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fix(services): convert fiat menu prices to sat via exchange rates

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Before this fix `_to_msat(item.price)` blindly did `price * 1000`,
treating any menu price as sat-denominated regardless of the item's
`currency` field. Quote and bolt11 were internally consistent but
charged ~0.1% of the real price for fiat-priced menus.

  Big Jay's seeded with GTQ:
    2× Tacos (Maíz, +Brisket, +Chicken)
    pre-fix:  170 GTQ → 170000 msat → 170 sat invoice (~$0.14)
    post-fix: 170 GTQ → 26968000 msat → 26968 sat invoice (~$22)

services.py:
  - Drop `_to_msat` in favor of a `_price_to_msat(amount, currency)`
    helper. Sat-aliased currencies ("sat", "sats", "satoshi",
    "msat", …) take the flat ×1000 path; everything else round-
    trips through lnbits.utils.exchange_rates.fiat_amount_as_satoshis
    (same pool the events extension uses).
  - Update _price_line_item: item.price AND each modifier.price_delta
    are converted using item.currency. Modifier deltas inherit the
    parent item's currency since we don't carry a per-modifier
    currency field.
  - Update quote_balance_required: same conversion via the item's
    currency.

Verified live against the seeded "Big Jay's Bustaurant":
  GTQ → sat conversion matches LNbits's bitcoin-price aggregate
  (Binance / Blockchain / Bitfinex / Bitstamp / Coinbase / yadio).
  Quote returns 26968 sats for 170 GTQ — within ~2% of expected
  rate from external sources.
This commit is contained in:
Padreug 2026-05-11 17:49:12 +02:00
commit 638f36e945
2 changed files with 51 additions and 12 deletions
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16
docs/order-flow.md
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@ -37,14 +37,22 @@ States and their meaning:
2. Re-prices every line item against the live menu (modifier ids
are matched server-side; the customer's claimed `price_delta`
values are ignored).
3. Sums `subtotal_msat`, applies `tax_rate`, adds `tip_msat` →
3. Converts each item's `price` from its declared `currency` to
msat. For sat-denominated items (`currency` ∈ `{sat, sats,
satoshi}`) this is a flat `× 1000`. For fiat (`USD`, `GTQ`, …)
it calls `lnbits.utils.exchange_rates.fiat_amount_as_satoshis`
to look up the live rate, then `× 1000`. The conversion lives
in `services._price_to_msat` so the rate lookup is the same path
the quote endpoint uses — a customer's preview and the recorded
`order.total_msat` cannot drift apart between request and place.
4. Sums `subtotal_msat`, applies `tax_rate`, adds `tip_msat` →
`total_msat`.
4. For Lightning / internal: calls
5. For Lightning / internal: calls
`lnbits.core.services.create_invoice` with
`extra={"tag": "restaurant", "restaurant_id": ...}`.
5. Persists the order with `id = payment_hash` so the listener can
6. Persists the order with `id = payment_hash` so the listener can
look it up cheaply, plus one `order_items` row per line.
6. For cash: `payment_method = "cash"` skips invoice creation and
7. For cash: `payment_method = "cash"` skips invoice creation and
marks the order `accepted` directly.
Returns `(Order, OrderInvoice | None)`. The webapp pays the bolt11.