangeDetectionResult, minSeverity: Severity = 'moderate'): boolean {
const severityOrder: Severity[] = ['minor', 'moderate', 'major'];
const resultIdx = severityOrder.indexOf(result.severity);
const minIdx = severityOrder.indexOf(minSeverity);
return resultIdx >= minIdx && result.confidence >= 0.7;
}
export { classifyFieldChange, determineSeverity, computeChangeConfidence };
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