From b4b5eab2a4928573b9241f0d38aa1c56694d101c Mon Sep 17 00:00:00 2001
From: Adam Soltys <adam@coinos.io>
Date: Fri, 23 Oct 2026 11:34:13 -0700
Subject: Switching the unit with an amount typed into the send form converts
 it: the same money in the new unit, round-tripping exactly

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QjVvE4YAcK3AGwV7kZXeN4
---
 src/app.js | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

(limited to 'src')

diff --git a/src/app.js b/src/app.js
index ffe9ba8..8d73b71 100644
--- a/src/app.js
+++ b/src/app.js
@@ -1209,31 +1209,44 @@ let unit = (() => {
 // been fetched — a third position showing blanks is worse than two that work.
 function toggleUnit() {
   const ring = haveRate() ? ['sats', 'btc', 'fiat'] : ['sats', 'btc'];
+  const was = unit;
   unit = ring[(ring.indexOf(unit) + 1) % ring.length];
   try {
     localStorage.setItem(UNIT_KEY, unit);
   } catch {}
+  // An amount already typed into the send form is the same money in the new
+  // unit, not the same digits: 1000 sats does not become 1000 BTC. Whatever
+  // doesn't parse is left as typed.
+  for (const r of (ui.send && ui.send.recipients) || []) {
+    if (!r.amount || !String(r.amount).trim()) continue;
+    const sat = parseField(r.amount, was);
+    if (sat) r.amount = amountField(sat);
+  }
   render();
 }
 
 // A sats figure as the amount field types it in the current unit — what a
 // Max button or a fixed-amount invoice fills in. Fiat is floored to the
 // cent so a filled-in maximum never parses back to more than was offered.
-// The figure it filled is remembered with its exact sats: a fiat maximum
+// The figures it filled are remembered with their exact sats: a fiat maximum
 // rounded to the cent would otherwise parse back a few sats short and leave
-// them behind. Typing anything else parses as typed.
-let lastFill = null;
+// them behind. Typing anything else parses as typed. Several are kept so a
+// form with more than one amount round-trips each of them.
+const fills = new Map();
 function amountField(sat) {
   let s;
   const r = unit === 'fiat' && rateNow();
   if (unit === 'sats') s = String(sat);
   else if (r) s = (Math.floor((sat / 1e8) * r * 100) / 100).toFixed(2);
   else s = (sat / 1e8).toFixed(8);
-  lastFill = { s, unit, sat };
+  fills.delete(unit + '|' + s);
+  fills.set(unit + '|' + s, sat);
+  while (fills.size > 16) fills.delete(fills.keys().next().value);
   return s;
 }
 function parseField(v, u = unit) {
-  if (lastFill && lastFill.unit === u && String(v).trim() === lastFill.s) return lastFill.sat;
+  const k = u + '|' + String(v).trim();
+  if (fills.has(k)) return fills.get(k);
   return parseAmount(v, u, rateNow());
 }
 
-- 
cgit v1.2.3