feat: add billing and usage domain cores

backend/internal/billing/ledger_test.go

@@ -0,0 +1,46 @@
+package billing
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+)
+
+func TestLedgerChargesAndRefundsThroughWalletPosterWithFrozenKeys(t *testing.T) {
+	poster := &recordingPoster{result: WalletPosting{LedgerID: "ledger-1", CreatedAt: time.Unix(1, 0)}}
+	ledger := Ledger{Poster: poster, NewID: func() string { return "new-ledger" }}
+	charge, err := ledger.Charge(context.Background(), ChargeRequest{OrganizationID: "org-1", AccountID: "a", JobID: "job-1", AmountFen: 125})
+	if err != nil || charge.LedgerID != "ledger-1" || poster.params.IdempotencyKey != "job-charge:job-1" || poster.params.DeltaFen != -125 || poster.params.Currency != "CNY" {
+		t.Fatalf("charge = %#v params=%#v err=%v", charge, poster.params, err)
+	}
+	_, err = ledger.Refund(context.Background(), RefundRequest{OrganizationID: "org-1", AccountID: "a", JobID: "job-1", AmountFen: 125})
+	if err != nil || poster.params.IdempotencyKey != "job-refund:job-1" || poster.params.DeltaFen != 125 {
+		t.Fatalf("refund params=%#v err=%v", poster.params, err)
+	}
+}
+
+func TestLedgerMapsWalletFailuresToFrozenStatuses(t *testing.T) {
+	for _, test := range []struct {
+		db     error
+		want   error
+		status int
+	}{{errors.New("BILLING_INSUFFICIENT_BALANCE"), ErrInsufficientBalance, 402}, {errors.New("BILLING_IDEMPOTENCY_PAYLOAD_MISMATCH"), ErrIdempotencyConflict, 409}} {
+		ledger := Ledger{Poster: &recordingPoster{err: test.db}, NewID: func() string { return "id" }}
+		_, err := ledger.Charge(context.Background(), ChargeRequest{OrganizationID: "o", JobID: "j", AmountFen: 1})
+		if !errors.Is(err, test.want) || HTTPStatus(err) != test.status {
+			t.Fatalf("error=%v status=%d", err, HTTPStatus(err))
+		}
+	}
+}
+
+type recordingPoster struct {
+	params WalletPostParams
+	result WalletPosting
+	err    error
+}
+
+func (p *recordingPoster) PostWalletEntry(_ context.Context, v WalletPostParams) (WalletPosting, error) {
+	p.params = v
+	return p.result, p.err
+}