Every payment remembers what it was worth.

A payment is worth what it was worth WHEN IT HAPPENED, and that number is
gone by the time you look at it unless someone wrote it down. So every price
the app fetches is kept as a sample — one an hour, a few months back — and a
payment's fiat value is read off the sample nearest its own timestamp. The
history rows and both detail pages (on-chain and Spending) pass the time the
money moved; balances and forms use the live price, as they should.

A payment older than any sample we hold is priced at today's number and says
so with a '~', because that is a different claim and shouldn't look like the
same one. The detail page spells it out: "Worth then $X · $Y now".

Fiat is a third position on the unit toggle rather than a second number
beside the first: sats → BTC → your money → sats. One figure, and which
figure is your choice. The ring skips fiat entirely until a price has been
fetched — a third position showing blanks is worse than two that work. Typing
an amount with the unit on USD means dollars, priced now.

The rates are coinos' own endpoint, a map of every currency it knows, so
there's no third party watching what the wallet asks about; the currency
picker under Settings → Network lists all of them. Changing it starts the
recorded history again rather than relabelling samples taken in another
currency.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_019mrt228Upn9nNCwGixzSLx

1 files changed, 7 insertions, 3 deletions

diff --git a/src/format.js b/src/format.js
index a7f49c2..febba22 100644
--- a/src/format.js
+++ b/src/format.js
@@ -39,11 +39,15 @@ export function fmtUsd(sats, price) {
   return usd.toLocaleString('en-US', { style: 'currency', currency: 'USD' });
 }
 
-// Parse a user-entered amount. Accepts BTC (default) or sats.
-export function parseAmount(value, unit) {
+// Parse a user-entered amount. Accepts BTC (default), sats, or — when the
+// display unit is the user's own money and a rate is passed — that: typing 5
+// with the unit on USD means five dollars' worth, priced right now.
+export function parseAmount(value, unit, rate = null) {
   const n = Number(String(value).trim().replace(/,/g, ''));
   if (!isFinite(n) || n < 0) return null;
-  return unit === 'sats' ? Math.round(n) : Math.round(n * SATS);
+  if (unit === 'sats') return Math.round(n);
+  if (unit === 'fiat') return rate ? Math.round((n / rate) * SATS) : null;
+  return Math.round(n * SATS);
 }
 
 export function shortAddr(a, head = 10, tail = 8) {