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pierrepierre
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Implement user story:
As a returning customer I want the billing engine to automatically apply a 25% discount to every third purchase So that I am rewarded for continued loyalty without needing to enter a promo code. Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
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‎pom.xml‎

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<scope>provided</scope>
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</dependency>
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<dependency>
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<groupId>org.mockito</groupId>
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<artifactId>mockito-core</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.testng</groupId>
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<artifactId>testng</artifactId>

‎src/main/java/org/killbill/billing/plugin/helloworld/HelloWorldInvoicePluginApi.java‎

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package org.killbill.billing.plugin.helloworld;
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import java.math.BigDecimal;
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import java.util.HashSet;
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import java.math.RoundingMode;
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import java.util.Collection;
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import java.util.EnumSet;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.Set;
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import org.killbill.billing.plugin.api.invoice.PluginInvoicePluginApi;
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import org.killbill.billing.util.callcontext.TenantContext;
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import org.killbill.clock.Clock;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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class HelloWorldInvoicePluginApi extends PluginInvoicePluginApi implements OSGIKillbillEventHandler {
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private static final Logger logger = LoggerFactory.getLogger(HelloWorldInvoicePluginApi.class);
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static final String LOYALTY_DISCOUNT_DESC = "Loyalty discount \u2013 25% off (every 3rd purchase)";
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static final BigDecimal DISCOUNT_RATE = new BigDecimal("0.25");
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static final int PURCHASE_CYCLE = 3;
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/**
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* Invoice item types that represent a customer charge (one-time or otherwise).
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*/
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private static final Set<InvoiceItemType> CHARGEABLE_TYPES = EnumSet.of(
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InvoiceItemType.FIXED,
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InvoiceItemType.EXTERNAL_CHARGE,
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InvoiceItemType.USAGE,
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InvoiceItemType.RECURRING
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);
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public HelloWorldInvoicePluginApi(final OSGIKillbillAPI killbillAPI, final OSGIConfigPropertiesService configProperties,
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final Clock clock) {
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super(killbillAPI, configProperties, clock);
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}
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/**
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* Returns additional invoice items to be added to invoice
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* Applies a 25% loyalty discount to every 3rd one-time purchase.
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* <p>
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* This method produces two types of invoice items a. Tax Item on Invoice Item
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* b. Adjustment Item on only the very first Historical Invoice Tax Item
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* automatically ( just for Demo purpose )
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* During invoice generation Kill Bill calls this method before the invoice is
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* committed. The plugin counts past one-time-purchase invoices for the account
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* and, when the current invoice is the 3rd (6th, 9th, …) purchase, returns
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* negative {@code ITEM_ADJ} items equal to 25% of each charge line item.
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*
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* @param newInvoice The invoice that is being created.
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* @param dryRun Whether it is dryRun or not
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* @param properties Any user-specified plugin properties, coming straight out
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* of the API request that has triggered this code to run.
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* @param callCtx The context in which this code is running.
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* @return A new immutable list of new tax items, or adjustments on existing tax
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* items.
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* @param newInvoice The invoice that is being created.
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* @param dryRun Whether it is a dry-run preview.
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* @param properties Any user-specified plugin properties.
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* @param invoiceContext The context in which this code is running.
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* @return Additional adjustment items representing the loyalty discount, or an
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* empty list when the discount does not apply.
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*/
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@Override
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public AdditionalItemsResult getAdditionalInvoiceItems(final Invoice newInvoice, final boolean dryRun,
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final Iterable<PluginProperty> properties, final InvoiceContext invoiceContext) {
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final UUID accountId = newInvoice.getAccountId();
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final Account account = getAccount(accountId, invoiceContext);
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final Set<Invoice> allInvoices = getAllInvoicesOfAccount(account, newInvoice, invoiceContext);
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final List<InvoiceItem> additionalItems = new LinkedList<InvoiceItem>();
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// Creating tax item for first Item of new Invoice
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final List<InvoiceItem> newInvoiceItems = newInvoice.getInvoiceItems();
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final InvoiceItem newInvoiceItem = newInvoiceItems.get(0);
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BigDecimal charge = new BigDecimal("80");
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final InvoiceItem taxItem = PluginInvoiceItem.createTaxItem(newInvoiceItem, newInvoiceItem.getInvoiceId(),
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newInvoice.getInvoiceDate(), null, charge, "Tax Item");
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additionalItems.add(taxItem);
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// Creating External Charge for first Item of new Invoice
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final InvoiceItem externalItem = PluginInvoiceItem.create(newInvoiceItem, newInvoiceItem.getInvoiceId(),
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newInvoice.getInvoiceDate(), null, charge, "External Item", InvoiceItemType.EXTERNAL_CHARGE);
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additionalItems.add(externalItem);
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// Adding adjustment invoice item to the first historical invoice, if it does not have the adjustment item
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for (final Invoice invoice : allInvoices) {
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if (!invoice.getId().equals(newInvoice.getId())) {
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final List<InvoiceItem> invoiceItems = invoice.getInvoiceItems();
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// Check for if any adjustment item exists for Historical Invoice
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if (checkforAdjustmentItem(invoiceItems)) {
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break;
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}
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for (final InvoiceItem item : invoiceItems) {
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charge = new BigDecimal("-30");
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final InvoiceItem adjItem = PluginInvoiceItem.createAdjustmentItem(item, item.getInvoiceId(),
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newInvoice.getInvoiceDate(), newInvoice.getInvoiceDate(), charge, "Adjustment Item");
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additionalItems.add(adjItem);
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break;
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}
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break;
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// --- Idempotency guard: skip if discount items were already added --------
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if (hasExistingLoyaltyDiscount(newInvoice)) {
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logger.info("Loyalty discount already present on invoice {} for account {} – skipping",
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newInvoice.getId(), accountId);
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return buildResult(additionalItems);
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}
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// --- Count past one-time-purchase invoices (excluding the current one) ---
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final Collection<Invoice> pastInvoices = getInvoicesByAccountId(account.getId(), invoiceContext);
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int pastPurchaseCount = 0;
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for (final Invoice invoice : pastInvoices) {
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if (!invoice.getId().equals(newInvoice.getId()) && isOneTimePurchaseInvoice(invoice)) {
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pastPurchaseCount++;
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}
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}
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return new AdditionalItemsResult() {
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@Override
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public List<InvoiceItem> getAdditionalItems() {
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return additionalItems;
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// The current invoice is purchase number (pastPurchaseCount + 1)
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// but only if this invoice itself qualifies as a one-time purchase.
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if (!isOneTimePurchaseInvoice(newInvoice)) {
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logger.debug("Invoice {} for account {} is not a one-time purchase – no loyalty discount",
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newInvoice.getId(), accountId);
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return buildResult(additionalItems);
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}
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final int currentPurchaseNumber = pastPurchaseCount + 1;
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logger.info("Account {}: this is one-time purchase #{}", accountId, currentPurchaseNumber);
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if (currentPurchaseNumber % PURCHASE_CYCLE != 0) {
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logger.info("Account {}: purchase #{} is not a multiple of {} – no discount",
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accountId, currentPurchaseNumber, PURCHASE_CYCLE);
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return buildResult(additionalItems);
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}
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// --- Apply 25% discount to every chargeable item on this invoice ---------
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BigDecimal totalDiscount = BigDecimal.ZERO;
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for (final InvoiceItem item : newInvoice.getInvoiceItems()) {
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if (isChargeableItem(item) && item.getAmount() != null && item.getAmount().compareTo(BigDecimal.ZERO) > 0) {
130+
final BigDecimal discountAmount = item.getAmount()
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.multiply(DISCOUNT_RATE)
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.setScale(2, RoundingMode.HALF_UP)
133+
.negate();
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135+
final InvoiceItem adjItem = PluginInvoiceItem.createAdjustmentItem(
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item,
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item.getInvoiceId(),
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newInvoice.getInvoiceDate(),
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newInvoice.getInvoiceDate(),
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discountAmount,
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LOYALTY_DISCOUNT_DESC);
142+
additionalItems.add(adjItem);
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totalDiscount = totalDiscount.add(discountAmount);
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}
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}
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112-
@Override
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public Iterable<PluginProperty> getAdjustedPluginProperties() {
114-
return null;
147+
if (dryRun) {
148+
logger.info("Account {}: dry-run – loyalty discount of {} would be applied on purchase #{}",
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accountId, totalDiscount, currentPurchaseNumber);
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} else {
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logger.info("Account {}: applying loyalty discount of {} on purchase #{}",
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accountId, totalDiscount, currentPurchaseNumber);
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}
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return buildResult(additionalItems);
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}
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// -------------------------------------------------------------------------
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// Helper methods
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// -------------------------------------------------------------------------
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/**
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* Determines whether an invoice represents a one-time purchase.
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* An invoice qualifies when it contains at least one chargeable item and
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* does <b>not</b> contain any {@link InvoiceItemType#RECURRING} items.
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*/
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boolean isOneTimePurchaseInvoice(final Invoice invoice) {
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boolean hasCharge = false;
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for (final InvoiceItem item : invoice.getInvoiceItems()) {
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if (item.getInvoiceItemType() == InvoiceItemType.RECURRING) {
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return false;
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}
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if (isChargeableItem(item)) {
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hasCharge = true;
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}
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};
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}
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return hasCharge;
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}
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/**
120-
* This method returns all invoices of account
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*
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* @param account The account to consider.
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* @param newInvoice New Invoice Item to be added to existing invoices of the
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* account
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* @param tenantCtx
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* @return All invoices of account
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* Returns {@code true} when the item type represents a customer charge.
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*/
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private Set<Invoice> getAllInvoicesOfAccount(final Account account, final Invoice newInvoice, final TenantContext tenantCtx) {
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final Set<Invoice> invoices = new HashSet<Invoice>();
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invoices.addAll(getInvoicesByAccountId(account.getId(), tenantCtx));
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invoices.add(newInvoice);
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return invoices;
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private boolean isChargeableItem(final InvoiceItem item) {
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return CHARGEABLE_TYPES.contains(item.getInvoiceItemType());
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}
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/**
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* Check whether adjustment item is already present in invoice Item of Invoice
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*
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* @param invoiceItems
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* @return
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* Idempotency check: returns {@code true} if the invoice already contains
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* an adjustment item with the loyalty-discount description.
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*/
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private boolean checkforAdjustmentItem(final List<InvoiceItem> invoiceItems) {
142-
boolean adjustmentItemPresent = false;
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for (final InvoiceItem invoiceItem : invoiceItems) {
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if (invoiceItem.getInvoiceItemType().equals(InvoiceItemType.ITEM_ADJ)) {
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adjustmentItemPresent = true;
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break;
191+
private boolean hasExistingLoyaltyDiscount(final Invoice invoice) {
192+
for (final InvoiceItem item : invoice.getInvoiceItems()) {
193+
if (InvoiceItemType.ITEM_ADJ.equals(item.getInvoiceItemType())
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&& LOYALTY_DISCOUNT_DESC.equals(item.getDescription())) {
195+
return true;
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}
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}
149-
return adjustmentItemPresent;
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return false;
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}
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152-
protected boolean isTaxItem(final InvoiceItem invoiceItem) {
153-
return InvoiceItemType.TAX.equals(invoiceItem.getInvoiceItemType());
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/**
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* Wraps the list of additional items into an {@link AdditionalItemsResult}.
203+
*/
204+
private AdditionalItemsResult buildResult(final List<InvoiceItem> additionalItems) {
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return new AdditionalItemsResult() {
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@Override
207+
public List<InvoiceItem> getAdditionalItems() {
208+
return additionalItems;
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}
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@Override
212+
public Iterable<PluginProperty> getAdjustedPluginProperties() {
213+
return null;
214+
}
215+
};
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}
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@Override
157219
public void handleKillbillEvent(final ExtBusEvent killbillEvent) {
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}
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}

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