From 4bd2cded6cad8dc3c022f19afd2e4ac4205cdf0f Mon Sep 17 00:00:00 2001
From: Conor Okus <conor.okus@hotmail.co.uk>
Date: Fri, 24 Mar 2023 21:46:55 +0000
Subject: [PATCH] Start sending payments page

---
 docs/.vuepress/config.js                      |   3 +-
 .../sending-payments.md                       | 169 ++++++++++++++++++
 2 files changed, 171 insertions(+), 1 deletion(-)
 create mode 100644 docs/tutorials/building-a-node-with-ldk/sending-payments.md

diff --git a/docs/.vuepress/config.js b/docs/.vuepress/config.js
index bd3135196..c8c02bbc7 100644
--- a/docs/.vuepress/config.js
+++ b/docs/.vuepress/config.js
@@ -101,7 +101,8 @@ const tutorialSidebar = [
           ['/tutorials/building-a-node-with-ldk/handling-events', 'Handling Events'],
           ['/tutorials/building-a-node-with-ldk/setting-up-a-peer-manager', 'Setting up a Peer Manager'],
           ['/tutorials/building-a-node-with-ldk/connect-to-peers', 'Connect to Peers'],
-          ['/tutorials/building-a-node-with-ldk/opening-a-channel', 'Opening a Channel']
+          ['/tutorials/building-a-node-with-ldk/opening-a-channel', 'Opening a Channel'],
+          ['/tutorials/building-a-node-with-ldk/sending-payments', 'Sending Payments']
         ]
       },
     ],
diff --git a/docs/tutorials/building-a-node-with-ldk/sending-payments.md b/docs/tutorials/building-a-node-with-ldk/sending-payments.md
new file mode 100644
index 000000000..f12d8544a
--- /dev/null
+++ b/docs/tutorials/building-a-node-with-ldk/sending-payments.md
@@ -0,0 +1,169 @@
+# Sending Payments
+
+Lightning payments are used to pay invoices, which are typically encoded as a
+string in accordance with BOLT 11. After parsing the invoice, you'll need to
+find a route from your node to the recipient and then make the payment using
+`ChannelManager`.
+
+<CodeSwitcher :languages="{rust:'Rust', java:'Java', kotlin:'Kotlin'}">
+  <template v-slot:rust>
+
+```rust
+// Parse the invoice.
+let invoice = Invoice::from_str(encoded_invoice)
+	.expect("ERROR: failed to parse invoice");
+
+let amt_pico_btc = invoice.amount_pico_btc()
+	.expect("ERROR: invalid invoice: must contain amount to pay");
+let amt_msat = amt_pico_btc / 10;
+let payer_pubkey = channel_manager.get_our_node_id();
+let network_graph = router.network_graph.read().unwrap();
+let payee_pubkey = invoice.recover_payee_pub_key();
+let payee_features = invoice.features().cloned();
+let first_hops = channel_manager.list_usable_channels();
+let last_hops = invoice.route_hints();
+let final_cltv = invoice.min_final_cltv_expiry() as u32;
+
+// Find a route and send the payment.
+let route = router::get_route(
+	&payer_pubkey, &network_graph, &payee_pubkey, payee_features,
+	Some(&first_hops.iter().collect::<Vec<_>>()), &last_hops,
+	amt_msat, final_cltv, logger.clone(),
+).expect("ERROR: failed to find route");
+
+let payment_hash = PaymentHash(invoice.payment_hash().clone().into_inner());
+let payment_secret = invoice.payment_secret().cloned();
+
+channel_manager.send_payment(&route, payment_hash, &payment_secret)
+	.expect("ERROR: failed to send payment");
+```
+
+  </template>
+  <template v-slot:java>
+
+```java
+String invoice_str = // get an invoice from the payee
+Result_InvoiceNoneZ parsed_invoice = Invoice.from_str(invoice_str);
+
+if (parsed_invoice instanceof Result_InvoiceNoneZ.Result_InvoiceNoneZ_OK) {
+	Invoice invoice = ((Result_InvoiceNoneZ.Result_InvoiceNoneZ_OK) parsed_invoice).res;
+    long amt_msat = 0;
+    if (invoice.amount_pico_btc() instanceof Option_u64Z.Some) {
+        amt_msat = ((Option_u64Z.Some)invoice.amount_pico_btc()).some / 10;
+    }
+    if (amt_msat == 0) {
+        // <Handle a zero-value invoice>
+    }
+
+    Route route;
+    try (LockedNetworkGraph netgraph = router.read_locked_graph()) {
+        NetworkGraph graph = netgraph.graph();
+        Result_RouteLightningErrorZ route_res = UtilMethods.get_route(
+			channel_manager.get_our_node_id(),
+            graph, invoice.recover_payee_pub_key(), invoice.features(),
+            channel_manager.list_usable_channels(), invoice.route_hints(),
+            amt_msat, invoice.min_final_cltv_expiry(), logger);
+        assert route_res instanceof Result_RouteLightningErrorZ.Result_RouteLightningErrorZ_OK;
+        route = ((Result_RouteLightningErrorZ.Result_RouteLightningErrorZ_OK) route_res).res;
+    }
+
+    Result_NonePaymentSendFailureZ payment_res = channel_manager.send_payment(
+		route, invoice.payment_hash(), invoice.payment_secret());
+    assert payment_res instanceof Result_NonePaymentSendFailureZ.Result_NonePaymentSendFailureZ_OK;
+}
+```
+
+  </template>
+    <template v-slot:kotlin>
+
+```java
+// Get an invoice from the recipient/payee
+val parsedInvoice = Invoice.from_str(recipientInvoice)
+if (!parsedInvoice.is_ok) {
+    // Unable to parse invoice
+}
+
+val invoice = (parsedInvoice as Result_InvoiceParseOrSemanticErrorZ.Result_InvoiceParseOrSemanticErrorZ_OK).res
+
+var amountSats: Long = 0
+if (invoice.amount_milli_satoshis() is Option_u64Z.Some) {
+    amountSats = (invoice.amount_milli_satoshis() as Option_u64Z.Some).some * 1000
+}
+
+if (amountSats == 0L) {
+    // Handle a zero-value invoice
+}
+
+val res = channelManagerConstructor.payer.pay_invoice(invoice)
+
+
+
+if (parsed_invoice instanceof Result_InvoiceNoneZ.Result_InvoiceNoneZ_OK) {
+	Invoice invoice = ((Result_InvoiceNoneZ.Result_InvoiceNoneZ_OK) parsed_invoice).res;
+    long amt_msat = 0;
+    if (invoice.amount_pico_btc() instanceof Option_u64Z.Some) {
+        amt_msat = ((Option_u64Z.Some)invoice.amount_pico_btc()).some / 10;
+    }
+    if (amt_msat == 0) {
+        // <Handle a zero-value invoice>
+    }
+
+    Route route;
+    try (LockedNetworkGraph netgraph = router.read_locked_graph()) {
+        NetworkGraph graph = netgraph.graph();
+        Result_RouteLightningErrorZ route_res = UtilMethods.get_route(
+			channel_manager.get_our_node_id(),
+            graph, invoice.recover_payee_pub_key(), invoice.features(),
+            channel_manager.list_usable_channels(), invoice.route_hints(),
+            amt_msat, invoice.min_final_cltv_expiry(), logger);
+        assert route_res instanceof Result_RouteLightningErrorZ.Result_RouteLightningErrorZ_OK;
+        route = ((Result_RouteLightningErrorZ.Result_RouteLightningErrorZ_OK) route_res).res;
+    }
+
+    Result_NonePaymentSendFailureZ payment_res = channel_manager.send_payment(
+		route, invoice.payment_hash(), invoice.payment_secret());
+    assert payment_res instanceof Result_NonePaymentSendFailureZ.Result_NonePaymentSendFailureZ_OK;
+}
+```
+
+  </template>
+</CodeSwitcher>
+
+An event is generated once a payment has completed. Successful payments result
+in a `PaymentSent` event with the preimage of the payment hash. Be sure to look
+out for a `PaymentFailed` event, if the payment fails for some reason, and act
+accordingly.
+
+<CodeSwitcher :languages="{rust:'Rust', java:'Java'}">
+  <template v-slot:rust>
+
+```rust
+// In the event handler passed to BackgroundProcessor::start
+match event {
+	Event::PaymentSent { payment_preimage } => {
+		// Handle successful payment
+	}
+	Event::PaymentFailed { payment_hash, rejected_by_dest } => {
+		// Handle failed payment
+	}
+	// ...
+}
+```
+
+  </template>
+  <template v-slot:java>
+
+```java
+// In the `handle_event` method of ChannelManagerPersister implementation
+else if (e instanceof Event.PaymentSent) {
+	// Handle successful payment
+	Event.PaymentSent event = ((Event.PaymentSent) e);
+}
+else if (e instanceof Event.PaymentFailed) {
+	// Handle failed payment
+	Event.PaymentFailed event = ((Event.PaymentFailed) e);
+}
+```
+
+  </template>
+</CodeSwitcher>