move coin selection function to coinSelection.ts and added a test placeholder, and some fixes:

 * selectCandidates was not save wire fee
 * selectCandidates show check wire fee time range

8 files changed, 681 insertions, 632 deletions

diff --git a/packages/taler-wallet-core/src/operations/deposits.ts b/packages/taler-wallet-core/src/operations/deposits.ts
index c6cd4732c..64217acab 100644
--- a/packages/taler-wallet-core/src/operations/deposits.ts
+++ b/packages/taler-wallet-core/src/operations/deposits.ts
@@ -76,9 +76,9 @@ import {
   extractContractData,
   generateDepositPermissions,
   getTotalPaymentCost,
-  selectPayCoinsNew,
 } from "./pay-merchant.js";
 import { getTotalRefreshCost } from "./refresh.js";
+import { selectPayCoinsNew } from "../util/coinSelection.js";
 
 /**
  * Logger.
diff --git a/packages/taler-wallet-core/src/operations/exchanges.ts b/packages/taler-wallet-core/src/operations/exchanges.ts
index 8a98c8299..d9051b32f 100644
--- a/packages/taler-wallet-core/src/operations/exchanges.ts
+++ b/packages/taler-wallet-core/src/operations/exchanges.ts
@@ -63,6 +63,7 @@ import {
   ExchangeRecord,
   WalletStoresV1,
 } from "../db.js";
+import { isWithdrawableDenom } from "../index.js";
 import { InternalWalletState, TrustInfo } from "../internal-wallet-state.js";
 import { checkDbInvariant } from "../util/invariants.js";
 import {
@@ -78,7 +79,6 @@ import {
 } from "../util/retries.js";
 import { WALLET_EXCHANGE_PROTOCOL_VERSION } from "../versions.js";
 import { runOperationWithErrorReporting } from "./common.js";
-import { isWithdrawableDenom } from "./withdraw.js";
 
 const logger = new Logger("exchanges.ts");
 
diff --git a/packages/taler-wallet-core/src/operations/pay-merchant.ts b/packages/taler-wallet-core/src/operations/pay-merchant.ts
index 25153f9fb..f8fa1d34d 100644
--- a/packages/taler-wallet-core/src/operations/pay-merchant.ts
+++ b/packages/taler-wallet-core/src/operations/pay-merchant.ts
@@ -24,12 +24,10 @@
 /**
  * Imports.
  */
-import { GlobalIDB } from "@gnu-taler/idb-bridge";
 import {
   AbortingCoin,
   AbortRequest,
   AbsoluteTime,
-  AgeRestriction,
   AmountJson,
   Amounts,
   ApplyRefundResponse,
@@ -44,9 +42,8 @@ import {
   CoinStatus,
   ConfirmPayResult,
   ConfirmPayResultType,
-  MerchantContractTerms,
+  constructPayUri,
   ContractTermsUtil,
-  DenominationInfo,
   Duration,
   encodeCrock,
   ForcedCoinSel,
@@ -54,11 +51,13 @@ import {
   HttpStatusCode,
   j2s,
   Logger,
+  makeErrorDetail,
+  makePendingOperationFailedError,
   MerchantCoinRefundFailureStatus,
   MerchantCoinRefundStatus,
   MerchantCoinRefundSuccessStatus,
+  MerchantContractTerms,
   NotificationType,
-  parsePaytoUri,
   parsePayUri,
   parseRefundUri,
   PayCoinSelection,
@@ -66,19 +65,24 @@ import {
   PreparePayResultType,
   PrepareRefundResult,
   RefreshReason,
-  strcmp,
+  TalerError,
   TalerErrorCode,
   TalerErrorDetail,
   TalerProtocolTimestamp,
+  TalerProtocolViolationError,
   TransactionType,
   URL,
-  constructPayUri,
-  PayMerchantInsufficientBalanceDetails,
 } from "@gnu-taler/taler-util";
+import {
+  getHttpResponseErrorDetails,
+  readSuccessResponseJsonOrErrorCode,
+  readSuccessResponseJsonOrThrow,
+  readTalerErrorResponse,
+  readUnexpectedResponseDetails,
+  throwUnexpectedRequestError,
+} from "@gnu-taler/taler-util/http";
 import { EddsaKeypair } from "../crypto/cryptoImplementation.js";
 import {
-  AllowedAuditorInfo,
-  AllowedExchangeInfo,
   BackupProviderStateTag,
   CoinRecord,
   DenominationRecord,
@@ -89,51 +93,29 @@ import {
   WalletContractData,
   WalletStoresV1,
 } from "../db.js";
-import {
-  makeErrorDetail,
-  makePendingOperationFailedError,
-  TalerError,
-  TalerProtocolViolationError,
-} from "@gnu-taler/taler-util";
 import { GetReadWriteAccess, PendingTaskType } from "../index.js";
 import {
   EXCHANGE_COINS_LOCK,
   InternalWalletState,
 } from "../internal-wallet-state.js";
 import { assertUnreachable } from "../util/assertUnreachable.js";
+import { PreviousPayCoins, selectPayCoinsNew } from "../util/coinSelection.js";
+import { checkDbInvariant } from "../util/invariants.js";
+import { GetReadOnlyAccess } from "../util/query.js";
 import {
-  CoinSelectionTally,
-  PreviousPayCoins,
-  tallyFees,
-} from "../util/coinSelection.js";
-import {
-  getHttpResponseErrorDetails,
-  readSuccessResponseJsonOrErrorCode,
-  readSuccessResponseJsonOrThrow,
-  readTalerErrorResponse,
-  readUnexpectedResponseDetails,
-  throwUnexpectedRequestError,
-} from "@gnu-taler/taler-util/http";
-import { checkDbInvariant, checkLogicInvariant } from "../util/invariants.js";
-import {
+  constructTaskIdentifier,
   OperationAttemptResult,
   OperationAttemptResultType,
   RetryInfo,
-  TaskIdentifiers,
   scheduleRetry,
-  constructTaskIdentifier,
+  TaskIdentifiers,
 } from "../util/retries.js";
 import {
   makeTransactionId,
   runOperationWithErrorReporting,
   spendCoins,
-  storeOperationError,
-  storeOperationPending,
 } from "./common.js";
-import { getExchangeDetails } from "./exchanges.js";
 import { createRefreshGroup, getTotalRefreshCost } from "./refresh.js";
-import { GetReadOnlyAccess } from "../util/query.js";
-import { getMerchantPaymentBalanceDetails } from "./balance.js";
 
 /**
  * Logger.
@@ -877,434 +859,6 @@ async function unblockBackup(
     });
 }
 
-export interface SelectPayCoinRequestNg {
-  exchanges: AllowedExchangeInfo[];
-  auditors: AllowedAuditorInfo[];
-  wireMethod: string;
-  contractTermsAmount: AmountJson;
-  depositFeeLimit: AmountJson;
-  wireFeeLimit: AmountJson;
-  wireFeeAmortization: number;
-  prevPayCoins?: PreviousPayCoins;
-  requiredMinimumAge?: number;
-  forcedSelection?: ForcedCoinSel;
-}
-
-export type AvailableDenom = DenominationInfo & {
-  maxAge: number;
-  numAvailable: number;
-};
-
-export async function selectCandidates(
-  ws: InternalWalletState,
-  req: SelectPayCoinRequestNg,
-): Promise<[AvailableDenom[], Record<string, AmountJson>]> {
-  return await ws.db
-    .mktx((x) => [
-      x.exchanges,
-      x.exchangeDetails,
-      x.denominations,
-      x.coinAvailability,
-    ])
-    .runReadOnly(async (tx) => {
-      // FIXME: Use the existing helper (from balance.ts) to
-      // get acceptable exchanges.
-      const denoms: AvailableDenom[] = [];
-      const exchanges = await tx.exchanges.iter().toArray();
-      const wfPerExchange: Record<string, AmountJson> = {};
-      for (const exchange of exchanges) {
-        const exchangeDetails = await getExchangeDetails(tx, exchange.baseUrl);
-        if (exchangeDetails?.currency !== req.contractTermsAmount.currency) {
-          continue;
-        }
-        let wireMethodSupported = false;
-        for (const acc of exchangeDetails.wireInfo.accounts) {
-          const pp = parsePaytoUri(acc.payto_uri);
-          checkLogicInvariant(!!pp);
-          if (pp.targetType === req.wireMethod) {
-            wireMethodSupported = true;
-            break;
-          }
-        }
-        if (!wireMethodSupported) {
-          break;
-        }
-        exchangeDetails.wireInfo.accounts;
-        let accepted = false;
-        for (const allowedExchange of req.exchanges) {
-          if (allowedExchange.exchangePub === exchangeDetails.masterPublicKey) {
-            accepted = true;
-            break;
-          }
-        }
-        for (const allowedAuditor of req.auditors) {
-          for (const providedAuditor of exchangeDetails.auditors) {
-            if (allowedAuditor.auditorPub === providedAuditor.auditor_pub) {
-              accepted = true;
-              break;
-            }
-          }
-        }
-        if (!accepted) {
-          continue;
-        }
-        let ageLower = 0;
-        let ageUpper = AgeRestriction.AGE_UNRESTRICTED;
-        if (req.requiredMinimumAge) {
-          ageLower = req.requiredMinimumAge;
-        }
-        const myExchangeDenoms =
-          await tx.coinAvailability.indexes.byExchangeAgeAvailability.getAll(
-            GlobalIDB.KeyRange.bound(
-              [exchangeDetails.exchangeBaseUrl, ageLower, 1],
-              [
-                exchangeDetails.exchangeBaseUrl,
-                ageUpper,
-                Number.MAX_SAFE_INTEGER,
-              ],
-            ),
-          );
-        // FIXME: Check that the individual denomination is audited!
-        // FIXME: Should we exclude denominations that are
-        // not spendable anymore?
-        for (const denomAvail of myExchangeDenoms) {
-          const denom = await tx.denominations.get([
-            denomAvail.exchangeBaseUrl,
-            denomAvail.denomPubHash,
-          ]);
-          checkDbInvariant(!!denom);
-          if (denom.isRevoked || !denom.isOffered) {
-            continue;
-          }
-          denoms.push({
-            ...DenominationRecord.toDenomInfo(denom),
-            numAvailable: denomAvail.freshCoinCount ?? 0,
-            maxAge: denomAvail.maxAge,
-          });
-        }
-      }
-      // Sort by available amount (descending),  deposit fee (ascending) and
-      // denomPub (ascending) if deposit fee is the same
-      // (to guarantee deterministic results)
-      denoms.sort(
-        (o1, o2) =>
-          -Amounts.cmp(o1.value, o2.value) ||
-          Amounts.cmp(o1.feeDeposit, o2.feeDeposit) ||
-          strcmp(o1.denomPubHash, o2.denomPubHash),
-      );
-      return [denoms, wfPerExchange];
-    });
-}
-
-function makeAvailabilityKey(
-  exchangeBaseUrl: string,
-  denomPubHash: string,
-  maxAge: number,
-): string {
-  return `${denomPubHash};${maxAge};${exchangeBaseUrl}`;
-}
-
-/**
- * Selection result.
- */
-interface SelResult {
-  /**
-   * Map from an availability key
-   * to an array of contributions.
-   */
-  [avKey: string]: {
-    exchangeBaseUrl: string;
-    denomPubHash: string;
-    maxAge: number;
-    contributions: AmountJson[];
-  };
-}
-
-export function selectGreedy(
-  req: SelectPayCoinRequestNg,
-  candidateDenoms: AvailableDenom[],
-  wireFeesPerExchange: Record<string, AmountJson>,
-  tally: CoinSelectionTally,
-): SelResult | undefined {
-  const { wireFeeAmortization } = req;
-  const selectedDenom: SelResult = {};
-  for (const aci of candidateDenoms) {
-    const contributions: AmountJson[] = [];
-    for (let i = 0; i < aci.numAvailable; i++) {
-      // Don't use this coin if depositing it is more expensive than
-      // the amount it would give the merchant.
-      if (Amounts.cmp(aci.feeDeposit, aci.value) > 0) {
-        tally.lastDepositFee = Amounts.parseOrThrow(aci.feeDeposit);
-        continue;
-      }
-
-      if (Amounts.isZero(tally.amountPayRemaining)) {
-        // We have spent enough!
-        break;
-      }
-
-      tally = tallyFees(
-        tally,
-        wireFeesPerExchange,
-        wireFeeAmortization,
-        aci.exchangeBaseUrl,
-        Amounts.parseOrThrow(aci.feeDeposit),
-      );
-
-      let coinSpend = Amounts.max(
-        Amounts.min(tally.amountPayRemaining, aci.value),
-        aci.feeDeposit,
-      );
-
-      tally.amountPayRemaining = Amounts.sub(
-        tally.amountPayRemaining,
-        coinSpend,
-      ).amount;
-      contributions.push(coinSpend);
-    }
-
-    if (contributions.length) {
-      const avKey = makeAvailabilityKey(
-        aci.exchangeBaseUrl,
-        aci.denomPubHash,
-        aci.maxAge,
-      );
-      let sd = selectedDenom[avKey];
-      if (!sd) {
-        sd = {
-          contributions: [],
-          denomPubHash: aci.denomPubHash,
-          exchangeBaseUrl: aci.exchangeBaseUrl,
-          maxAge: aci.maxAge,
-        };
-      }
-      sd.contributions.push(...contributions);
-      selectedDenom[avKey] = sd;
-    }
-
-    if (Amounts.isZero(tally.amountPayRemaining)) {
-      return selectedDenom;
-    }
-  }
-  return undefined;
-}
-
-export function selectForced(
-  req: SelectPayCoinRequestNg,
-  candidateDenoms: AvailableDenom[],
-): SelResult | undefined {
-  const selectedDenom: SelResult = {};
-
-  const forcedSelection = req.forcedSelection;
-  checkLogicInvariant(!!forcedSelection);
-
-  for (const forcedCoin of forcedSelection.coins) {
-    let found = false;
-    for (const aci of candidateDenoms) {
-      if (aci.numAvailable <= 0) {
-        continue;
-      }
-      if (Amounts.cmp(aci.value, forcedCoin.value) === 0) {
-        aci.numAvailable--;
-        const avKey = makeAvailabilityKey(
-          aci.exchangeBaseUrl,
-          aci.denomPubHash,
-          aci.maxAge,
-        );
-        let sd = selectedDenom[avKey];
-        if (!sd) {
-          sd = {
-            contributions: [],
-            denomPubHash: aci.denomPubHash,
-            exchangeBaseUrl: aci.exchangeBaseUrl,
-            maxAge: aci.maxAge,
-          };
-        }
-        sd.contributions.push(Amounts.parseOrThrow(forcedCoin.value));
-        selectedDenom[avKey] = sd;
-        found = true;
-        break;
-      }
-    }
-    if (!found) {
-      throw Error("can't find coin for forced coin selection");
-    }
-  }
-
-  return selectedDenom;
-}
-
-export type SelectPayCoinsResult =
-  | {
-      type: "failure";
-      insufficientBalanceDetails: PayMerchantInsufficientBalanceDetails;
-    }
-  | { type: "success"; coinSel: PayCoinSelection };
-
-/**
- * Given a list of candidate coins, select coins to spend under the merchant's
- * constraints.
- *
- * The prevPayCoins can be specified to "repair" a coin selection
- * by adding additional coins, after a broken (e.g. double-spent) coin
- * has been removed from the selection.
- *
- * This function is only exported for the sake of unit tests.
- */
-export async function selectPayCoinsNew(
-  ws: InternalWalletState,
-  req: SelectPayCoinRequestNg,
-): Promise<SelectPayCoinsResult> {
-  const {
-    contractTermsAmount,
-    depositFeeLimit,
-    wireFeeLimit,
-    wireFeeAmortization,
-  } = req;
-
-  const [candidateDenoms, wireFeesPerExchange] = await selectCandidates(
-    ws,
-    req,
-  );
-
-  // logger.trace(`candidate denoms: ${j2s(candidateDenoms)}`);
-
-  const coinPubs: string[] = [];
-  const coinContributions: AmountJson[] = [];
-  const currency = contractTermsAmount.currency;
-
-  let tally: CoinSelectionTally = {
-    amountPayRemaining: contractTermsAmount,
-    amountWireFeeLimitRemaining: wireFeeLimit,
-    amountDepositFeeLimitRemaining: depositFeeLimit,
-    customerDepositFees: Amounts.zeroOfCurrency(currency),
-    customerWireFees: Amounts.zeroOfCurrency(currency),
-    wireFeeCoveredForExchange: new Set(),
-    lastDepositFee: Amounts.zeroOfCurrency(currency),
-  };
-
-  const prevPayCoins = req.prevPayCoins ?? [];
-
-  // Look at existing pay coin selection and tally up
-  for (const prev of prevPayCoins) {
-    tally = tallyFees(
-      tally,
-      wireFeesPerExchange,
-      wireFeeAmortization,
-      prev.exchangeBaseUrl,
-      prev.feeDeposit,
-    );
-    tally.amountPayRemaining = Amounts.sub(
-      tally.amountPayRemaining,
-      prev.contribution,
-    ).amount;
-
-    coinPubs.push(prev.coinPub);
-    coinContributions.push(prev.contribution);
-  }
-
-  let selectedDenom: SelResult | undefined;
-  if (req.forcedSelection) {
-    selectedDenom = selectForced(req, candidateDenoms);
-  } else {
-    // FIXME:  Here, we should select coins in a smarter way.
-    // Instead of always spending the next-largest coin,
-    // we should try to find the smallest coin that covers the
-    // amount.
-    selectedDenom = selectGreedy(
-      req,
-      candidateDenoms,
-      wireFeesPerExchange,
-      tally,
-    );
-  }
-
-  if (!selectedDenom) {
-    const details = await getMerchantPaymentBalanceDetails(ws, {
-      acceptedAuditors: req.auditors,
-      acceptedExchanges: req.exchanges,
-      acceptedWireMethods: [req.wireMethod],
-      currency: Amounts.currencyOf(req.contractTermsAmount),
-      minAge: req.requiredMinimumAge ?? 0,
-    });
-    let feeGapEstimate: AmountJson;
-    if (
-      Amounts.cmp(
-        details.balanceMerchantDepositable,
-        req.contractTermsAmount,
-      ) >= 0
-    ) {
-      // FIXME: We can probably give a better estimate.
-      feeGapEstimate = Amounts.add(
-        tally.amountPayRemaining,
-        tally.lastDepositFee,
-      ).amount;
-    } else {
-      feeGapEstimate = Amounts.zeroOfAmount(req.contractTermsAmount);
-    }
-    return {
-      type: "failure",
-      insufficientBalanceDetails: {
-        amountRequested: Amounts.stringify(req.contractTermsAmount),
-        balanceAgeAcceptable: Amounts.stringify(details.balanceAgeAcceptable),
-        balanceAvailable: Amounts.stringify(details.balanceAvailable),
-        balanceMaterial: Amounts.stringify(details.balanceMaterial),
-        balanceMerchantAcceptable: Amounts.stringify(
-          details.balanceMerchantAcceptable,
-        ),
-        balanceMerchantDepositable: Amounts.stringify(
-          details.balanceMerchantDepositable,
-        ),
-        feeGapEstimate: Amounts.stringify(feeGapEstimate),
-      },
-    };
-  }
-
-  const finalSel = selectedDenom;
-
-  logger.trace(`coin selection request ${j2s(req)}`);
-  logger.trace(`selected coins (via denoms) for payment: ${j2s(finalSel)}`);
-
-  await ws.db
-    .mktx((x) => [x.coins, x.denominations])
-    .runReadOnly(async (tx) => {
-      for (const dph of Object.keys(finalSel)) {
-        const selInfo = finalSel[dph];
-        const numRequested = selInfo.contributions.length;
-        const query = [
-          selInfo.exchangeBaseUrl,
-          selInfo.denomPubHash,
-          selInfo.maxAge,
-          CoinStatus.Fresh,
-        ];
-        logger.info(`query: ${j2s(query)}`);
-        const coins =
-          await tx.coins.indexes.byExchangeDenomPubHashAndAgeAndStatus.getAll(
-            query,
-            numRequested,
-          );
-        if (coins.length != numRequested) {
-          throw Error(
-            `coin selection failed (not available anymore, got only ${coins.length}/${numRequested})`,
-          );
-        }
-        coinPubs.push(...coins.map((x) => x.coinPub));
-        coinContributions.push(...selInfo.contributions);
-      }
-    });
-
-  return {
-    type: "success",
-    coinSel: {
-      paymentAmount: Amounts.stringify(contractTermsAmount),
-      coinContributions: coinContributions.map((x) => Amounts.stringify(x)),
-      coinPubs,
-      customerDepositFees: Amounts.stringify(tally.customerDepositFees),
-      customerWireFees: Amounts.stringify(tally.customerWireFees),
-    },
-  };
-}
-
 export async function checkPaymentByProposalId(
   ws: InternalWalletState,
   proposalId: string,
@@ -1704,9 +1258,7 @@ export async function confirmPay(
 
   const contractData = d.contractData;
 
-  let selectCoinsResult: SelectPayCoinsResult | undefined = undefined;
-
-  selectCoinsResult = await selectPayCoinsNew(ws, {
+  const selectCoinsResult = await selectPayCoinsNew(ws, {
     auditors: contractData.allowedAuditors,
     exchanges: contractData.allowedExchanges,
     wireMethod: contractData.wireMethod,
diff --git a/packages/taler-wallet-core/src/operations/refresh.ts b/packages/taler-wallet-core/src/operations/refresh.ts
index 477a00503..70f0579c0 100644
--- a/packages/taler-wallet-core/src/operations/refresh.ts
+++ b/packages/taler-wallet-core/src/operations/refresh.ts
@@ -85,10 +85,8 @@ import {
 } from "../util/retries.js";
 import { makeCoinAvailable } from "./common.js";
 import { updateExchangeFromUrl } from "./exchanges.js";
-import {
-  isWithdrawableDenom,
-  selectWithdrawalDenominations,
-} from "./withdraw.js";
+import { selectWithdrawalDenominations } from "../util/coinSelection.js";
+import { isWithdrawableDenom } from "../index.js";
 
 const logger = new Logger("refresh.ts");
 
diff --git a/packages/taler-wallet-core/src/operations/withdraw.ts b/packages/taler-wallet-core/src/operations/withdraw.ts
index 2c91d4184..643737e93 100644
--- a/packages/taler-wallet-core/src/operations/withdraw.ts
+++ b/packages/taler-wallet-core/src/operations/withdraw.ts
@@ -93,7 +93,6 @@ import {
   runLongpollAsync,
   runOperationWithErrorReporting,
 } from "../operations/common.js";
-import { walletCoreDebugFlags } from "../util/debugFlags.js";
 import {
   HttpRequestLibrary,
   HttpResponse,
@@ -123,6 +122,11 @@ import {
   getExchangeTrust,
   updateExchangeFromUrl,
 } from "./exchanges.js";
+import {
+  selectForcedWithdrawalDenominations,
+  selectWithdrawalDenominations,
+} from "../util/coinSelection.js";
+import { isWithdrawableDenom } from "../index.js";
 
 /**
  * Logger for this file.
@@ -130,162 +134,6 @@ import {
 const logger = new Logger("operations/withdraw.ts");
 
 /**
- * Check if a denom is withdrawable based on the expiration time,
- * revocation and offered state.
- */
-export function isWithdrawableDenom(d: DenominationRecord): boolean {
-  const now = AbsoluteTime.now();
-  const start = AbsoluteTime.fromTimestamp(d.stampStart);
-  const withdrawExpire = AbsoluteTime.fromTimestamp(d.stampExpireWithdraw);
-  const started = AbsoluteTime.cmp(now, start) >= 0;
-  let lastPossibleWithdraw: AbsoluteTime;
-  if (walletCoreDebugFlags.denomselAllowLate) {
-    lastPossibleWithdraw = start;
-  } else {
-    lastPossibleWithdraw = AbsoluteTime.subtractDuraction(
-      withdrawExpire,
-      durationFromSpec({ minutes: 5 }),
-    );
-  }
-  const remaining = Duration.getRemaining(lastPossibleWithdraw, now);
-  const stillOkay = remaining.d_ms !== 0;
-  return started && stillOkay && !d.isRevoked && d.isOffered;
-}
-
-/**
- * Get a list of denominations (with repetitions possible)
- * whose total value is as close as possible to the available
- * amount, but never larger.
- */
-export function selectWithdrawalDenominations(
-  amountAvailable: AmountJson,
-  denoms: DenominationRecord[],
-): DenomSelectionState {
-  let remaining = Amounts.copy(amountAvailable);
-
-  const selectedDenoms: {
-    count: number;
-    denomPubHash: string;
-  }[] = [];
-
-  let totalCoinValue = Amounts.zeroOfCurrency(amountAvailable.currency);
-  let totalWithdrawCost = Amounts.zeroOfCurrency(amountAvailable.currency);
-
-  denoms = denoms.filter(isWithdrawableDenom);
-  denoms.sort((d1, d2) =>
-    Amounts.cmp(
-      DenominationRecord.getValue(d2),
-      DenominationRecord.getValue(d1),
-    ),
-  );
-
-  for (const d of denoms) {
-    let count = 0;
-    const cost = Amounts.add(
-      DenominationRecord.getValue(d),
-      d.fees.feeWithdraw,
-    ).amount;
-    for (;;) {
-      if (Amounts.cmp(remaining, cost) < 0) {
-        break;
-      }
-      remaining = Amounts.sub(remaining, cost).amount;
-      count++;
-    }
-    if (count > 0) {
-      totalCoinValue = Amounts.add(
-        totalCoinValue,
-        Amounts.mult(DenominationRecord.getValue(d), count).amount,
-      ).amount;
-      totalWithdrawCost = Amounts.add(
-        totalWithdrawCost,
-        Amounts.mult(cost, count).amount,
-      ).amount;
-      selectedDenoms.push({
-        count,
-        denomPubHash: d.denomPubHash,
-      });
-    }
-
-    if (Amounts.isZero(remaining)) {
-      break;
-    }
-  }
-
-  if (logger.shouldLogTrace()) {
-    logger.trace(
-      `selected withdrawal denoms for ${Amounts.stringify(totalCoinValue)}`,
-    );
-    for (const sd of selectedDenoms) {
-      logger.trace(`denom_pub_hash=${sd.denomPubHash}, count=${sd.count}`);
-    }
-    logger.trace("(end of withdrawal denom list)");
-  }
-
-  return {
-    selectedDenoms,
-    totalCoinValue: Amounts.stringify(totalCoinValue),
-    totalWithdrawCost: Amounts.stringify(totalWithdrawCost),
-  };
-}
-
-export function selectForcedWithdrawalDenominations(
-  amountAvailable: AmountJson,
-  denoms: DenominationRecord[],
-  forcedDenomSel: ForcedDenomSel,
-): DenomSelectionState {
-  const selectedDenoms: {
-    count: number;
-    denomPubHash: string;
-  }[] = [];
-
-  let totalCoinValue = Amounts.zeroOfCurrency(amountAvailable.currency);
-  let totalWithdrawCost = Amounts.zeroOfCurrency(amountAvailable.currency);
-
-  denoms = denoms.filter(isWithdrawableDenom);
-  denoms.sort((d1, d2) =>
-    Amounts.cmp(
-      DenominationRecord.getValue(d2),
-      DenominationRecord.getValue(d1),
-    ),
-  );
-
-  for (const fds of forcedDenomSel.denoms) {
-    const count = fds.count;
-    const denom = denoms.find((x) => {
-      return Amounts.cmp(DenominationRecord.getValue(x), fds.value) == 0;
-    });
-    if (!denom) {
-      throw Error(
-        `unable to find denom for forced selection (value ${fds.value})`,
-      );
-    }
-    const cost = Amounts.add(
-      DenominationRecord.getValue(denom),
-      denom.fees.feeWithdraw,
-    ).amount;
-    totalCoinValue = Amounts.add(
-      totalCoinValue,
-      Amounts.mult(DenominationRecord.getValue(denom), count).amount,
-    ).amount;
-    totalWithdrawCost = Amounts.add(
-      totalWithdrawCost,
-      Amounts.mult(cost, count).amount,
-    ).amount;
-    selectedDenoms.push({
-      count,
-      denomPubHash: denom.denomPubHash,
-    });
-  }
-
-  return {
-    selectedDenoms,
-    totalCoinValue: Amounts.stringify(totalCoinValue),
-    totalWithdrawCost: Amounts.stringify(totalWithdrawCost),
-  };
-}
-
-/**
  * Get information about a withdrawal from
  * a taler://withdraw URI by asking the bank.
  *
diff --git a/packages/taler-wallet-core/src/util/coinSelection.test.ts b/packages/taler-wallet-core/src/util/coinSelection.test.ts
new file mode 100644
index 000000000..7814a9233
--- /dev/null
+++ b/packages/taler-wallet-core/src/util/coinSelection.test.ts
@@ -0,0 +1,29 @@
+/*
+ This file is part of GNU Taler
+ (C) 2022 Taler Systems S.A.
+
+ GNU Taler is free software; you can redistribute it and/or modify it under the
+ terms of the GNU General Public License as published by the Free Software
+ Foundation; either version 3, or (at your option) any later version.
+
+ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License along with
+ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+import test, { ExecutionContext } from "ava";
+
+function expect(t: ExecutionContext, thing: any): any {
+  return {
+    deep: {
+      equal: (another: any) => t.deepEqual(thing, another),
+      equals: (another: any) => t.deepEqual(thing, another),
+    },
+  };
+}
+
+test("should have a test", (t) => {
+  expect(t, true).equal(true);
+});
diff --git a/packages/taler-wallet-core/src/util/coinSelection.ts b/packages/taler-wallet-core/src/util/coinSelection.ts
index 0bd624bf7..176d636fc 100644
--- a/packages/taler-wallet-core/src/util/coinSelection.ts
+++ b/packages/taler-wallet-core/src/util/coinSelection.ts
@@ -23,13 +23,35 @@
 /**
  * Imports.
  */
+import { GlobalIDB } from "@gnu-taler/idb-bridge";
 import {
+  AbsoluteTime,
   AgeCommitmentProof,
+  AgeRestriction,
   AmountJson,
   Amounts,
+  CoinStatus,
+  DenominationInfo,
   DenominationPubKey,
+  DenomSelectionState,
+  ForcedCoinSel,
+  ForcedDenomSel,
+  j2s,
   Logger,
+  parsePaytoUri,
+  PayCoinSelection,
+  PayMerchantInsufficientBalanceDetails,
+  strcmp,
 } from "@gnu-taler/taler-util";
+import {
+  AllowedAuditorInfo,
+  AllowedExchangeInfo,
+  DenominationRecord,
+} from "../db.js";
+import { getExchangeDetails, isWithdrawableDenom } from "../index.js";
+import { InternalWalletState } from "../internal-wallet-state.js";
+import { getMerchantPaymentBalanceDetails } from "../operations/balance.js";
+import { checkDbInvariant, checkLogicInvariant } from "./invariants.js";
 
 const logger = new Logger("coinSelection.ts");
 
@@ -125,7 +147,7 @@ export interface CoinSelectionTally {
  * Account for the fees of spending a coin.
  */
 export function tallyFees(
-  tally: CoinSelectionTally,
+  tally: Readonly<CoinSelectionTally>,
   wireFeesPerExchange: Record<string, AmountJson>,
   wireFeeAmortization: number,
   exchangeBaseUrl: string,
@@ -193,3 +215,576 @@ export function tallyFees(
     lastDepositFee: feeDeposit,
   };
 }
+
+export type SelectPayCoinsResult =
+  | {
+      type: "failure";
+      insufficientBalanceDetails: PayMerchantInsufficientBalanceDetails;
+    }
+  | { type: "success"; coinSel: PayCoinSelection };
+
+/**
+ * Given a list of candidate coins, select coins to spend under the merchant's
+ * constraints.
+ *
+ * The prevPayCoins can be specified to "repair" a coin selection
+ * by adding additional coins, after a broken (e.g. double-spent) coin
+ * has been removed from the selection.
+ *
+ * This function is only exported for the sake of unit tests.
+ */
+export async function selectPayCoinsNew(
+  ws: InternalWalletState,
+  req: SelectPayCoinRequestNg,
+): Promise<SelectPayCoinsResult> {
+  const {
+    contractTermsAmount,
+    depositFeeLimit,
+    wireFeeLimit,
+    wireFeeAmortization,
+  } = req;
+
+  const [candidateDenoms, wireFeesPerExchange] = await selectCandidates(
+    ws,
+    req,
+  );
+
+  const coinPubs: string[] = [];
+  const coinContributions: AmountJson[] = [];
+  const currency = contractTermsAmount.currency;
+
+  let tally: CoinSelectionTally = {
+    amountPayRemaining: contractTermsAmount,
+    amountWireFeeLimitRemaining: wireFeeLimit,
+    amountDepositFeeLimitRemaining: depositFeeLimit,
+    customerDepositFees: Amounts.zeroOfCurrency(currency),
+    customerWireFees: Amounts.zeroOfCurrency(currency),
+    wireFeeCoveredForExchange: new Set(),
+    lastDepositFee: Amounts.zeroOfCurrency(currency),
+  };
+
+  const prevPayCoins = req.prevPayCoins ?? [];
+
+  // Look at existing pay coin selection and tally up
+  for (const prev of prevPayCoins) {
+    tally = tallyFees(
+      tally,
+      wireFeesPerExchange,
+      wireFeeAmortization,
+      prev.exchangeBaseUrl,
+      prev.feeDeposit,
+    );
+    tally.amountPayRemaining = Amounts.sub(
+      tally.amountPayRemaining,
+      prev.contribution,
+    ).amount;
+
+    coinPubs.push(prev.coinPub);
+    coinContributions.push(prev.contribution);
+  }
+
+  let selectedDenom: SelResult | undefined;
+  if (req.forcedSelection) {
+    selectedDenom = selectForced(req, candidateDenoms);
+  } else {
+    // FIXME:  Here, we should select coins in a smarter way.
+    // Instead of always spending the next-largest coin,
+    // we should try to find the smallest coin that covers the
+    // amount.
+    selectedDenom = selectGreedy(
+      req,
+      candidateDenoms,
+      wireFeesPerExchange,
+      tally,
+    );
+  }
+
+  if (!selectedDenom) {
+    const details = await getMerchantPaymentBalanceDetails(ws, {
+      acceptedAuditors: req.auditors,
+      acceptedExchanges: req.exchanges,
+      acceptedWireMethods: [req.wireMethod],
+      currency: Amounts.currencyOf(req.contractTermsAmount),
+      minAge: req.requiredMinimumAge ?? 0,
+    });
+    let feeGapEstimate: AmountJson;
+    if (
+      Amounts.cmp(
+        details.balanceMerchantDepositable,
+        req.contractTermsAmount,
+      ) >= 0
+    ) {
+      // FIXME: We can probably give a better estimate.
+      feeGapEstimate = Amounts.add(
+        tally.amountPayRemaining,
+        tally.lastDepositFee,
+      ).amount;
+    } else {
+      feeGapEstimate = Amounts.zeroOfAmount(req.contractTermsAmount);
+    }
+    return {
+      type: "failure",
+      insufficientBalanceDetails: {
+        amountRequested: Amounts.stringify(req.contractTermsAmount),
+        balanceAgeAcceptable: Amounts.stringify(details.balanceAgeAcceptable),
+        balanceAvailable: Amounts.stringify(details.balanceAvailable),
+        balanceMaterial: Amounts.stringify(details.balanceMaterial),
+        balanceMerchantAcceptable: Amounts.stringify(
+          details.balanceMerchantAcceptable,
+        ),
+        balanceMerchantDepositable: Amounts.stringify(
+          details.balanceMerchantDepositable,
+        ),
+        feeGapEstimate: Amounts.stringify(feeGapEstimate),
+      },
+    };
+  }
+
+  const finalSel = selectedDenom;
+
+  logger.trace(`coin selection request ${j2s(req)}`);
+  logger.trace(`selected coins (via denoms) for payment: ${j2s(finalSel)}`);
+
+  await ws.db
+    .mktx((x) => [x.coins, x.denominations])
+    .runReadOnly(async (tx) => {
+      for (const dph of Object.keys(finalSel)) {
+        const selInfo = finalSel[dph];
+        const numRequested = selInfo.contributions.length;
+        const query = [
+          selInfo.exchangeBaseUrl,
+          selInfo.denomPubHash,
+          selInfo.maxAge,
+          CoinStatus.Fresh,
+        ];
+        logger.info(`query: ${j2s(query)}`);
+        const coins =
+          await tx.coins.indexes.byExchangeDenomPubHashAndAgeAndStatus.getAll(
+            query,
+            numRequested,
+          );
+        if (coins.length != numRequested) {
+          throw Error(
+            `coin selection failed (not available anymore, got only ${coins.length}/${numRequested})`,
+          );
+        }
+        coinPubs.push(...coins.map((x) => x.coinPub));
+        coinContributions.push(...selInfo.contributions);
+      }
+    });
+
+  return {
+    type: "success",
+    coinSel: {
+      paymentAmount: Amounts.stringify(contractTermsAmount),
+      coinContributions: coinContributions.map((x) => Amounts.stringify(x)),
+      coinPubs,
+      customerDepositFees: Amounts.stringify(tally.customerDepositFees),
+      customerWireFees: Amounts.stringify(tally.customerWireFees),
+    },
+  };
+}
+
+function makeAvailabilityKey(
+  exchangeBaseUrl: string,
+  denomPubHash: string,
+  maxAge: number,
+): string {
+  return `${denomPubHash};${maxAge};${exchangeBaseUrl}`;
+}
+
+/**
+ * Selection result.
+ */
+interface SelResult {
+  /**
+   * Map from an availability key
+   * to an array of contributions.
+   */
+  [avKey: string]: {
+    exchangeBaseUrl: string;
+    denomPubHash: string;
+    maxAge: number;
+    contributions: AmountJson[];
+  };
+}
+
+function selectGreedy(
+  req: SelectPayCoinRequestNg,
+  candidateDenoms: AvailableDenom[],
+  wireFeesPerExchange: Record<string, AmountJson>,
+  tally: CoinSelectionTally,
+): SelResult | undefined {
+  const { wireFeeAmortization } = req;
+  const selectedDenom: SelResult = {};
+  for (const denom of candidateDenoms) {
+    const contributions: AmountJson[] = [];
+
+    // Don't use this coin if depositing it is more expensive than
+    // the amount it would give the merchant.
+    if (Amounts.cmp(denom.feeDeposit, denom.value) > 0) {
+      tally.lastDepositFee = Amounts.parseOrThrow(denom.feeDeposit);
+      continue;
+    }
+
+    for (
+      let i = 0;
+      i < denom.numAvailable && Amounts.isNonZero(tally.amountPayRemaining);
+      i++
+    ) {
+      tally = tallyFees(
+        tally,
+        wireFeesPerExchange,
+        wireFeeAmortization,
+        denom.exchangeBaseUrl,
+        Amounts.parseOrThrow(denom.feeDeposit),
+      );
+
+      const coinSpend = Amounts.max(
+        Amounts.min(tally.amountPayRemaining, denom.value),
+        denom.feeDeposit,
+      );
+
+      tally.amountPayRemaining = Amounts.sub(
+        tally.amountPayRemaining,
+        coinSpend,
+      ).amount;
+
+      contributions.push(coinSpend);
+    }
+
+    if (contributions.length) {
+      const avKey = makeAvailabilityKey(
+        denom.exchangeBaseUrl,
+        denom.denomPubHash,
+        denom.maxAge,
+      );
+      let sd = selectedDenom[avKey];
+      if (!sd) {
+        sd = {
+          contributions: [],
+          denomPubHash: denom.denomPubHash,
+          exchangeBaseUrl: denom.exchangeBaseUrl,
+          maxAge: denom.maxAge,
+        };
+      }
+      sd.contributions.push(...contributions);
+      selectedDenom[avKey] = sd;
+    }
+  }
+  return Amounts.isZero(tally.amountPayRemaining) ? selectedDenom : undefined;
+}
+
+function selectForced(
+  req: SelectPayCoinRequestNg,
+  candidateDenoms: AvailableDenom[],
+): SelResult | undefined {
+  const selectedDenom: SelResult = {};
+
+  const forcedSelection = req.forcedSelection;
+  checkLogicInvariant(!!forcedSelection);
+
+  for (const forcedCoin of forcedSelection.coins) {
+    let found = false;
+    for (const aci of candidateDenoms) {
+      if (aci.numAvailable <= 0) {
+        continue;
+      }
+      if (Amounts.cmp(aci.value, forcedCoin.value) === 0) {
+        aci.numAvailable--;
+        const avKey = makeAvailabilityKey(
+          aci.exchangeBaseUrl,
+          aci.denomPubHash,
+          aci.maxAge,
+        );
+        let sd = selectedDenom[avKey];
+        if (!sd) {
+          sd = {
+            contributions: [],
+            denomPubHash: aci.denomPubHash,
+            exchangeBaseUrl: aci.exchangeBaseUrl,
+            maxAge: aci.maxAge,
+          };
+        }
+        sd.contributions.push(Amounts.parseOrThrow(forcedCoin.value));
+        selectedDenom[avKey] = sd;
+        found = true;
+        break;
+      }
+    }
+    if (!found) {
+      throw Error("can't find coin for forced coin selection");
+    }
+  }
+
+  return selectedDenom;
+}
+
+export interface SelectPayCoinRequestNg {
+  exchanges: AllowedExchangeInfo[];
+  auditors: AllowedAuditorInfo[];
+  wireMethod: string;
+  contractTermsAmount: AmountJson;
+  depositFeeLimit: AmountJson;
+  wireFeeLimit: AmountJson;
+  wireFeeAmortization: number;
+  prevPayCoins?: PreviousPayCoins;
+  requiredMinimumAge?: number;
+  forcedSelection?: ForcedCoinSel;
+}
+
+export type AvailableDenom = DenominationInfo & {
+  maxAge: number;
+  numAvailable: number;
+};
+
+export async function selectCandidates(
+  ws: InternalWalletState,
+  req: SelectPayCoinRequestNg,
+): Promise<[AvailableDenom[], Record<string, AmountJson>]> {
+  return await ws.db
+    .mktx((x) => [
+      x.exchanges,
+      x.exchangeDetails,
+      x.denominations,
+      x.coinAvailability,
+    ])
+    .runReadOnly(async (tx) => {
+      // FIXME: Use the existing helper (from balance.ts) to
+      // get acceptable exchanges.
+      const denoms: AvailableDenom[] = [];
+      const exchanges = await tx.exchanges.iter().toArray();
+      const wfPerExchange: Record<string, AmountJson> = {};
+      for (const exchange of exchanges) {
+        const exchangeDetails = await getExchangeDetails(tx, exchange.baseUrl);
+        // 1.- exchange has same currency
+        if (exchangeDetails?.currency !== req.contractTermsAmount.currency) {
+          continue;
+        }
+        let wireMethodFee: string | undefined;
+        // 2.- exchange supports wire method
+        for (const acc of exchangeDetails.wireInfo.accounts) {
+          const pp = parsePaytoUri(acc.payto_uri);
+          checkLogicInvariant(!!pp);
+          if (pp.targetType === req.wireMethod) {
+            // also check that wire method is supported now
+            const wireFeeStr = exchangeDetails.wireInfo.feesForType[
+              req.wireMethod
+            ]?.find((x) => {
+              return AbsoluteTime.isBetween(
+                AbsoluteTime.now(),
+                AbsoluteTime.fromTimestamp(x.startStamp),
+                AbsoluteTime.fromTimestamp(x.endStamp),
+              );
+            })?.wireFee;
+            if (wireFeeStr) {
+              wireMethodFee = wireFeeStr;
+            }
+            break;
+          }
+        }
+        if (!wireMethodFee) {
+          break;
+        }
+        wfPerExchange[exchange.baseUrl] = Amounts.parseOrThrow(wireMethodFee);
+        // 3.- exchange is trusted in the exchange list or auditor list
+        let accepted = false;
+        for (const allowedExchange of req.exchanges) {
+          if (allowedExchange.exchangePub === exchangeDetails.masterPublicKey) {
+            accepted = true;
+            break;
+          }
+        }
+        for (const allowedAuditor of req.auditors) {
+          for (const providedAuditor of exchangeDetails.auditors) {
+            if (allowedAuditor.auditorPub === providedAuditor.auditor_pub) {
+              accepted = true;
+              break;
+            }
+          }
+        }
+        if (!accepted) {
+          continue;
+        }
+        //4.- filter coins restricted by age
+        let ageLower = 0;
+        let ageUpper = AgeRestriction.AGE_UNRESTRICTED;
+        if (req.requiredMinimumAge) {
+          ageLower = req.requiredMinimumAge;
+        }
+        const myExchangeCoins =
+          await tx.coinAvailability.indexes.byExchangeAgeAvailability.getAll(
+            GlobalIDB.KeyRange.bound(
+              [exchangeDetails.exchangeBaseUrl, ageLower, 1],
+              [
+                exchangeDetails.exchangeBaseUrl,
+                ageUpper,
+                Number.MAX_SAFE_INTEGER,
+              ],
+            ),
+          );
+        //5.- save denoms with how many coins are available
+        // FIXME: Check that the individual denomination is audited!
+        // FIXME: Should we exclude denominations that are
+        // not spendable anymore?
+        for (const coinAvail of myExchangeCoins) {
+          const denom = await tx.denominations.get([
+            coinAvail.exchangeBaseUrl,
+            coinAvail.denomPubHash,
+          ]);
+          checkDbInvariant(!!denom);
+          if (denom.isRevoked || !denom.isOffered) {
+            continue;
+          }
+          denoms.push({
+            ...DenominationRecord.toDenomInfo(denom),
+            numAvailable: coinAvail.freshCoinCount ?? 0,
+            maxAge: coinAvail.maxAge,
+          });
+        }
+      }
+      // Sort by available amount (descending),  deposit fee (ascending) and
+      // denomPub (ascending) if deposit fee is the same
+      // (to guarantee deterministic results)
+      denoms.sort(
+        (o1, o2) =>
+          -Amounts.cmp(o1.value, o2.value) ||
+          Amounts.cmp(o1.feeDeposit, o2.feeDeposit) ||
+          strcmp(o1.denomPubHash, o2.denomPubHash),
+      );
+      return [denoms, wfPerExchange];
+    });
+}
+
+/**
+ * Get a list of denominations (with repetitions possible)
+ * whose total value is as close as possible to the available
+ * amount, but never larger.
+ */
+export function selectWithdrawalDenominations(
+  amountAvailable: AmountJson,
+  denoms: DenominationRecord[],
+): DenomSelectionState {
+  let remaining = Amounts.copy(amountAvailable);
+
+  const selectedDenoms: {
+    count: number;
+    denomPubHash: string;
+  }[] = [];
+
+  let totalCoinValue = Amounts.zeroOfCurrency(amountAvailable.currency);
+  let totalWithdrawCost = Amounts.zeroOfCurrency(amountAvailable.currency);
+
+  denoms = denoms.filter(isWithdrawableDenom);
+  denoms.sort((d1, d2) =>
+    Amounts.cmp(
+      DenominationRecord.getValue(d2),
+      DenominationRecord.getValue(d1),
+    ),
+  );
+
+  for (const d of denoms) {
+    let count = 0;
+    const cost = Amounts.add(
+      DenominationRecord.getValue(d),
+      d.fees.feeWithdraw,
+    ).amount;
+    for (;;) {
+      if (Amounts.cmp(remaining, cost) < 0) {
+        break;
+      }
+      remaining = Amounts.sub(remaining, cost).amount;
+      count++;
+    }
+    if (count > 0) {
+      totalCoinValue = Amounts.add(
+        totalCoinValue,
+        Amounts.mult(DenominationRecord.getValue(d), count).amount,
+      ).amount;
+      totalWithdrawCost = Amounts.add(
+        totalWithdrawCost,
+        Amounts.mult(cost, count).amount,
+      ).amount;
+      selectedDenoms.push({
+        count,
+        denomPubHash: d.denomPubHash,
+      });
+    }
+
+    if (Amounts.isZero(remaining)) {
+      break;
+    }
+  }
+
+  if (logger.shouldLogTrace()) {
+    logger.trace(
+      `selected withdrawal denoms for ${Amounts.stringify(totalCoinValue)}`,
+    );
+    for (const sd of selectedDenoms) {
+      logger.trace(`denom_pub_hash=${sd.denomPubHash}, count=${sd.count}`);
+    }
+    logger.trace("(end of withdrawal denom list)");
+  }
+
+  return {
+    selectedDenoms,
+    totalCoinValue: Amounts.stringify(totalCoinValue),
+    totalWithdrawCost: Amounts.stringify(totalWithdrawCost),
+  };
+}
+
+export function selectForcedWithdrawalDenominations(
+  amountAvailable: AmountJson,
+  denoms: DenominationRecord[],
+  forcedDenomSel: ForcedDenomSel,
+): DenomSelectionState {
+  const selectedDenoms: {
+    count: number;
+    denomPubHash: string;
+  }[] = [];
+
+  let totalCoinValue = Amounts.zeroOfCurrency(amountAvailable.currency);
+  let totalWithdrawCost = Amounts.zeroOfCurrency(amountAvailable.currency);
+
+  denoms = denoms.filter(isWithdrawableDenom);
+  denoms.sort((d1, d2) =>
+    Amounts.cmp(
+      DenominationRecord.getValue(d2),
+      DenominationRecord.getValue(d1),
+    ),
+  );
+
+  for (const fds of forcedDenomSel.denoms) {
+    const count = fds.count;
+    const denom = denoms.find((x) => {
+      return Amounts.cmp(DenominationRecord.getValue(x), fds.value) == 0;
+    });
+    if (!denom) {
+      throw Error(
+        `unable to find denom for forced selection (value ${fds.value})`,
+      );
+    }
+    const cost = Amounts.add(
+      DenominationRecord.getValue(denom),
+      denom.fees.feeWithdraw,
+    ).amount;
+    totalCoinValue = Amounts.add(
+      totalCoinValue,
+      Amounts.mult(DenominationRecord.getValue(denom), count).amount,
+    ).amount;
+    totalWithdrawCost = Amounts.add(
+      totalWithdrawCost,
+      Amounts.mult(cost, count).amount,
+    ).amount;
+    selectedDenoms.push({
+      count,
+      denomPubHash: denom.denomPubHash,
+    });
+  }
+
+  return {
+    selectedDenoms,
+    totalCoinValue: Amounts.stringify(totalCoinValue),
+    totalWithdrawCost: Amounts.stringify(totalWithdrawCost),
+  };
+}
diff --git a/packages/taler-wallet-core/src/util/denominations.ts b/packages/taler-wallet-core/src/util/denominations.ts
index ef35fe198..fb766e96a 100644
--- a/packages/taler-wallet-core/src/util/denominations.ts
+++ b/packages/taler-wallet-core/src/util/denominations.ts
@@ -20,12 +20,16 @@ import {
   Amounts,
   AmountString,
   DenominationInfo,
+  Duration,
+  durationFromSpec,
   FeeDescription,
   FeeDescriptionPair,
   TalerProtocolTimestamp,
   TimePoint,
   WireFee,
 } from "@gnu-taler/taler-util";
+import { DenominationRecord } from "../db.js";
+import { walletCoreDebugFlags } from "./debugFlags.js";
 
 /**
  * Given a list of denominations with the same value and same period of time:
@@ -443,3 +447,26 @@ export function createTimeline<Type extends object>(
     return result;
   }, [] as FeeDescription[]);
 }
+
+/**
+ * Check if a denom is withdrawable based on the expiration time,
+ * revocation and offered state.
+ */
+export function isWithdrawableDenom(d: DenominationRecord): boolean {
+  const now = AbsoluteTime.now();
+  const start = AbsoluteTime.fromTimestamp(d.stampStart);
+  const withdrawExpire = AbsoluteTime.fromTimestamp(d.stampExpireWithdraw);
+  const started = AbsoluteTime.cmp(now, start) >= 0;
+  let lastPossibleWithdraw: AbsoluteTime;
+  if (walletCoreDebugFlags.denomselAllowLate) {
+    lastPossibleWithdraw = start;
+  } else {
+    lastPossibleWithdraw = AbsoluteTime.subtractDuraction(
+      withdrawExpire,
+      durationFromSpec({ minutes: 5 }),
+    );
+  }
+  const remaining = Duration.getRemaining(lastPossibleWithdraw, now);
+  const stillOkay = remaining.d_ms !== 0;
+  return started && stillOkay && !d.isRevoked && d.isOffered;
+}