# Multi-account Fio sync + switch QR target to 2502035405/2010

## Context

The club is opening a second Fio transparent account, **`2502035405/2010`** (IBAN
`CZ??...0000002502035405`). Going forward:

- **Sync** must pull transactions from **both** accounts into the existing
  payments sheet — the old `2800359168/2010` stays active so historical fees
  paid to it still reconcile.
- **QR codes** generated by `/qr` should default to the **new** account
  (`2502035405/2010`), so new payers send money there.

The payments sheet schema and `sync_id` hash stay **unchanged** — no
"Source Account" column, no migration, no risk of re-appending historical rows.
Bank-ID uniqueness from Fio plus the existing hash inputs are good enough to
dedupe across two transparent accounts in practice.

Implementation order: Go first, then port to Python. Both apps use the same
`PaymentsSheetID`, so once Go writes from two accounts the Python code only
needs to do the same when invoked.

### Decisions locked in with the user
- **Config style:** hardcoded list of accounts in `config.go` / `config.py`
  (sheet IDs are already hardcoded; tokens stay env-driven).
- **Source tagging:** no schema change, `sync_id` formula unchanged.
- **Old account:** kept syncing in parallel; only QR target changes.

---

## Go implementation

### 1. Config — hardcoded `Accounts` list, derived `QRAccount`

[go/internal/config/config.go](../../go/internal/config/config.go)

- Replace scalar `BankAccount` + `FioAPIToken` with a hardcoded slice and a
  primary pointer. Tokens stay env-driven via per-account env names.

  ```go
  // Account describes one Fio bank account we sync from.
  type Account struct {
      IBAN     string // e.g. "CZ0820100000002502035405"
      AcctNum  string // bare account number, e.g. "2502035405"
      TokenEnv string // env var name holding the Fio API token (empty token => transparent scraper path)
      Primary  bool   // true for the QR-code default account
  }

  var Accounts = []Account{
      {IBAN: "CZ0820100000002502035405", AcctNum: "2502035405", TokenEnv: "FIO_API_TOKEN_NEW", Primary: true},
      {IBAN: "CZ8520100000002800359168", AcctNum: "2800359168", TokenEnv: "FIO_API_TOKEN_OLD"},
  }
  ```
  Compute the **real** IBAN check digit for `2502035405` once and bake it in
  (replace the `85` placeholder above). The same `IBANAccountNum` helper at
  [config.go:66](../../go/internal/config/config.go#L66) keeps producing
  `AcctNum`, but having it on the struct avoids re-parsing at every call site.

- `Config` struct:
  - Drop `BankAccount` and `FioAPIToken` fields.
  - Add `QRAccount string` (the IBAN of `Accounts[i].Primary == true`).
  - Add `LoadedAccounts []LoadedAccount` where each entry pairs an `Account`
    with the token resolved from `os.Getenv(account.TokenEnv)`.
- `Load()` reads each `TokenEnv` and stores tokens with the account. Logs a
  warning (info-level) if no token is set — that's the transparent-scraper
  path, which is fine.

### 2. Sync loop — one `fio.Client` per account, single dedup pass

[go/internal/services/banksync/sync.go](../../go/internal/services/banksync/sync.go)

Change `SyncToSheets` to accept a slice of clients instead of one:

```go
func SyncToSheets(
    ctx context.Context,
    spreadsheetID string,
    fioClients []fio.Client, // was: fioClient fio.Client
    sh sheetsWriter,
    opts SyncOpts,
) (int, error)
```

Inside:

- Keep steps 1 (read existing IDs) and 2 (date window) as-is.
- Step 3 (fetch) becomes a loop: call `FetchTransactions` on each client; tag
  each `fio.Transaction` with the account it came from for logging only
  (don't write it to the sheet). Concatenate into one slice `txns`.
- Steps 4a–4c (sync_id calc, debug table, row build, dedup) are unchanged —
  the combined `txns` slice flows through the same code path. Existing
  `sync_id` collisions across accounts are dropped silently, which is the
  desired dedup behaviour.
- `printFioTable` (dry-run debug) should print an extra column showing the
  source account so per-account fetches are visible — small change in
  [fio_table.go](../../go/internal/services/banksync/fio_table.go).

Logger output: log fetched count per account and the total combined count.

### 3. Call sites — build clients from the config list

Both entry points construct `[]fio.Client`, one per `LoadedAccount`:

- [go/cmd/fuj/main.go:91](../../go/cmd/fuj/main.go#L91) — server `BankSync` action.
- [go/cmd/fuj/main.go:200](../../go/cmd/fuj/main.go#L200) — `fuj sync` CLI.

Helper to add somewhere in `cmd/fuj/main.go` or a new
`internal/services/banksync/clients.go`:

```go
func clientsFromConfig(cfg config.Config) []fio.Client {
    out := make([]fio.Client, 0, len(cfg.LoadedAccounts))
    for _, a := range cfg.LoadedAccounts {
        out = append(out, fio.New(a.Token, a.AcctNum, nil))
    }
    return out
}
```

The existing factory at
[go/internal/io/fio/client.go:35](../../go/internal/io/fio/client.go#L35)
already routes per-account between the API path and the transparent scraper
based on whether the token is empty — no change there.

### 4. QR endpoint — default to `QRAccount`

[go/internal/web/html_handler.go:129](../../go/internal/web/html_handler.go#L129)
and [html_handler.go:135](../../go/internal/web/html_handler.go#L135):
swap `h.apiHandler.Config.BankAccount` → `h.apiHandler.Config.QRAccount`.

API DTOs that surface the payment account in JSON:
[build_adults.go:141](../../go/internal/web/api/build_adults.go#L141) and
[build_juniors.go:137](../../go/internal/web/api/build_juniors.go#L137) — same
swap.

The fields on the API structs at
[adults.go:40](../../go/internal/web/api/adults.go#L40) and
[juniors.go:39](../../go/internal/web/api/juniors.go#L39) keep their JSON
names so the Python parity binary doesn't see a schema diff.

### 5. Tests

- **New** [go/internal/services/banksync/sync_test.go](../../go/internal/services/banksync/sync_test.go):
  add a test `TestSyncToSheets_MultiAccount` that wires up two fake
  `fio.Client`s (via the existing
  [fake.go](../../go/internal/io/fio/fake.go)), one returning a txn unique to
  it and one returning a txn that duplicates an existing sync_id. Assert:
  rows from both accounts get appended, the duplicate is dropped.
- **Update** [go/internal/web/html_handler_test.go:207](../../go/internal/web/html_handler_test.go#L207)
  `TestServeQR` and [qr_test.go](../../go/internal/web/qr_test.go)
  `TestQRBuildSPD` — expected SPD strings now contain the new IBAN by default.
- **Update** any config tests asserting `cfg.BankAccount` directly to use
  `cfg.QRAccount` and the new `LoadedAccounts` slice. (Grep for `BankAccount`
  under `go/` after the rename.)
- Existing fio parser tests
  ([fio_test.go](../../go/internal/io/fio/fio_test.go)) and sync_id test
  ([synch_test.go](../../go/internal/domain/synch/synch_test.go)) need no
  changes — they don't know about the account list.

### 6. Verification (Go)

1. `cd go && go build ./... && go test ./...` — all green.
2. `FIO_API_TOKEN_NEW="" FIO_API_TOKEN_OLD="" ./build/fuj sync --dry-run --print-fio-table --days 7`
   — see fetched transactions from **both** accounts, with NEW/DUP status,
   without writing.
3. `./build/fuj server` then visit
   `http://localhost:8080/qr?amount=700&message=test` — QR payload SPD must
   contain the new IBAN `CZ??...2502035405`.
4. Real sync once dry-run looks right: `./build/fuj sync --days 30` — confirm
   in the Google sheet that rows from the old account still appear and no
   duplicates are written.

---

## Python port (after Go is merged)

The Python app uses the same payments sheet and the same column schema, so
the port mirrors the Go change one-for-one. Goal: one round-trip of
`make sync-2026` pulls from both accounts.

### 1. `scripts/config.py`

- Replace the scalar `BANK_ACCOUNT` constant at
  [scripts/config.py:25](../../scripts/config.py#L25) with a hardcoded list
  plus a derived primary:

  ```python
  ACCOUNTS = [
      {"iban": "CZ0820100000002502035405", "acct_num": "2502035405", "token_env": "FIO_API_TOKEN_NEW", "primary": True},
      {"iban": "CZ8520100000002800359168", "acct_num": "2800359168", "token_env": "FIO_API_TOKEN_OLD", "primary": False},
  ]
  BANK_ACCOUNT = next(a["iban"] for a in ACCOUNTS if a["primary"])  # QR / template default
  ```
  Use the real check-digit IBAN for `2502035405` (the same one baked into Go).

- Resolve tokens at module load time with `os.environ.get(token_env, "")` and
  stash them on a parallel `LOADED_ACCOUNTS` list (or attach to the dicts) so
  other modules don't all re-read env.

### 2. `scripts/fio_utils.py`

- [fio_utils.py:106](../../scripts/fio_utils.py#L106) and
  [fio_utils.py:219](../../scripts/fio_utils.py#L219): drop the hardcoded
  `"2800359168"` default for `account_id`. Make it a required argument.
- `fetch_transactions(date_from, date_to, *, account)` — change signature to
  take one account dict, return that account's transactions. Internally still
  routes via `FIO_API_TOKEN` if the account dict has a token, otherwise the
  transparent scraper at
  [fio_utils.py:105](../../scripts/fio_utils.py#L105).
- Add `fetch_transactions_all(date_from, date_to, accounts=None)` that loops
  over `accounts` (default `config.LOADED_ACCOUNTS`), calls the per-account
  fetch, concatenates results. Logs per-account counts.

### 3. `scripts/sync_fio_to_sheets.py`

- Where it currently calls `fio_utils.fetch_transactions(...)`, switch to
  `fio_utils.fetch_transactions_all(...)`. The dedup at
  [sync_fio_to_sheets.py:62](../../scripts/sync_fio_to_sheets.py#L62) and
  append at
  [sync_fio_to_sheets.py:248](../../scripts/sync_fio_to_sheets.py#L248) need
  no changes — same as in Go, the combined list flows through unchanged.

### 4. `app.py` (QR + template defaults)

- `/qr` at [app.py:321](../../app.py#L321) already reads `BANK_ACCOUNT` from
  config; since the config default now points at the new IBAN, this is a
  zero-line change in `app.py`.
- The `BANK_ACCOUNT` passed into templates at
  [app.py:180](../../app.py#L180), [app.py:204](../../app.py#L204),
  [app.py:255](../../app.py#L255), [app.py:291](../../app.py#L291) likewise
  picks up the new default automatically.

### 5. Tests

The Python suite has **no** existing coverage of `fio_utils`,
`sync_fio_to_sheets`, or `/qr`. Don't add new tests — keep the port minimal
and rely on the Go test suite + manual verification for correctness.

### 6. Verification (Python)

1. `make test` — existing suite stays green (the config refactor must not
   break [tests/test_app.py](../../tests/test_app.py)).
2. `make sync-2026` against the real sheet, dry-run first if the script
   supports it, then real run — confirm rows from both accounts arrive.
3. `make web-debug` → open `/qr?amount=700&message=test` → QR payload SPD
   contains the new IBAN.

---

## Branching

Per `CLAUDE.md`: this is a feature, so `feat/multi-account-bank-sync` off
`main`. Two MRs:

1. `feat/multi-account-bank-sync-go` — Go change end-to-end.
2. `feat/multi-account-bank-sync-py` — Python port, opened after (1) is
   merged.

Each MR opened via `tea pr create`. CHANGELOG.md entry per MR.

## Out of scope

- No sheet schema migration.
- No change to `sync_id` hash inputs at
  [domain/synch/synch.go:14](../../go/internal/domain/synch/synch.go#L14) or
  [sync_fio_to_sheets.py:67](../../scripts/sync_fio_to_sheets.py#L67).
- No UI surface for switching the QR account per-request (the existing
  `?account=` query param on `/qr` keeps working as an override).
- No backfill / dedup pass over historical rows.