Parse and Show Sat Amount from Cashu tokens

app/src/main/java/com/vitorpamplona/amethyst/ui/components/CashuRedeem.kt

@@ -21,15 +21,29 @@ import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import androidx.core.content.ContextCompat.startActivity
+import com.google.gson.JsonParser
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.theme.QuoteBorder
 import com.vitorpamplona.amethyst.ui.theme.subtleBorder
+import java.util.Base64
 
 @Composable
 fun CashuPreview(cashutoken: String, accountViewModel: AccountViewModel) {
     val context = LocalContext.current
     val lnaddress = accountViewModel.account.userProfile().info?.lud16
+    val base64token = cashutoken.replace("cashuA", "")
+    val cashu = JsonParser.parseString(String(Base64.getDecoder().decode(base64token)))
+
+    val token = cashu.asJsonObject.get("token").asJsonArray[0].asJsonObject
+    val proofs = token["proofs"].asJsonArray
+    val mint = token["mint"]
+
+    var totalamount = 0
+    for (proof in proofs) {
+        totalamount += proof.asJsonObject["amount"].asInt
+    }
+
     Column(
         modifier = Modifier
             .fillMaxWidth()
@@ -65,12 +79,28 @@ fun CashuPreview(cashutoken: String, accountViewModel: AccountViewModel) {
 
             Divider()
 
+            totalamount?.let {
+                Text(
+                    text = "$it ${stringResource(id = R.string.sats)}",
+                    fontSize = 25.sp,
+                    fontWeight = FontWeight.W500,
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .padding(vertical = 10.dp)
+                )
+            }
+
             Button(
                 modifier = Modifier
                     .fillMaxWidth()
                     .padding(vertical = 10.dp),
                 onClick = {
                     runCatching {
+                        // Alternative directly from client: call POST https://{mint}/melt with body
+                        // {
+                        //  "proofs: {proofs},
+                        //  "pr": {create ln invoice with totalamount * 0.98, at least -2 sats}
+                        // }
                         val url = "https://redeem.cashu.me?token=$cashutoken&lightning=$lnaddress&autopay=true"
                         val intent = Intent(Intent.ACTION_VIEW, Uri.parse(url))
                         startActivity(context, intent, null)

app/src/main/res/values/strings.xml

@@ -457,7 +457,7 @@
     <string name="auth">Auth</string>
     <string name="payment">Payment</string>
     <string name="cashu">Cashu ecash</string>
-    <string name="cashu_redeem">Redeem Sats</string>
+    <string name="cashu_redeem">Redeem</string>
 
     <string name="live_stream_live_tag">LIVE</string>
     <string name="live_stream_offline_tag">OFFLINE</string>